described in the preceding Paper. 309 



compound of 112 oxide of lead and 62 arsenic acid ,• and ar- 

 seniate of lime, of 28 lime and 62 acid. 



Making a fair allowance for the minute quantities operated 

 on, we must infer that the subject of each analysis is composed 

 of the same ingredients, united, with respect to the acid and 

 lime, in the same proportion. If we suppose that this arseni- 

 ate, which forms the basis of both minerals, contains an atom 

 of each constituent, it will be composed of 



Arsenic acid, 62 68.89 



Lime, - 28 31.11 



If we regard Mr Haidinger's second species, — the diato- 

 mous gypsum-haloide, as composed of two atoms of water, 

 with one of the arseniate of lime ; and the hemiprismatic of 

 three atoms of water to one of the salt, they will be composed 



of— 



Diatomous. Hemiprismatic. 



Arseniate of lime, 90 83.34 90 76.92 



Water, - 18 16.66 27 23.08 



It is probable that Klaproth's pharmacolite from Wittichen, 

 as also that from Andreasberg, analysed by John, is identical 

 in composition with the hemiprismatic gypsum-haloide of Mr 

 Haidinger. The analyses are, 



Klaproth. John. 



Arsenic acid, 50.54 45.68 



Lime, - 25.00 27.28 



Water, - 24.46 23.86 



100.00 96.82 



Mr Haidinger has pronounced, from mineralogical consi- 

 derations, that the decomposed substance, found on the same 

 specimen with the two preceding minerals, did not arise from 

 the decomposition of either of them. The accuracy of this 

 observation is confirmed by analysis. The first point of dif- 

 ference is, that it contains, even in its effloresced state, consi- 

 derably more water than either of the other species. For in 

 one experiment, 1.445 grains of it lost from ignition 0.43 gr. 

 or 29.0G.5 percent, of water; and in a second, 1.60 grains 

 lost 0.545 gr. or 34.062 per cent, of water. 



