134 Literary and Philosophical Society. 



an acid, but one of the nitrous sort ; and provided this 

 liquor were putrefied, and the marine salt, with which all 

 nitrous leys greatly abound, carefully removed, we cannot 

 help thinking that upon being boiled down to a due 

 consistence it would yield the crystals of saltpetre. The 

 author must acknowledge he has boiled down many of 

 these mixtures without success : but it was at a time when 

 he was ignorant of the necessity of attending to the above 

 circumstances. 



' That all putrid substances, and consequently their 

 juices, are of a volatile alkaline nature, is not to be denied, 

 owing to an union of their acid and oily parts with their 

 earth, which is equally subtilised by the putrid process.' 



P. 193. ' But the strongest proof of the existence of an 

 acid in putrid juices, if the earths of stables and cow-stalls 

 do not afford an equal one, must be drawn from the soil at 

 the bottoms of graves, which can certainly derive its nitrous 

 acid quality from nothing but the corrupt bodies with 

 which it lies in contact ; and this may satisfy us in respect 

 to the source from which other absorbent earths may 

 derive it. 



'Other earths, in common use among the saltpetre 

 makers, are those of stables and cow-stalls, that have drunk 

 up much animal urine ; the bottoms of stinking pits and 

 ditches and the like. These they take out and lay in heaps, 

 till by repeated trials they find them fit for their purpose. 

 It is commonly supposed that, during this period, they draw 

 their nitrous quality from the air ; but for this there is 

 certainly no just foundation, seeing they are brought to 

 maturity as soon in the closest vault or cellar as in the 

 most open exposure. The truth is, that all putrid juices 



