TRANSACTIONS OF THE SECTIONS. 47 



The Caldbeck fell mineral was in botryoidal concretions, upon 

 quartz. When examined by the microscope many of the nodules had 

 the aspect of cylinders. 



Colour honey yellow, similar to that of the Cornish arseniate of lead, 

 first described and analyzed by Mr. Gregor, but lighter, and much less 

 translucent. 



The lustre is resinous, and it has much greater brilliancy than speci- 

 mens of vanadiate of lead. 



The hardness is not easily determined, from the shape of the no- 

 dules. Calcareous spar v.as not sci'atched by rubbing them against it 

 while selenite was scratched by them with great facility. The specific 

 gravity by two diiferent trials was 7*272. This specific gravity is 

 decisive that the mineral is not vanadiate of lead, for the specific gra- 

 vity of native crystals of vanadiate is only 6"663. The specific gravity 

 of Cornish arseniate of lead is still lower, being 6*41. 



When exposed to a red heat on platinum foil it undergoes no altei'a- 

 tion, except becoming a shade lighter in colour. Before the blow-pipe 

 on platinum it melts into a transparent globvde, which assumes nearly 

 its original appearance on cooling, and does not crystallize like phos- 

 phate of lead. On charcoal it gives out abundance of arsenical fumes, 

 when acted on by the blow-pipe, and a globule of metallic lead is ob- 

 tained. 



It was analyzed twice in Dr. Thomson's laboratory, with every at- 

 tention to accuracy, by Mr. Stenhouse. During the first analysis he 

 suspected the presence of a minute quantity of phosphoric acid ; but 

 he did not succeed in separating it from the arsenic, and of course the 

 actual existence of this acid in the mineral is still problematical. The 

 quantity is certainly very minute, and cannot amount to so much as 

 half per cent., otherwise it would have been separable from the arsenic 

 acid. 



The two analyses were very similar : the following are the consti- 

 tuents as determined by the second analysis, which Mr. Stenhouse 

 considers as most to be depended on : 



Chlorine .... 2*46 

 Lead .... 7-10 



Arsenic acid . . . 18*20 

 Protoxide of lead . . 70*14 



Peroxide of iron • . 1*20 



Volatile matter . . . 1*00 



100*1 

 The moisture and peroxide of iron are obviously accidental impuri- 

 ties. The chloride of lead in 100 grains of the mineral amounts to 

 about half an atom, the arsenic acid to 24- atoms, and the oxide of lead 

 to 5 atoms. If we abstract the chloride of lead, which exists in nearly 

 the same proportion in phosphate of lead, vanadiate of lead, and arse- 

 niate of lead, as in this mineral, the constituents are 1 atom arsenic acid, 

 and 2 atoms protoxide of lead. It is therefore a diarseniate of lead, 

 constituting a new species of lead ore, which has bepn met with 



