more than 1/250 to 1/230 of its weight of ashes. The soluble matter may be
removed by washing it, first, with very dilute hydrochloric acid, and
secondly, with distilled water.
The 'Munktell' Swedish filtering paper[301] is composed of flax fibres
very much crushed and broken, and owes its value to the broken pieces of
the fibres filling up the pores, and thus preventing solids from passing
through the paper. Rhenish filtering paper is also made from flax, but in
consequence of the more perfect condition of its fibres, is more porous
than Munktell's, and therefore inferior to it for filtering purposes.
Another kind of Rhenish paper, also of flax, in which the fibres are much
torn, is manufactured and is said to be a useful article, and to allow the
rapid passage of fluids through it. The white filtering papers of English
make have a small quantity of cotton mixed with the flax; and the fibres
are much torn and crushed; hence they make serviceable filters.
[Footnote 301: Dr F. Mohr says that Swedish filtering paper is now
undeserving its traditional reputation, and that it contains soluble
alumina.]
The grey, circular cut filtering paper of varying sizes, of foreign make,
as well as the grey sheet filtering paper of Dutch and English
manufacture, contains a large quantity of wool, much of which is coloured;
as well as jute and esparto grass, both of these latter in an unbleached
state. The amount of ash in the Munktell paper has of late increased in
quality.[302]
[Footnote 302: Greenish.]
[Illustration]
For filtering a larger quantity of a liquid than can be conveniently
managed with a funnel, and also for substances that are either too viscid
or too much loaded with feculence to allow them to pass freely through
paper, conical bags made of flannel, felt, tweeled cotton cloth or Canton
flannel, linen or calico, and suspended to iron-hooks by rings or tapes,
are commonly employed. The first two of the above substances are
preferable for saccharine, mucilaginous, and acidulous liquors; the third
for oily ones; and the remainder for tinctures, weak alkaline lyes, and
similar solutions. These bags have the disadvantage of sucking up a
considerable quantity of the fluid poured into them, and are therefore
objectionable, except for large quantities, or when they are to be
continued in actual use as filters for some time. On the large scale, a
number of them are usually worked together, and are generally enclosed in
cases to prevent evaporation, and to exclude dirt from the filtered liquor
that trickles down their sides. These arrangements will be noticed further
on.
[Illustration]
A simple mode of filtering aqueous fluids, which are not injured by
exposure to the air, is to draw them off from one vessel to another, by
means of a number of threads of loosely twisted cotton or worsted,
arranged in the form of a syphon. (See _engr._) The little cotton rope at
once performs the operations of decantation and filtration. This method is
often convenient for sucking off the water from a small quantity of a
precipitate.
For fuller information on the subject of laboratory filtration, the reader
is referred to the following papers (which are too long for quotation
here) in 'The Chemical News':--
"On a New Mode of Filtration," by J. B. Cooke, May 30th, 1873; "Filtering
Apparatus," by John F. Kerr, February 6th, 1874; "Implements for
Filtration," by P. Casamajor, July 23rd, 1875, and 30th, 1875; Ibid, by W.
Jago, February 4th, 1876; "On Rapid Filtration," by E. C. H. Hildebrand,
August 11th, 1876; also to 'Journal of the Chemical Society,' for papers
on:--"Simple Suction arrangement for Rapid Filtering," by C. Holthof, vol.
xxxii, part 2, p. 508; "Employment of Compressed Air on Filtering
Solutions," by W. Leübe, vol. xxxii, part 1, p. 270.
When solid substances, as porous stone or earthenware, are used as the
media for filtrations, vessels of metal, wood, or stone-ware, are employed
to contain them and the supernatant liquid. In these cases the filtering
medium is usually arranged as a shelf or diaphragm, and divides the vessel
into two compartments; the upper one being intended to contain the dirty
liquid, and the under one to receive the same when filtered. Such an
apparatus is set in operation by merely filling the upper chamber, and may
at any time be readily cleared out by reversing it, and passing clean
water through it in an opposite direction. Small arrangements of this
kind, intended to be screwed on to the water supply-pipe by either end,
and which answer the purpose intended in the most satisfactory manner,
have been manufactured and vended under the name of 'REVERSIBLE' or
'SELF-CLEANING FILTERS,' When pulverulent substances, as sand, coarsely
powdered charcoal, &c., are employed, a similar arrangement is followed;
but in this case the shelf or diaphragm must consist of any convenient
substance pierced with numerous holes, over which must be placed, first a
stratum of coarse pebbles, next some of a finer description, and on this a
proper quantity of the sand, charcoal, or other medium. Over the whole
should be placed another layer of pebbles, or a board or plate of metal or
earthenware, pierced with a number of holes, to allow the liquid to be
poured into the filter without disturbing its arrangement. Apparatus of
this kind, of a permanent description, and arranged for filtering large
quantities of liquids, are properly denominated 'FILTERING MACHINES,'
Among the liquids usually submitted to filtration, the following may be
mentioned as the principal--water, oils, syrups, tinctures, vegetable
juices, infusions, and decoctions.
The filtration of water may now be considered. The water of our wells is
presented by nature ready filtered to the hand of man, and often exhibits
an admirable degree of transparency and purity. It acquires this state by
percolating through the mineral strata of the earth, which deprives it of
the organic matter it derives from the soil and subsoil, but, at the same
time, it dissolves a portion of the saline and earthy media through which
it passes, and hence acquires that peculiar 'hardness' which is constantly
found in spring water. On the large scale, this natural system of
filtration has been imitated by some of the commercial companies that
supply our cities and towns with water. Extensive beds of sand and gravel
have been employed, with variable success, as the filtering media; and
were it not that filters gradually lose their porosity by the accumulation
of the retained matter in their pores, such a method would be excellent.
But the great expense of such filters precludes the possibility of
frequently cleaning or renewing them, by which means they can alone be
kept in an efficient state.
A filter which possesses the advantages of being easily and cheaply
cleaned when dirty, and which frees water from mechanical impurities with
immense rapidity, may be formed by placing a stratum of sponge between two
perforated metallic plates, united by a central screw, and arranged in
such a manner as to permit of the sponge being compressed to any required
degree. Water, under gentle pressure, flows with such rapidity through the
pores of compressed sponge, that it is said that a few square feet of this
substance will perfectly filter several millions of gallons of water
daily. This method of filtration has been made the subject of a patent,
and has been favorably noticed by the legislature.
A few barrels or hogsheads of water may be easily filtered daily, by the
arrangement represented in the engraving.
[Illustration:
_A._ A common water-pipe or cock.
_b._ A false bottom fitting in perfectly water-tight.
_c._ A perforated wooden or metallic vessel or box covered with a
bag of felt or other filtering substance (not shown in the
engraving). _d._ A small tube, fitting water-tight into the
false bottom and uniting the _interior_ of the filter with the
lower portion of the cask.]
It is evident that when water is poured into the upper portion _B_ of a
vessel, so arranged, it will sink through the filter _c_, and pipe _d_,
into the lower chamber _C_, and this filtration will go on as long as the
supply continues, and water is drawn from the cock _e_. By uniting the
cock _e_ with a tank or casks, and by keeping the upper portion _B_ always
full by means of a ball-cock, a considerable quantity of water may be thus
filtered. The advantage of this plan is, that the filter _c_ can be always
readily got at, and easily cleaned or renewed.
For filtering water on the small scale, and for domestic use,
'alcarazzas,' diaphragms of porous earthenware and filtering-stone and
layers of sand and charcoal, &c., already referred to, are commonly
employed as filtering media. The filtering power of porous stone or
earthenware may be greatly increased by adopting the arrangement
represented in the margin, which consists in making the diaphragm of the
shape of a disc (_d_), supporting plates of the same material, the whole
forming but one piece. The 'PLATYLITHIC WATER-FILTERS,' which are formed
of porous stone cut on this plan, present 200 to 300 square inches of
filtering surface. A cheap, useful form of portable filter, is the
following, given in the 'Proceedings of the British Association,' "Take
any common vessel, perforated below, such as a flower-pot, fill the lower
portion with coarse pebbles, over which place a layer of finer ones, and
on these a layer of clean coarse sand. On the top of this a piece of burnt
clay, perforated with small holes, should be put, and on this again a
stratum of three or four inches thick, of well burnt pounded animal
charcoal. A filter thus formed will last a considerable time, and will be
found particularly useful in removing noxious and putrescent substances
held in solution by water."[303] The 'PORTABLE-FILTERS,' set up in
stone-ware, that are commonly sold in the shops, contain a stratum of
sand, or coarsely-powdered charcoal;[304] before, however, having access
to this, the water has to pass through a sponge, to remove the coarser
portion of the impurities. Among the many new kinds of portable filters
now offered for sale, which claim special notice, are the following,
viz.--
[Footnote 303: A very similar filter to this was invented by the late Mr
George Robins, the celebrated auctioneer. Mr Robins' filter differed from
the above in having a lid with a hole in the centre in which a sponge was
placed; an arrangement which by keeping back the suspended matter
contained in the water, prevented the filter from being clogged up.]
