The Liquefaction of Chlorine Gas first effected by Mr. Faraday,
and witnessed by the Author.--Sir H. Davy continues the
investigation.--His paper on the application of Liquefiable
Gases as mechanical agents.--Other probable uses of these
bodies.--He proposes several methods to prevent the fumes which
arise from Smelting-furnaces.--Importance of the subject. His
Letters to Mr. Vivian.--The Government solicit the advice of
the Royal Society on the subject of protecting the Copper
Sheathing of Ships from the action of sea-water.--Sir H.
Davy charges himself with this enquiry.--He proposes a plan
of protection founded on Voltaic principles.--His numerous
experiments.--He embarks on board the Comet steam-vessel
bound to Heligoland, in order to try his plan on a vessel
in motion.--He arrives at Mandal, lands, and fishes in the
lakes.--The Protectors washed away.--He teaches the inhabitants
of Christiansand to crimp fish--He remains a few days at
Arendal.--A Norwegian dinner.--The Protectors are examined and
weighed.--Results of the experiment.--The steam-vessel proceeds
up the Glommen.--He visits the great waterfall--Passes into
Sweden.--Has an interview with the Crown Prince of Denmark,
and afterwards with Prince Christian at Copenhagen.--He
visits Professor Oersted.--He proceeds to Bremen to see Dr.
Olbers.--Returns to England.--His third paper read before the
Royal Society.--Voltaic influence of patches of rust.--A small
quantity of fluid sufficient to complete the circuit.--He
receives from the Royal Society the Royal Medal.--The Progress
of Voltaic discovery reviewed.--The principle is of extensive
application.--The Author's researches into the cause of the
solution of Lead in spring water.--An account of the numerous
trials of Protectors.--Failure of the plan.--Report of the
French on the state of the protected frigate La Constance.--Dr.
Revere's new plan of Protection.
Every incident, however trifling, if it relates to a great
scientific discovery, merits the attention of the historian. As
it accidentally occurred to me, and to me alone, to witness the
original experiment by which Mr. Faraday first condensed chlorine
gas into a liquid, I shall here state the circumstances under which
its liquefaction was effected.
I had been invited to dine with Sir Humphry Davy, on Wednesday
the 5th of March 1823, for the purpose of meeting the Reverend
Uriah Tonkin, the heir of his early friend and benefactor of that
name.[80] On quitting my house for that purpose, I perceived that
I had time to spare, and I accordingly called in my way at the
Royal Institution. Upon descending into the laboratory, I found
Mr. Faraday engaged in experiments on chlorine and its hydrate
in closed tubes. It appeared to me that the tube in which he was
operating upon this substance contained some oily matter, and I
rallied him upon the carelessness of employing soiled vessels.
Mr. Faraday, upon inspecting the tube, acknowledged the justness
of my remark, and expressed his surprise at the circumstance. In
consequence of which, he immediately proceeded to file off the
sealed end; when, to our great astonishment, the contents suddenly
exploded, and the oily matter vanished!
[80] Sir Humphry had expressed to me, on the preceding Thursday,
at the Royal Society, his wish to purchase the old house in
Penzance, which, as the reader will remember, was the early scene
of his chemical operations; and, at his request, I conversed with
Mr. Tonkin upon the subject; but it immediately appeared that
the interest which the Corporation of Penzance possessed in the
estate presented an insurmountable obstacle to the accomplishment
of his object.
Mr. Faraday was completely at a loss to explain the occurrence, and
proceeded to repeat the experiment with a view to its elucidation.
I was unable, however, to remain and witness the result.
Upon mentioning the circumstance to Sir Humphry Davy after dinner,
he appeared much surprised; and after a few moments of apparent
abstraction, he said, "I shall enquire about this experiment
to-morrow."
Early on the next morning, I received from Mr. Faraday the
following laconic note:
DEAR SIR,
The _oil_ you noticed yesterday turns out to be liquid chlorine.
Yours faithfully,
M. FARADAY.
It is well known that, before the year 1810, the solid substance
obtained by exposing chlorine, as usually procured, to a low
temperature, was considered as the gas itself reduced into that
form: Sir Humphry Davy, however, corrected this error, and first
showed it to be a hydrate, the pure gas not being condensable even
at a temperature of-40° Fahrenheit.
Mr. Faraday had taken advantage of the cold season to procure
crystals of this hydrate, and was proceeding in its analysis,[81]
when Sir Humphry Davy suggested to him the expediency of observing
what would happen if it were heated in a close vessel; but this
suggestion was made in consequence of the inspection of results
already obtained by Mr. Faraday, and which must have led him to the
experiment in question, had he never communicated with Sir Humphry
Davy upon the subject. This avowal is honestly due to Mr. Faraday.
[81] The results are contained in a short paper in the Quarterly
Journal of Science, vol. xv.
On exposing the hydrate, in a tube hermetically sealed, to a
temperature of 100°, the substance fused, the tube became filled
with a bright yellow atmosphere, and, on examination, was found
to contain two fluid substances: the one, about three-fourths of
the whole, was of a faint yellow colour, having very much the
appearance of water; the remaining fourth was a heavy, bright
yellow fluid, lying at the bottom of the former, without any
apparent tendency to mix with it.
By operating on the hydrate in a bent tube hermetically sealed,
Mr. Faraday found it easy, after decomposing it by a heat of 100°,
to distil the yellow fluid to one end of the tube, and thus to
separate it from the remaining portion. If the tube were now cut in
the middle, the parts flew asunder, as if with an explosion, the
whole of the yellow portion disappeared, and there was a powerful
atmosphere of chlorine produced; the pale portion, on the contrary,
remained, and when examined, proved to be a weak solution of
chlorine in water, with a little muriatic acid, probably from the
impurity of the hydrate used. When that end of the tube in which
the yellow fluid lay was broken under a jar of water, there was an
immediate production of chlorine gas.
After several conjectures as to the nature of the changes thus
produced, Mr. Faraday arrived at its true explanation; viz. that
the chlorine had been entirely separated from the water by the
heat, and condensed into a dry fluid by the mere pressure of its
own abundant vapour. He subsequently confirmed these views by
condensing chlorine in a long tube, by mechanical pressure, applied
by means of a condensing syringe, and which farther enabled him to
ascertain that the degree of pressure necessary for this effect was
about that of four atmospheres.
To Mr. Faraday's paper upon this subject, published in the
Philosophical Transactions for the year 1823, Sir Humphry Davy
thought proper to add a "Note on the condensation of muriatic acid
gas into the liquid form."
The circumstances under which this was effected are briefly these.
On the morning (Thursday, March 6th,) after Mr. Faraday had
condensed chlorine, Sir Humphry Davy had no sooner witnessed the
result, than he called for a strong glass tube, and, having placed
in it a quantity of muriate of ammonia and sulphuric acid, and then
sealed the end, he caused them to act upon each other, and thus
condensed the muriatic acid, which was evolved, into a liquid. The
condensation of carbonic acid gas, nitrous oxide gas, and several
others, were in succession treated with similar success; but, as I
regard the discovery as strictly belonging to Mr. Faraday, I shall
confine myself to the relation of those experiments and deductions
which, with equal justice, I must assign to Sir Humphry Davy.
He observes, "that the generation of elastic substances in close
vessels, either with or without heat, offers much more powerful
means of approximating their molecules than those dependent upon
the application of cold, whether natural or artificial: for, as
gases diminish only about 1/450 in volume for every--degree of
Fahrenheit's scale, beginning at ordinary temperatures, a very
slight condensation only can be produced by the most powerful
freezing mixtures, not half as much as would result from the
application of a strong flame to one part of a glass tube, the
other part being of ordinary temperature: and when attempts
are made to condense gases into liquids by sudden mechanical
compression, the heat, instantly generated, presents a formidable
obstacle to the success of the experiment; whereas, in the
compression resulting from their slow generation in close vessels,
if the process be conducted with common precautions, there is no
source of difficulty or danger; and it may be easily assisted by
artificial cold in cases when gases approach near to that point of
compression and temperature at which they become vapours."
On the 17th of April 1823, he communicated to the Royal Society a
paper "On the application of Liquids formed by the condensation of
Gases as mechanical agents."
He states that doubts may, for various philosophical reasons, exist
as to the economical results to be obtained by employing the steam
of water under great pressures, and at very elevated temperatures;
but that no doubts can arise with respect to the use of such
liquids as require for their existence even a compression equal to
that of the weight of thirty or forty atmospheres; and where common
temperatures, or slight elevations of them, are sufficient to
produce an immense elastic force; and when the principal question
to be discussed is, whether the effect of mechanical motion is to
be most easily produced by an increase or diminution of heat by
artificial means.
With the assistance of Mr. Faraday, he made several experiments
on the differences between the increase of elastic force in gases
under high and low pressures, by similar increments of temperature.
In an experiment made with carbonic acid, its force was found to be
nearly equal to that of air compressed to one-twentieth at 12° Fah.
and of air compressed to one-thirty-sixth at 32 degrees, making an
increase equal to the weight of thirteen atmospheres by an increase
of twenty of temperature!
In applying, however, the condensed gases as mechanical agents,
Davy admits that there will be some difficulty; "the materials
of the apparatus must be as strong and as perfectly joined as
those used by Mr. Perkins in his high-pressure steam-engine:
but the small differences of temperature to produce an elastic
force equal to the pressure of many atmospheres, will render the
risk of explosion extremely small;" and he adds, "that if future
experiments should realize the views here developed, the mere
difference of temperature between sunshine and shade, and air and
water, or the effects of evaporation from a moist surface, will be
sufficient to produce results, which have hitherto been obtained
only by a great expenditure of fuel."
If this be true, who can say that future generations shall not
perform their voyages in _gas_-vessels, across the Atlantic Ocean,
with no other fuel than that which a common taper may supply? I
fear, however, that in this scientific reverie, Davy merely looked
at the difference of the sensible temperatures, and entirely
neglected, in his calculation, the quantity of heat rendered latent
during the change of the liquid into the gaseous state; and which,
perhaps, is far more considerable in the application of these
fluids than in that of water; but even in this latter case, the
great expenditure of heat in working the steam-engine, is in the
portion rendered latent, and which cannot, by any contrivance, be
brought again into operation, after it has performed its duty. That
a philosopher who had, during the whole progress of his researches,
directed such unremitting attention to the subject of Heat, should
have wholly overlooked an objection arising out of one of its most
familiar phenomena, is scarcely less extraordinary than his having,
on another occasion,[82] advanced to a conclusion in direct
opposition to the very principle of Electricity, which his own
discoveries had established.
[82] I here allude to an anecdote related by Mr. Babbage, in
his "Reflections on the Decline of Science in England;" a work,
by the by, which strongly reminds me of a practical bull. A
gentleman, anxious to escape the tax on armorial bearings,
wrote a long letter to the Commissioners, stating I do not know
how many reasons to show that he could never have used them;
and, after all, sealed the letter with his own coat of arms!
Had Mr. Babbage hoped to convince the reader that Science was
actually on the decline in this country, he should never have
written a work which gives the lie to the title-page. Now for
the anecdote.--"Meeting Dr. Wollaston one morning in the shop
of a bookseller, I proposed this question: If two volumes of
hydrogen and one of oxygen are mixed together in a vessel, and
if by mechanical pressure they can be so condensed as to become
of the same specific gravity of water, will the gases, under
these circumstances, unite and form water? 'What do you think
they will do?' said Dr. W. I replied, that I should rather expect
they would unite. 'I see no reason to suppose it,' said he. I
then enquired whether he thought the experiment worth making.
He answered, that he did not, for that he should think it would
certainly _not_ succeed.
"A few days after, I proposed the same question to Sir Humphry
Davy. He at once said, 'They will become water of course:' and
on my enquiring whether he thought the experiment worth making,
he observed that it was a good experiment, but one which it was
hardly necessary to make, as it must succeed.
"These were off-hand answers, which it might perhaps be hardly
fair to have recorded, had they been of persons of less eminent
talent; and it adds to the curiosity of the circumstance to
mention, that I believe Dr. Wollaston's reason for supposing no
union would take place, arose from the nature of the electrical
relations of the two gases remaining unchanged: an objection
which did not weigh with the philosopher whose discoveries had
given birth to it."
