42 Examination of a 



is soft and unctuous to the feel, and strongly marks the fin- 

 gers or paper, like common plumbago. It is a csnductor 

 of electricity. The specific gravity of the pure substance 

 I could not ascertain, as it was intimately blended with its 

 matrix ; but when separated as miiCh as possible from earthy 

 particles, it was 1*6, distilled water being 1. I have not 

 been able to learn its geological situation, or the nature of 

 the rocks with which it is associated ; but from the cir- 

 cumstance of its occupying distinct strata, and from its 

 specific characters, it probably resulted from the degrada- 

 tion of the primary granite, and might be classed among 

 that order of rocks termed secondary. If regard were only 

 paid to its external characters, this substance would pro- 

 bably find a place among the ores of molybdena ; but the 

 effects of chemical agents on it proved that it could not 

 belong to this class of bodies. It was unaltered before the 

 blow-pipe on platina, charcoal, and borax. It was scarcely 

 affected by any of the mineral acids. A little of it was 

 boiled successively in concentrated test nitric, muriatic, 

 nitro-muri.itic, and sulphuric acids ; but its lustre remained 

 uninipaired, and it lost no perceptible weight. On exa- 

 mination, however, these acids were found to have taken 

 up a minute quantity of iron, which was indicated by a 

 slight blue precipitate on the addition of prussiate of potash. 

 When the ore was exposed to the agency of pure potash, 

 or to nitre at a red heat, it appeared to be unaffected, and 

 in the first trials with these substances no satisfactory re- 

 sults were obtained. Decided evidences of its composition 

 were gained by heating it to redness in contact with arsenic 

 acid, an experiment which I found had been previously 

 made by the illustrious Scheele*, who seems to have con- 

 sidered the carbonic acid not as a product, but as a consti- 

 tuent part of plumbago. 



Analysis. 



I was necessarily confined to the use of very small por- 

 tions of the ore, not only on account of the limited quan- 

 tity in my possession, but likewise in consequence of its 

 highly refractory nature. In no instance was I able to 

 consume so much as five grains in close vessels, so as to 

 obtain decisive results. From several experinnents I have 

 selected three of the most accurate, and from them I shall 

 venture to state its composition. 



First Experiment. T\ grains of the ore (carefully separated 

 from the matrix) were mixed with 30 grains of arsenic 



Memoires de Chimie de M. Scheele, tome ii. p. 31. 



acid 