[Footnote 304: Frankland and Byrne have shown that animal is greatly
superior to vegetable charcoal when employed for water-filters.]
[Illustration]
=1.= The MOULDED CARBON FILTER, consisting of a spherical or cylindrical
vessel formed of compressed carbon.
=2.= The SILICATED CARBON FILTER, in which the medium is a compact
substance, formed of animal charcoal and the ashes of Boghead coal.
Of the many forms of this filter, we may mention the 'Syphon Filter for
Travellers,' by means of which wholesome water may be drunk from any pond
or stream by simply immersing the filter therein and drawing the water
through the tube by suction. Of the 'Silicated Carbon Filter,' Professor
Wanklyn says that it will render river water containing a considerable
amount of free and albuminoid ammonia as pure as deep spring water.
=3.= BISCHOFF'S PATENT SPONGY-IRON FILTER.--This differs from one invented
many years ago by Dr Medlock, in bringing the water into contact with
spongy iron instead of thin iron rods, and thus effecting filtration much
more rapidly. Medlock believed that the iron rods brought about the
oxidation of the nitrogenous organic matter and its consequent conversion
into nitrites and nitrates. Bischoff states that he has experimentally
investigated the properties of spongy iron, and finds that it--
_a._ Decomposes even distilled water, which has been previously boiled.
_b._ That it reduces nitric acid to ammonia.
_c._ That the amounts of organic nitrogen and albuminoid ammonia are
always much reduced after filtration through spongy iron.
_d._ That a minute quantity of iron is dissolved by the carbonic acid
contained in the water, ferrous bicarbonate being formed. The latter being
soon oxidised and precipitated is easily removed by filtration.
_e._ That the action of spongy iron on impure water is two fold, viz.
chemical and mechanical. "The chemical action is clearly indicated by the
decomposition of water. The readiest explanation for the decomposition of
water, is, the intimate contact between the electro-positive and
electro-negative bodies, such as metallic iron and carbon, or even
metallic iron and any ferric oxide, which has escaped reduction, or which
has been reoxidised by exposure to air or water; and it may well be
supposed that, consequent to the galvanic current thus produced, the
atmospheric oxygen dissolved in water is ozonised, and caused to act as a
powerful oxidising agent in organic matter."
We extract the tables on the next page from the Sixth Report of the Royal
Commission on Rivers' Pollution. The Commissioners, we may here state,
speak in high terms of this filter.
=4.= The so-called MAGNETIC CARBIDE OF IRON FILTER. In this, the filtering
material is said to be prepared by heating hæmatite with sawdust. This
filter has a good repute.
[asterism] The Royal Commission "on Rivers Pollution" strongly recommend
filters of animal charcoal to be recharged every three to six months,
"since they found that myriads of minute worms were developed in the
animal charcoal, and passed out with the water when these filters were
used for Thames water, and when the charcoal was not renewed at
sufficiently short intervals."
_Cleansing of Filters._--Every two or three months (according to the kind
of water) air should be blown through, and if the charcoal be in the block
form it should be brushed. Then four to six ounces of the pharmacop[oe]ial
solution of potassium permanganate, or twenty to thirty grains of the
solid permanganate in a quart of distilled water, and ten drops of strong
sulphuric acid, should be poured through, and subsequently a quarter to
half an ounce of pure hydrochloric acid in two to four gallons of
distilled water. This plan would be useful on foreign stations where the
filter cannot be sent home, or taken to pieces; if it can be taken to
pieces, the charcoal should be spread out in a thin layer, and exposed for
some time to air or sun, or heated in an oven.
_The Average Composition of Thames Water, before and
after Filtration through Spongy Iron._
------------------+----------------------------------------------------------
| Dissolved Matters.
|---------+-------+---------+--------+-----------+---------
Description. | Total |Organic| Organic |Ammonia.| Nitrogen, | Total
| solid |carbon.|nitrogen.| |as nitrates|combined
|impurity.| | | | and |nitrogen.
| | | | | nitrites. |
------------------+---------+-------+---------+--------+-----------+---------
As delivered from | | | | | |
Chelsea | | | | | |
Waterworks | 28·04 | ·198 | ·042 | ·0009 | ·117 | ·220
The same water | | | | | |
filtered through | | | | | |
spongy iron | 16·8 | ·069 | ·018 | ·019 | ·018 | ·049
------------------+---------+-------+---------+--------+-----------+---------
The mean of the | | | | | |
14th and 15th | | | | | |
taken after the | | | | | |
spongy iron | | | | | |
filter had been | | | | | |
in operation in | | | | | |
the Rivers | | | | | |
Commission | | | | | |
Laboratory for | | | | | |
upwards of eight | | | | | |
months.[305] As | | | | | |
supplied from | | | | | |
Waterworks | 24·47 | ·170 | ·055 | ·001 | ·098 | ·154
After filtration | | | | | |
through spongy | | | | | |
iron | 14·26 | ·083 | ·016 | 0 | 0 | ·016
------------------+---------+-------+---------+--------+-----------+---------
---------------+-------------------------------------------------------------
| Dissolved Matters.
+---------+---------+-------------------------------+---------
| | | Hardness. |
| | +----------+----------+---------+
Description. |Previous |Chlorine.|Temporary.|Permanent.| Total. | No. of
| Sewage | | | | | samples
|or Animal| | | | |analysed.
|contamin-| | | | |
| ation. | | | | |
---------------+---------+---------+----------+----------+---------+---------
As delivered | | | | | |
from Chelsea | | | | | |
Waterworks | 1·464 | 2·01 | 15·5 | 6·2 | 21·7 | 15
The same | | | | | |
filtered | | | | | |
through | | | | | |
spongy iron | ·177 | 2·00 | 6·8 | 4·9 | 11·7 | 15
---------------+---------+---------+----------+----------+---------+---------
The mean of the| | | | |Analysis |
14th and 15th | | | | | of the |
samples taken | | | | | 15th |
after the | | | | | sample. |
spongy iron | | | | | |
filters had | | | | | |
been in | | | | | |
operation in | | | | | |
the Rivers | | | | | |
Commission | | | | | |
Laboratory for| | | | | |
upwards of | | | | | |
eight | | | | | |
months.[305] As | | | | |
supplied from | | | | | |
Waterworks | ·675 | 1·95 | --- | --- | 19·1 | ---
After | | | | | |
filtration | | | | | |
through spongy| | | | | |
iron | 0 | 1·95 | --- | --- | 9·6 | ---
---------------+---------+---------+----------+----------+---------+---------
[Footnote 305: The figures demonstrate that the purifying action of spongy
iron, if at all altered, has been _increased_, as regards the most
important impurities of water, viz., nitrogenous matters and hardness.]
If sponges are at all used, they should be removed from time to time, and
thoroughly washed in hot water.[306]
[Footnote 306: Parkes 'Practical Hygiene.']
Oils are filtered, on the small scale, through cotton-wool, or unsized
paper, arranged in a funnel; and on the large scale, through long bags,
made of tweeled cotton-cloth (Canton flannel). These bags are usually made
about 12 or 15 inches in diameter, and from 4 to 8 feet long (see
_engr._), and are inclosed in bottomless casings, or bags of coarse
canvas, about 5 to 6 or 8 inches in diameter, for the purpose of
condensing a great extent of filtering surface into the smallest possible
space. A number of these double bags (from 1 to 50 or 60) are connected
with corresponding holes in the bottom of a block-tin or tinned-copper
cistern, into which the oil to be filtered is poured. The mode in which
these bags are fastened to the cistern is of the utmost importance, as on
the joint being close and secure depends the integrity of the apparatus.
