228 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
ponent whatever, as in the kieselguhr dynamites, to 60 per cent 
of sodium nitrate in straight wood-pulp dynamites; and this last 
material may be partly or wholly replaced by ammonium or potas- 
sium or cellulose nitrates in other dopes and compositions. Because 
of a similar wide variation in their components the compositions 
made from picric acid, its salts, and other nitro-substitution com- 
pounds are also omitted. Notwithstanding these omissions, it is be- 
lieved that the data set forth in the table may prove useful in the 
development and checking of the statistics of manufacture. But, 
unfortunately, owing to the different manners in which the nitrogen 
atoms are grouped, as regards the other atoms, in the molecules of 
the different kinds of explosives, no direct relation is to be observed 
between the properties and behavior of these different bodies and the 
percentages of nitrogen they contain, and this want of relation be- 
comes the more marked the larger the number of different nitrogen- 
containing substances that we consider. What, however, is empha- 
sized by this presentation of data, is that the element nitrogen is a 
characteristic and important component of all explosives that have 
been accepted and used for military purposes. 
From the time of the invention of gunpowder until the middle 
of the lgst century the only recognized available source of this nitro- 
gen was India saltpeter, which is the potassium nitrate, and which 
was obtained from the niter found or formed in soil or rocks. The 
production of nitrates in the soil or rocks is brought about usually 
through the agency of nitrifying bacteria. In order that the process 
of nitrification may go on there is required a supply of nitrogenous 
organic matter, a slightly alkaline medium, a temperature range be- 
tween definite limits, a limited amount of moisture,a supply of oxygen 
or air, complete or semi darkness, and the presence of the nitrify- 
ing organisms. The nitrification proceeds most rapidly at 100° F. 
and within a few inches of the surface of soil or rock which is well 
aerated and moderately moist. When potash salts are present in 
sufficient quantity the potassium nitrate is produced, but the native 
niter usually consists largely of calcium nitrate with some magnesium 
nitrate and other salts. All of these nitrates are readily soluble in 
water and may therefore, after formation, be to a great extent washed 
away by frequent rainfalls, but where there is only a moderate 
amount of water present the solution may be brought to the surface 
by capillarity, and as the water evaporates the nitrates will be left 
as an efflorescence on the surface of the soil or rock. It is evident, 
therefore, that accumulations of niter will be largest in those locall- 
ties where not only the best conditions for its production obtain, but 
where also it is least likely to be washed away after being formed. 
The native sources of supply are therefore found as efflorescences on 
the soil in semiarid countries, in limestone caverns, where the remains 
