district, moistened and kneaded and generally strengthened by a sort
of skeleton of strips of flexible wood. In form it varies from a
cylinder, more or less circular, diverging into a tolerably acute
cone, the walls being about 3 in. thick. The height is generally
about 3 ft. and the mean internal diameter about 1 ft., but all these
dimensions vary with different workmen and in different localities.
There are two apertures at the base of the furnace; one in front,
about 1 ft. in height, and rather less in width than the internal
diameter of the furnace, through which, when the smelting of one
charge is finished, the resulting mass of spongy iron is extracted,
and which during the smelting is well plastered up, the small conical
tuyere being inserted at the bottom. This tuyere is usually made of
the same material as the furnace--namely, of a sandy soil; worked by
hand into the required form and sun-dried; but sometimes no other
tuyere is employed than a lump of moist clay with a hole in it, into
which the bamboo pipes communicating with the bellows are inserted.
The other aperture is smaller, and placed at one side of the furnace,
and chiefly below the ground, forming a communication between the
bottom of the furnace chamber and a small trench into which the slag
flows and filters out through a small pile of charcoal. It is this
slag being found in places where iron is not now made that shows that
iron smelting was an occupation there, perhaps many centuries before.
The inclined tray shown at the top of the furnace on Fig. 1 is made of
the same material as the furnace itself, and when kneaded into shape
is supported on a wooden framework. On it is piled a supply of
charcoal, which is raked into the furnace when required.
The blowing apparatus is singularly ingenious, and is certainly as
economical of manual labor as a blowing arrangement depending on
manual labor well can be. A section of the bellows forms the portion
to the right of Fig. 1, showing tuyere forming the connection between
bellows and furnace. It consists of a circular segment of hard wood,
rudely hollowed, and having a piece of buffalo hide with a small hole
in its center tied over the top. Into this hole a strong cord is
passed, with a small piece of wood attached to the end to keep it
inside the bellows, while the other end is attached to a bent bamboo
firmly fixed into the ground close by. This bamboo acts as a spring,
drawing up the string, and consequently the leather cover of the
bellows, to its utmost stretch, while air enters through the central
hole. When thus filled, a man places his foot on the hide, closing the
central hole with his heel, and then throwing the whole weight of his
body on to that foot, he depresses the hide, and drives the air out
through a bamboo tube inserted in the side and communicating with the
furnace. At the same time he pulls down the bamboo with the arm of
that side. Two such bellows are placed side by side, a thin bamboo
tube attached to each, and both entering the one tuyere; and so by
jumping on each bellows alternately, the workman keeps up a continuous
blast.
[Illustration: Fig. 2.--PLAN OF INDIAN BLAST FURNACE AND BLOWING
MACHINE.]
The Figs. 1 and 2 are taken from sketches, and the description from
particulars, by Mr. Blandford, who was for some years on the
Geological Survey of India, and had exceptional opportunities in his
journeyings of observing the customs and occupations of the Indian
iron smelters. The blowing machine is an especially wonderful and
effective machine, and was first described and illustrated by Mr.
Robert Rose, in a Calcutta publication, more than half a century ago.
He also had seen it used in iron making in India.--_Colliery
Guardian._
* * * * *
WOOD OIL.
Wood oil is now made on a large scale in Sweden from the refuse of
timber cuttings and forest clearings, and from stumps and roots.
Although it cannot well be burned in common lamps, on account of the
heavy proportion of carbon it contains, it is said to furnish a
satisfactory light in lamps specially made for it; and in its natural
state it is the cheapest illuminating oil. There are some thirty
factories engaged in its production, and they turn out about 40,000
liters of the oil daily. Turpentine, creosote, acetic acid, charcoal,
coal-tar oils, etc., are also obtained from the same materials as the
wood oil.
* * * * *
SOAP.
By HENRY LEFFMANN, M.D.