Three methods of doing this are figured in the engraving, which, with the
references, will explain themselves, the same letters referring to the
same parts of each.
[Illustration: Filtering-bag of cotton-cloth.
Cotton filtering-bag, '_creased_,' or enclosed in its canvas envelope,
ready for fixing.]
The second of the above arrangements is the least expensive, and certainly
the most convenient in practice; and when the cylinder _l_ fits the hole
closely (allowing for the bag), is as safe, or safer, than an ordinary
screw.
[Illustration:
_a._ Bottom of cistern.
_b._ Filtering-bag.
_c._ Screw of the conical nozzle fitting into the cistern.
_d._ Binding cord connecting bag and nozzle.
_e._ Binding cord connecting bag and lower nozzle.
_f._ Bayonet-catch, connecting the lower portion of the nozzle
fastened to the bag with the upper and fixed part, _g_.
_i._ The thick hem at the top of the bag (purposely made large by
enclosing a piece of thick cord therein), resting on the
shoulders, _k_.
_l._ A metallic cylinder, loosely fitting the hole in the cistern,
and over which the top of the bag is drawn, before being put
into its place; when fitted, as in the engraving, it retains
the hem _i_ securely in its place above the shoulder _k_.]
The bags are surrounded by a wooden screen fitted up with doors for the
purpose of keeping off the dust; and the bottom of the apartment is
furnished with large steam-pipes, by which a proper temperature may be
kept up in cold weather. The use of heat should, however, never be had
recourse to when it can be avoided, as although it vastly increases the
rate of filtration, the oil so filtered is more apt to become opaque in
cold weather than when the process is conducted at the natural temperature
of the atmosphere. This is particularly the case with castor oil and sperm
oil. In the United States of America, where the latter is consumed in
enormous quantities for illumination, the best is always 'winter
strained,' as it is popularly called. In practice, it is more convenient
to have a number of small cisterns at work (say 50 or 100 galls. each),
than one or two larger ones, as any accident that may occur is more easily
remedied, and that without stopping the whole operation.
When cotton-cloth bags are employed without being 'creased,' or enclosed
in others of canvas, they should not be longer than about 3 or 4 feet, and
not wider than about 5 or 6 inches when filled. When larger they are
dangerous.
[Illustration]
A convenient method of filtering a single cask of oil is, to insert the
pipe of a two-way patent filter into the cork-hole, by which means the
whole will be filtered as drawn off, without any trouble on the part of
the operator. This filter consists of a porous bag stretched over a
perforated metallic vessel, nearly the shape and size of the exterior
casing, and its edge is tightly screwed between the sides and bottom of
the latter, so as to be quite water-tight. The cock communicates with the
interior of the perforated plate and filter, and the supply-pipe with the
exterior. By this means the interior chamber, which occupies 5/6ths of the
vessel, rapidly fills with filtered oil, and continues full as long as any
liquor remains in the cask. This arrangement is also well adapted to the
filtration of wines, beer, cordials, porter, and various other liquors. It
is unequalled in simplicity and usefulness. The same filter may be removed
from cask to cask, with the facility of a common cock.
The filtration of SYRUPS is now generally effected on the large scale by
passing them through the 'CREASED BAG FILTER' just described. On the small
scale, as employed by confectioners and druggists, they are usually passed
through CONICAL FLANNEL BAGS. (See page 726.) The filtration of thick
syrups is, however, attended with some difficulty, and it is therefore a
good plan to filter them in a somewhat dilute state, and afterwards to
reduce them to a proper consistence by evaporation in clean vessels of
tinned copper, by steam heat. Syrups, when filtered in a heated state, run
well for a time, but the pores of the fabric rapidly get choked, from the
thickening of the syrup and partial crystallization of the sugar,
occasioned by the evaporation of the aqueous portion from the surface of
the bag. This may be partially prevented by enclosing the bag in a
metallic casing. On the whole clarification is preferable for syrups to
filtration on the small scale. They need only be well beaten up while cold
with a little white of egg, and then heated; a scum rises, which must be
removed as soon as it becomes consistent, and the skimming continued until
the liquid becomes clear. Any floating portions of scum that may have
escaped notice are easily removed by running the syrup through a coarse
flannel strainer, whilst hot. The most extensive application of the
process of filtration in the arts is in the refining of sugars.
TINCTURES AND DILUTE SPIRITS are usually filtered, on the small scale,
through BIBULOUS or UNSIZED PAPER placed on a funnel; and on the large
scale, through thin and fine COTTON BAGS. In general, however, tinctures
clarify themselves by the subsidence of the suspended matter, when allowed
to repose for a few days. Hence it is the bottoms alone that require
filtering; the supernatant clear portion need only be run through a small
hair sieve, a piece of tow or cotton placed in the throat of a funnel, or
some other coarse medium, to remove any floating substances, as pieces of
straw, &c. Spirits which are largely loaded with essential oil, as those
of ANISEED, &c., run rapidly through paper or calico, but usually require
the addition of a spoonful or two of magnesia before they will flow quite
clear. When possible, tinctures, spirits, and all similar volatile fluids,
are better and more economically cleared by subsidence or clarification
than by filtration, as, in the latter way, a portion is lost by
evaporation, and the strength of the liquid is thereby altered.
Vegetable juices should be allowed to deposit their feculous portion
before filtration. The supernatant liquid will then be often found quite
clear. It is only when this is not the case that filtration should be had
recourse to. A small quantity may be filtered through coarse or woollen
filtering paper, supported on a piece of coarse calico placed on a funnel;
when the quantity is large, one of the CONICAL BAGS before described
should be employed. The bottoms from which the clear portion has been
decanted should be placed on a separate filter, or else not added until
the whole of the other portion has drained through. Vegetable juices are
often rendered clear by simply heating them to about 180° or 200° Fahr.,
by which their albumen is coagulated; they are also frequently clarified
by the addition of a little white of egg and heat, in the same way as
syrups. Many of them (as those of hemlock, henbane, aconite, &c.) are
greatly injured by heat, and must consequently be filtered, or only simply
decanted after repose. In all cases they should be exposed to the air as
little as possible, as they rapidly suffer decomposition.
Vegetable infusions and decoctions may be cleared by defecation followed
by filtration. The conical bags of flannel before described are usually
employed for this purpose. When the liquid is to be evaporated to an
extract, they are commonly suspended by a hook over the evaporating pan. A
convenient method of straining these fluids, practised in the laboratory,
is to stretch a square of flannel on a frame or 'horse,' securing it at
the corners by pieces of string. (See _engr._) Such a frame, laid across
the mouth of a pan, is more easily fed with fresh liquid than a bag, whose
mouth is 40 or 50 inches higher. The same purpose, for small quantities of
liquid, is effected by laying the flannel across the mouth of a coarse
hair sieve. The concentrated infusions and decoctions being usually weak
tinctures, may be filtered in the same way as the latter. (See _above_.)
Many vegetable solutions, that from the viscidity of the suspended matter
can scarcely be filtered, may be readily clarified with white of egg in
the cold, or pass the filter rapidly if a very small quantity of acetic,
tartaric, sulphuric, or other strong acid, is previously added.
[Illustration]
Corrosive liquids, as the STRONG ACIDS, are filtered through powdered
glass, or SILICEOUS SAND, supported on pebbles in the throat of a glass
funnel, or through asbestos or gun-cotton placed in the same manner.
Charcoal has also been employed for the same purpose, but is not fit for
some acids. Strong caustic alkaline lyes are also filtered through
powdered glass or sand. Weak alkaline lyes may be filtered through fine
calico, stretched across the mouth of a funnel. Many corrosive liquids, as
solution of potassa, &c., require to be excluded from the air during
filtration. The simplest apparatus that can be employed for this purpose
is that figured in the margin:--(_a_) is a globular bottle fitted with the
ground stopper (_d_), and having a perforated neck (_f_) ground to the
bottle (_b_); (_c_) is a small tube, wrapped round with as much asbestos,
linen, or calico, as is required to make it fit the under neck of the
bottle through which it passes. The tube (_c_) may also be fixed by
placing pebbles and powdered glass or sand round it, as before mentioned.
