Vol. XXIV. No. 5.] 
POPULAE SCIENCE E^EWS. 
69 
Practical Cljeniistry aijd tlje ^rts. 
GELATINE AND ITS USES. 
In ^•al■ious animal tissues, such as the skin, 
bones, intestines, etc., is found an interesting 
group of organic compounds, very closely 
resembling each other, aTid which, when 
treated with boiling water, are transformed 
into the well-known and exceedingly useful 
substance gelatine, which is the same as 
ordinary glue, ditteringfrom it only in purity. 
The most characteristic property of gelatine 
is that of solidifying, or gelatinizing, when 
solutions containing it are cooled below 68°. 
A solution in water containing only one per 
cent, of gelatine, will form the characteristic 
"jelly" when cooled. 
Common glue is prepared from the trim- 
mings of hides, and the refuse of slaughter- 
houses and tanneries. The skins are cleaned 
and steeped in lime water, and afterwards 
exposed to the air for some days. They are 
then boiled in water, and the resulting liquid 
run off and allowed to settle, after which it is 
left to cool and gelatinize in shallow boxes. 
The resulting cakes of soft glue are then dried 
on nets in large buildings, provided with 
movable blinds, so that the air can freely 
circulate through them in pleasant weather, 
while during .storms the glue can be protected 
from the weather. This process of drying 
requires great care, as a rise in the tempera- 
ture may cause the partially dried glue to 
liquefy, making a "mess" which requires 
much labor to clear up, to say nothing of the 
loss or damage to the stock. It was formerly 
supposed that glue could only be dried at 
temperatures above the freezing-point, but it 
was ijccidentally discovered in this country 
that frozen glue was of equally good quality, 
and the manufacture is now carried on all the 
3ear round. 
Cooking-gelatine is practically made by the 
same process, but much greater care is taken 
in selecting the stock, and the utmost cleanli- 
ness is necessary in all the processes. It 
forms a healthful and attractive article of diet, 
but its nutritive value is not very great. 
By long continued boiling, gelatine loses its 
its gelatinizing power! The same result is 
obtained by adding nitric or acetic acid to its 
solution. The ordinary liquid glues are made 
in this way, and a very good article may be 
extemporaneously prepared by throwing some 
pieces of glue into a bottle of vinegar, and 
shaking occasionally until it is dissolved. 
When chlorine gas is passed through a solu- 
tion of gelatine, it unites directly with it, 
precipitating an insoluble substance, and 
forming a very peculiar looking solid froth. 
Gelatine also imites with tannin to form an 
insoluble compound. This reaction is the 
basis of the tanning process by which raw 
hides are converted into leather. A minor 
application of this reaction is found in the 
use of fish-skin for settling coflee. The 
tannin of the coflee and the gelatine of the 
fish-skin unite, forming a solid, tenacious 
mass, which mechanically encloses the im- 
purities suspended in the coffee, in the same 
way as the coagulating albumen of the white 
of an egg, often used for the same purpose. 
When gelatine is placed in cold water, it 
softens and swells, but does not dissolve. 
On heating the water, however, it dissolves 
immediately. If some bichromate of potash 
is added to the gelatine, it still remains solu- 
ble if kept in the dark, but, if exposed to the 
sunlight, a chemical change — probably an 
oxidation — takes place, and it becomes per- 
fectly insoluble, even in boiling water. This 
property is of the greatest value anil impor- 
tance, as it is the basis of all the _iiiodern 
processes of photo-engraving, which have 
enabled us to make exact reproductions of 
the most celebrated works of art at a nominal 
cost. The ordinary kind of gelatine is also 
indispensable in the manufacture of photog- 
raphers' dry plates, which are coated with an 
emulsion of gelatine and finely-divided sensi- 
tive salts of silver, and, afler drying, will 
retain their sensitiveness for years without 
change. The collodion-coated plates formerly 
in use became worthless in a very short time 
after being prepared. 
