NATIVE ARSENIATE OF LEAD. Q/!0 



nitrate of lead, an abundant white precipitate, which, 

 urged by the flame of the blowpipe on a support of char- 

 coal, resolves itself into reduced lead and arsenical va- 

 pours. 



These preliminary experiments led me to the probable Inferenc«. 

 conclusion, that this fossil chiefly consisted of oxide of lead, 

 arsenic acid, and a small quantity of the muriatic acid. 



§ 4. A. 1. Fifty grains, carefully selected from crystals Analysis. 

 of a pale Isabella-colour, were reduced to a fine powder, 

 and exposed to a low red heat for about an hour. Their 

 weight was diminished by 0*15 of a grain, 



2. The yellowish powder was now transferred to a vessel 

 of pure silver, and mixed Avith a lixivium containing fifty 

 grains of potash, prepared by the means of alcohol; a 

 quantity, which I had previously ascertained to be sufficient 

 to eflfect a complete decomposition of this mineral. The ley 

 was gradually evaporated to dryness in a sand-bath. The 

 soluble part was extracted by distilled water, and poured off 

 from a yellowish white matter, which was sufficiently edul- 

 corated (a). 



3. Liquid nitrate of ammonia was now dropped into the 

 alkaline fluid, as long as it produced any cloudiness: the 

 clear fluid was now decanted from a small quantity of white 

 matter, which had subsided, and rendered acid by nitric 

 acid; ammonia, added to excess, produced a slight turbid- 

 ness. These precipitates, after sufficient cdulcoration, were 

 added to the yellowish white residuum («). 



4. The liquid was now rendered slightly acid by nitric 

 acid, and a solution of nitrate * of lead in distilled water 

 was dropped into it, as long as it separated any precipitate. 

 The clear fluid was poured off, and evaporated nearly to 

 dryness, and a small quantity of white matter, thus obtain- 

 ed, was added to the former precipitate, which dried, and 



* If the colourless liquid oxinitrate of lead be dropped into a Oxinitrate of 

 dilute solution of arsenic acid, or of arseniate of potash acidulated lea<l- 

 by nitric acid, no immediate precipitation of an arseniate of lead 

 is produced ; but crystalline grains are, after a time, gradually de- 

 posited at the bottom of the vessel. But liquid nitrate of lead 

 causes an immediate and abundant precipitate from these same di- 

 lute solutions. These two combinations therefore must be different. 



exposed 