For use, the solution to be filtered is poured into the bottle (_a_)
nearly as high as the top of the tube (_c_), and the stopper is replaced.
The liquid then descends into (_b_), and a similar quantity of air passes
up the tube into (_a_). LIQUOR POTASSÆ may be always obtained fine by
depuration in close vessels, when the sediment of lime only need be
filtered, which may be effected with calico fixed across the mouth of a
funnel.
[Illustration]
When a precipitate, or the suspended matter in a liquid, is the object of
the filtration, the filter should be of such a nature that the powder may
be easily separated from it, when dry, and that with the least loss
possible. Linen filters are for this reason preferable for large
quantities, and those of smooth bibulous paper for small ones. The powder
should be washed down the sides of the filter, and collected, by means of
a small stream of water, in one spot at the bottom, assisting the
operation with a camel-hair pencil; and, when the whole is dry, it should
be swept off the paper or cloth with a similar pencil or brush, and not
removed by a knife, as is commonly done, when it can be possibly avoided.
The 'first runnings' of liquid from a filter are commonly foul, and are
pumped back or returned until the fluid runs perfectly limpid and
transparent, when it is 'turned into' the 'filtered liquor cistern,' or
proper receiver. In many cases the liquid does not readily become
transparent by simply passing through the filter; hence has arisen the use
of FILTERING POWDERS, or substances which rapidly choke up the pores of
the media in a sufficient degree to make the fluid pass clear. In the
employment of these powders care should be taken that they are not in too
fine a state of division, nor used in larger quantities than are
absolutely necessary, as they are apt to choke up the filter, and to
absorb a large quantity of the liquid. The less filtering powder used, the
more rapid will be the progress of the filtration, and the longer will be
the period during which the apparatus will continue in effective action.
For some liquids these substances are employed for the double purpose of
decolouring or whitening, as well as rendering them transparent. In such
cases it is preferable first to pass the fluid through a layer of the
substance in coarse powder, from which it will 'run' but slightly
contaminated into the filter; or, if the powder is mixed with the whole
body of the liquid, as in bleaching almond oil, &c., to pass the mixture
through some coarser medium to remove the cruder portion before allowing
it to run into the filter. Another plan is, after long agitation and
subsequent repose, to decant the clearer portion from the grosser
sediment, and to employ separate filters for the two. Granulated animal
charcoal is used according to the first method, to decolour syrups, oils,
&c.; and filtering powder by the second and third, to remove a portion of
the colour, and to clarify castor and other oils. The common plan of
mixing large quantities of filtering powder with castor oil, and throwing
the whole into the filter, as adopted by the druggists, is injudicious.
When simple filtration is required, it is better to use little or no
powder, and to continue returning the oil that 'runs' through, until, by
the swelling of the fibres of the filter bags, it flows quite clear. By
this plan the same filters may be used for a long period of time (for many
years), and will continue to work well; whilst, by the usual method, they
rapidly decline in power, and soon deliver their contents slowly, and
after a short time scarcely at all.
It is often of great advantage to render a filter 'self-acting,' or to
construct it in such a way that it may 'feed itself,' so that it may
continue full and at work without the constant attention of the operator.
On the small scale, this may be readily effected on the principle of the
common fountain lamp (see _engr._); and on the large scale, by placing the
vessel containing the unfiltered liquid on a higher level than the filter,
and by having the end of the supply-pipe fitted with a ball-cock, to keep
the liquid in the filter constantly at the same height.
[Illustration]
The rapidity of filtration depends upon--the porosity of the filtering
medium--the extent of the filtering surface--the relative viscidity or
mobility of the filtering liquid--the pressure or force by which the
liquid is impelled through the pores of the filter, and--the porosity and
fineness of the substances it holds in suspension. The most efficient
filter is produced when the first two or the first three are so graduated
to the others that liquid filters rapidly, and is at the same time
rendered perfectly transparent.
In the common method of filtration no pressure is exerted beyond that of
the weight of the column of the liquid resting on the filtering medium,
but in some cases additional pressure is employed. This is had recourse to
for the purpose of producing a more rapid filtration, and more especially
for filtering liquids that, from their viscidity, will scarcely pass
through the pores of substances sufficiently fine to remove their
impurities in the ordinary way.
[Illustration]
One of the easiest means of employing pressure in filtration is to
increase the height of the column of the filtering liquid. From the
peculiar properties of fluids, by which they transmit pressure in an equal
degree in all directions, this column need not be of equal diameter
throughout, but may be conveniently contracted to the size of a small
pipe, as in the accompanying engraving, which represents a small filter on
this construction at work. (_a_) Is the funnel or reservoir of foul
liquid; (_b_) a small pipe conveying the liquid to the filter; (_c c_) a
chamber, of which the upper portion (_d_) is filled with the descending
liquid, and the lower portion (_e_) with the filtering media; (_i i_) are
screws by which the bottom plate is fastened on, which plate is removed to
clean out or renew the filter. For use, the cocks (_k_) and (_l_) are
closed, and the liquid poured into the funnel (_a_); the cock (_k_) is
next opened, and, in a few minutes after, the cock (_l_), when an
uninterrupted flow of filtered liquor will be obtained as long as any
fluid remains in the funnel (_a_) and the tube (_b_). The length of the
tube determines the degree of pressure. Care must be taken first to pass
the foul liquid through a hair sieve, or some other strainer, to remove
any substance that might choke up the pipe (_b_).
Another method of employing pressure in filtration is the withdrawal of
the air from the receiving vessel, as in the vacuum filter, by which a
pressure of about 14-1/2 lbs. to the square inch becomes exerted on the
surface of the liquid by the atmosphere. The vacuum in the receiving
vessel may be produced by the air-pump, by steam, or by the Bunsen or
Sprengel pump.
A commoner method of applying pressure than either of those already
mentioned is to condense the air over the surface of the liquid by means
of a forcing-pump, or by steam.
On the small scale, pressure may be applied to filtration by means of a
syphon, whose shorter leg has its mouth blown into the shape of a bell or
funnel, over which filtering paper or fine calico may be stretched.
The application of pressure to filtration is not always advantageous, and
beyond a certain limit is generally attended with inconvenience, if not
with absolute disadvantage. It is found in practice that fluids under
pressure take a longer period to run clear than without pressure, and that
ruptures of the media more frequently take place in the former case, or
with pressure, than in the latter. Great pressure is in no case
advantageous.
The filters already noticed are those that act by the fluid descending
through the media; but in some cases the reverse method is employed, and
the liquid filters upwards, instead of downwards. These are called
ascending filters, and are often preferable to those on the descending
principle, because the suspended matters that require removal by
filtration usually sink, and thus a portion escapes being forced into the
pores of the filter. They are also more convenient when pressure is
employed. The construction depends upon the same principles as the common
filter, and merely requires that the feeding vessel should be higher than
the upper surface of the filtering media. OILS are conveniently filtered
in this way, because of their little specific gravity. By fixing a small
filter on this principle into the head of a cask, and pouring in water
through a funnel, whose neck reaches nearly to the bottom of the cask, the
oil will float up and pass the filter, leaving the sediment behind. In
cold weather hot water may be employed.
[Illustration:
_a._ Cask of oil.
_b._ Stand.
_c._ Funnel for water.
_d._ Filter.]
In some cases the upward and downward systems of filtration are united in
the same apparatus, and this plan is advantageous where the space for
operating is limited. For this purpose it is merely necessary to connect
the bottom of an ascending filter with the top of a descending one, or the
reverse; the proper pressure being in either case applied.
=Filtration, the Laws of.= The 'Revue Universelle des Mines,' 1874, pp.
469, 551 contains a paper by M. Paul Havre recording his investigations on
the rapidity of the filtration of water through sand, wool, &c., which
resulted in ascertaining and measuring the influences which may modify the
flow of water. In all cases of filtration, the influences which are
exerted are:--the pressure and temperature of the water, the thickness of
the filtering medium, compression in the case of fibrous filters, the size
of the grains and their mixture in the case of a filtering medium
analogous to sand. The influence of obstruction, due to the dirtiness of
the filter, depends on circumstances too variable to be taken into
account. The delivery of a filter per square mètre per 24 hours is equal
to two cubic mètres multiplied by the pressure of water in mètres, divided
by the thickness of the filtering medium in mètres. An application of this
formula is made to existing filter beds, including those at Southwark and
at the Chelsea waterworks.
