described in the preceding Paper. 307 



They are both arseniates of lime, and contain water of 

 crystallization. The water quickly comes into view when 

 they are exposed, in a clean glass tube, to the flame of a spi- 

 rit-lamp ; but a red heat is requisite to expel the last portions 

 of it. The water, as it condensed on the cold parts of the 

 glass, was carefully tested, but it did not affect the most deli- 

 cate litmus-paper in the slightest degree. The arseniates, in 

 losing their water of crystallization, become opaque and white, 

 but can afterwards bear an intense heat without further 

 change, requiring the strongest temperature which can be 

 given with the common blow-pipe for fusion. From this 

 cause, it is difficult to decompose them on charcoal ; but when 

 intimately mixed with charcoal powder, and heated in a glass 

 tube, a distinct layer of metallic arsenic is readily procured. 



When reduced to powder, and boiled in distilled water for 

 one or two hours, a small quantity is taken up, though the 

 greaterpart remains undissolved. The solution gives a brick-red 

 precipitate with nitrate of silver, and a white one with nitrate of 

 lead and oxalate of ammonia. Nitric acid, whether strong or 

 diluted, dissolves them readily without effervescence, and the 

 salts .of silver, lead, and oxalic acid, occasion the same preci- 

 pitates as just mentioned, when the excess of acid is neutralized 

 to a sufficient degree. They contain nothing but water, lime, 

 and arsenic acid ; the absence of magnesia and phosphoric 

 acid, in particular, having been proved by careful examination. 



Analysis of the First Species. 



3.455 grains were heated to redness in a green glass tube, 

 and lost 0.72 grains, or 20.839 per cent, of water. 



2.175 grains were treated in like manner, and lost 0.46 

 gr. or 21.149 per cent, of water. The mean is 20.994. 



6.18 grains of the anhydrous mineral were dissolved in wa- 

 ter by aid of the smallest possible quantity of pure nitric acid. 

 Nitrate of lead in slight excess was added, and the whole 

 brought, by a gentle heat, to perfect dryness. The soluble 

 parts were taken up by water, and the precipitate collected on 

 a filtre. The arseniate of lead, after being ignited, weighed 

 11.32 grains, equivalent to 4.033 grains, or 65.259 per cent, 

 of arsenic acid. 



The excess of lead, in the solution, after the separation of 