Davy succeeded in liquefying gases by a method which, at first
view, appears very paradoxical--_by the application of heat!_ The
method consists in placing them in one leg of a bent sealed tube,
confined by mercury, and applying heat to ether, or alcohol, or
water, in the other end. In this manner, by the pressure of the
vapour of ether, he liquefied prussic gas and sulphurous acid gas;
which gases, on being reproduced, occasioned cold.
There can be little doubt, he thinks, that these general facts
of the condensation of the gases will have many practical
applications. They offer, for instance, easy methods of
impregnating liquids with carbonic acid and other gases, without
mechanical pressure. They afford means of producing great
diminutions of temperature, by the rapidity with which large
quantities of liquids may be rendered aëriform; and as compression
occasions similar effects to cold, in preventing the formation of
elastic substances, there is great reason to believe that it may be
successfully employed for the preservation of animal and vegetable
substances for the purposes of food.
Davy might also have added, that the same general views will
explain natural and other phenomena not previously understood. They
certainly afford a plausible explanation of the nature of _blowers_
in coal-mines; and they may lead to more satisfactory views on
other subjects of geology. They assign a limit to the expansive
force of gas under increasing pressure, and account for effects
connected with the _blasting_ of rocks, which would otherwise
appear anomalous.[83]
[83] In the year 1812, Mr. Babbage attempted to ascertain whether
pressure would prevent decomposition: for this purpose, a hole
about thirty inches deep, and two inches in diameter, was bored
downward into a limestone rock, into which was then poured a
quantity of strong muriatic acid, and a conical wooden plug, that
had been previously soaked in tallow, was immediately driven
hard into the mouth of the hole. It was expected either that the
decomposition would be prevented, or that the gas developed would
split the rock by its expansive force: but nothing happened.
Now, it is most probable that a part of the carbonic acid had
condensed into a liquid, and thus prevented that developement of
power which Mr. Babbage had expected would have torn the rock
asunder.
It may be stated, greatly to the honour of Davy, that there never
occurred any question of scientific interest or difficulty in
which he did not cheerfully offer his advice and assistance. Few
Presidents of the Royal Society have ever exerted their influence
and talents with so much unaffected zeal for the promotion of
scientific objects, and for the welfare of scientific men. In the
year 1821, the Great Hafod copper-works, in the neighbourhood
of Swansea, were indicted for a nuisance, in consequence of the
alleged destructive effects of the fumes which arose during the
smelting of the ores. When we learn that the amount of wages
paid by the proprietors of the works in this district exceeds
50,000_l._, per annum; that twelve thousand persons, at least,
derive their support from the smelting establishments; that a sum
of not less than 200,000_l._ sterling is annually circulated in
Glamorganshire and the adjoining county, in consequence of their
existence; that they pay to the collieries no less than from
100,000_l._ to 110,000_l._ per annum for coal; that one hundred and
fifty vessels are employed in the conveyance of ore, and, supposing
each upon an average to be manned by five seamen, that they give
occupation to seven hundred and fifty mariners, a more serious
calamity can scarcely be imagined than the stoppage of such works:
we may therefore readily believe, that Davy entered most ardently
into the consideration of some plan by which the fumes might be
prevented, and the alleged nuisance abated.
Through the kind attention of my friend Mr. Vivian, I am enabled to
insert the following letters.
TO JOHN HENRY VIVIAN, ESQ.
London, Jan. 9, 1822.
MY DEAR SIR,
As you expressed a wish that I should commit to writing those
opinions which I mentioned in conversation, when I had the
pleasure of visiting you at Marino, after inspecting your
furnaces and witnessing your experiments on the smoke arising
from them, I lose no time in complying with your desire.
It is evident that the copper ore cannot be properly calcined
without a copious admission of air into the furnaces, which
must cause the sulphurous acid gas formed in the calcination
to be mixed with very large quantities of other elastic
fluids, which presents great mechanical, as well as chemical
difficulties to its condensation or decomposition.
To persons acquainted with chemistry, a number of modes of
effecting these objects are known. Of condensation, for
instance, by water, by the formation of sulphuric acid, by
alkaline lixivia, by alkaline earths, &c. Of decomposition,
by hydrogen, by charcoal, by hydro-carbonous substances, and
by metals; but to most of these methods there are serious and
insurmountable objections, depending upon the diluted state of
the acid gas, and the expenses required.
To form sulphuric acid, or to decompose by charcoal or
hydrogen, or to condense by alkaline lixivia, or by alkaline
earths, from the nature of the works, and of the operations for
which they were intended, I conceive impracticable except at an
expense that could not be borne; and the only processes which
remain to be discussed are those by hydro-carbonous substances,
and by the action of water.
There can be no doubt that the gas may be decomposed by the
action of heated hydro-carbonous gases from the distillation
of coal; but for this purpose there must be a new construction
of the furnaces, and more than double, probably triple,
the quantity of fuel would be required, supposing even the
Swansea coal to contain the common average of bitumen; and
this method must be infinitely more expensive, and liable to
many more objections, than the one you have so ingeniously
employed--absorption by water.
As water costs nothing, and as a supply is entirely in
your power, the application of it offers comparatively few
difficulties; and it has the great advantage of freeing the
smoke from fluoric and arsenious compounds, which would not be
perfectly effected by any other method.
The experiments of MM. Phillips and Faraday prove, that your
shower baths have already entirely destroyed all the fluoric
and arsenious fumes of the smoke, and by a _certain_ quantity
of water, the smoke may undoubtedly be entirely freed from
sulphurous acid gas.
This, _your own_ plan, is the one that I strongly recommend to
you to proceed with, and, if necessary, to extend.
Perhaps you may find an additional shower bath near the colder
part of the flue useful. I have no idea that steam passed into
the hot part of the flue can be of the least service; but if
passed out with the smoke through the stack, it may tend to
convert such residual portion of sulphurous acid gas, exposed
to fresh air, into sulphuric acid. Could you not likewise
try a stream of _cold_ water passing along the bottom of the
horizontal flue?[84]
I do not think the advantages of your improvements can be
fairly appreciated, till the effects of your smoke are
determined by actual experiments and fair trials.
Yours, &c.
H. DAVY.
[84] For the purpose of acting by its cooling power in condensing
vapour, which would carry down sulphurous acid with it. It would
likewise assist by direct absorption. H. D.
TO THE SAME.
London, May 12, 1823.
MY DEAR SIR,
I return you my thanks for the copies you were so good as
to send me of your work on the modes you have adopted for
rendering copper smoke innoxious, &c. I have read it with very
great pleasure, and I am sure there can be but one feeling, and
that of strong admiration, at the exertions you have made, and
the resources you have displayed, in subduing the principal
evils of one of our most important national manufactures. I
trust you will have no more trouble on this subject, and that
it will only occur to you in an agreeable form, with the high
approbation as well as grateful feelings of your neighbours;
and that your example will be followed.
A Committee of the Royal Society has been formed for
investigating the causes of the decay of copper sheeting in
the Navy, as I mentioned to you. The Navy Board has sent us a
number of specimens of copper in different stages of decay. We
have our first meeting to examine them on Thursday, and I shall
have much pleasure in communicating to you our results. I wish
I could do it in person.
I am going into Hampshire on Sunday next to fish near
Fordingbridge for a week, and to try the Avon and its tributary
streams.
I was going to give you an account of some experiments which
Mr. Faraday has made by my directions in generating gases in
close vessels as liquids, but I find I have not time. I have
already found an application of this discovery, which I hope
will supersede _steam_, as a difference of a few degrees of
temperature gives the elastic force of many atmospheres.
Hoping to see you soon, I am, with best respects to Mrs.
Vivian, and love to the charming little Bessy,
My dear Sir, yours sincerely obliged,
H. DAVY.
* * * * *
I proceed now to relate the history of an elaborate experimental
enquiry, instituted for the purpose of ascertaining the chemical
nature and causes of the well-known corrosive action of sea-water
upon metallic copper; in order, if possible, to obviate that
serious evil in naval economy--the rapid decay of the copper
sheathing on the bottoms of our ships. An investigation which Sir
Humphry Davy commenced in the year 1823, and prosecuted with his
characteristic zeal and happy talent during a considerable period;
when, at length, paradoxical as it may appear, the truth of his
theory was completely established by the failure of his remedy!
From the several original documents which have been placed at my
disposal, and from the valuable communications and kind assistance
of my friend Mr. Knowles, I trust I shall be enabled to offer to
the scientific reader a more complete and circumstantial history
of this admirable enquiry than has been hitherto presented to the
public.
The results he produced are equally interesting and important,
whether we contemplate them biographically, as indicative of the
peculiar genius by which they were obtained; or, scientifically, in
their connexion with the electro-chemical theory, to the farther
developement and illustration of which they have so powerfully
contributed; or, economically, as the probable means by which the
hand of Time may be averted, an increased durability imparted to
rapidly perishable works of art, and monuments of human genius
transmitted to posterity, in all their freshness, through a long
succession of ages.
It is probable that, in the earliest period of naval architecture,
some expedient[85] was practised, in order to protect ships'
bottoms from the ravages of marine worms.[86] The use of metallic
sheathing, however, is of ancient date. The galley supposed to
have belonged to the Emperor Trajan was sheathed with sheets of
lead, which were fastened with copper nails.[87] The same metal
was also used in the earlier periods of our naval history;[88] and
it is worthy of remark, that the circumstances which led to its
disuse, were the rapid corrosion of the _rother irons_, (from the
formation of a Voltaic circle,) and the accumulation of sea-weed.
[85] Mr. Knowles, in his "Inquiry into the Means which have been
taken to preserve the British Navy," observes, that the first
sheathing was probably the hides of animals covered with pitch,
or with asphaltum, which led to the use of thin boards, having,
in some cases, lime, and in others lime and hair, between them
and the bottom of the ships.
[86] The worms infesting the timber of ships are--the _Teredo_,
the _Lepisma_, and the _Pholas_. The first of these, however,
which was imported from India, is by far the most destructive;
and I am informed by Mr. Knowles, that it is more abundant at
Plymouth than on any other part of the coast where there is a
dock-yard; and although on the shores of England it is not of a
very large size, yet it is a formidable enemy to the safety of
those ships which have not a metallic sheathing to cover their
bottoms. In the East Indies, and off the coast of Africa, the
_Teredo_ is of very large size; and holes have been bored by them
in the timber of at least seven-eighths of an inch in diameter.
[87] Alberti Archeti.
[88] In the year 1670, an Act of Parliament was passed, granting
unto Sir Philip Howard and Francis Watson, Esq. the sole use of
the manufacture of milled lead for sheathing ships; and, in the
year 1691, twenty ships had been sheathed with lead, manufactured
by them, and which was fastened with copper nails.--See
_Knowles's Inquiry_.
In the year 1761, copper plates were first used as sheathing on
the Alarm frigate, of thirty-two guns;[89] a second underwent this
operation in 1765, a third in 1770, four in 1776, nine in 1777;
and, in the course of the three following years, the whole British
navy was coppered: an event which may be considered as forming an
important era in the naval annals of the country.
[89] The copper sheathing was removed from this ship in 1763,
when all the iron was found to be much corroded, the pintles and
braces nearly eaten through, and the false keel lost, from the
decay of the keel staples and the bolt fastenings. Thus, in the
very first coppered ship, the Voltaic effect, produced by the
contact of copper and iron, was displayed in a very striking
manner.
The expense attending the use of copper for this purpose, in
consequence of its corrosion and decay by salt-water, has
always been felt as a serious objection to its use, and various
suggestions have from time to time occurred, and numerous
experiments been made, in the hope of obviating the evil,[90] but
without any great degree of success.
[90] An experiment was tried by painting or varnishing their
inner surfaces, but the use of brown paper which has been dipped
in tar, and placed between the wood and copper, is now considered
to be the best mode. A solution of caoutchouc spread on paper
was tried on the bottom of Sir W. Curtis's yacht; but, on
examination, it was pronounced to be less efficacious than tarred
paper.
The solution of the metal, however, has been found to vary in
degree at different anchorages: at Sheerness, for instance,
its rapidity is very great, in consequence of the copper being
subjected to the alternate action of the sea, which flows in there
from the British Channel, and to the flux of water down the two
great rivers, the Thames and Medway, loaded, as they necessarily
must be, with the products of animal and vegetable decomposition.