Although the use of soap dates from a rather remote period, the
chemist is still living, at an advanced age, to whom we are indebted
for a knowledge of its composition and mode of formation. Considerably
more than a generation has elapsed since Chevreul announced these
facts, but a full appreciation of the principles involved is scarcely
realized outside of the circle of professional chemists. Learned
medical and physiological writers often speak of glycerin as the
"sweet principle of fats," or term fats compounds of fatty acids and
glycerin. Indeed, there is little doubt that the great popularity of
glycerin as an emollient arose from the view that it represented the
essential base of the fats. With regard to soap, also, much erroneous
and indistinct impression prevails. Its detergent action is sometimes
supposed to be due to the free alkali, whereas a well-made soap is
practically neutral.
A desire to secure either an increased detergent, cleansing, or other
local effect has led in recent years to the introduction into soaps of
a large number of substances, some of which have been chosen without
much regard to their chemical relations to the soap itself. The result
has been the enrichment of the materia medica with a collection of
articles of which some are useful, and others worse than useless. The
extension of the list of disinfectant and antiseptic agents and the
increased importance of the agents, in surgery, have naturally
suggested the plan of incorporating them with soaps, in which form
they will be most convenient for application. Accordingly, the
circulars of the manufacturing pharmacists have prominently displayed
the advantages of various disinfecting soaps.
Among these is a so-called corrosive sublimate soap, of which several
brands are on sale. One of these, containing one per cent. of
corrosive sublimate, is put on the market in cakes weighing about
sixteen hundred grains, and each cake, therefore, contains sixteen
grains of the drug--a rather large quantity, perhaps, when it is
remembered that four grains is a fatal dose. Fortunately, however, for
the prevention of accidents, but unfortunately for the therapeutic
value of the soap, a decomposition of the sublimate occurs as soon as
it is incorporated in the soap mass, by which an insoluble mercurial
soap is formed. This change takes place independently of the alkali
used in the soap; in fact, as mentioned above, a well-made soap
contains no appreciable amount of free alkali, but is due to the
action of the fat acids. Corrosive sublimate is _incompatible_ with
any ordinary soap mass, and this incompatibility includes not only
other soluble mercurial salts, but also almost all the mineral
antiseptics, such as zinc chloride, copper sulphate, iron salts. Some
of the preparations of arsenic may, however, be incorporated with soap
without decomposition.
Such being the chemical facts, we must admit that no reliance can be
placed in corrosive sublimate soaps as germicide agents. It must not
be supposed that this incompatibility interferes with the use of these
soaps for general therapeutic purposes. It is only the specific
germicide value which is destroyed. Since the fats used in soap
manufacture yield oleic acid, we will have a certain amount of
mercuric oleates formed together with stearate and other salts, and
for purposes of inunction these salts might be efficient. Still the
physician would prefer, doubtless, to use the specially prepared
mercurial.
In producing, therefore, a disinfecting soap, being debarred from
using the metallic germicides, we are fortunate in the possession of a
number of efficient agents, organic in character, which may be used
without interference in soaps.
Among these are thymol, naphthol, oil of eucalyptus, carbolates, and
salicylates. There is no chemical incompatibility of these with soap,
and as they are somewhat less active, weight for weight, than
corrosive sublimate, they are capable of use in larger quantities with
less danger, and can thus be made equally efficacious.
It is in this direction, therefore, that we must look for the
production of a safe and reliable antiseptic soap.
There is not much exact knowledge as to the usefulness of such
additions to soap as borax and glycerin. They are frequently added,
and highly spoken of in advertisements. Borax is a mild alkaline body,
and as a detergent is probably equivalent to a slight excess of
caustic soda. Glycerin, although originally considered an emollient,
probably on account of its source and physical properties, is in
reality, to some skins at least, a slight irritant. It is, in fact, an
alcohol, not a fat. It does not pre-exist in fats, but is formed when
the fat is decomposed by alkali or steam.
In ordinary cases, soap owes its detergent effect to a decomposition
which occurs when it is put in water.