The first experiments for ascertaining the influence of a head of water on
the delivery led to the following results:--The delivery increases in a
higher ratio than the square root of the pressure, due to the height
(TORRECELLI'S LAW); the delivery increases in direct ratio to the height
of the column of water above the filter, admitting a previous initial
delivery, due solely to the pressure of water above the filter; the
co-efficient of the increase of delivery is constant, and in this case of
a filtering substance 8·662 inches (22 centimètres) thick, is equal to
0·106 pint (6 centilitres) for sand to 0·528 pint (30 centilitres) for
compressed wool, and to 0·792 pints (45 centilitres) for wool only
slightly compressed.
The subsequent experiments were made with graduated transparent cylinders,
3·28 feet (1 mètre) high, with the ends perfectly level, the filtering
substances being kept in place by a thick double cloth tied tightly under
the bottom of the tube. This apparatus presented no other obstacle to the
running of the water than the layer of filtering substance; it permitted
experiments to be made at all temperatures, and the thickness of the
filtering medium to be measured exactly.
In these experiments sand is 'taken as the type of pulverulent
substances,' but an unexpected difficulty was encountered in the settling
or partial agglomeration of the large and small grains of the unsifted
sand, thus diminishing the delivery of water to one half, one third, and
ultimately to one fifth of its previous volume. This led to the adoption
of sand--the grains of which were uniform in size, and to the discovery
of the fact that, other tissues being equal, the resistance of filtration
is constant when the sand is coarse, when the grains of fine sand are of
nearly equal size, and when there is but little fine sand mixed with the
coarse. From experiments in filtering through a layer of coarse sand
approximately 4 inches (10 centimètres) thick, it was found that the
higher the temperature the more rapid was the delivery, and by filtering
through a layer of coarser sand 11·8 inches (30 centimètres) thick, the
conclusion was arrived at that the temperature exerts an influence in
proportion to the thickness of the layer.
See AIR-PUMP, BUNSEN'S WATER-AIR PUMP; CLARIFICATION; DEFECATION; FININGS,
&c.
=FI'NINGS.= Substances used by publicans, brewers, wine merchants, &c., to
clarify their liquors.
_Prep._ 1. (BREWER'S FININGS; COOPER'S F.) Isinglass (finely shredded), 1
lb., and sour beer or cider or vinegar, 3 or 4 pints, are macerated
together, and more of the sour liquor added as the isinglass swells, until
about a gallon has been used, agitation with a whisk or a small bundle of
twigs being occasionally had recourse to, for the purpose of promoting the
solution. As soon as the whole of the isinglass is dissolved, the mixture
is reduced to the consistence of thin syrup, with weak mild beer, or
cider, or any other liquid that the finings are intended for. The whole is
next strained through a tammy cloth or a hair sieve, and at once reduced
to a proper state of dilution, by the addition of more liquor. _Product_,
6-1/2 to 7 galls. "A pound of good isinglass will make about 12 galls. of
finings." (Ure.) Used to clarify fermented liquors, especially beer. 1 to
1-1/2 pint is the usual dose for a barrel of ale or porter; and a quart
for a hogshead of cider or wine.
2. (SPIRIT FININGS.)--_a._ Alum (ord. cryst.), 1 lb.; powder, and divide
it into 12 equal portions, which are to be separately wrapped in blue
paper, and marked No. 1. Next take of carbonate of soda (sesquicarbonate
of the shops), 6 oz.; divide this as the last, wrap it in white paper, and
mark each parcel No. 2. Keeps dry anywhere.
_b._ From alum, 1 lb.; salt of tartar (dry), 1/4 lb.; proceed as before.
The white papers containing the salt of tartar must be kept in a dry,
well-corked, wide-mouthed bottle or jar. Both of the last two are used to
clarify gin and cordials. The contents of one of the blue papers are
dissolved in about a pint of hot water, and the resulting solution is well
'rummaged up' with the liquor. A solution of the contents of one of the
white papers, in about 1/2 pint of hot water, is then added, and the
agitation continued for some minutes longer; after which the cask is
'bunged' close and the whole allowed to repose until the next day. This is
sufficient for a barrel (say 30 to 36 galls.), but many persons use double
the quantity. The effect is not only to clarify, but also to 'blanch' the
liquor.
_Obs._ Good liquors, either fermented or spirituous, need no artificial
'fining,' as they always clarify themselves by repose. With those,
however, which are out of 'condition,' or of inferior quality, it is often
necessary, as, without such a proceeding, they remain unsaleable. This is
particularly the case with malt liquor. "Attempts to clarify it in the
cask seldom fail to do harm. The only thing that can be used with
advantage for fining foul or muddy beer is isinglass." (Ure.) The
disadvantages resulting from the artificial clarification of fermented
liquors are--that they do not afterwards 'stand well on draught,' that
much of the conservative astringent matter which they contain is
precipitated with the 'finings,' that their piquancy and flavour is more
or less diminished, and that they are more than usually liable to become
flat and vapid, whether in cask or bottle. The larger the proportion of
'finings' used, the more marked are their injurious effects, and the
shorter the interval which elapses before the accession of the several
symptoms referred to. We have seen the most disastrous consequences follow
the injudicious use of 'finings,' more especially in respect to those
liquors in which a certain amount of piquancy, astringency, and briskness,
is an essential condition. In one instance which came under our notice
upwards of 30 barrels of 'underground' (a very strong old ale) was thus
reduced in value to less than 1-3rd its original cost; and in another, a
large bottled stock of the 'finest old Burton' was found to be utterly
unsaleable. In both cases the 'spoiled liquor' was got rid of by mixing it
in and selling it with 3d. and 4d. beer.
Liquors which 'refuse to fine' or become clear, when treated with
'finings' in the usual manner, are called 'stubborn' by coopers and
cellarmen. See BREWING, GIN, MALT, LIQUORS, WINES, &c.
=FIRE.= The calamities resulting from this destructive agent are of such
frequent occurrence, as to justly claim a notice of the subject here. The
causes of fires are numerous, and of a varied character, and, in most
instances, difficult to determine, because it is the interest of those
concerned to suppress all evidence connected with the matter. Accident,
that convenient word given to the imaginary hack to which so many fires
are referred, if truthfully interpreted, will, in general, be found to be
equivalent to carelessness, recklessness, or guilt. We believe that there
are few fires which have happened that might not have been prevented by
the exercise of common prudence, and that a vast number have been caused
by direct negligence, arising from sheer laziness and indifference, to use
no harsher terms. As familiar instances, may be mentioned--allowing
sparks to fall on the ground and remain there without extinguishing them;
carrying a naked candle into rooms containing inflammable substances;
smoking carelessly and in dangerous places, as workshops, warehouses, on
shipboard, &c.; keeping instantaneous light matches in improper places,
and neglecting to pick up those that may happen to fall on the ground, &c.
&c. The list might easily be extended, but we believe every reflecting
reader can do so for himself. The great increase in the number of fires
since the introduction of lucifer matches, and the almost general use of
tobacco, cannot fail to have attracted the attention of every one. The
danger of matches falling about might be avoided by the use of those which
can only be ignited by rubbing them on the prepared surface of the box.
These 'safety matches' are coming into general use, and must eventually
supersede all the more dangerous kinds.
The late Mr Braidwood classes the causes of fires under the following
heads:--1. Inattention in the use of fires and lights. 2. Improper
construction of buildings, &c. 3. Furnaces or close fires, for heating
buildings, or for mechanical purposes. 4. Spontaneous ignition. 5.
Incendiarism.
Amongst many other causes of fire, too numerous to specify, may be
noticed--incautiously approaching window- and bed-curtains with a candle
or lamp, airing linen before the fire, allowing children to play with
fire, women's dresses taking fire, and taking off the burning coals from a
fire and laying them on the hearth. Another very common cause of fire is
covering up a fire-place when not in use with wood, or paper and canvas,
&c. The soot falls either from the flue itself or an adjoining one into
the grate; a neighbouring chimney takes fire, a spark from this falls down
the blocked-up flue, ignites the soot in the grate, which smoulders until
the covering is burnt through, and thus sets the building on fire.
