ARSENIC. 305 



diseases, but without producing those beneficial effects which 

 might, a priori, have been expected from its administration. It 

 is never exhibited in a pure state, but requires to be diluted with 

 from ten to twenty parts of atmospheric air, increasing the pro- 

 portion of oxygen according to the effects produced. From one 

 to two quarts may be given, by breathing it, at intervals, from the 

 gazometer, or from a silk bag, to which a tube with a stop cock is 

 affixed. The use of the grey manganese ore in fumigations, for 

 the purpose of destroying infection, will be mentioned in a sub- 

 sequent part of the work. 



Genus XI.— ARSENIC. 



Arsenic, Fr. ; Arsenico, It.; Arsenica, Sp. ; Arsenic, Gcr. 



This metal occurs sometimes native and alloyed with other metals, 

 but more commonly mineralized with sulphur or with oxygen. 

 Combined with oxygen, it forms substances which have the pro- 

 perties of acids. The arsenic acid combines with various metals, 

 and forms distinct species of ore, as the arseniates of lead, of cop- 

 per, and of iron. 



Sp. 1. Native Arsenic. — Gedicgen arsenik, Werner ; Arsenic 

 natif, Hauy. — Its colour, when fresh broken, is tin-white, and the 

 lustre glistening, sometimes shining, and metallic ; but it soon 

 becomes dark and nearly black by exposure to the air. It occurs 

 amorphous, also disseminated, reniform, cellular, and in botryoidal 

 or mamillated masses. Its fracture is small and fine-grained, 

 uneven. It yields to the knife, and is easily frangible. Before 

 the blow-pipe it burns with a white flame, diffuses an arsenical 

 odour, and is entirely volatilized, except a minute portion of iron, 

 gold, or silver, with which it is sometimes alloyed. Native Arsenic 

 occurs with the ores of silver, copper, and cobalt, in various parts 

 of Europe and America. 



Sp. 2. Arsenical Pyrites. — Arsenikkies, Werner ; Fer sul- 

 furo arscnicale, Haiti/. — Pl. XLIII. fig. 2. — Its colour is tin-white 