A perfectly neutral soap, that is, one which contains the exact
proportion of alkali and fat acid, will, when placed in cold water,
decompose into two portions, one containing an excess of the acid, the
other an excess of alkali. The latter dissolves, and gives a slightly
alkaline solution; the former precipitates, and gives the peculiar
turbidity constituting "suds." These reactions must be kept in mind in
determining the effect of the addition of any special substance to the
soap.--_The Polyclinic._
* * * * *
OPTICAL ERRORS AND HUMAN MISTAKES.[1]
[Footnote 1: Read before the American Association, Buffalo,
August, 1886.]
By ERNST GUNDLACH.
I wish to call attention to a few mistakes that are quite commonly
made by microscopists and writers in stating the result of their
optical tests of microscope objectives.
If the image of an object as seen in the microscope appears to be
unusually distorted and indistinct toward the edge of the field, and
satisfactory definition is limited to a small portion of the center,
the cause is often attributed to the spherical aberration of the
objective, while really this phenomenon has nothing to do with that
optical defect of the objective, if any exists, but is caused by a
lack of optical symmetry. If a perfectly symmetrical microscope
objective could be constructed, then, with any good eye-piece, it
would make no difference to the definition of the object were it
placed either in the center or at the edge of the field, even if the
objective had considerable spherical aberration. But, unfortunately,
our most symmetrical objectives, the low powers, leave much to be
desired in this respect, while our wide angle, high powers are very
far from symmetrical perfection.
There are two causes of this defect in the latter objectives, one
being the extreme wideness of their angular apertures, and the other
the great difference in the distances of the object and the image from
the optical center of the objectives.
Another mistake is often made in regard to the cause of certain
prismatic colors that are sometimes, in a striking degree, produced by
otherwise good objectives. According to the nature of these colors,
whether yellow or blue, green or indigo, they are generally regarded
as evidences of either chromatic over or under correction of the
objective. Of course the presence of either of these defects is
certainly and correctly indicated by the appearance of one or the
other of the colors, under certain circumstances; but the simple
visibility of prismatic color is by no means a reliable indication of
over or under correction of color, and, indeed, to the honor of our
opticians, it may be stated that very few objectives are made that
cannot justly be called achromatic in the general sense of the term.
By far the most common causes of prismatic color, in otherwise
carefully constructed objectives, are the so-called chromatic
aberrations of second or higher order. Every achromatic lens which is,
as it should be, at its best at about two-thirds of its aperture, is
inside of this ring or zone, toward the center slightly under and
outside, toward the edge, slightly over corrected. This defect is the
greater, the less the difference of the dispersive powers of the two
glasses used in the construction of the lens, for a given proportion
of their refractive indexes, and therefore the degree of visibility of
the colors of the aberrations of the second order depends greatly on
the nature of the glass employed in the construction of the lens.
This defect may be corrected by a suitable combination of two or more
lenses, though not without again having similarly, as in the
correction of the first color, some faint remnants of color, the
aberrations of third or still higher order. But even the correction of
the third or still higher order may, if the angular aperture is very
wide, leave quite visible and disturbing remnants of color.
Another and not uncommon explanation of the cause of this unwelcome
color, though not so serious and damaging a charge to the maker of the
objectives, is its attribution to the so-called "secondary spectrum."
This error, like that previously mentioned, is certainly indicated by
the appearance of certain colors under certain conditions, but being,
as a rule, one of the least defects of even our best objectives in
most cases, it is probably not the true source of the disturbance.
The secondary spectrum is very commonly confounded with the chromatic
aberration of higher order. While the latter is produced by
imperfections in the form of the lens, the former is due to an
imperfection of the optical qualities of the material from which the
lens is constructed, the crown and flint glass.
A glass prism of any angle will project upon a white surface a
spectrum of any length, according to the arrangement of the light
source, the screen, and the prism. So with two prisms of the same kind
of glass, but of different angles, two spectra can be produced of
exactly equal length, so that if one is brought over the other, with
the corresponding colors in line, they will appear as one spectrum.
