58 C. I/udeking — Sijnihesisof Crocoite and PhcBnicochroite. 



to the calculated values. Rather strong solutions of caustic 

 potash should be used and much precipitated lead chroinate 

 dissolved. 



The crystals obtained are rather small, but can readily be 

 studied by means of a lens, or better, a microscope. They 

 show many modifications of the primitive form, as do also the 

 natural crystals. 



I was able to obtain by the same method- crystals of (2PbO) 

 (H„0), by exposing to the air for several months a saturated 

 solution of litharge in caustic potash.* 



It was intended to produce by this means cerussite. The re- 

 action is of course quite clear. The carbon dioxide of the air 

 acting upon the alkali converts it into carbonate which is not 

 a solvent for PbO. Consequently this latter very slowly sep- 

 arates out as a crystalline hydrate, being slightly soluble itself, 

 a necessary condition for crystallization. 



So likewise the solution of PbCr0 4 in KOH on exposure to 

 the air yielded crystals of crocoite and of phcenicochroite. 

 The formation of the former is due simply to the slow abstrac- 

 tion of the solvent by the carbon dioxide of the air. The 

 formation of the latter, the phcenicochroite, is on the contrary 

 effected by another reaction, a portion of the chromic acid 

 being appropriated by the KOH. The lead being thus de- 

 prived of the normal quantity of chromic acid, a basic com- 

 pound, phcenicochroite, is formed. 



On reflection it seemed that it might be possible to obtain 

 each of these minerals alone instead of in mixture as above. 



By using a large excess of very strong solution of KOH, 

 phcenicochroite only was formed, or rather only very little 

 crocoite. When on the contrary much PbCr0 4 is dissolved 

 and in addition K 2 Cr0 4 is added to the KOH solution, crocoite 

 alone is formed. I need not enter upon an explanation of 

 these phenomena as they are almost self-evident. I shall now 

 briefly describe the minerals obtained. 



The PbCr0 4 crystals are oblique rhombic prisms with many 

 modifications. The fracture is uncertain ; luster adamantine ; 

 color hyacinth-red. They are stable in the air. The phcenico- 

 chroite crystals are tabular, of resinous luster, of cochineal 

 color and appear to be orthorhombic. They, like the natural 

 crystals have but little stability and soon change to a light yel- 

 low powder on exposure. 



At Beresowsk, crocoite and phcenicochroite are associated. 

 It is not impossible that they were formed also by the action 

 of the carbon dioxide of the air upon an alkaline solution of 

 PbCr0 4 , as in my first experiment. 



*Amer. Ohem. Journ.. vol. siii, p. 120. 



