RETURN FROM PITTSBURG 345 



men is convinced that this earth merely leached also 

 crystallizes into pure saltpetre, but with the loss of a 

 third to a half of what may be obtained by the help 

 and addition of ash-lye. This is the case because if 

 the leached earth is boiled of itself over the fire, a 

 great part of the saltpetre-acid, fixed only in particles 

 of earth, escapes unused for lack of an adequate alka- 

 line basis. In the average there could be obtained in 

 this way 8-10 pounds of saltpetre from a bushel of 

 earth. No birds have been found in these caves and 

 clefts, although it has been the opinion of sundry per- 

 sons that the alkaline element of the saltpetre must 

 have been occasioned by the droppings of birds long 

 accumulated and rotted. To be sure, there were seen 

 the dens and excreta of bears and foxes, but in amount 

 insignificant. 



During the war tobacco-stalks + were also used for 

 saltpetre. Several sorts of tobacco, on being burnt, 

 have the property of crackling and scattering sparks. 

 This sort, commonly covered with a white salt-dust, is 

 called ' Salt-Marsh Tobacco,' grows chiefly in low 

 spots in Virginia and Maryland and, on account of the 

 property mentioned, is extremely disliked by the 

 tobacconists. From two pounds of the rough stems of 

 this sort, not previously used, more than an ounce of 

 good saltpetre-crystals are obtained by leaching. The 

 saltpetre seems to lie ready ; other kinds, it has been 

 found by experiment, yield saltpetre only on the addi- 

 tion of ash-lye, and then but very little. It appears 

 also that certain kinds of soil are better adapted for 

 supplying the tobacco with active saltpetre, which is 

 the case with some other plants, as turnersol, fennel, 

 borage &c. Besides, the tobacco-warehouses and the 