In order, if possible, to obtain a remedy for this evil, the naval
departments of the Government requested, in the latter part of the
year 1823, the advice of the President and Council of the Royal
Society, as to the best mode of manufacturing copper sheets, or of
preserving them, while in use, against the corrosive effects of
oxidation.
Sir H. Davy charged himself with this enquiry; the results of
which he communicated to the Royal Society, in three elaborate
memoirs. The first was read on the 22nd of January 1824; the
second, on the 17th of June, in the same year; and the third, and
concluding paper, on the 9th of June 1825.
A very general belief prevailed, that sea-water had little or no
action on _pure_ copper, and that the rapid decay of that metal on
certain ships was owing to its impurity. On submitting, however,
various specimens of copper to the action of the sea-water, Sir
H. Davy came to a conclusion, in direct opposition to such an
opinion;[91] and Mr. Knowles informed me, in a late conversation
upon the subject, that the attempts to purify the metal, since the
Government has manufactured its own copper sheathing, has been the
cause of its more rapid decay. It will however presently appear,
that the relative durability of the metallic sheets must also be
influenced by circumstances wholly independent of their quality,
some of which are very probably, even in our present advanced state
of chemical knowledge, not thoroughly understood.
[91] In two instances, the copper (from the Batavier and from
the Plymouth yacht) which had remained perfect for twenty-seven
years, was found to be alloyed. In the former one there was an
alloy of one three-hundredth part of zinc; and, in the latter,
the same proportion of tin. On the other hand, in the case of
the copper on the Tartar's bottom, which was nearly destroyed in
four years, upon being submitted to chemical examination by Mr.
Phillips, it was found to be very pure copper.
Alloys of copper have generally been found more durable than the
unmixed metal; and various patents have been taken out for the
fabrication of such compounds; but metallic sheets so composed
have been found to be too hard and brittle, and not to admit of
that flexibility which is necessary for their application to a
curved surface; the consequence of which has been, that they have
cracked upon the ship's bottom.
Sir H. Davy, on entering upon the examination of this subject,
very justly considered, that to ascertain the exact nature of the
chemical changes which take place in sea-water, by the agency of
copper, ought to be the first step in the enquiry; for, unless the
cause were thoroughly understood, how could the evil be remedied?
On keeping a polished piece of copper in contact with sea-water,
the following were the effects which successively presented
themselves. In the course of two or three hours, the surface of
the metal exhibited a yellow tarnish, and the water in which it
was immersed contracted a cloudiness, the hue of which was at
first white, but gradually became green. In less than a day, a
bluish-green precipitate appeared, and constantly continued to
accumulate in the bottom of the vessel; at the same time, the
surface of the copper corroded, appearing red in the water, and
grass-green where it was in contact with air. Upon this grass-green
matter carbonate of soda formed; and these changes continued
until the water became much less saline. The green precipitate he
ascertained to consist of an insoluble compound of copper, (which
he thinks may be considered as a _hydrated sub-muriate_,) and
hydrate of magnesia.[92]
[92] The Muriate of Magnesia is the most active salt in sea-water.
According to his own views of the nature of chlorine, he
immediately perceived that neither soda nor magnesia could appear
in sea-water by the action of a metal, unless in consequence of an
absorption or transfer of oxygen, which in this case must either be
derived from the atmosphere, or from the decomposition of water:
his experiments determined that the former was the source which
supplied it. By reasoning upon these phenomena, and applying for
their explanation his electro-chemical theory, which had shown
that chemical attractions may be exalted, modified, or destroyed,
by changes in the electrical states of bodies, he was led to the
discovery of a remedy for the corrosion of copper, by the very
principle which enabled him, sixteen years before, to decompose the
fixed alkalies.
When he considered that copper is but weakly positive in the
electro-chemical scale, and that it can only act upon sea-water
when in a positive state, it immediately occurred to him that, if
it could be rendered slightly negative, the corroding action of
sea-water upon it would be null. But how was this to be effected?
At first, he thought of using a Voltaic battery; but this could
hardly be applicable in practice. He next thought of the contact of
zinc, tin, or iron; but he was prevented for some time from trying
this, by the recollection that the copper in the Voltaic battery,
as well as the zinc, was dissolved by the action of dilute nitric
acid; and by the fear, that too large a mass of oxidable metal
would be required to produce decisive results. After reflecting,
however, on the slow and weak action of sea-water on copper, and
the small difference which must exist between their electrical
powers; and knowing that a very feeble chemical action would be
destroyed by a very feeble electrical force, he was encouraged to
proceed; and the results were highly satisfactory and conclusive. A
piece of zinc, not larger than a pea, or the point of a small iron
nail, was found fully adequate to preserve forty or fifty square
inches of copper,--and this, wherever it was placed, whether at the
top, bottom, or in the middle of the sheet of copper, and whether
the copper was straight or bent, or made into coils. And where the
connexion between the different pieces of copper was completed by
wires, or thin filaments of the fortieth or fiftieth of an inch in
diameter, the effect was the same; every side, every surface, every
particle of the copper, remained bright; whilst the iron, or the
zinc, was slowly corroded.
A piece of thick sheet copper, containing on both sides about sixty
square inches, was cut in such a manner as to form seven divisions,
connected only by the smallest filaments that could be left, and
a mass of zinc, of the fifth of an inch in diameter, was soldered
to the upper division. The whole was plunged under sea-water;
the copper remained perfectly polished. The same experiment was
repeated with iron, and after the lapse of a month, the copper was
in both instances found as bright as when it was first introduced;
whilst similar pieces of copper, undefended, underwent in the same
water very considerable corrosion, and produced a large quantity of
green deposit in the bottom of the vessel.
Numerous other experiments were performed, and with results equally
conclusive of the truth of the theory which had suggested them.
There was however one point which still remained for enquiry. As
the ocean may be considered in its relation to the quantity of
copper in a ship, as an infinitely extended conductor, it became
necessary to ascertain whether that circumstance would influence
the results. For this purpose, he placed two very fine copper
wires, one undefended, the other defended by a particle of zinc, in
a very large vessel of sea-water, which water might be considered
to bear the same relation to so minute a portion of metal, as the
sea to the metallic sheathing of a ship. The result was perfectly
satisfactory. The defended copper underwent no change; the
undefended tarnished, and deposited a green powder.[93]
[93] During the course of some experiments in which I have been
lately engaged, a simple mode of exhibiting the principle of
protection occurred to me, which, I believe, has not before
been suggested; at least, I cannot find any notice of such
an experiment. As I consider it admirably calculated for
illustration, I will here describe it. Let two slips of copper
of equal size, the one protected with a piece of zinc, the other
unprotected, be plunged into two wine-glasses filled with a
solution of ammonia. In a short time, the liquor containing the
unprotected copper will assume an intensely blue colour; the
other will remain colourless for any length of time. The theory
is obvious. When metallic copper is placed in contact with an
ammoniacal solution, a protoxide of the metal is formed which
is colourless,--and will remain so, if the contact of air be
prevented; but on exposure to the atmosphere, it passes into
a state of peroxide, which is dissolved by the ammonia, and
produces an intensely blue solution. In the case of the protected
copper, the metal is incapable of attracting a single atom of
oxygen, in consequence of having been rendered negative by the
zinc, and consequently no solution can take place.
Davy having thus satisfied his own mind as to the truth of his
views, communicated to Government, in January 1824, the important
fact of his having discovered a remedy for the evil of which they
had complained; and that the corrosion of the copper sheathing of
his Majesty's ships might be prevented by rendering the copper
electro-positive, by means of the contact of tin, zinc, lead, iron,
or any other easily oxidable metal; and that he was prepared to
carry his plan into effect.
A proposition from a philosopher of such known science, and upon a
subject of such great importance to the navigation and commerce of
the country, immediately obtained all the attention it deserved;
and an order was made that the plan of protection should, under the
superintendence of Sir H. Davy, be forthwith tried upon the bottom
of a sailing cutter.
To give to his discovery farther publicity, Sir Humphry requested
that three models of ships might be exhibited in the spacious hall
of the Navy Office in Somerset House; the copper of one of which he
proposed should be protected by bands of zinc, that of another by
plates of wrought iron soldered on the sheathing, while the third
should have its copper exposed without any protection whatever.
These models were floated in sea-water for several months; and the
experiment fully confirmed the results he had previously obtained
in his laboratory. The models were from time to time examined by
persons of the highest scientific character, as well as by others
of great naval celebrity; and so alluring was the theory, and so
conclusive the experiments, that, instead of waiting the result
of the slow but more certain ordeal to which the plan had been
submitted, it was immediately put into extensive practice, both in
the Government service and on the bottoms of ships belonging to
private individuals.
To those the least acquainted with the principles of Voltaic
action, it was only necessary to state the proposition, in order
to command their assent to its truth. The utility of the plan
therefore was never questioned, but the claims of Davy to the
originality of the invention were doomed to meet with immediate
opposition.[94]
[94] Amongst other counter-claims, there appeared, in a weekly
publication entitled "The Mechanic's Magazine," a statement in
favour of a person of the name of Wyatt, founded on the following
advertisement in "The World" newspaper of April 16, 1791. "By
the King's Patent, tinned copper sheets and pipes manufactured
and sold by Charles Wyatt of Birmingham. These sheets, amongst
other advantages, are particularly recommended for sheathing of
ships, as they possess all the good properties of copper, with
others obviously superior." It is unnecessary to observe that,
except their object, there is nothing in common in the inventions
of Davy and Wyatt. The superiority claimed by Wyatt consisted
merely in coating the copper with some substance less corrosive
by sea-water than that metal: an idea borrowed from the common
practice of tinning copper vessels.
The correctness of the principle having been established, it
became, in the next place, necessary to determine the most eligible
metal to be used for protection; the proportion which it must bear
to the surface of the copper-sheathing below the waterline; the
form least likely to offer resistance to the sea, and to impede the
sailing of the vessel; and lastly, its most convenient position on
the ship's bottom. To ascertain these several points, Lord Melville
and the Lords of the Admiralty desired the Commissioners of the
Navy Board, and of the Dock-yards, to afford Sir Humphry every
assistance and facility for prosecuting the necessary experiments;
and he accordingly made many very extensive trials, not only on
copper sheets which were immersed in the sea, but also on the
bottoms of a considerable number of boats which had been coppered
for that purpose, and exposed to the flow of the tide in Portsmouth
harbour; upon which occasions he varied the nature as well as the
proportions of the protecting metal. The results were communicated
to the Royal Society, and they constituted the materials for his
second memoir on the subject.
"When the metallic protector was from 1/20 to 1/110 parts of
its surface, there was no corrosion nor decay of the copper;
with smaller quantities, such as from 1/200 to 1/400, the copper
underwent a loss of weight, which was greater in proportion as the
protector was smaller; and, as a proof of the universality of the
principle, it was found that even 1/1000 part of cast iron saved a
certain proportion of the copper.
"The sheeting of boats and ships, protected by the contact of zinc,
or cast and malleable iron in different proportions, compared with
those of similar boats and sides of ships unprotected, exhibited
bright surfaces; whilst the unprotected copper underwent rapid
corrosion, becoming first red, then green, and losing a part of
its substance in scales. Fortunately, in the course of these
experiments, it was proved that cast iron, the substance which is
cheapest and most easily procured, is likewise most fitted for the
protection of the copper. It lasts longer than malleable iron, or
zinc; and the plumbaginous substance which is left by the action of
sea-water upon it, retains the original form of the iron, and does
not impede the electrical action of the remaining metal."
In the earlier stage of the investigation, it had been suggested
by Mr. Knowles, and several other persons, that by rendering the
copper innoxious, it was probable sea-weeds might adhere to the
sheets; but this objection he answered by stating, that negative
electricity could not be supposed favourable to animal and
vegetable life; and as it occasioned the deposition of magnesia,
a substance exceedingly noxious to land vegetables, upon the
copper surface, he entertained no difficulty upon that subject: in
this, however, he was fatally mistaken. He found, after a trial
of several weeks, that the metallic surface became coated with
carbonate of lime and magnesia, and that, under such circumstances,
weeds adhered to the coatings, and marine insects collected upon
them; but at the same time he observed, that when the proportion of
cast iron, or zinc, was below 1/150, the electrical power of the
copper being less negative, no such deposition occurred; and that
although the surface had undergone a slight degree of solution,
it remained perfectly clean: a fact which he considered of great
importance, as it pointed out the _limits of protection_; and makes
the application of a _very small_ quantity of the oxidable metal
more advantageous, in fact, than that of a larger one.
