heat, generated in the
process of combustion, considerably facilitates the strength
of the powder, in consequence of producing the expansion of
these airs."

Recently, under the pressure of a national necessity, which will not
soon be forgotten, the problem of getting nitre--nitrates and kindred
bodies--had the earnest attention of chemists. So, in the period
before and after 1808, methods of forming nitre had grave
consideration. For instance, this question, now amusing, was
propounded--

"How much nitre could be manufactured from the refuse animal
and vegetable matter of the City of Philadelphia in case of
emergency? What quantity could be prepared by elixating or
washing the rubbish of old buildings, the earth of stables,
cellars, etc., and the soil of certain tracts of the United
States?"

It is quite proper that mention should have also been made of the
natural _nitre beds_, as well as of the artificial beds built up from
slow experience. Reference is made that in France nitre was won from
the lime and rubbish of old, ruinous buildings, and from the floors of
stables and pigeon houses, while it is also recorded that during the
American Revolution, the

"same means, by the hand of economy and industry, afforded
quantities of this article in certain of the then Colonies,
and"

that in the Southern portions it was obtained from the earthen floors
of tobacco houses.

The presentation of the earliest methods of getting nitre is extremely
interesting, extended and elaborate, giving the reader a full view of
pioneer conditions and endeavor. The scheme of purification of nitre
for gunpowder use is illuminating and attractive. Attention is
directed to the saltpetre rock and caves of the western portion of
our country.

The preparation of charcoal is discussed. The adaptability of charcoal
from various sources receives careful thought in connection with its
use in gunpowder; so, too, the sulphur used for this particular
purpose, and there is recommended as a source of this ingredient, the
common pyrites so abundant throughout the States. Among other topics,
of vital interest in these days, discussed in the continuing articles,
is the manufacture of spirit from potatoes. The method employed in
Germany is presented in detail after which it is said--

"Potato spirit of excellent quality has been made in this
city (Philadelphia). It is found, not only to be muc