But if one of the prisms is made of crown and the other of flint
glass, then their spectra cannot be arranged so that all their
corresponding colors would be in line, for the proportional distances
of the different colors differ in the two spectra. If two colors of
the spectra are, by suitable arrangement, brought exactly in line,
then the others will be out. The two spectra do not coincide, and the
result, if an achromatic lens be made of these glasses, must be a
remnant of color which cannot be neutralized. This remnant is the
secondary spectrum.
Although this peculiar disharmony in the dispersive powers of the two
glasses, crown and flint, was discovered almost immediately after
achromatism was invented, it was only recently that the first
successful attempts were made to produce different glasses, which,
possessing the other requirements for achromatic objectives, would
produce coincident spectra, or nearer so than the ordinary crown and
flint glass do. It was about twelve years ago, if my memory serves me,
when I learned that a well-known English firm, engaged in the
manufacture of optical glass, had brought out some new glass possessed
of the desired qualities, and a little later I received a circular
describing the glass. But at the same time I learned that the new
glass was very soft and difficult to polish, and also that it had to
be protected from the atmosphere, and further, that an English
optician had failed to construct an improved telescope objective from
it. I had ordered some samples of the glass, but never received any.
A few months ago, news from Europe reached this country that another
and seemingly more successful attempt had been made to produce glass
that would leave no secondary spectrum, and that Dr. Zeiss, the famous
Jena optician, had constructed some new improved objectives from it.
But the somewhat meager description of these objectives, as given by
an English microscopist, did not seem fit to excite much enthusiasm
here as to their superiority over what had already been done in this
country. Besides this, the report said that the new objectives were
five system, and also that extra eye-pieces had to be used with them.
I confess I am much inclined to attribute the optical improvement,
which, according to Dr. Abbe's own remark, is very little, more to the
fact that the objectives are five system than to the new glass used in
their construction.
After a close study of a descriptive list of the new glass, received a
week or two ago from the manufacturers, I find, to my great regret,
that this new glass seems to suffer from a similar weakness to that
made by the English firm twelve years ago; as all the numbers of the
list pointed out by the makers as having a greatly reduced secondary
spectrum are accompanied with the special remark "to be protected."
Furthermore, from a comparison of the dispersive and refractive powers
of these glasses, as given in the list, I find that objectives
constructed from them will leave so great aberrations of higher order,
both spherical and chromatic, that the gain by the reduction of the
secondary spectrum would be greatly overbalanced.
In conclusion, I wish to say that while I would beware of
underestimating the great scientific and practical value of the
endeavor of the new German glass makers to produce improved optical
glass, and the great benefit accruing to opticians and all others
interested in the use of optical instruments, I think it wise not to
overestimate the real value of the defects of the common crown and
flint glass, which I have sought to explain in this paper. And, for
myself, I prefer to fight the more serious defects first, and when its
time has come I will see what can be done with the secondary spectrum.
* * * * *
PROBABLE ISOLATION OF FLUORINE. DECOMPOSITION OF HYDROFLUORIC ACID
BY AN ELECTRIC CURRENT.
By M.H. MOISSAN.
In a former memoir[1] we showed that it was possible to decompose
anhydrous hydrofluoric acid by the action of an electric current. At
the negative pole hydrogen collects; at the positive pole a gaseous
body is disengaged, having novel properties. The experiment was
performed in a platinum U tube, closed by stoppers of fluorite, and
having at the upper part of each branch a small delivery tube, also of
platinum. Through the stopper passes a platinum rod, which acts as
electrode. The metal employed for the positive pole is an alloy
containing 10 per cent. of iridium.
[Footnote 1: _Comptes Rendus_, vol. cii., p. 1543, and _Chemical
News_, vol. liv., p. 36.]
To obtain pure anhydrous hydrofluoric acid, we begin by preparing
fluorhydrate of fluoride of potassium, taking all the precautions
pointed out by M. Fremy. When the salt is obtained pure, it is dried
on a water bath at 100°, and the platinum capsule containing it is
then placed in a vacuum in the presence of concentrated sulphuric
acid, and two or three sticks of potash fused in a silver crucible.