During the course of these experiments, many singular facts occurred
to him, which tended to confirm his views of electro-chemical
action. Amongst the various details which remained for his
investigation, the relations between the surface of the
protector, and that of the copper sheathing, under the different
circumstances of temperature, saltness of the sea, and rapidity
of the ship's motion, presented themselves as objects of great
importance; and an opportunity occurred which enabled him to
pursue them by actual observation and experiment.
In the month of June 1824, a steam-vessel, H.M. ship the Comet,
was, at the express request of the King of Denmark, ordered to
proceed to Heligoland, for the purpose of fixing with precision, by
means of numerous chronometers, the longitude of that island, in
order to connect the Danish with the British survey; and the Board
of Longitude having recommended that the voyage should be extended
as far as the Naze of Norway, for the purpose of ascertaining also
the longitude of that important point, Sir H. Davy thought that
this vessel would afford him the means of performing his desired
experiments upon protected and unprotected copper sheets, when
under the influence of rapid motion; and upon application to the
Board of Admiralty, he obtained the entire disposal of the vessel
after the required observations had been completed, as long as the
season would allow her going to sea; and, that every facility might
be afforded him, a skilful carpenter was put on board, to prepare
whatever might be necessary for the prosecution of the enquiry.
For the following account of his adventures upon this occasion I
am indebted to Dr. Tiarks, who, in his character of astronomical
observer, superintended the expedition.
In the first instance, Davy directed to be constructed a number of
oblong, rectangular, thin plates of copper, the surface of which
should exceed that of a square foot: in the centre of these plates
was fastened a slip of copper, by means of which other pieces
of copper, which had small plates of iron of various dimensions
attached to them, were fixed to the plate, by merely sliding them
into the groove thus prepared for their reception. The plates
were all carefully weighed previously to the experiment, and
the pieces of iron were considered as representing the various
proportions of iron and copper surfaces within whose limits Sir H.
Davy had been led, by former experiments, to expect that the best
proportion would be found. These plates were afterwards slipped
into wooden frames, and nailed to the ship's side, over a piece
of thick canvass, for the purpose of intercepting every possible
communication between them and the copper sheathing.
It was proposed that, after each trip, these plates should be
accurately weighed, in order to ascertain the loss which they
severally might sustain from the corrosive action of the sea, while
thus protected by different proportions of iron surface; and, to
ensure every possible accuracy, he carried with him the excellent
balance, constructed by Ramsden, which is in possession of the
Royal Society.
Sir H. Davy, accompanied by Lord Clifton, embarked at Greenwich on
the 30th of June, and the vessel arrived at Heligoland on the 2nd
of July. Here, as they remained not more than one day, the plates
were not examined, although the Master expressed strong doubts
as to their safety. The vessel then proceeded, by order of Sir
Humphry, to Norway, a country which he was, for several reasons,
very desirous of visiting, especially for the sake of determining
a doubtful point in ornithology, upon which he subsequently
corresponded with Professor Rheinhard, of Copenhagen.
The difference of longitude, also, between that country and
Greenwich, not having been accurately ascertained, offered perhaps
an additional reason for thus deviating from a course which, it
must be confessed, was at variance with the original plan of the
expedition.
After a severe gale of wind on the 4th of July, the vessel arrived,
on the day following, at Rleve, near Mandal, and afterwards
proceeded to this latter place, at which Davy remained for several
days, during which interval the vessel made a tour to the Naze, and
took in coal.
On the arrival of the vessel in the port, the plates were
immediately examined; but, to the great disappointment of Sir
Humphry, it was discovered that every one of the protectors had
been washed away, and that most of the plates had sustained
considerable injury.
With the country around Mandal he was much pleased; for, although
it is far from being fertile, the scenery is rendered exceedingly
striking and beautiful by the numerous lakes which wash the feet of
high and sometimes perpendicular mountains, at that time clothed
with the rich verdure of their summer herbage.
Sir Humphry made several excursions into the interior of the
country, and derived much amusement from angling in the lakes;
and had it not been from his own inspection of the roads, and the
information which he collected respecting them, together with an
indisposition of his fellow-traveller, Lord Clifton, he would have
made an extensive land journey through the country; but, under the
existing circumstances, he determined to return to England through
Denmark and Germany. He therefore at once resolved to take the
steam-boat with him as far as Sweden, where the excellent roads
would enable him, without inconvenience, to reach Gottenburg, and
thence to continue his route through Denmark to Germany. The vessel
proceeded accordingly to Christiansand, the chief town of a country
of the same name.
Having been provided with some spare plates and protectors, he
fixed them to the ship's side at Mandal, as he was informed that
the voyage could be entirely performed within the rocks, with which
the whole coast of Norway is so plentifully studded; but a short
traverse through an open part of the sea, not far from Mandal,
again defeated his object. The protectors were washed away, and no
result was obtained.
At Christiansand he remained a few days, in order to try some new
plates, which were constructed there under his own inspection. Upon
this occasion he made an excursion to the falls of the Torjedahl,
distant about six miles from the town. The river abounds with
salmon, which were easily caught in their descent from the falls,
by an apparatus contrived for that purpose. Sir Humphry amused
himself by teaching the inhabitants the operation of _crimping_,
and he declared the flavour of the fish to be superior to any
salmon he had ever tasted.
It was at Christiansand that he became acquainted with the
Norwegian race of ponies, so well adapted for mountainous
countries; and which, at his recommendation, were afterwards
introduced into England by Mr. Knight, of Downton Castle.
From Christiansand the vessel proceeded on her route eastward to
Arendal, where she arrived on the 12th, after a passage of only a
few hours. The route lay entirely within the rocks,--and so narrow
were the passages, that the vessel could frequently not pass the
rocks on either side without touching them.
At Arendal, which is the chief place of a remarkable mining
district, Sir Humphry was well received by the Messrs. Dedehamys,
two brothers, and the leading merchants of the place, with whom
he made several excursions to the neighbouring mines. He was also
invited by them to meet at their beautiful country seats the most
respectable inhabitants of the town.
In the house of Mr. Dedehamy, Davy was introduced into Norwegian
society, and, for the first time, had an opportunity of witnessing
the customs and manners of the country.
A short time before dinner, the guests were summoned to partake
of pickled fish, anchovies, and smoked salmon, with rum, brandy,
and wine, which were placed on small tables in the drawing-room in
which the company assembled. This custom of taking salt provisions,
together with spirits, just before dinner, is very general in
the North, and is considered as the best means of preparing the
stomach, and of provoking an appetite for the approaching meal.
The very numerous party, which, with the exception of the hostess
and her daughter, consisted entirely of men, were then ushered
into two large rooms, one not being sufficiently spacious to
accommodate them, and each person took his seat promiscuously. At
the beginning of the dinner, large basins filled with sugar were
carried round by the host's daughter, followed by a servant, from
which each gentleman took a large handful. Sir Humphry, surprised
at so singular a ceremony, enquired its meaning; when the host very
good-humouredly answered, that in Norway they thought, if the wine
was good it could not be spoiled by sugar,--and if bad, that it
would be improved by it. Davy immediately followed the example of
the company, and helped himself to the sugar.
Amongst the party present were several members of the Diet
(Storthing), which had recently refused the applications of the
King for various grants of money. This subject excited much
animated conversation, and the majority of the persons present
expressed their approbation at so bold and independent a measure.
This called forth a political toast relating to the situation
of their country; when the whole company, elated with wine and
conversation, simultaneously burst forth into the national chorus
of Norway, which had been composed as a prize poem during the short
struggle against the union of that country with Sweden, and which
was much admired by the Norwegians, and on all occasions sung by
them with the utmost enthusiasm of feeling; but, notwithstanding
the liberal politics of the party, they drank Sir Humphry's
toast--"THE KING OF NORWAY AND SWEDEN"--with much apparent loyalty.
A succession of toasts followed, the last of which recommended
"THE BRITISH CONSTITUTION AS A MODEL FOR ALL THE WORLD." With
this sentiment the festivities concluded--a momentary silence
ensued; the custom of the country assigned to a stranger the
honourable office of returning to the host and hostess the thanks
of the company for their hospitable reception; all eyes were
anxiously fixed upon the English philosopher; and as soon as he
was made acquainted with the duty he was expected to perform, he
rose from his seat, and in allusion to the sentiment so recently
drunk in compliment to himself, he proposed as a concluding toast,
"NORWEGIAN HOSPITALITY A MODEL FOR ALL THE WORLD."
From Arendal the vessel proceeded to Laurvig, where she stopped
only a few hours; but Sir Humphry seized this opportunity to go on
shore to view the country, and he afterwards weighed the copper
plates which had been attached to the ship in Christiansand, as
the vessel was now to cross that deep bay, at the bottom of which
is situated Christiana, the capital of the kingdom. The few plates
were found to be in good order; and the results, which however
must be allowed to have been very incomplete, confirmed, as far
as they went, the conclusions to which he had been led by former
experiments, viz. that 1/200 of iron surface was the proportion
best calculated to defend the copper, without so overprotecting
it as to favour the adhesion of marine productions; while they
moreover proved that there is a mechanical as well as a chemical
wear of the copper, which, in the most exposed part of the ship,
and in the most rapid course, bears a relation to it of nearly 2 to
4.55.
The country increased in fertility towards the eastern parts of it;
but it possessed much less beauty than the neighbourhood of Mandal.
As soon as Davy perceived that the vessel had to pass near the
mouth of the Glommen, the largest river of Norway, he directed that
she should enter it. Steam-boats appeared to have been entirely
unknown in that part of the country. The inhabitants of the town of
Frederickstadt were alarmed by the belief that the vessel was on
fire, and they ran down to the beach in multitudes. As the vessel
proceeded up the river, the people every where left their work,
looked on awhile in silent amazement, and then shouted with delight.
The vessel anchored a mile below the great fall of the Glommen,
called _Sarpen_, and which Davy visited on the following day
(July 15). Three Kings of Denmark have visited this fall, and a
name commemorates the spot whence they viewed this grand scene of
nature. The fall is not one perpendicular descent, but consists
of three sheets of water closely succeeding each other; and, by
means of a barometer, he ascertained the entire altitude to be
little more than a hundred feet. In comparing the character of this
waterfall with those of the others he had visited, he observes,
that size is merely comparative; and that he prefers the Velino at
Terni, on account of the harmony that exists in all its parts. It
displays all the force and power of the element, in its rapid and
precipitous descent; and you feel that even man would be nothing in
its waves, and would be dashed to pieces by its force. The whole
scene is embraced at once by the eye, and the effect is almost as
sublime as that of the Glommen, where the river is at least one
hundred times as large; for the Glommen falls, as it were, from a
whole valley upon a mountain of granite; and unless where you see
the giant pines of Norway, fifty or sixty feet in height, carried
down by it and swimming in its whirlpools like straws, you have no
idea of its magnitude and power. Considering these waterfalls in
all their relations, he is disposed to think, that while that of
Velino is the most perfect and beautiful, the fall of the Glommen
is the most awful.
On both sides of this fall are extensive saw-mills, with machinery
of very imperfect construction. Davy spent some time with the
proprietors of these mills, who were acquainted with the English
language, and showed him every attention in their power. As an
angler, he spoke with regret of the immense quantity of sawdust
which floated in the water, and formed almost hills along the
banks, and which, he observed, must be poisonous to the fish,
by sometimes choking their gills, and interfering with their
respiration.
From the Glommen the steam-vessel passed through the Svinesund
to Strömstadt, the first town in Sweden beyond the frontier of
Norway, from which Charles XII. essayed to besiege the neighbouring
fortress of Frederickstadt in Norway. From Strömstadt, Davy set out
on the 17th of July, and reached Gottenburg by land in two days,
where he remained for a short time, in consequence of a slight
indisposition. On his journey, he had a conversation with Oscar,
the Crown Prince of Denmark, who, under the direction of Berzelius,
had diligently devoted himself to the study of chemistry. He
conversed with our philosopher upon various subjects connected with
that science; and Davy, on his return to England, declared that he
had never met with a more enlightened person.
