180 
POPULAR SCIENCE NEWS. 
[December, 1S90. 
Practicai Gb.eiijistry aijd tlje ]^rts. 
GLYCERINE. 
Many 3'ears ago, in an obscure mining vil- 
lage in Sweden, the apothecary, while making 
lead plaster in the ordinary way by heating 
olive-oil with litharge and water, chanced to 
notice that the liquid which was mingled 
with the pasty lead compound had a strangely 
sweet taste. On further investigation he 
found that the sweet taste was caused by the 
presence of an oily liquid which was dis- 
solved in the water. No such substance was 
described in the books of the day. Evidently 
a discovei-y had been made. The discoverer, 
although poor and with slight advantages 
of education, was a man of more than ordi- 
nary ability. Already he had attracted the 
attention of the learned men of the day by 
publishing his quaint chemical theories of 
combustion ( Uber die Lnft und das 
Feuer^ ; nor was this'his first discovery of a 
substance hitherto unknown to science. 
We can easily imagine, then, with what 
enthusiasm Scheele — for that was his name — 
plunged into the study of the strange liquid 
in the occasional respite that was granted 
him from the pestle and the dispensing 
counter. He soon found that the sweet sub- 
stance was not the product of olive-oil alone, 
but that other oils and fats would yield it 
under the same treatment. So he named it 
the " sweet principle of fats," or "oil-sugar." 
Soon after, his work was cut short by death. 
More than a century has passed since 
Scheele's discovery, yet it is scarcely fifty 
years since "oil-sugar" was found to be 
of practical value, except, perhaps, for a 
limited use in medicine. Many famous 
chemists had taught the world much as to its 
nature and production, had given it the more 
formal name of glycerine^ derived from a 
Greek word meaning sweet., but to the every- 
day world the substance remained only a 
curiosity. Nowadays, everyone is familiar 
with the clear, thick liquid so commonly used 
for toilet purposes. Its soothing and soften- 
ing effect on dry or inflamed skin is the 
quality by which it is best known in most 
households ; but few people have any idea 
of the variety of purposes for which glycerine 
is used. This will not seem strange when 
we find how many valuable properties are 
possessed by this remarkable liquid. Among 
the most striking of these are its great solvent 
power, its chemical stability, and it^, sweet- 
ness. Besides these, it is not indigestible, 
will not evaporate, and, owing to this and its 
hygroscopic qualities, will prevent drying and 
hardening of materials with which it is mixed. 
These peculiar qualities make it most valu- 
able in the preparation of medicines, and 
various food-products, as preserves arid mus- 
tards ; likewise in beer, wines, and other 
bottled goods, where it is said to act as a pre- 
servative. The fact that strong solutions 
of gljxerine and water will not freeze in the 
lowest winter temperatures has caused its use 
in our "wet" gas-meters. In short, the list 
of purposes to which this most useful liquid 
is put is almost exhaustless. Among the 
more important industries in which it is used 
are vulcanizing india-rubber, silvering and 
gilding glass, dressing leather for kid gloves, 
preserving anatomical and botanical speci- 
mens, and the manufacture of what is, per- 
haps, the most powerful explosive known to 
science, without whose aid some of the 
grandest triumphs of modern engineering 
would have been impossibilities — nitro-gly- 
cerine. 
Scientifically considered, glycerine is most 
interesting. Mention has already been made 
of many of its physical characteristics. In 
the pure state glycerine is somewhat more 
than a fourth heavier than water (1.269). 
After long exposure to a freezing temperature 
it will deposit rhombic crystals resembling 
those of sugar-candy. Strangely enough, 
when quickly cooled to very low temperature 
( — 40° F.) it forms a gummy mass which will 
not harden nor crystalize. Indeed, it was not 
till 1867 that it was thought possible to crys- 
talize it. The boiling-point of glycerine is 
about 490° F. At this point it decomposes 
slightly. As already stated, glycerine will 
not evaporate at ordinary temperatures, but at 
the boiling-point of water (212° F.) there is 
a perceptible loss. 
