144 PHYSIOGRAPHY. 



Comptonite. 



Lustre vitreous. Color white. Streak white. Trans- 

 parent . . . semi-transparent. 

 Hardness =5-0... 5-5. 



1. Before the blow-pipe it gives off water, intumesces a little, and be- 

 comes opake ; then it melts imperfectly into a vesicular glass. The 

 globule obtained with borax is transparent, but vesicular ; that obtained 

 with salts of phosphorus contains a skeleton of silica, and becomes opake 

 on cooling. With a little soda, it melts imperfectly ; but with a larger 

 quantity, it becomes infusible. The glass, with solution of cobalt, is 

 dirty bluish-grey. It forms a gelatine when exposed in the state of pow- 

 der to the action of nitric acid. 



2. It occurs in the cavities of an amygdaloidal rock, along with Har- 

 raotome, at Mount Vesuvius. 



CONDURRITE. 



Massive : composition columnar, dividing into irregular por- 

 tions like starch. Fracture flat conchoidal. 



Lustre metallic. Color brownish-black. Sometimes highly 

 polished, with a tinge of blue. In powder, soot black. 



Hardness, does not scratch glass ; is brittle, but yields to the 

 knife, leaving a polished metallic-looking surface nearly of a lead- 

 grey color. 



1. A fragment placed on a red-hot coal, affords a copious white vapor, 

 leaving behind a metallic substance, in a semi-fluid state of a yellowish 

 color. It dissolves entirely in nitric acid. 



2. Analysis. 



By FARADAY. 



Water . . . 8-98 



Arsenious acid . . . 25 944 



^Copper . . . 60-498 



Alloy of } Sulphur . . . 3-064 



v Arsenic . . . 1 ( 504 



Iron . . .a trace. 



It is probably a mechanical mixture of metallic arsenic, arseniate of 

 copper, oxide of copper, and a little Copper Pyrites, one or more of these 

 substances being in combination with water. Should this suggestion 

 prove correct, it will not deserve to be ranked among the species of 

 mineralogy. 