The Crown Prince expressed great surprise, as indeed did every body
in Sweden, on hearing that it was not Davy's intention to visit
Professor Berzelius at Stockholm; and his astonishment was still
farther increased, when he was informed by himself, that he came to
Norway and Sweden with no other view than to enjoy the diversion
of hunting and fishing! He however did by accident afterwards meet
Berzelius, but his interview was but of short duration.
From Gottenburg he hastened to Copenhagen, where he renewed his
acquaintance with Prince Christian of Denmark, cousin of the
King, and heir presumptive of the crown; in whose company he
had some years before observed an eruption of Mount Vesuvius.
He also visited Professor Oersted, and earnestly requested that
he might see the apparatus by which that philosopher had made
those electro-magnetic experiments which had rendered his name so
celebrated throughout Europe.
He next proceeded to Neuburg and Altona, where he intended to
re-embark for England in the steam-vessel which had, during the
interval of his continental tour, made a voyage to England, and
was again on her way to the Elbe. At the suggestion, however, of
Professor Schumacher, the astronomical professor at Copenhagen,
but residing at Altona, in whose society he passed a great portion
of his time, he accompanied that gentleman to Bremen, in order to
make the acquaintance of the venerable Dr. Olbers, who, since his
retirement from an extensive medical practice, had entirely devoted
his time to the pursuit of his favourite science astronomy; as well
as to be introduced to Professor Gauss, of Gottingen, who happened
to be at that time carrying on his geodetical operations for the
admeasurement of the kingdom of Hanover.
Davy expressed a great desire to see the telescope with which Dr.
Olbers had discovered the two planets, Pallas and Vesta, and which
to his great surprise turned out to be a very ordinary instrument.
His personal intercourse with these two celebrated philosophers
appeared to afford him the highest satisfaction; and he spent two
days most agreeably in their society.
In his "Salmonia," he gives us some account of his adventures as
an angler during this short excursion to Norway and Sweden. "All
the Norwegian rivers," says he, "that I tried (and they were in
the southern parts) contained salmon. I fished in the Glommen, one
of the largest rivers in Europe; in the Mandals, which appeared
to me the best fitted for taking salmon; and in the Arendal; but,
though I saw salmon rise in these rivers, I never took a fish
larger than a sea-trout; of these I always caught many--and even
in the _fiords_, or small inland salt-water bays; but, I think,
never any one more than a pound in weight. It is true that I was
in Norway in the beginning of July, in exceedingly bright weather,
and when there was no night; for even at twelve o'clock the sky
was so bright, that I read the smallest print in the columns of
a newspaper. I was in Sweden later--in August: I fished in the
magnificent Gotha, below that grand fall, Trollhetta, which to see
is worth a voyage from England; but I never raised there any fish
worth taking. I caught, in this noble stream, a little trout about
as long as my hand; and the only fish I got to eat at Trollhetta
was bream."
He again embarked, on the 14th of August, on board the Comet
steam-vessel, which had ascended the Weser as high as her draught
of water would allow, and reached England, after a very boisterous
passage, on the 17th of the same month; indeed, the vessel left
the mouth of the Weser with a contrary wind, and the pilot was
unwilling to put to sea, but Davy insisted on proceeding without
delay. During the whole passage he suffered extremely from
sea-sickness, and in a letter written to Professor Schumacher,
shortly after landing, he remarks that "the sea is a glorious
dominion, but a wretched habitation."
* * * * *
On the 9th of June 1825, Sir Humphry read before the Royal
Society his third and most elaborate paper upon Copper sheathing,
entitled "Farther Researches on the Preservation of Metals by
Electro-chemical Means."
In this memoir, he states it to be his belief, that there is
nothing in the poisonous nature of the copper to prevent the
adhesion of weeds and testaceous animals; for he observes, that
they will readily adhere to the poisonous salts of lead which
commonly form upon the metal protecting the fore-part of the keel;
and even upon copper, provided it be in such a state of chemical
combination as to be insoluble. It is then, in his opinion, the
_solution_ of the metal--the _wear_ of its surface, by keeping it
smooth, which prevents the adhesion of foreign matter. Whenever the
copper is unequally worn, deposits will, without doubt, rest in the
rough parts, or depressions in the metal, and afford a soil or bed
in which sea-weeds can fix their roots, and to which zoophytes and
shell-fish can adhere; but there is another cause of foulness on
the protected sheathing, arising from the deposit of earthy matter
upon the copper, in consequence of its electro-negative condition.
In relation to this subject, Davy has offered some observations
upon the effects produced by partial formations of rust, which
appear to me to be exceedingly interesting and important.
When copper has been applied to the bottom of a ship for a
certain time, he says, a green coating, or rust, consisting of
oxide, sub-muriate, and carbonate of copper, forms upon it; not
equally throughout, but partially, and which, it is evident, must
produce a _secondary_, partial, and unequal action, since those
substances are negative with respect to metallic copper, and will
consequently, by producing with it a Voltaic circuit, occasion a
more rapid corrosion of those parts still exposed to sea-water:
from this cause, sheets are often found perforated with holes in
one part, after having been used for five or six years; while in
other parts they are comparatively sound.[95] In like manner, the
heads of the mixed metal nails, consisting of copper alloyed by a
small quantity of tin, which are in common use in the Navy, give
rise to oxides that are negative with respect to the copper, so
that the latter is often worn into deep and irregular cavities in
their vicinity.
[95] The rusting of a common piece of iron, if carefully
inspected, furnishes a beautiful illustration of this secondary
action. The oxide, at first a mere speck, and formed perhaps by a
globule of water, becomes negative with respect to the contiguous
surface, and by thus forming a Voltaic circuit, exalts its
oxidability, and the rust consequently extends in a circle.
A series of very interesting experiments, fully detailed in this
memoir, which were instituted for the purpose of ascertaining the
extent of the diminution of electrical action in instances of
imperfect or irregular conducting surfaces, led him to the general
conclusion, that a very small quantity of the imperfect or fluid
conductor was sufficient to transmit the electrical power, or to
complete the chain. This induced him to try whether copper, if
nailed upon wood, and protected merely by zinc or iron on its
_under_ surface, or on that next the wood, might not be defended
from corrosion: a question of great practical moment with regard
to the arrangement of protectors. For this purpose, he covered
a piece of wood with small sheets of copper, a nail of zinc of
about 1/100 part of the surface having been previously driven
into the wood: the copper surface remained perfectly bright in
sea-water for many weeks; and when the result was examined, it
was found that the zinc had only suffered partial corrosion; that
the wood was moist, and that, on the interior of the copper there
was a considerable portion of revived zinc, so that the negative
electricity, by its operation, provided materials for its future
and constant excitement. In several trials of the same kind, iron
was used with similar results; and in all these experiments there
appeared to be this peculiarity in the appearance of the copper,
that unless the protecting metal below was in a large mass, there
were no depositions of calcareous or magnesian earths upon the
metal; it was clean and bright, but never coated. The copper in
these experiments was nailed sometimes upon paper, sometimes upon
the mere wood, and sometimes upon linen; and the communication was
partially interrupted between the external and internal surfaces by
cement; but even one side or junction of a sheet seemed to allow
sufficient communication between the moisture on the under surface
and the sea-water without, to produce the electrical effect of
preservation. This last experiment of Davy is of greater importance
than may at first appear, in showing what a small proportion of
conducting fluid will complete a circuit, and in thus explaining
phenomena, as I shall presently show, which might not otherwise be
suspected to have an electrical origin.
These results upon perfect and imperfect conductors led him
to another enquiry, important as it relates to the practical
application of the principle, namely, as to the extent and nature
of the contact or relation between the copper and the preserving
metal. He was unable to produce any protecting action of zinc
or iron upon copper through the thinnest stratum of air, or the
finest leaf of mica, or of dry paper; but the action of the metals
did not seem to be much impaired by the ordinary coating of
oxide or rust; nor was it destroyed when the finest bibulous, or
_silver-paper_, as it is commonly called, was between them, being
moistened with sea-water. He made an experiment with different
folds of this paper. Pieces of copper were covered with one, two,
three, four, five, and six folds; and over them were placed pieces
of zinc, which were fastened closely to them by thread; each piece
of copper, thus protected, was exposed in a vessel of sea-water, so
that the folds of paper were all moist.
It was found in the case in which a single leaf of paper was
between the zinc and the copper, there was no corrosion of the
copper; in the case in which there were two leaves, there was a
very slight effect; with three, the corrosion was distinct; and it
increased, till with six folds the protecting power appeared to
be lost; and in the case of the single leaf, the result differed
only from that produced by immediate contact, in there not being
any deposition of earthy matter. Other experiments likewise proved
that there was no absolute contact of the metals through the moist
paper; for, although a thin plate of mica, as before stated,
entirely destroyed the protecting effect of zinc, yet when a hole
was made in it, so as to admit a very thin layer of moisture
between the zinc and copper, the corrosion of the latter, though
not prevented, was considerably diminished.
The experimental part of this paper concludes with an account of
various trials to determine the electro-chemical powers of metals
in menstrua out of the contact, or to a certain extent removed
from the contact of air; in order, if possible, to diminish the
rapid waste of the protecting metals. In the progress of these
experiments he exhibits, in a most beautiful manner, the singular
effect of different proportions of a fixed alkali, when mixed with
sea-water, in rendering the iron, in its Voltaic connection with
copper, more or less negative.
He terminates the paper with some observations of a practical
nature, relative to the best modes of rendering iron applicable
to the purposes of protection; but, as these have been already
embodied in the investigation, it is not necessary to notice them
farther in this place.
That I may give to the history of this subject all the perspicuity
which it can derive from the connexion of its several parts, I
shall now, in defiance of chronological order, proceed to consider
his last Bakerian Lecture, "On the Relations of Electrical
Changes," which was read before the Royal Society, on the 8th
of June 1826. In which, after referring to his former papers
on the chemical agencies of electricity, and the general laws
of decomposition which were developed in them, he enters into
some historical details respecting the origin and progress of
electro-chemical science; being induced so to do, from a knowledge
of the very erroneous statements which had been published upon the
subject abroad, and repeated in this country. At the conclusion of
this lecture, in reverting to the subject of Voltaic protection, he
says: "A great variety of experiments, made in different parts of
the world, have proved the full efficacy of the electro-chemical
means of preserving metals, particularly the copper sheathing
of ships; but a hope I had once indulged, that the peculiar
electrical state would prevent the adhesion of weeds or insects,
has not been realized; protected ships have often indeed returned,
after long voyages, perfectly bright,[96] and cleaner than
unprotected ships; yet this is not always the case; and though
the _whole_ of the copper may be preserved from chemical solution
in steam-vessels (from the rapidity of their motion) by these
means,--yet they must be adopted in common ships only so as to
preserve a portion,--so applied, as to suffer a certain solution
of the copper;[97] and an absolute remedy for adhesions is to be
sought for by other more refined means of protection, and which
appear to be indicated by these researches.
[96] The Carnbrea Castle, a large vessel, of upwards of six
hundred and fifty tons, was furnished with four protectors,
two on the stern, and two on the bow, equal together to about
1-104th of the surface of copper. She had been protected more
than twelve months, and had made the voyage to Calcutta and back.
She came into the river perfectly bright; and, when examined in
the dry-dock, was found entirely free from any adhesion, and
offered a beautiful and almost polished surface; and there seemed
to be no greater wear of copper than could be accounted for from
mechanical causes.
[97] A common cause of adhesions of weeds or shell-fish, is the
oxide of iron formed and deposited round the protectors. In the
only experiment in which zinc has been employed for this purpose
in actual service, the ship returned after two voyages to the
West Indies, and one to Quebec, perfectly clean. The experiment
was made by Mr. Lawrence, of Lombard Street, who states that the
rudder, which was not protected, had corroded in the usual manner.
"The nails used in ships are an alloy of copper and tin, which I
find to be slightly negative with respect to copper, and it is
on these nails that the first adhesions uniformly take place: a
slightly positive and slightly decomposable alloy would probably
prevent this effect, and I have made some experiments favourable to
the idea."
He next proceeds to state some circumstances, in addition to
those he had formerly noticed, by which the electrical relations
of copper are altered. "I found," says he, "copper hardened by
hammering, _negative_ to rolled copper;--copper (to use the
technical language of manufacturers) both _over-poled_ and
_under-poled_,[98] containing, in one case, probably a little
charcoal, and in the other a little oxide, _negative_ to pure
copper. A specimen of brittle copper, put into my hands by Mr.
