there is one million of pounds of nitre.* Nitre is also man¬ 
ufactured in Virginia, and Tennessee, where it is found in 
limestone caves. A natural saltpetrous earth has been late¬ 
ly discovered in the former state, along the banks of the 
Potomac.f 
In the making of gun powder, it is of the first importance 
that all the materials be perfectly pure, as well as mixed in 
proper proportions. Above all, it is necessary that no for¬ 
eign substances be contained in the salt petre. If sulphate 
of soda be united with it, the compound is found to efflor¬ 
esce, whereas a combination with the nitrate of lime causes 
deliquescence. The dampness of American gun powder 
has already been complained of,| and can alone be remedi¬ 
ed by a strict attention to the purity of the ingredients. It 
is extensively manufactured in several states, particularly 
Delaware and Maryland,§ and though it is still imported in 
considerable quantities, may doubtless at any period be pro¬ 
duced in proportion to the demand. 
The sulphates of iron and copper , when they do occur na¬ 
tive, are generally the result of the spontaneous decomposi¬ 
tion of iron and copper pyrites. The sulphate of zinc or 
white vitriol is made from blende. 
Jlum or sulphate of alumine may be obtained from the 
decomposition of pyrites, and is not unfrequently manufac¬ 
tured from aluminous shale or schistus , a substance found 
at various places in this country. Its important use is as a 
mordant in dying. 
The yiuriate of ammonia or sal ammoniac is made in Phi¬ 
ladelphia. 
* Description of a cave on Crooked creek, with remarks, 8cc. 
on nitre and gun powder; by Samuel Brown, M. D. (Amer. 
Philos. Trans, vol. 6, p. 235.) 
f Med. Repos, vol. 12, p. 296. 
£ Vide Dr. Mitchill’s letter on this subject to the Secretary of 
the Navy, Med. Repository, vol. 6, p. 426. 
§ Gallatin’s Report. The mills at Brandywine makes 250,000 
lbs. annually, and two near Baltimore 450,000. According to 
Mitchill, the gun powder mills in 1810 amounted to 207, and the 
quantity annually made to 1,450,000 ibs. Modes of preventing 
the explosion of mills are detailed in the Med. Repository, voh 
12, p. 389, and Mease’s Archives, vol. 2, p. 403. 