The acid and potash are renewed every morning for a fortnight, and the
vacuum is kept at 2 cm. of mercury. Care must be taken during this
desiccation to pulverize the salt every day in an iron mortar, so as
to renew the surface. When the fluorhydrate contains no more water it
falls to powder, and is then fit to serve for the preparation of
fluoric acid; the fluorhydrate of fluoride of potassium, if well
prepared, is much less deliquescent than the fluoride.
When the fluoride is quite dry, it is quickly introduced into a
platinum alembic, which has just been dried by heating it to redness.
The whole is kept at a gentle temperature for an hour or an hour and a
half, so as to allow the decomposition to commence very slowly; the
first portions of acid which come over are rejected as they carry with
them traces of water remaining in the salt. The platinum receiver is
then attached, and the heat increased, allowing the decomposition to
proceed with a certain degree of slowness. The receiver is then
surrounded with a mixture of ice and salt, and from this moment all
the hydrofluoric acid is condensed as a limpid liquid, boiling at
19.5°, very hygroscopic, and, as is well known, giving abundant fumes
in presence of the atmospheric moisture.
During this operation the platinum U tube, dried with the greatest
care, has been fixed with a cork in a cylindrical glass vessel
surrounded with chloride of methyl. Up to the moment of introducing
the hydrofluoric acid, the leading tubes are attached to drying tubes
containing fused caustic potash. To introduce the hydrochloric acid
into the apparatus, it may be absorbed through one of the lateral
tubes in the receiver in which it is condensed.
In some experiments we have directly condensed the hydrofluoric acid
in the U tube surrounded with chloride of methyl; but in this case
care must be taken that the tubes are not clogged up by small
quantities of fluoride carried over, which would infallibly lead to an
explosion and projections, which are always dangerous with so
corrosive a liquid.
When we have introduced in advance in the small platinum apparatus a
determined amount of hydrofluoric acid cooled with chloride of methyl,
in tranquil ebullition at a temperature of -23°, the current of 20
cells of Bunsen large size, arranged in series, is passed through by
means of the electrodes. An amperemeter in the circuit admits of the
intensity of the current being observed.
If the hydrofluoric acid contains a small quantity of water, either by
accident or design, there is always disengaged at the positive pole
ozone, which has no action on crystallized silicium. In proportion as
the water contained in the acid is thus decomposed, it is seen by the
amperemeter that the conductivity of the liquid rapidly decreases.
With absolutely anhydrous hydrofluoric acid the current will no longer
pass. In many of our experiments we have succeeded in obtaining an
acid so anhydrous that a current of 25 amperes was entirely arrested.
To render the liquid conducting, we have added before each experiment
a small quantity of dried and fused fluorhydrate of fluoride of
potassium. In this case, decomposition proceeds in a continuous
manner; we obtain at the negative pole hydrogen, and at the positive
pole a regular disengagement of a colorless gas in which crystallized
silicium in the cold burns with great brilliancy, becoming fluoride of
silicium. This latter gas has been collected over mercury, and
accurately characterized.
Deville's adamantine boron burns in the same manner, but with more
difficulty, becoming fluoride or boron. The small quantity of carbon
and aluminum which it contains impedes the combination. Arsenic and
antimony in powder combine with this gaseous body with incandescence.
Sulphur takes fire in it, and iodine combines with a pale flame,
losing its color. We have already remarked that it decomposes cold
water, producing ozone and hydrofluoric acid.
The metals are attacked with much less energy. This is due, we think,
to the small quantity of metallic fluoride formed preventing the
action being very deep. Iron and manganese in powder, slightly heated,
burn with sparks. Organic bodies are violently attacked. A piece of
cork placed near the end of the platinum tube, where the gas is
evolved, immediately carbonizes and inflames. Alcohol, ether, benzol,
spirit of turpentine, and petroleum take fire on contact.
The gas evolved at the negative pole is hydrogen, burning with a pale
flame, and producing none of these reactions.
When the experiment has lasted several hours, and there is not enough
hydrofluoric acid left at the bottom of the tube to separate the two
gases, they recombine in the apparatus in the cold, with violent
detonation.