The minor uses of gelatine are innumer- 
able. When combined with glycerine, it 
forms a soft, elastic mass, which is used for 
printers' ink-rollers, electrotype moulds, and 
for taking casts of irregularly shaped objects. 
The surface of this compound readily absorbs 
the aniline dyes, and this property is taken 
advantage of in the hektograph copying pad, 
which consists mainly of a shallow tray filled 
with this composition. Characters written on 
paper witli aniline ink are transferred to the 
surface by simple pressure, and a large num- 
ber of copies may be taken in the same way, 
as the gelatine readily yields sufficient of the 
color to fresh sheets of paper, when pressed 
upon it, to give a clear reproduction. 
Some fruits contain gelatinous principles 
known as pectic and pectosic acids, but they 
are entirely diflerent substances from the true 
■gelatine. It is these substances which render 
it possible to prepare fruit jellies, but they 
have much less gelatinizing power than the 
animal product. The cheap manufactured 
fruit jellies are frequently found to consist of 
animal gelatine, properly flavored, and to be 
entirely free from the pectose compounds 
which should legitimately be present. 
THE TWO FORMS OF PHOSPHORUS. 
Phosphorus is an element dear to the 
heart of every amateur chemist, its remark- 
able inflammability and its ready adaptability 
to explosive and pyrotechnical eflects giving 
it an attractiveness to the youthful experi- 
menter, which is not justified when the great 
danger accompanying its use is taken into 
account. Some time ago, one of our readers 
wrote us an amusing account of his eacly 
experiments, in which he made up a mixture 
of phosphorus and chlorate of potash into 
" torpedoes," and placed them in his pocket 
for safe keeping and to avoid the observation 
of the teacher. As might be expected, how- 
ever, the treacherous compound soon made 
itself evident in the most unmistakable 
manner, and nothing but that special Prov- 
idence which is said to watch over bo\s 
and intoxicated persons prevented serious 
results. 
Phosphorus is one of the most active 
chemical elements we are acquainted with, 
being exceeded only by fluorine. It rushes 
into combination with other elements, espec- 
ially oxygen, on the smallest provocation. 
A temperature of 112° F. is sufficient to 
cause it to burst into flame, while, even at 
ordinary temperatures, when exposed to the 
air, a slow oxidation takes place, causing it 
to glow and emit luminous vapors. The 
slightest friction will raise its temperature to 
the igniting pdint, while if it is mixed with 
substances rich in oxygen, — like nitrate or 
chlorate of potash, or peroxide of lead, — a 
slight concussion causes the oxidation to take 
place with explosive violence. It is also 
excessively poisonous, when taken into the 
system, and even a burn from ignited phos- 
phorous produces a most painful sore, and 
one very slow in healing.* 
Like many other elements, however, phos- 
phorus exists in an allotrojjic form, known as 
red, or amorphous phosphorus. Although 
this is chemically identical with the ordinary 
variety, its physical characteristics are very 
different. When ordinary phospM)rus is 
iieated in a vacuum, or in a gas in which it 
cannot burn, to a temperature of about 4^0° 
F. for a considerable length of time, it 
becomes converted into a red, infusible sub- 
stance, which has a much higher specific 
gravity than the ordinary variety (2.14 as 
compared with 1.83), and is insoluble in the 
usual solvents of phosphorus. It cannot be 
ignited by friction, and, in fact, is uninflam- 
mable until a temperature of 500° F. is 
reached, when it changes back into ordinary 
phosphorus. When mixed and rubbed with 
dry bichromate of potash, it does not explode, 
and when mixed with nitrate of potash it will 
not explode by friction, but if ignited burns 
off quietly. It cannot resist, however, the 
influence of chlorate of potash or peroxide of 
lead, but, when mixed with these substances, 
explodes more or less violently by heat and 
friction. It is also, apparently, non-poisonous. 
Amorphous phosphorus is extensively used 
in the composition of the surfaces for iirnitino- 
safety matches. The matches are tipped with 
an inflammable composition containing chlo- 
rate of potash, which, when rubbed upon the 
