2JATITE ARSENIATE OF LEA©. 



J.\jstre. The external lustre, in some specimens, is Titreoua; m 



others, resinous: but in some instances their surface is 

 partially covered by tender and delicate filaments of a silkj 

 lustre. These filaments are sometimes found in a separate 

 state loosely adhering to q,uartz ; and they form a variety of 

 this f©ssil, 



hardness, Yhe crystals vary as to hardness. The angnlar fragmentas. 



of the most transpa,ren,t are siiifitiea,tl,y hard to scratch 

 glass. 



Tenacity. This mineral is easily reduced to powder, whi^h has the 



appearance of pounded resin : it contracts a yellower tiiit 

 by long exposure to the air. 



Spec, gra-vity. The specific gravity of the purest crystals, talj^ea at the 

 temp, of 50** Fahrenheit, was §'41. 



Action of tlie § 3. A fragment pf crystal, exposed to the flame of the 



blow-pipe on ifej^jj^^p-pg -^^ ^ g^j^ spoon, melted into a brownish yellow 

 mass, which on co/gJing did not assume any angular figure. 

 It remained in a state of ignition; apjrayrently unaltered; 

 but when a piece of it was exposed to t&e flame o» char* 

 coal, a rapid decomposition took, place, arsenical vapours 

 were extricated, and globules of a metal, possessing the 

 common properties of lead, were left behind. 



and of nitric This mineral, in a state of fiae powder, is soluble in nitric 



*^^*^- acid, even without the aid of heat. Care, however, must 



be taken, that it does not concrete into lumps. The vessel: 

 therefore which contains it must be frequently shaken, and, 

 the nitrate of lead produced must be, from time to time,, 

 dissolved in water, and poured oif from the residuum. The 

 process of solution is, however, accelerated by a digesting 

 heat. Some silica remains, which, as the quantity of it is 

 variable according to circumstances, appears not to be a» 

 essential ingredient of this fossil. 



Nitric solution. The nitric solution is colourless ; its transparency is not 

 disturbed by nitrate of barytes. Nitrate of silver renders 

 it turbid, and a small quantity of white curdly matter is 

 deposited. Sulphuric acid and the liquid sulphates produce 

 copious precipitates of a white heavy matter. If the fluid 

 he poured off from this subsided matter, and it be freed 

 from the superfluous sulphuric acid, by the means of ni- 

 trate of barytes, it will yield, on the aff'usion of liquid 



nitrate 