Vivian, but in which no impurity could be detected, was negative
with respect to soft copper. In general, very minute quantities of
the oxidable metals render the alloy positive, unless it becomes
harder, in which case it is generally negative."
[98] The _poling_ of copper is an operation, the theory of which
is involved in a great deal of mystery. Copper, when taken from
the smelting furnace, is what is termed _dry_, that is, it is
brittle, has an open grain and crystalline structure, and is of a
purplish red colour. The following is the process by which it is
refined, or _toughened_, by the process of _poling_. The surface
of the melted metal in the furnace is, in the first place,
covered with charcoal. A pole, commonly of birch, is then plunged
into the liquid metal, which produces a considerable ebullition
from the evolution of gaseous matter, and this operation is
continued, fresh charcoal being occasionally added, so that the
surface may be always kept covered, until the refiner judges
from the assays that the metal is malleable. The delicacy of the
operation consists in the difficulty of hitting the exact mark:
if the surface should by accident be uncovered, it will return to
its _dry_ state; and should the process be carried too far, it
will be _over-poled_, by which the metal would be rendered even
more brittle than when in a _dry_ state. When this is found to be
the case, or, as they say, _gone too far_, the refiner directs
the charcoal to be drawn off from the surface of the metal, and
the copper to be exposed to the action of the air, by which means
it is again brought back to its _proper pitch_, that is, become
again malleable. Now the question is, what are the changes thus
produced in the copper? Is the metal in its _dry_ state combined
with a minute portion of oxygen, of which _poling_ deprives it,
and thus renders it malleable? and does the _over-poling_ impart
to it a minute portion of carbon, and is copper, like iron, thus
rendered brittle both by oxygen and carbon? Or, is the effect of
the pole merely mechanical, that of closing the grain, and of
altering the texture of the metal? Something might be said in
support of all these opinions. Mr. Faraday, who has attentively
examined the subject, is unable to detect any chemical difference
between _poled_ and _unpoled_ copper. On the other hand, when the
metal is _over-poled_, it is found to oxidate more slowly, and
its surface when in the furnace is so free from oxidation, that
it is like a mirror, and reflects every brick in the roof. This
certainly looks very much like carbonization.--See "An Account of
Smelting Copper, as conducted at the Hafod Copper-works; by J. H.
Vivian, Esq."--_Annals of Philosophy_, vol. v. p. 113.
These are important facts, and should dispose those who may preside
over judicial enquiries, to pause before they infer the inferiority
of copper sheeting from the rapidity of its decay.[99]--I have
now concluded a review of those admirable researches which led
Sir Humphry Davy to suggest and mature a plan for arresting the
corrosion of the copper sheathing of vessels by Voltaic action.
Mr. Babbage has said that he was authorised in stating, that "this
was regarded by Laplace as the greatest of Davy's discoveries." I
do not think, however, that it should be considered in the light
of a separate performance: we do injustice to the philosopher by
regarding it as an independent and isolated discovery; for it
was the result of a long series of enquiries, which commenced by
establishing the laws of electro-chemistry,--which led him to
the decomposition of the alkalies and earths,--suggested to his
unwearied genius a succession of novel researches, in a new field
of enquiry,--and concluded, as we have seen, in producing the most
striking results by means of the greatest simplicity. Not once
during the progress of this enquiry had he any occasion to retrace
his steps for the purpose of correction: justly has he observed
in his last Bakerian Lecture, that, notwithstanding the various
novel views which have been brought forward in this and other
countries, and the great activity and extension of science, it is
peculiarly satisfactory to find that he has nothing to alter in the
fundamental theory laid down in his original communication; and
which, after the lapse of twenty years, has continued, as it was in
the beginning, the guide and foundation of all his researches.
[99] This observation was suggested by an examination of a late
judgment of the Court of Common Pleas, in the case of Jones
_v._ Bright and others, on showing cause against rule for a new
trial. This was an action brought by the Plaintiff against the
Defendants for selling him copper, for the purpose of sheathing
the ship Isabella, which, from the rapidity of its corrosion,
was inferred to have an inherent defect in its composition. In
this case it was held, that with respect to _warranty_, there is
a very wide difference as it applies to articles which are not
the subject of manufacture, and those which are the produce of
manufacture and of human industry. In the one case, it may be
that no prudence, no care, could have guarded against a secret
defect; in the other, by using due care, and providing proper
materials, any defect in the manufacture may be guarded against.
"In the case of the bowsprit, the man did not make the timber
which composed the bowsprit; he merely cut it out, and fitted
it to meet the purpose, and could therefore by no means have
guarded against the rottenness in the centre of that bowsprit:
but if a man makes copper, he may guard against inherent defects
in that copper, by taking care that the copper contains a proper
proportion of pure copper; and also by taking care that it is so
well manufactured, that it does not drink in a greater quantity
of oxygen than ought to be admitted into it, and that that
oxygen, which of necessity gets in, (for some will,) shall be
so distributed, that it shall not operate, as in the opinion of
an intelligent witness the oxygen in this case did operate, by
forming itself in patches, and thereby rendering it soft, and
rendering the copper incapable of resisting the influence of
salt-water--that he can guard against." With all due deference
to the learned Judge, suppose it be shown that no human wisdom
can guard against those circumstances by which a portion of the
copper surface may be rendered more highly electro-positive,
what becomes of the judgment? That the decay of copper sheathing
is effected by extrinsic causes, and does not necessarily
depend upon an inherent defect in the metal, may be proved in
numerous ways. If it were owing to the quality of the copper,
why should five, ten, or twenty sheets out of a hundred, made
from the same charge of metal in a furnace and manufactured under
precisely similar circumstances, be affected, and the remainder
be perfectly sound? Why, again, should sheets, made from several
distinct charges, placed on a particular vessel, be acted upon,
while the same copper on other bottoms is not more than usually
dissolved? Did any inherent defect exist in the metal, it surely
must have equally affected the whole batch.
It is possible that, in some cases, in consequence of the sheets
not having been properly cleansed before they are rolled, a
portion of the oxide may be pressed into them by the rollers. In
such a case, a Voltaic effect might be produced, and portions of
the metallic surface rendered more electro-positive.
The President and Council of the Royal Society appear to have
been swayed by this consideration, when they adjudged to him "A
Royal Medal,[100] for his Bakerian Lecture on the relations of
electrical changes, considered as the last link, in order of time,
of the splendid chain of discoveries in chemical electricity, which
have been continued for so many years of his valuable life."
[100] In the year 1825, His Majesty George IV. communicated to
the Royal Society, through Mr. Peel, his intention to found two
gold medals, of the value of fifty guineas each, to be awarded
annually by the Council of the Royal Society, in such a manner
as shall, by the excitement of competition among men of science,
seem best calculated to promote the object for which the Royal
Society was instituted.
Thus had Davy now received from the Royal Society all the honours
they were capable of conferring upon him. In the year 1805, they
adjudged to him the medal on Sir Godfrey Copley's donation for his
various communications published in the Philosophical Transactions;
in 1817, they awarded him the Rumford medals for his papers on
combustion and flame; and in 1827, upon the grounds just stated,
the President and Council expressed their unabated admiration
by conferring upon him the only medal which remained for his
acceptance--that which had been recently founded by their patron,
his late Majesty.
Having thus disposed of the speculative part of his admirable
enquiry, it will be interesting to pause in our narrative, in
order to take a philosophical review of the progress of Voltaic
discovery, in its relations to this particular object. It is
a subject well calculated to afford a valuable lesson to the
experimentalist, and at the same time to furnish illustrations,
more striking even than that of the safety-lamp, of the necessity
of that complicated species of machinery, without which the human
mind is frequently unable to grapple with the simplicities of
truth. It is true, that the fact of a galvanic effect being
excited by the contact of two dissimilar metals was noticed in the
earliest stages of the enquiry, but it is equally evident that the
phenomena which attended it, and the laws by which it was directed,
required for their discovery and elucidation the assistance of the
Voltaic battery. In reference to Davy, it may be here repeated,
that the power of obtaining simple results, through complicated
means, was one of the most distinguishing features of his genius.
It has been stated, that the Alarm frigate, the first coppered ship
in our Navy, displayed very striking evidence of the effect of
Voltaic action, in the rapid corrosion of its iron.[101] As early
as 1783, after copper sheathing had become general, the Government
issued orders that all the bolts under the line of fluitation
should, in future, be of copper; but at that period, it was not
possible that any idea could be entertained as to the true nature
of the operation by which the iron was thus rapidly corroded, for
it was only in the year 1797 that Dr. Ash noticed, for the first
time, a phenomenon which was subsequently referred to the action of
a simple Voltaic circuit.
[101] Numerous are the instances of later date which might be
adduced in illustration of the same fact; and it is now generally
supposed that it may have been a frequent cause of ships
foundering at sea. By oxidation, the volume of the iron at first
increases, and then diminishes; in consequence of which the ship
leaks, or, to use a technical expression, becomes "_bolt sick_."
When the Salvador del Mundo was docked at Plymouth, in February
1815, the iron fastenings were in such a state of corrosion, that
five planks near the bilge dropped into the dock when the water
left her.
It is a very curious circumstance in the history of this subject,
that, for many years after the Voltaic influence had been
recognised as the agent in metallic corrosion, so far from the
existence of the accompanying phenomenon of preservation being
suspected, it was even supposed that the metals mutually corroded
each other. At so late a date as 1813, we find Davy himself, in the
letter addressed to M. Alavair, published in these memoirs,[102]
dwelling upon the necessity of avoiding metallic contact, in order
to prevent _corrosion_, without throwing out the most distant hint
as to the simultaneous production of a converse effect.
[102] Page 13 of this Volume.
The first distinct notice of a metal being preserved from oxidation
by the contact of a dissimilar metal, is at once referred to a
chemical law, without a reference even to its possible connection
with Voltaic action; and, striking as the fact may now appear, it
never attracted much attention. M. Proust observed, that although
copper vessels be so imperfectly tinned, as to leave portions of
the surface uncovered, still, in cooking utensils, we shall be
equally protected from the poisonous effects of the former metal;
because, says he, the superior readiness with which tin is oxidized
and acted upon by acids, when compared with copper, will not
allow this latter metal to appropriate to itself a single atom of
oxygen.[103] The same chemist observes, that if lead be associated
with tin, it will be incapable of furnishing to acids any saturnine
impregnation, since the latter, being more oxidable than the
former, will exclusively dissolve, and thus prevent the former from
being attacked.
[103] As far as the principle of Voltaic protection goes,
this may be very true; but it must be remembered that the
acid generally present upon these occasions is acetic acid,
which rises in distillation with water, so that at the boiling
temperature it will be carried beyond the sphere of Voltaic
influence, and may thus act upon the denuded copper as much as
though tin were not present.
Whether the principle of Voltaic protection be applicable or not to
the purpose of preserving copper sheathing, it is evident that it
will suggest numerous other expedients of high importance in the
arts, while it will explain phenomena previously unintelligible.
By introducing a piece of zinc, or tin, into the iron boiler of
the steam-engine, we may prevent the danger of explosion, which
generally arises, especially where salt-water is used, as in those
of steam-boats, from the wear of one part of the boiler. Another
important application is in the prevention of the wear of the
paddles, or wheels, which are rapidly dissolved by salt-water.
Mr. Pepys has also extended the principle for the preservation of
steel instruments by guards of zinc: razors and lancets may be thus
defended with perfect success. In the construction of monuments
which are to transmit to posterity the record of important events,
the artist will be careful in avoiding the contact of different
metals: it is thus that the Etruscan inscriptions, engraved upon
pure lead, are preserved to the present day; while medals of mixed
metals of a much more recent date are corroded.
Numerous are the facts daily presented before us, which receive
from this principle a satisfactory explanation. To the philosopher,
the examination of its agencies will furnish a perpetual source of
instruction and amusement; and I will here enumerate a few simple
instances of its effects: in the first place, for the purpose of
showing that, whenever a principle or discovery involves or unfolds
a law of Nature, its applications are almost inexhaustible, and
that, however abstracted it may appear, it is sooner or later
employed for the common purposes of life; and in the next place, in
the hope of convincing the reader, that there does not exist any
source of pleasure so extensive and so permanent as that derived
from the stores of philosophy. The saunterer stumbles over the
stone that may cross his path, and vents only his vexation at the
interruption; but to the philosopher there is not a body, animate
or inanimate, with which he can come in contact, that does not
yield its treasures at his approach, and contribute to extend the
pleasures of his existence.
