the natural Production of Saltpetre. 425 



cence in question from the walls of the laboratory, &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 

 endent by the addition of the oxalate of ammonia in the solution 

 of the saltjjetre. I therefore pulverised small portions of cal- 

 careous spar, of the common limestone of this country, and of 

 whitewash ; and having agitated accurately distilled water, at 

 the common temperature, with each of these portions, I then 

 filtered the water, and tested it with oxalate of ammonia. la 

 each instance there was fully as copious a precipitate as when 

 the oxalate of ammonia 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 ibis single dif- 

 ference, that the precipitate ol)tained by the addition of oxalate 

 of ammonia was much more copious : and I found this to be the 

 case from whatever part of the laboratory or elsewhere the salt- 

 petre had been detached, provided it had been formed during 

 the winter. I could not extend the experiment on the saltpetre 

 formed during the summer, having only reserved a portion from 

 one spot. 



Judging from such experiments as I have made, it appears that 

 the saltpetre formed in the situations described in this paper 

 consists of full 99 parts in 100 of nitrate of potasli ; with a very 

 minute proportion of some calcareous salt, which is either not 

 at all present in in the saltpetre formed during summer, or is 

 present in smaller quantity than in that formed during winter — 

 though even in the latter instance it scarcely amounts to one 

 part in 200. 



The proportion of sulphuric and of muriatic acid, and the 

 bases with which these acids are combined, I have not attempted 

 to ascertain, on account of the minuteness of the proportion in 

 which they evidently exist. 



In considering the relative situations of the different parts of 

 the laboratory, and the other buildings also, in which saltpetre 

 is naturally formed, it is evident that the efflorescence takes 

 place only where the exterior of the wall on which it is formed 

 is either exposed to the direct influence of the weather, or is in 

 contact with the adjacent ground ; not taking place at all in 

 those instances in which the wall is neither exposed to the 

 weather on either side, nor is in contact with the adjacent ground : 

 from which it might be argued, that the effect depends upon the 



action 



