[ 62 | 
Mr. Wenzel decompofed 480 grs. of allum.by the nitrous 
folution of lead, through ‘a double affinity. The precipitate 
which confifted of vitriol of lead, well wafhed in warm water 
and dried in a red heat, weighed 144 grs. and ‘this he fuppofed 
contained all the acid in the ounce of allum. Now by a former 
experiment he found that 240 grs. of vitriol of lead contain 
72,57 of the ftrongeft vitriolic acid, that is 30,23 per cent. and 
hence 144 ers of this falt contain 43,54. This then he con- 
cludes to be the quantity contained in an ounce of allum, at 
this rate too parts allum contain only 9,07 of the ftrongeft 
acid. This~énormous difference evidently proceeds from the de- 
of allum were evaporated to drynefs, the nitrous allum was ne- 
ceffarily mixed with the vitriol of lead, - and in wafhing it away 
much of the vitriol of lead muft have been carried off, and if it 
were not evaporated. to drynefs part.of the vitriol of lead 
remained in the folution. However, to find a more fecure method 
of ufing this ufeful precipitant, which operates much quicker 
than any Barytic folution, I repeated this experiment. 
For this purpofe I diffolved 30 grs. of lead in 400 ers. of 
nitrous acid, 1,1477 diluted. with 200 of water in a heat, of go°, 
7 ers. were loft-by evaporation, or air, the remaining 623 grs. 
contained 30 of lead. . 
1 vHEN diffolved- 109, grs.. of allum_ in 1600 of pure water, 
and placing it in a fand heat gradually added the folution of lead, 
as the precipitate fettled and the liquor evaporated; when the 
whole 