Another cause of fire, and one which cannot be too strongly condemned, is
the dangerous practice of reading in bed by candle-light. A very serious
annual loss of property is also caused by want of proper care in hanging
up or removing the goods in linendrapers' shop windows when the gas is
burning. Another frequent cause of fire is the employment of young
children in lighting fires, from their propensity to play with flame.
The employment of close fires with brick flues is also a frequent source
of danger. Frequently, from various causes, the furnace almost always
cracks, thus giving egress to smoke and flame. When this occurs no time
should be lost in thoroughly repairing the defect, or building a new
furnace; merely plastering over the surface will be found an ineffective
and dangerous remedy.
To guard against the dangers arising from the ignition of wearing apparel
many methods have been suggested for rendering fabrics flame proof, all of
them consisting in soaking the dress in a weak solution of a
non-inflammable substance, such as chloride of zinc, alum, tungstate of
sodium, sulphate of ammonia, &c. Of these alum has the advantage of
greatly improving the appearance of the fabrics, especially if they be
coloured.
Fire-guards, particularly where there are children, ought to be adopted
much more generally than they appear to be.
_Prev._ This consists of the exercise of those ordinary precautions which
the good sense of every careful and trustworthy man, be he taskmaster or
servant, cannot fail to suggest. It would be useless to enumerate them.
Immediately on the fire being discovered, secure an alarm being given to
the nearest of the fire escape stations, not delaying an instant; do not
wait "to see if it is wanted." Life is more valuable than property, and
events have often proved how fatal even a moment's hesitation is in
sending for the fire-escape.[307]
[Footnote 307: 'Handbook for Emergencies,' Cassell.]
The late Mr Braidwood's advice was, "that if the fire appears at all
serious, and there are fire-engines within a reasonable distance, that it
is best to wait until they arrive; many buildings have been destroyed from
opening doors, and trying to extinguish fires with insufficient means. If
no engines are within reach it is advisable to keep a hand-pump. If that
is not to be had, the next best thing is to collect as many buckets
outside the room on fire as can be obtained, keeping the door shut; then
to creep into the room on hands and knees (if the heat and smoke are
considerable), and throw the water as nearly in the direction of the fire
as possible, keeping the door shut while more water is being collected.
"The police of the metropolis understand shutting up fires so well, that
they have in many instances kept fires two or three miles distant from the
engine-stations, shut up till the fireman arrived in time to extinguish
them."
Fires might often be readily extinguished when first discovered by the
timely application of a few buckets of water. When an apartment is found
to be on fire, the door, chimney, and windows should be immediately
closed, if possible, and only opened for the purpose of projecting water
on the flames. By this means the supply of air will be cut off, and rapid
combustion prevented. The same applies to the lower doors and windows of a
house (especially the shop window), which are often injudiciously kept
open or removed, under the pretence of rendering assistance. The neglect
of this precaution has often caused a mere smouldering fire, that might
have been easily put out, to burst into an unextinguishable mass of flame.
It has been proposed at various times to make certain additions to the
water used for the purpose of extinguishing fires, in order to render its
action more certain and effective. It is found that sal ammoniac (5 oz.
to the gall.) exerts this property in a remarkable degree. Several other
articles, as common salt, pearlash, and kitchen soda, act in the same way,
though less effectively. A few buckets of such water will speedily arrest
the progress of a fire before it has much extended itself. Such a plan is
easily applied, by adding the saline matter to the buckets of water, which
are either used by hand, or to feed the engine for the first few minutes
of its working. When, however, a fire has made much progress, the action
of such substances becomes scarcely perceptible.
Chimneys on fire are readily extinguished in several ways, without having
recourse to throwing water down them from the top, by which much damage is
frequently done to the furniture in the rooms. One of the simplest methods
is, to cautiously scatter a handful of flowers of sulphur over the dullest
part of the burning coals; the sulphurous vapours, being incapable of
supporting combustion, rapidly extinguish the flames. Another method is,
to shut the doors and windows, and to stop up the bottom of the chimney
with a piece of wet carpet or blanket, throwing a little water or flowers
of sulphur, or even common salt, on the fire immediately before doing so.
By this means the draught is stopped, and the burning soot extinguished
for want of air. In many of the first-class houses recently erected,
'fire-place shutters' are provided, which, when partly drawn down, act as
powerful bellows or 'blowers' and which, when wholly drawn down, so as to
touch the hearth-stone, entirely close up the fireplace, and instantly
extinguish the combustion of the fuel in the grate, or that of the soot in
the chimney. This simple arrangement, the advantages of which were pointed
out in an early edition of this work, renders fires in chimneys of little
moment, as it is only necessary to draw down the shutter to put them out.
If a chimney is stopped at top, instead of at the bottom, the whole of the
smoke must, of necessity, be driven into the apartment.
In France, M. Marateuh has successfully applied the principle of Davy's
safety lamp for the prevention of fires in chimneys. He places fire-frames
of iron work near the base of the chimney, one above the other, about one
foot apart; no flame passes through them, whilst the draught in the
chimney is not interfered with, the result being that no fire can happen
in the chimney.
Escape from apartments on fire may be best effected by creeping on the
hands and knees. In this way the window or door may be reached. It is
found that the atmosphere of a room so full of smoke as to produce
suffocation to a person standing upright, may generally be safely breathed
on nearly a level with the floor. A damp cloth, or handkerchief, tied over
the mouth and nostrils, or, still better, over the whole face and head,
will enable a person to effect a passage through the densest smoke, and,
in many cases, to escape from buildings on fire, when otherwise it would
be impracticable. Should descent by the staircase be found impossible,
then the window should be immediately sought, and a ladder or fire-escape
waited for. In the absence of either, if the danger is imminent, a rope
should be made by tying the sheets and blankets of the bed together, one
end of which should be firmly secured to a chair or table, or preferably
to one of the bed-posts, and with this apparatus descent should be
cautiously attempted. Jumping out of the window should be avoided, as
persons who have not been brought up as clowns, or harlequins, run just as
much danger in performing such an exploit as they do by remaining in the
burning building. When it is impossible to escape from a burning building
by the stairs or windows, retreat may be sometimes secured by a trap door
opening on to the roof, or by a skylight, when, unless it be an isolated
house, the roof of one of the adjoining buildings may probably be gained
with safety.
Fire-escapes of various kinds have been employed of late years in the
metropolis, and have proved of the greatest value in rescuing persons from
burning buildings.
It is said that there is no instance on record of a person being burnt to
death in a dwelling-house in Edinburgh, where the houses are usually high;
yet in London, where fire-engines and fire-escapes are provided in greater
numbers, deaths are very frequent from this cause. The reason of this
difference is, that in the former city the stairs are all made of stone,
by which means a road of escape is secured.
The clothes of females and children, when on fire, may be most readily
extinguished by rolling the sufferer in the carpet, hearth-rug,
table-cover, a great-coat, cloak, or any other woollen article at hand. If
this be expertly done, the flames may be rapidly put out, unless the
skirts of the dress be distended by hoops or crinoline, when there is
great difficulty in staying the progress of the flames. Should assistance
not be at hand, the person whose clothes are on fire should throw herself
on the ground, and roll the carpet round her, as before described; or if
such a thing is not in the room, she should endeavour to extinguish the
flames with her hands, and by rapidly rolling over and over on the floor.
In this way the fire will be stifled, or at least the combustion will
proceed so slowly that less personal injury will be experienced before
assistance arrives. The advantage of assuming the horizontal position is
manifest from the fact that nine times out of ten it is the lower parts of
the dresses of females that first catch fire.[308]
[Footnote 308: For the mode of rendering muslin and other inflammable
articles of ladies' apparel fire-proof, see INCOMBUSTIBLE FABRICS.]
