Discovery of the Vauquelinite. 77 



of iron, and oxide of lead. The malachite was seldom in 

 large pieces, but was occasionally well characterized. Mr. 

 F. Cozzens found at the mine some fine specimens of green 

 phosphate of lead. 



On carefully examining the specimens given to me by Pro- 

 fessor Moore, I observed a green, and a brownish-green sub- 

 stance, in small mammillary concretions, and also in a granular 

 and subpulverulcnt form. The mammillary portions were from 

 one to four lines in diameter. When broken they exhibited a 

 radiating structure, and a resinous lustre. They were brittle, 

 and yielded a greenish yellow powder. Before the blowpipe 

 this substance grows darker and decrepitates, but preserves its 

 green color. With borax it forms a fine green bead. Its 

 powder boiled, with a solution of potassa, is decomposed, 

 and the product yields a golden yellow solution. When ace- 

 tate of lead is added to this solution, a copious yellow preci- 

 pitate falls, having exactly the appearance of chrome-yellow. 

 Nitrate of silver produced a crimson precipitate, and nitrate of 

 mercurjr, a deep red. Some of the yellow alcaline solution, 

 when concentrated by evaporation, yielded crystals agreeing in 

 character with those of chromate of potassa. A few grains of 

 the powdered mineral were mixed with fused chloride of sodi- 

 um and placed in a tube-retort; on the addition of concentrated 

 sulphuric acid, dense red vapours of peroxide of chromium 

 were disengaged, part of which condensed into a liquid, resem- 

 bling in all respects the liquid called chloro-chromic acid, 

 by Dr. Thomson. The existence of chromic acid being now 

 rendered certain, it only remained to determine the base or 

 bases. A very few experiments showed that the acid was in 

 combination with oxide of lead, and oxide of copper. Hence 

 the mineral is a chromate of lead and copper, and is identical 

 with the Vauquelinite of Berzclius, the cupreous chromate of 

 lead of Cleaveland, and plomb chromi of Brongniart, (his 

 plomb chromate' being the red chromate of lead.) The min- 

 eral was first examined by Vauquelin, and noticed by him in 



