the natural production of Saltpetre, 523 
that nitrate of lime is a principal constituent part of saltpetre 
formed by a natural process, I was much surprised by the very 
slight trace oflime evident in the present instance; though I 
had felt assured previously that but little would be found in 
the natural saltpetre which I have had an opportunity of exa- 
mining; having never observed in it any tendency towards 
deliquescence. Having had frequent occasion to suppose that 
carbonate of lime is much more readily soluble in water than 
is commonl}^ believed, and having never been able to detach 
the saline efflorescence in question from the walls of the labo- 
ratory, &c. without admixture of particles of the limestone, or 
of the whitewash, amounting to at least seven or eight parts 
in a hundred, it struck me that these particles might be the 
source of the lime rendered evident by the addition of the 
oxalate of ammonia in the solution of the saltpetre. I there- 
fore pulverised small portions of calcareous spar, of the com- 
mon limestone of this country, and of whitewash; and having 
agitated accurately distilled water, at the common tempera- 
ture, with each of these portions, I then filtered the water, 
and tested it with oxalate of ammonia, hi each instance there 
was fully as copious a precipitate as when the oxalate of am- 
monia had been added to an equal quantity of the solution of 
saltpetre. 
Similar preliminary experiments having been made on some 
saltpetre detached from the same part with that already sub- 
mitted to examination, but formed during the winter instead 
of the summer, the same results were obtained with this sin^xle 
difference, that the precipitate obtained by the addition of ox- 
alate of ammonia was much more copious : and I found this 
to be the case from whatever part of the laboratory or else- 