The extinction of fires on board ships by means of carbonic-acid gas was
some years since suggested to the Admiralty by Mr J. R. Hancorn. He
proposes that a simple and economical apparatus should be attached to
every decked vessel capable of supplying this gas, which is a well-known
non-supporter of combustion, and will extinguish fire at the very instant
of coming in contact with the burning matter. Chalk with sulphuric acid
diluted with water (vinegar with any other acid will do) yields 44% of the
gas; hence, a ton of chalk, and a fourth part of that quantity of
sulphuric acid, will be found sufficient to extinguish any fire on board a
ship. Mr Hancorn also proposed this as a method of destroying vermin in
ships, such as rats and cockroaches, for which purpose it is more easily
applied and more effectual than that usually adopted. This plan was
rejected by the Admiralty, from a fear that the destructive action of the
gas might extend to the crew as well as the fire. But "it surely is
possible by mechanical means to expel the gas before again entering the
ship's hold. At any rate, the grand point would be obtained of
extinguishing the fire, though the crew might have only the deck to stand
on."
_Precautions to be taken against a Fire amongst Farming Stock._--The
following are the suggestions of Mr Beaumont, the secretary of the County
Fire Office:--
"Forbid your men to use lucifer matches, to smoke or light pipes or
cigars, destroy wasp nests, or fire off guns in or near the rickyard, or
to throw hot cinders into or against any wooden out-building on the farm,
on pain of instant dismissal.
"Place your ricks in a single line, and as far distant from each other as
you conveniently can. Place hayricks and cornstacks alternately; the
hayrick will check the progress of the fire. Keep the rickyard, and
especially the spaces between the stacks and ricks, clear of all loose
straw, and in all respects in a neat and clean state. The loose straw is
more frequently the means of firing than the stack itself. Have a pond
close to the rickyard, although there may be a bad supply of water. When a
steam thrashing machine is to be used, place it on the lee-side of the
stack or barn, so that the wind may blow the sparks away from the stacks.
Let the engine be placed as far from the machine as the length of the
strap will allow. Have the loose straw continually cleared away from the
engine; see that two or three pails of water are kept close to the ashpan,
and that the pan itself is kept constantly full of water."
It is often difficult to get horses out of buildings on fire, but it is
said that they will readily come out if, after being blindfolded, the
saddle and bridle, or the harness, &c., to which they are accustomed, are
thrown over them as usual.
We learn from the last report issued by Captain Shaw that the actual
number of fires in the year 1877 in London was 1533. Of these fires 1374,
or 90 per cent., were slight, no persons being endangered, and no
considerable destruction of property taking place. The number of really
serious conflagrations was 150; in 88 of these life was endangered, and in
24 cases there was loss of life. The actual number of persons whose lives
were in danger was 165; but of these 136 were saved, and the lives
eventually lost amounted only to 29. The smallness of the loss is due in
great degree to the courage of the members of the Brigade, seven of whom
have been commended for special efforts for saving life during the year.
Even of the twenty-nine persons who perished fourteen were taken alive out
of the burning buildings, and died in hospital of their wounds. It is very
satisfactory in view of the vast height of buildings used in business, and
the flimsy character of so many London houses, that the risk of death from
fire should be so small. It is one of the very slightest risks to which we
are exposed in modern London. The fire-escapes must of course be credited
with much of this security. There are now 108 stations of these useful
machines; and instances of their utility in rescuing the inmates of
burning houses are constantly occurring.
The various tables which Captain Shaw appends to his report give some very
curious details as to the character of London fires. The hours at which
they most commonly break out are by no means those which are popularly
supposed to be the most dangerous. No considerable proportion occur after
people have gone to bed. From seven o'clock in the evening till eleven
o'clock there are more alarms of fire than in an equal portion of the
twenty-four hours. Not a third of the number which occur in these evening
hours take place in the small hours of the morning, which are in fact less
destructive than the same period in the afternoon. There are, moreover, in
the detailed list of fires some curious statistics, illustrating the
comparative security of private houses over places of business. A very
large part of the half million houses in London must come under the
description of private dwellings, yet the alarms of fire in this class of
buildings were only 316 in the year, and only in five of those were there
serious conflagrations. In the lists of business premises nearly every
trade in the metropolis is mentioned; and next to houses let out in
lodgings, public-houses seem to suffer most. The causes of fires tell the
old story of carelessness. They were instances of the almost inconceivable
folly of seeking for an escape of gas with a lighted candle. The throwing
down of lights is responsible for a considerable number of fires. Ordinary
cases of chimneys on fire are not included in Captain Shaw's summary; but
they give the brigade a good deal of work. The number of calls of this
kind was 3744, of which 1256 proved to be false alarms. The number of
these false alarms will probably be reduced when the stations at which men
with hose are situated are more numerous.
=Fire Anni'hilator (Phillips's).= This is essentially a gaseous fire
engine, which at any moment can be made to discharge a stream of mixed
gases and vapours having the power of checking combustion. When first
introduced it was generally regarded as a most important invention, but it
has not proved an effective substitute for the common water engine. For
extinguishing fires on board ship and in close apartments it is
undoubtedly well adapted, but as a street engine it is comparatively
useless, owing to the unmanageable nature of its fire-annihilating
vapours.
The composition with which the 'Fire Annihilator' is charged is a mixture
of dried ferrocyanide of potassium, sugar, and chlorate of potassa. It is
set in action by a blow on a glass vessel containing oil of vitriol,
which, being fractured, permits the acid to flow over the 'charge,' when
the anti-combustion gas is liberated, and rushes forth with great
impetuosity.
=Fire-damp.= See HYDROGEN (Light Carburetted).
=Fire-engine.= The common fire-engine is a compound forcing-pump,
consisting of two 'forcing-pumps' placed on opposite sides of an
'air-vessel,' with which both communicate. The 'fulcrum' of the 'lever' by
which both pumps are worked is placed midway between them; consequently
they act alternately in charging the air-vessel. In order to obtain a very
forcible jet it is necessary to prevent the escape of any portion of the
contents of the air-vessel until the confined air is considerably
compressed. The lever is connected with handrails on each side of the
engine, and these are alternately raised and depressed by the workers.
Engines worked by steam power are now common in London and most of our
large towns.
=Fire-Extinguishing Powder (Feuerloschpulver)=, Bucher Leipzig. Nitre, 59
parts; sulphur, 36 parts; coal, 4 parts; iron oxide, 1 part. (Wittstein.)
=Fire, how to light a.= In a close stove the first thing is to empty the
fireplace. Take out the larger cinders and half-burnt coal with your
fingers, and lay them on one side for lighting the fire; then rake out all
the ashes (this can be done with the lids on, then it will not make so
much dust). Next take off all the lids, and sweep all the soot carefully
out; once or twice a week the flue pipe must be taken off and cleared out,
also the flues under the oven. The soot should be carried away at once, as
it blows about. Then blacklead the stove; put in a few cinders, lay on
them a piece of paper and a few sticks crossing each other; on these lay
very lightly some pieces of half-burnt coal and a few cinders, leaving
space for the draught.
Do not fill the grate full; put the lids on, draw out the damper, light
the fire, and shut the front door. An open fire is lighted in much the
same way. There are no flues to clean out; but the chimney, as high as one
can reach and behind the register door, should be cleared from soot
daily.[309]
[Footnote 309: 'Household Management, &c.,' by W. T. Tegetmeier.]
=Fire-proofing.= See INCOMBUSTIBILITY, &c.
=Fireworks.= See PYROTECHNY, and _below_.
=FIRES.= (In pyrotechny.) Coloured fires may be termed, not inaptly, the
_chefs-d'[oe]uvre_ of the pyrotechnist's art, since on their excellence
the attractions of most other varieties of fireworks depend. The following
forms, under judicious management, yield fires of remarkable beauty.
=Blue Fire.= _Prep._ 1. From metallic antimony, 1 part; sulphur, 2 parts;
nitre, 5 parts.
2. From realgar, 2 parts; charcoal, 3 parts; chlorate of potassa, 5 parts;
sulphur, 13 parts; nitrate of baryta, 77 parts.
3. (Mr A. Bird.) Charcoal and orpiment, of each 1 part; black sulphuret of
antimony, 16 parts; nitre, 48 parts; sulphur, 64 parts.
4. (Fownes.) Tersulphuret of antimony, a part; sulphur, 2 parts; dry
nitre, 6 parts. This is the composition used for the Bengal or blue signal
light employed at sea.