I well remember some years ago, that, in passing through Deptford,
my curiosity was excited by the extraordinary brilliancy of a
portion of the gilded sign of an inn in that town, while its other
parts had entirely lost their metallic lustre. Having obtained a
ladder, I ascended to the sign, in order, if possible, to solve the
problem that had so greatly interested me: the mystery immediately
vanished; for an iron nail appeared in the centre of the spot,
which had protected the copper leaf for several inches around it.
Any person may easily satisfy himself of the efficacy of such
protection, in his rambles through the metropolis, by noticing
the gilded, or rather coppered, sugar-loaves[104] so commonly
suspended over the shops of grocers, when he will frequently
perceive that the parts into which the iron supports have
entered, unless the latter have been painted, shine preeminently
brilliant. If a still more familiar example of the effect of a
simple Voltaic circuit be required, it is afforded by the iron
palisadoes, where the iron is constantly corroded at its point
of contact with the lead by which it is cemented into the stone.
These examples are not only interesting from their simplicity,
but from their demonstrating the small quantity of a conducting
fluid which is sufficient to transmit the electrical power, or to
complete a simple circuit: a fact which, it will be remembered, the
experiments of Davy had before established.[105]
[104] There is an excellent example at this time in the London
Road leading to the Elephant-and-Castle.
[105] Page 248 of this Volume.
As our knowledge advances, these principles will no doubt derive
other illustrations, and be found capable of more extensive
application; for as yet we are but in the infancy of the enquiry.
I have lately been engaged in a series of experiments, the results
of which, I confidently anticipate, will lead to some new facts
connected with the changes produced on the negative metal of a
Voltaic circuit; an account of which I hope shortly to submit to
the Royal Society. I shall on this occasion merely notice one
result, which appears to me to admit of an immediate application
to one of the most important circumstances of life--the purity of
water contained in leaden cisterns.
My attention has for several years been directed to the state of
the water with which the metropolis is supplied; and upon having
been lately requested to propose a remedy for preventing the
action of a spring in the neighbourhood of London upon lead, which
it had been found to corrode in a very rapid manner, I suggested
the expediency of protecting the pipes and cisterns with surfaces
of iron; but before such a plan was put in execution, I proposed
to try its efficacy in the laboratory:--the first result was very
startling; for, instead of preventing, as I had anticipated, I
found that it greatly increased, the solution of the lead. After
various experiments, I arrived at the conclusion, that lead, when
rendered negative by iron, and placed in contact with weak saline
solutions,--such, for instance, as common spring water,--was
dissolved; in consequence of the decomposition of the salts and
the transference of their elements according to the general law,
the acid passing to the iron, and the alkali to the lead; and so
powerfully is this latter body acted upon by an alkali, that, if
a slip of it be immersed in a solution of potash or soda, its
crystalline texture is so rapidly developed, that its surface
exhibits an appearance similar to that presented by tin-plate, and
which is designated by the term _moirée_.
I apprehend that most of the anomalous cases of the solution of
lead in common water, which have for so many years embarrassed the
chemist, may thus receive an explanation. An eminent physician
lately informed me, that some time since he was called upon to
attend a family who had evidently suffered from the effects of
saturnine poison, and that he well remembers there was an iron
pump in the cistern that supplied the water. Upon showing the
results of my experiment to a no less eminent chemist, he was
immediately reminded of a circumstance which occurred at Islington,
where the water was found to corrode the lead in which it was
received: in this vessel there was an iron bar; and the fact would
not have attracted his notice, nor have been impressed upon his
recollection, but from the unusual state of corrosion in which it
appeared.
I shall conclude these observations by an account of "the change
which some musket balls, taken out of Shrapnell's shells, had
undergone," by Mr. Faraday, and which is published in the 16th
volume of the Quarterly Journal of Science, for the year 1823. This
history is not only interesting on account of the high chemical
character of its author, but satisfactory as being in direct
opposition to previously established facts; and cannot therefore
have received any bias from preconceived theory.
"Mr. Marsh of Woolwich gave me some musket balls, which had been
taken out of Shrapnell's shells. The shells had lain in the
bottoms of ships, and probably had sea-water amongst them. When
the bullets are put in, the aperture is merely closed by a common
cork. These bullets were variously acted upon: some were affected
only superficially, others more deeply, and some were entirely
changed. The substance produced is hard and brittle; it splits
on the ball, and presents an appearance like some hard varieties
of hæmatite; its colour is brown, becoming, when heated, red; it
fuses on platinum foil into a yellow flaky substance like litharge.
Powdered and boiled in water, no muriatic acid or lead was found in
solution. It dissolved in nitric acid without leaving any residuum,
and the solution gave very faint indications only of muriatic
acid. It is a _protoxide of lead_, perhaps formed, in some way, by
the galvanic action of the iron shell and the leaden ball, assisted
probably by the sea-water. It would be very interesting to know the
state of the shells in which a change like this has taken place
to any extent. _It might have been expected, that as long as any
iron remained, the lead would have been preserved in the metallic
state._"
In one experiment, I found that a piece of lead protected by iron
underwent solution in water containing nitrate of potash, while it
resisted the action of very dilute nitric acid: upon this point,
however, farther enquiry is necessary; for I subsequently failed in
producing the same effect, owing, no doubt, to having employed too
strong an acid.
Let us return from this digression to the subject of Sir Humphry
Davy's Protectors. It only remains for me to relate the results
which followed the practical application of the Voltaic principles
which his various experiments had developed.
In the month of May 1824, directions were issued by the Lords of
the Admiralty to protect, in future, the copper sheathing of all
his Majesty's ships which might be taken into dock, upon the plan
proposed by Sir Humphry Davy.
The protectors were bars of iron six inches wide at their base,
three inches in thickness in their centre, and, in outward form,
the segment of an extended circle. They were usually placed on each
side of the ship in a horizontal position, viz. in midships about
three feet under water--on the keel in a line with these--and the
remainder in the fore and afterparts of the ship (about three feet
under the line of fluitation), as far forward and abaft as the
curvatures of their respective bodies would allow of their lying
flat upon the surface of the copper.
As it is difficult by verbal description alone to convey a
sufficiently distinct idea of this subject to persons unacquainted
with naval architecture, I have introduced a sketch, exhibiting
the _general_ position of the _Protectors_, although they are
necessarily exaggerated in size, or they would have appeared as
mere specks upon the drawing.
[Illustration: A. A. Line of Fluitation.]
On several ships, some of the protectors, in the stem and the
stern, were placed _vertically_; in which case they were fastened
to the stems and stern-posts; and in this manner they were found
to act more powerfully in preserving the copper, than when they
were all placed horizontally. The ends of the protectors were
rounded, in order to prevent any great resistance to the water,
and they were fastened to the bottoms of the ships with copper
bolts, the iron being counter-sunk to receive their heads, and
the holes were then filled with carbonate of lime, or Parker's
cement. To bring about the best possible contact of all the copper
sheets, their edges, which lap over each other, where the nails are
driven to fasten them to the ships, were rubbed bright, first with
sand-paper, and finally with glass-paper.
Shortly after the ships thus protected were sent to sea, it was
evident to all on board, from their dull sailing, that the bottoms
had become very foul; and on being examined in dry docks, it
was found that the copper was completely covered with sea-weed,
shell-fish of various kinds, and myriads of small marine insects.
Upon their removal, however, it was found, on weighing the sheets,
that the copper had suffered little or no loss; thus proving that,
although its practical application had failed from unforeseen
circumstances, the principle of protection was true, and had fully
justified the expectation of its success.
The copper near the protectors was much more foul than that at a
greater distance from them; and there was, moreover, a considerable
deposit of carbonate of lime, and of carbonate and hydrate of
magnesia, in their vicinity.
Sir Humphry Davy immediately suggested, as a remedy for this evil,
that the bottoms should be scraped, and the copper washed with a
small quantity of acidulous water; and he also proposed that the
protectors should in future be placed under, instead of over, the
copper sheathing. This plan was immediately adopted. Discs of
cast-iron three and a half inches in diameter, and one-fourth of
an inch in thickness, were let into the plank of the bottom of the
Glasgow, of fifty guns, on the starboard side only--the larboard
side having been left without any protection. These discs were in
the proportion of one to every four sheets of copper, and over
them were placed pieces of brown paper, and over the paper thin
sheet-lead, so that the latter metal was in contact with the
copper sheathing. A similar experiment was also tried on the Zebra,
of eighteen guns, substituting, however, discs of zinc[106] for
those of iron.
[106] It would appear that Davy latterly preferred zinc to
iron, as the protecting metal. In a letter, dated October
1826, addressed to a ship-owner, who had made some enquiries
of him upon the subject, he says--"The rust of iron, if a ship
is becalmed, seems to promote the adhesion of weeds; I should
therefore always prefer pieces of zinc, which may be very much
smaller, and which, in the cases I have heard of their being
used, have had the best effect."
The bottom of the Glasgow was examined twelve months afterwards,
when the discs of iron were found oxidated throughout, presenting
in their appearance the characters of plumbago. The copper on
the starboard side was preserved, but covered with weeds and
shell-fish. The sheets on the larboard had undergone the usual
waste, but were clean.
The Zebra was docked four years after the experiment had commenced,
when the zinc protectors were perfect, and it did not appear that
they had exerted any influence in preserving the copper, as it
had wasted equally on both sides. It may be presumed in this case
that the Voltaic circuit had by some fault in the arrangement been
interrupted.
The apparent conversion of iron into a substance resembling
plumbago, by the action of sea-water, has been frequently noticed.
The protectors thus changed[107] were, to a considerable depth from
the surface, so soft as to be easily cut by a knife; but after
being exposed for some time to the action of the atmosphere, they
became harder, and even brittle. A portion of this soft substance
having been wrapped in paper for the purpose of examination, and
placed in the pocket of a shipwright, gave rise to a very curious
and unexpected result: at first, the artist, like Futitorious with
his chestnuts, thought he perceived a genial warmth; but the effect
was shortly less equivocal; the substance became hot, and presently
passed into a state of absolute ignition. Various theories have
been suggested for its explanation: Mr. Daniell has advanced an
opinion which supposes the formation of silicon, and thus accounts
for the spontaneous ignition by the action of air.
[107] In the Annals of Philosophy (vol. v.) may be found a paper
by Dr. Henry, on the conversion of cast iron pipes into plumbago.
This change appears to have been effected by the action of water
containing muriate of soda, and the muriates of lime and of
magnesia. Cast iron contains a considerable portion of carbon;
the change is therefore readily explained on the supposition of
the removal of the principal metallic part by these salts. The
muriates of lime and magnesia have been observed by Dr. Henry to
discharge writing ink from the labels of bottles, to which they
had been accidentally applied; and the same ingenious chemist has
been baffled in his attempts to restore the legibility of ink
upon paper which had been exposed to sea-water. The texture of
the paper was not injured, but the iron basis of the ink, as well
as the gallic acid, was entirely removed.
The disadvantages which arise from the foulness of ships' bottoms,
particularly when on foreign stations, where there are no dry docks
to receive them, are so serious, that the Government was obliged,
in July 1825, to order the discontinuance of the protectors on
all sea-going ships; but directed that they should still be used
upon all those that were laid up in our ports. When, however, an
examination of the latter took place, they were found to be much
more foul than those which had been in motion at sea: shell-fish
of various kinds had adhered to them so closely, that it was even
necessary to use percussion to remove them, which not only indented
the copper, but in many instances actually fractured it.
Under all these discouraging circumstances, the unwelcome
conviction was forced upon the agents of Government, that the plan
was incapable of successful application, and it was accordingly
altogether abandoned in September 1828.
Such were the results of the experiments carried on in the ports of
England, for the protection of copper sheathing, from the success
of which Sir H. Davy justly expected honours, fame, and reward.