Pure glycerine will burn readily, if first 
heated to about 300° F., giving a pale-blue 
flame, similar to that of alcohol. Heated in- 
tensely it decomposes into acrolein, a most 
pungent-smelling compound, one whiff of 
which is usually sufficient to fix it indelibly on 
the memory. 
To the chemist glycerine is an alcohol, be- 
ing, like other alcohols, a hydrate of an "or- 
ganic radical," that is to say, the hydrate of a 
combination of carbon and hydrogen which 
forms salts as if it were a metallic element. 
From its chemical behavior, glycerine can be 
considered a "tri-atomic alcohol," or tri-hy- 
drate, with the formula C3H6(OH)3, on the 
same analogy as sodic hydrate, NaOH, or 
calcic hydrate, Ca(OH)2; the group repre- 
sented by the formula C3H5 acting as a base 
and known chemically as glyceryl or pro- 
perty I. Just as we can make salts of a metal 
from the hydrate, so can we make salts of 
glyceryl in essentially the same way, although 
the methods employed are diflerent. Nitro- 
glycerine, so-called, is one of these salts of 
glyceryl, being an impure tri-nitrate (C8H6[N 
03]3). 
By far the most important salts of glyceryl 
are oils and fats. The majority of these are 
salts of glycerj'l and organic acids. The 
principal of these acids, out of many which 
are present in our common fats, are stearic. 
oleic and palmitic acids. We now under- 
stand how it was that Scheele made his gly- 
cerine. We remember that olive-oil was the 
basis of his lead planter. This oil is, in 
the main, glyceryl oleate (C3H5[Ci}iH3302]:i). 
Hence the reaction between the lead and the 
oil and water can be expressed by the follow- 
ing equations : 
2 C3H,(CisHs,02)3+3 PbO+3 H2O 
glycerol oleate. litharge, water. : 
=2 C.iH5(OH)3+3Pb(Ci«Hs302)3 ■ 
glycerine. lead oleate (lead plaster). 
For many years this reaction was the basis 
of the manufacture of glycerine. Cheaper 
fats than olive oil, of course, were used, 
while traces of lead in solution were removed 
by sulphuretted hydrogen. 
As the use of glycerine became more 
extensive, there arose the necessity for a 
cheaper method of production. Attention 
naturally was directed to the spent lye of the 
soap manufacturer, for soaps are sodium or 
potassium salts, principally of stearic acid, 
made by a reaction similar to that used in 
making lead plaster, but substituting caustic 
alkalis for litharge. By the method of soap 
manufacture, however, the liquors containing 
the glycerine are so contaminated by alkalies 
and salt, and are so diluted, that until recently 
it has not paid to recover the glycerine. 
A process, which has proved most profit- 
able, has been invented to decompose animal 
fat directly into stearic acid and glycerine, by 
subjecting it to the action of super-heated 
steam, at a temperature of about 300° F. 
The resulting glycerine is concentrated, and 
purified by steam distillation, while the stearic 
acid, which much resembles wax, and in 
no way answers to our ordinary conception of 
an acid, is in great demand for candles. fl 
In this way thousands of tons of glycerine 
are made yearly, not to mention the immense 
number of excellent candles which are also 
products of the process. 
SILVER. 
Silver has always ranked next to gold 
among the cominon precious metals. Like 
gold, it is a "noble" metal in that it does not 
oxidize when heated in tiie air; and although 
it forms more stable compounds with otiicr 
elements than gold, yet it is readily reduced 
to the metallic state by comparatively we.dv 
reducing agents. This quality, together with 
its beautiful appearance and its great mallea- 
bility and ductility, renders it particularly 
adapted for its manifold ornamental uses, 
while its wide diffusion, in comparatively 
small amounts, formerly rendered it an excel- 
lent material as a standard of monetary value ; 
but of late years the greatly increased supply 
from the Western mines has made its value 
much more variable, and unfitted it for pur- 
poses of coinage. 
Silver is found native, or in the metallic 