5. (Prof. Marchand.) Sulphur, sulphate of potassa, and ammonio-sulphate of
copper, of each 15 parts; nitre, 27 parts; chlorate of potassa, 28 parts.
For theatrical illuminations. This may be rendered either lighter or
darker coloured by lessening or increasing the quantities of the sulphate
of potassa and ammonio-sulphate of copper.
6. (LIGHT BLUE--Marchand.) Sulphur, 16 parts; calcined alum, 23 parts;
chlorate of potassa, 61 parts.
7. (DARK BLUE--Marchand.) Calcined alum and carbonate of copper, of each
12 parts; sulphur, 16 parts; chlorate of potassa, 60 parts.
8. (Marsh.) Sulphate of copper, 7 parts; sulphur, 24 parts; chlorate of
potassa, 69 parts.
9. (Ruggieri.) Nitre, 2 parts; sulphur and zinc, of each 3 parts;
gunpowder, 4 parts.
10. From sulphur, 1 part; dried verdigris, 2 parts; chlorate of potassa, 9
parts.
=Fire, Crimson.= _Prep._ 1. (Marsh.) Chlorate of potassa, 4-1/4 parts;
charcoal (alder or willow), 5-3/4 parts; sulphur, 22-1/2 parts; nitrate of
strontia, 67-1/2 parts. For pots.
2. (Marsh.) Charcoal, 4-1/4 parts; sulphuret of antimony, 5-1/2 parts;
chlorate of potassa, 17-1/4 parts; sulphur, 18 parts; nitrate of strontia,
55 parts. For boxes and stars.
3. (Marchand.) Sulphur, 16 parts; chalk (dry), 23 parts; chlorate of
potassa, 61 parts. Turns on the purple. See RED FIRE (_below_).
=Fire, Green.= _Prep._ 1. Nitrate of baryta, 77 parts; chlorate of
potassa, 8 parts; fine charcoal, 3 parts; sulphur, 13 parts.
2. From metallic arsenic, 2 parts; charcoal, 3 parts; chlorate of potassa,
5 parts; sulphur, 13 parts; nitrate of baryta, 77 parts. Very beautiful,
particularly when burnt before a reflector.
3. (Mr A. Bird.) Charcoal and black sulphuret of antimony, of each 2
parts; chlorate of potassa, 5 parts; sulphur, 6 parts; nitrate of baryta,
80 parts.
4. (Fownes.) Lampblack, 1 part; chlorate of potassa, 4 parts; sulphur, 6
parts; dry nitrate of baryta, 18 parts.
5. (Marchand.) Boracic acid, 10 parts; sulphur, 17 parts; chlorate of
potassa, 73 parts. Very beautiful.
6. (Marchand.) Chlorate of potassa, 18 parts; sulphur, 22 parts; nitrate
of baryta, 60 parts. For theatrical illuminations.
7. (LIGHT GREEN--Marchand.) Sulphur, 16 parts; carbonate of baryta, 24
parts; chlorate of potassa, 60 parts. Extremely delicate.
8. (Marsh.) Charcoal and sulphuret of arsenic, of each 1-3/4 parts;
sulphur, 10-1/2 parts; chlorate of potassa, 23-1/4 parts; nitrate of
baryta, 62-1/2 parts. For pots or stars.
=Fire, Lilac.= _Prep._ 1. (Marsh.) Black oxide of copper, 6 parts; dry
chalk, 20 parts; sulphur, 25 parts; chlorate of potassa, 49 parts. For
pans.
2. (Marsh.) From black oxide of copper, 3 parts; dried chalk, 22 parts;
sulphur, 25 parts; chlorate of potassa, 50 parts. For stars.
=Fire, Orange.= See RED FIRE, No. 8 (_below_).
=Fire, Pink.= _Prep._ (Marchand.) Charcoal, 1 part; chalk and sulphur, of
each 20 parts; chlorate of potassa, 27 parts; nitre, 32 parts. For
theatrical illuminations. See RED FIRE, No. 10 (_below_).
=Fire, Purple.= _Prep._ 1. From lampblack, realgar, and nitre, of each 1
part; sulphur, 2 parts; chlorate of potassa, 5 parts; fused nitrate of
strontia, 16 parts.
2. (Marsh.) Sulphuret of antimony, 2-3/4 parts; black oxide of copper, 10
parts; sulphur and nitrate of potassa, of each 22-3/4 parts; chlorate of
potassa, 42 parts. For pans.
3. (Marsh.) Sulphate of copper, 9-3/4 parts; sulphur, 13 parts; chlorate
of potassa, 77-1/4 parts. For stars.
4. From sulphur, 12 parts; black oxide of copper, 12 parts; chlorate of
potassa, 30 parts. See CRIMSON FIRE, No. 3 (_above_), and RED FIRE, No. 9
(_below_).
=Fire, Red.= _Prep._ 1. From sulphur, sulphuret of antimony, and nitre, of
each 1 part; dried nitrate of strontia, 5 parts.
2. (Mr A. Bird.) Charcoal, 1 part; black sulphuret of antimony, 4 parts;
chlorate of potassa, 5 parts; sulphur, 13 parts; dried nitrate of
strontia, 40 parts.
3. (Fownes.) Lampblack, 2 parts; chlorate of potassa, 8 parts; sulphur, 9
parts; dried nitrate of strontia, 32 parts.
4. (Marchand.) Sulphur, 16 parts; carbonate of strontia, 23 parts;
chlorate of potassa, 61 parts.
5. (Marchand.) Chlorate of potassa, 20 parts; sulphur, 24 parts; nitrate
of strontia, 56 parts. For theatrical illuminations.
6. (Marsh.) Coaldust, 2 parts; gunpowder, 6 parts; sulphur, 20 parts;
dried nitrate of strontia, 72 parts.
7. (Ruggieri.) Sulphuret of antimony, 4 parts; chlorate of potassa, 5
parts; sulphur, 13 parts; fused nitrate of strontia, 40 parts. A little
charcoal or lampblack makes it burn quicker.
8. (ORANGE RED--Marchand.) Sulphur, 14 parts; chalk, 34 parts; chlorate of
potassa, 52 parts.
9. (PURPLE RED--Marchand.) Sulphur, 16 parts; chalk, 23 parts; chloride of
potassa, 61 parts.
10. (ROSE-RED--Marchand.) Sulphur, 16 parts; dried chloride of calcium, 23
parts; chlorate of potassa, 61 parts. See PINK FIRE.
11. From charcoal, 2 parts; chlorate of potassa, 6 parts; sulphur, 13
parts; dried nitrate of strontia, 40 parts.
=Fire, Violet.= _Prep._ 1. From charcoal, 8 parts; sulphur, 10 parts;
metallic copper, 15 parts; chlorate of potassa, 30 parts.
2. (DARK VIOLET--Marchand.) Alum and carbonate of potassa, of each 12
parts; sulphur, 16 parts; chlorate of potassa, 60 parts.
3. (PALE VIOLET--Marchand.) Sulphur, 14 parts; alum and carbonate of
potassa, 16 parts; chlorate of potassa, 54 parts.
=Fire, White.= _Prep._ 1. From nitre, 60 parts; sulphur, 20 parts; black
antimony, 10 parts; meal powder, 6 parts; powdered camphor, 4 parts. For
either pans or stars.
2. (Mr A. Bird.) White arsenic, 1 part; charcoal, 2 parts; black antimony,
16 parts; nitre, 48 parts; sulphur, 64 parts.
3. (Marchand.) Charcoal, 2 parts; sulphur, 22 parts; nitre, 76 parts. For
theatrical illuminations.
4. (Marchand.) Gunpowder, 15 parts; sulphur, 21 parts; nitre, 64 parts. As
the last.
5. (Marsh.) Gunpowder, 12-1/2 parts; zinc filings, 18 parts; sulphur, 23
parts; nitre, 46-1/2 parts. For pans.
6. (Marsh.) Zinc dust or filings, 15 parts; sulphur, 28 parts; nitre, 57
parts. For stars.
7. (Ruggieri.) Sulphur, 13-1/4 parts; sulphuret of antimony, 17-1/4 parts;
nitre, 48 parts.