152 Nitro-Glycerine : [April, 
and the diluted acid rises to the surface. After the separation in 
this manner into two layers is effected, the upper layer may be 
removed by the process of decantation or by means of a siphon, 
and the remaining nitro-glycerine is washed and re-washed with 
fresh water till not a trace of acid reaction is indicated by blue 
litmus paper. ‘The final purifying process pursued by Mr. Nobel,* 
is to crystallize the nitro-glycerine from its solution in wood 
naphtha. Every chemist knows that by this means the substance 
will be chemically pure and of uniform composition and quality. 
Before enlarging on the properties of nitro-glycerine and its 
applications, we may just glance at its chemical nature for a 
moment or two. Glycerine is a ternary compound, a sort of 
oxidized hydrocarbon, its formula in the ordinary notation being 
C; H, Os. The combined action of the strong sulphuric and nitric 
acids is to transform it into a quaternary compound, a substitution 
product, in which three equivalents of peroxide of nitrogen (3 NO.) 
are substituted for three equivalents of hydrogen, which are re- 
moved during the reaction. The chemical constitution of nitro- 
glycerine may therefore be indicated in the following manner :— 
H 
c, { (NO}).f Oc, or Cs Hs (NO,)s Os.t 
As a substitution-product, or nitvo-compound, nitro-glycerine very 
much resembles gun-cotton, the mitro-cellulose of the chemist ; 
indeed, it may almost be regarded as liquid gun-cotton; and cer- 
tainly it has a great amount of interest for the scientific chemist, as 
much even as for the practical man who employs it as an industrial 
agent. 
°As prepared in the manner already mentioned, nitro-glycerine is 
an oily-looking liquid, of a faint yellow colour, perfectly inodorous, 
and possessed of a sweet, aromatic, and somewhat piquant taste. 
It is poisonous, small doses of it producing headache, which may 
also be produced if the substance is absorbed into the blood through 
the skin, and hence it is not desirable to allow it to remain long in 
contact with the skin, but rather to wash it off as soon as possible 
with soap and water. Glycerine has a specific gravity of about 
1:25-1:26, but the nitro-glycerine has a specific gravity of almost 
1:6, so that it is a heavy liquid. It is practically insoluble in water, 
but it readily dissolves in ether, in ordinary vinic alcohol, and in 
methylic alcohol or wood spirit. If it be simply exposed to contact 
with fire it does not explode, although it 1s so powerful as an 
* Letter in ‘The Times, 27th December, 1867. 
+ Mr. Nobel regards nitro-glycerine as having the following composition 
(ordinary notation) :—C, H,; O, (NO,),, and alleges, as a reason, that a solution of 
caustie potash will decompose the nitro-glycerine, resolving it into glycerine and 
nitric acid, and, with the latter, forming nitrate of potash. 