That his disappointment was great, may be readily imagined, and
it is supposed to have had a marked influence upon his future
character. It is much to be regretted that his vexation should
have been heightened by the unjust and bitter attacks made upon
him by the periodical press, and by those subalterns in science,
who, unable to appreciate the beauty of the principle he had so
ably developed, saw only in its details an object for sarcasm,
and in its failure an opportunity for censure; while those whose
stations should have implied superior knowledge, in the pride and
arrogance of assumed contempt, sought a refuge from the humiliation
of ignorance.
That Davy was severely hurt by these attacks, is a fact well known
to his friends. In a letter to Mr. Children he says: "A mind of
much sensibility might be disgusted, and one might be induced
to say, Why should I labour for public objects, merely to meet
abuse?--I am irritated by them more than I ought to be; but I am
getting wiser every day--recollecting Galileo, and the times when
philosophers and public benefactors were burnt for their services."
In another letter he alludes to the sycophancy of a chemical
journal, which, after the grossest abuse, suddenly turned round,
and disgusted him with its adulation. "I never shake hands," says
he, "with chimney sweepers, even when in their May-day clothes, and
when they call me '_Your honour_.'"
While the trials above related were proceeding in the ports of
England, the naval department of France was prosecuting a similar
enquiry; and as experiments of this nature are conducted with
greater care, and examined with superior science, in that country,
it may not be uninteresting to the English reader to receive a
detail of the examination of the bottom of La Constance frigate, in
which the protectors bore a much larger proportion to the copper
surface than was ever practised in the British navy. This document,
I may observe, is now published for the first time.
"The inspection of the bottom of the frigate La Constance, has
given rise to some interesting observations on the effect of
protectors, and it has confirmed the fact before advanced of the
great inconvenience which attends the application of too large a
proportion of the protecting metal.
"The surface of this metal, which was of cast iron, placed on each
side of the keel, and in long scarphs of iron plates situated
towards the stem and stern-post and the water line, appeared to
have been about the 1-30th part of the surface of the copper,
instead of the 1-250th part as now practised.
"The galvanic action has been extreme, both in rapidity and
intensity. The scarphs are entirely destroyed, and have absolutely
disappeared; and we should have been ignorant of their having ever
existed, had we not been informed of the fact, and observed dark
stains which marked their position, and discovered the nails still
entire by which they had been fastened.
"The plates, which were in the first instance about three inches
thick, were covered throughout their whole length by a thick,
unequal coating, spotted with yellow oxide. This was principally
owing to the absorption of about twenty-five per cent. of its
weight of water. Under this, the iron was as soft as plumbago, and
there remained scarcely an inch of metal of its original metallic
hardness.
"The bulky and irregular appendage (the protectors) at the lower
part of the ship's bottom caused a great noise in the sea, in
consequence of the dead water which it occasioned, and doubtless
lessened the speed of the vessel. But that which contributed most
to this unfortunate result, was the exceedingly unclean state of
the copper, arising from the excess of the iron employed: this,
carried to so great an extent, having the effect of extracting
matter from the water, which, forming a concretion on the sheets,
enabled the marine animals the more easily to attach themselves.
The sheathing was covered with a multitude of _lepas anatifera_,
shells with five valves, suspended by a pedicle of three or four
centimetres long, collected into groups; of _lepas tintinnabulum_,
a shell with six valves; of oysters with _opercula_; of _polypi_,
&c. No part of the bottom was free from them.
"Below, the copper was certainly preserved from oxidation; and up
to within a few sheets of the water line, it did not appear to be
worn. But to save expense, it was obliged to be cleansed without
removal, by rubbing it hard with bricks and wet sand, which has
succeeded very well in restoring its copper colour."
The following is the description of shells above enumerated:--
Genus _Anatifa_, Encyclopedia.--(_Lepas_, Linnæus.)
[Illustration: Fig. 1.]
FIG. 1. Smooth _Anatifa_ (_Lepas anatifera_, Linn.)--Shell
consisting of five valves, of which two larger and two smaller
ones are opposite to each other; and a fifth, which is narrow, is
arched and rests upon the ends of the first four: these valves
are not connected by any hinge; they are held together by the
skin of the animal, which lines their interior and opens in front
by a longitudinal separation. Their colour is orange during
the life of the animal. The base of the shell is united to a
fleshy tube, tendinous, cylindrical, susceptible of contraction,
saffron-coloured, becoming brown and black in drying.
[Illustration: Fig. 2.]
FIG. 2. Smooth _Anatifa_, as seen from the other side, the pedicle
dry and contracted.
[Illustration: Fig. 3.]
FIG. 3. Smooth _Anatifa_, as seen in front, showing the
longitudinal separation.
Genus _Anomia_.
[Illustration]
Shell with valves, unequal, irregular, having an operculum;
adhering by its operculum; valve usually pierced, flattened, having
a cavity in the upper part; the other valve a little larger,
concave, entire; operculum small, elliptical, bony, fixed on some
foreign body, and to which the interior muscle of the animal is
attached.
[Illustration]
Species, Onion-peel _Anomia_.--(_Ephippium_, Linn.)
Shell common, whitish and yellowish, found in the Mediterranean and
the ocean.
Besides the abovementioned species, which were found in large
quantities, there were also some muscles and oysters.--(_Mytilus
afer. Baccina._--Linn. Gmel. 3358.)
Genus "_Balane de Blainville_."
(_Balanite_, Encyclopedia.--_Lepas_, Linn.)
[Illustration: Fig. 1.]
FIG. 1. Tulip Balanus.--(_Lepas tintinnabulum_, Linn.)
Shell with six unequal valves articulated by a scaly suture, of
which the edges appear to be finely crenellated in the cavity;
the form of the valves is conical, aperture ample, and nearly
quadrangular.
Operculum composed of four triangular pieces crenellated and marked
with very projecting transverse striæ, which appear to extend from
the top to the bottom; the two posterior pieces are perpendicular,
and are applied to the hinder partition of the cavity of the
shell; they are terminated by two conical prolongations, of which
the points are sharp and diverging. The two foremost pieces are
placed in the aperture, in an oblique direction. The colour of this
balanus from clear red to violet and brown.
[Illustration: Fig. 2.]
FIG. 2. View of the upper part of the Tulip Balanus.
[Illustration: Fig. 3.]
FIG. 3. View of the base.
Genus Oyster, (_Ostrea._)
[Illustration]
Species of oyster, nearly similar to the common oyster, (_Ostrea
edulis_,) and of the Huître cuilier, (_Ostrea cochlear_,) their
shell rather fragile, almost without lamellæ; upper valve concave,
colour rather deep violet, form variable.
"Besides these three kinds of Molluscæ, of which the number was
considerable, several species of calcareous polypi were found; but
those which could be obtained were too imperfect to allow of their
being correctly described.
"The iron which was used to protect the copper on the bottom of the
Constance frigate having been subjected to chemical analysis, the
following are the results.
"This iron, which was in small fragments, very friable, little
attracted by the loadstone, soft to the touch, and soiling the
fingers like plumbago, gave out in rubbing it a very strong smell,
very much like that of burnt linseed oil. Its colour on the
exterior was a brownish yellow, and its interior a blackish grey,
studded with little points extremely brilliant.
"A short time after they had been taken from the keel of the
frigate, where they were covered with a layer of hydrated peroxide
of iron, of six or eight lines in thickness, and been enclosed in
a paper box, these fragments became strongly heated, and underwent
a real combustion by means of the oxygen of the atmosphere; the
combustion was accompanied by the production of a certain quantity
of aqueous vapour.
"In order to ascertain whether this elevation of temperature
was really alone owing to the absorption of the oxygen, a case
containing twelve _grammes_ of this iron was placed under a
receiver, which contained two hundred millimetres, inverted over
a tube of mercury; and it was observed, in the course of an hour,
that this air had diminished by forty millimetres, or one-fifth
of its volume. Examining afterwards that which remained in the
receiver, it was discovered that it had no effect whatever either
on lime-water or the tincture of _tournesol_,--that it was not
inflammable,--that it extinguished a candle; in a word, that it
presented all the negative qualities of azotic gas, strongly
infected with the smell before stated.
"It must be evident that the oxygen which was absorbed in this
experiment was employed solely in burning the iron, which was
already in a state of _protoxide_, as was indicated by its little
degree of cohesion, by the avidity with which it seized this
principle, and by its dissolving in sulphuric acid, which operated
without effervescence, and without disengaging hydrogen gas.
"Five _grammes_ of this oxidized iron being reduced to an
impalpable powder, and then made red-hot in a platina crucible,
and mixed with three parts of _potasse à l'alcool_, were reduced
to a clammy mass, coloured on its edges with a clear beautiful
green, and with a greenish yellow on the other parts; which at once
indicated the presence of a small portion of manganese, and that
of a little _chrôme_; metals which are found united in almost all
sorts of iron. Treated in the usual way, this mass exhibited--
"First, Traces, scarcely sensible, of these two metals.
"Secondly, One _gramme_ of brilliant black powder, soft to the
touch, staining paper, insoluble in muriatic acid when applied
boiling: it was therefore a true percarburet of iron.
"Thirdly, Three _grammes_ and ten _decigrammes_ of peroxide of iron.
"On being subjected to the action of boiling water, five grammes
of this pulverized iron gave out three _decigrammes_ of soluble
matter, composed, for the greater part, of _hydrochlorate_ of
iron, and a trace of hydrochlorate of magnesia, together with a
little organic matter, the combination of which with the iron will
account for the insufferable smell which it gave out when the iron
was heated. This saline solution sensibly reddened the litmus
paper: an effect which was owing to the muriatic acid, which, in
uniting with oxidized iron, and with most other metallic oxides,
never forms combinations which are perfectly neutral, but which are
always more or less acid.
"It has in vain been attempted to discover in this oxidized iron
the presence of silex, of alumina, and of the sulphuric and
carbonic acids, either free, or in combination.
"It results from this analysis, that the fragments of the
protectors, which have been the object of it, are composed, in a
hundred parts, of about
64 oxidized iron,
20 of plumbago, or percarburet of iron,
6 of matter soluble in water, hydrochlorate of magnesia,
hydrochlorate of iron, hydrochlorate of soda, hydrochlorate of
magnesia, and organic matter, and
10 of water; as in fragments pulverised and heated for half an
hour at a temperature of 100°, they lost 1-10th of their weight.
"As to the reddish yellow matter, with small protuberances
like nipples, which formed a thick layer on the surface of the
protectors, it was formed of 75 parts of oxide of iron at the most,
and 25 parts of water, besides some atoms of hydrochlorate of iron,
hydrochlorate of soda, and hydrochlorate of magnesia."
* * * * *
Had not the health of Davy unfortunately declined at the very
period when his energies were most required, such is the unbounded
confidence which all must feel in his unrivalled powers of
vanquishing practical difficulties, and of removing the obstacles
which so constantly thwart the applications of theory, that little
doubt can be entertained but he would soon have discovered some
plan by which the adhesion of marine bodies to the copper sheathing
might have been prevented, and his principle of Voltaic protection
thus rendered available. An experiment indeed, altogether founded
upon this same principle, has been already proposed, and will be
shortly tried in the British navy, by building a schooner, and
fastening its materials together with copper bolts, and afterwards
sheathing the bottom with thin plates of iron, which are to be
protected by bands of zinc. At the same time, another schooner is
to be built, in which the fastenings are to consist entirely of
iron bolts and nails, the former to be protected by a zinc ring
under each head or clench, and the latter to have a small piece of
zinc soldered under its head.
This plan of protection was first adopted in America, at the
recommendation of Dr. Revere; and upon its successful issue, that
gentleman was lately induced to take out letters patent not only
in England, but in all the maritime countries of Europe, for the
sole right of manufacturing iron sheathing, bolts, and nails, thus
protected.
As no doubt now exists as to the principle of the protection of
iron by zinc, the bolts and nails may be expected to remain free
from rust as long as the more oxidable metal lasts; but with
regard to the success of the iron sheathing, it is impossible
to entertain the same confidence; for what, in this case, is to
prevent the adhesion of shell-fish and sea-weed upon its surface?
Let it be remembered, that it is only when the copper is in the act
of solution in sea-water that the sheathing remains clean. In the
year 1829, the Tender to the Flagship at Plymouth had her copper on
one side of the bottom painted with white lead: in six months, this
side was covered with long weeds; while the other side, which had
been left bright, and consequently exposed to the solvent action of
the salt-water, was found entirely free from all such adhesions.