1871.] Dr. A. Schrauf on Molybdates and Vanadates of Lead. 453 



the crystal fixed to the axis being duly adjusted and centred, the pro-- 

 ceedings go on as usual. Two acicular crystals, duly adjusted, gave as 

 results : 



0°, 

 60°, 

 120°, 

 180°, 



from which the planes, including them, must be admitted to be those of a 

 regular hexagonal prism. 



Their colour, and even their streak, being light yellow, they may be 

 either mimesite or pyromorphite on vanadate of lead. A drop of hydro- 

 chloric acid poured on such a crystal makes its tint vanish gradually 

 without bringing to view a dark-brown nucleus (as is the case with vana- 

 date of lead), and finally produces a pseudomorph of white chloride of 

 lead. By heating on charcoal, a brown globule with facetted surfaces is 

 produced ; traces of lead are obtained ; the smell of arsenic is very insignifi- 

 cant. Fusing with bisulphate of potash in a platinum spoon gives merely 

 a portion of white saline substance. All these tests were indicative of 

 pyromorphite without any admixture of vanadium ; the quantities submitted 

 to operation being, however, very minute, a definitive judgment is not to be 

 pronounced. 



§ 2. Chemical Characters of Eosite. 



The crystals of this mineral are all below % millim. in size, and difficult 

 to be freed from the acicular pyromorphite covering them. They are 

 easily detached from the cerussite, on whose surface they are fixed. Their 

 hardness lies between 3 and 4 (Mohs's scale). When compressed, they 

 are crushed into small, irregular granules, showing slight traces of cleavage. 



The colour of the eosite is a saturated aurora-red, even deeper than that 

 of chromate of lead, and approaching the tint of realgar ; the red tint of 

 the wulfenite from Rusk berg (Banat) is less intense, that of the Phenix- 

 ville specimens has more of yellow in it ; the tints of dechenite and des- 

 cloizite vary between brownish carnation and greenish brown. 



The powder resulting from the friction on a hard surface is brownish 

 orange in eosite, somewhat darker than that from red chromate of lead. 



Like the powder from chromate of lead, or from red wulfenite, that from 

 eosite loses its colour and becomes white by contact with hydrochloric 

 acid. This solution, diluted and spread over a glass plate, shows under 

 the microscope the formation of chloride of lead in white acicular crystals. 

 A minute splinter of eosite, when put on a glass plate and a drop of cold 

 hydrochloric acid poured on it, undergoes, within a quarter of an hour, a 

 partial solution along its margins, pseudomorphising into white chloride 

 of lead, the interior still remaining partly unaltered. The solution in 

 hyd ochloric acid is slightly tinted with yellow; chromate of lead and 

 vanadinite are more easily dissolved, and the tints of their solutions are more 



