species of Plumhago from Africa. . 43 



acid and exposed to a strong red heat for about 25 minutes 

 over mercury, in a small green glass retort coated with 

 clav. Nine cubical inches of carbonic* acid gas were ob- 

 tained, besides a quantity of oxygen, and white crystallized 

 oxide of arsenic sublimed. After the residuum had been 

 well washed with distilled water, and dried at a low red 

 heat, it weighed 4^ grains, and appeared to be unaltered in 

 its General characters. A half of a, grain of earthy matter 

 was now separated from the 4| grains, which, on examina- 

 tion, was found to be silex, alumine, and a minute quantity 

 of iron. Now, from the accurate experiments of Messrs. 

 Allen and Pepysf, 100 cubical inches of carbonic acui gas 

 contain 28-t"'0 grains of carbon. And 9 cubical inches 

 contain 2-57 grains. Hence these 7-| grains of the ore 

 furnished 4'25 grains of ore-nnafiecled 



2*57 carbon 



0-5 silex, alumine and iron 



0-18 loss 



7-50 



Second Experiment. 5 grains of the ore were heated with 

 35 grains of oxymuriate of potash, in a similar manner as 

 the preceding; experiment. 6 cubical inches of carbonic 

 acid gas were obtained, and a quantity of oxygene. The re- 

 siduum carefully collected was treated with pure muriatic 

 acid, and digested for some minutes at about 70^ Fahren- 

 heit. The acid solution was then passed through a filter, 

 and the solid matter collected, washed, dried, and heated to 

 redness. It weighed 3*1 chains, and had all the appearance 

 of the native ore, except that its lustre was very slightly 

 inii)aired. A few minute particles of silex were disse- 

 minated in it. The acid solution gave only a slight indi- 

 cation of iron with prussiate of potash, and no ascertain- 

 able quantity of earthy matter separated, when it was neu- 

 tralized with carbonate of potash. 



Hence these 5 grains of the ore afforded v/ith oxy- 

 muriate of potash, 



6 cubic in. carbonic acid gas = 1*71 carbon 



3* 1 ore scarcely af- 

 fected 

 •19 silex with a little 



■ iron. 



5 



* The quantity of carbonic acid gas in these experiments was determined 

 by the absorption with lime water, and a 3t^ong sulutiun of caustic potash. 

 f Phil. Trans, vol. xcvij. p. 290. 



With 



