110 ESSAY VI. 



the form of vapours in a quarter of an hour ; if the crucible, 

 during the time the acid is evaporating, be put under a 

 convex glass vessel, the inside will be covered with a white 

 powder, which is arsenic, and not acid of arsenic. In the 

 crucible there remains a little clear and difficultly fusible 

 glass, with which the crucible is likewise covered ; it consists 

 of clay and acid of arsenic, (c) Acid of arsenic digested 

 with charcoal powder undergoes no change ; but if this 

 mixture be put into a retort, the moisture all driven off, a 

 receiver then luted on, and the heat increased till the bottom 

 of the retort begins to grow red hot, the whole mass takes 

 fire with violence, and all the acid is reduced and sublimed 

 into the neck of the retort ; a shining regulus is obtained, 

 mixed with a little arsenic and charcoal dust. A few drops 

 of water are found in the receiver, but they do not contain 

 a particle of acid. The same thing happens when the acid 

 of arsenic has been prepared with manganese, (d) The acid, 

 after some days' digestion with oil of turpentine, unctuous 

 oil, and sugar, becomes thick and black. If some muriatic 

 acid be abstracted with a gentle heat from this mass, and 

 then a few drops of nitrous acid dropped into it, and the 

 abstraction repeated, a little arsenical acid will remain 

 behind. It appears from this that the arsenical acid attracts 

 a little phlogiston from these oils, in consequence of which 

 some arsenic is regenerated and carried over by the muriatic 

 acid into the receiver. Spirit of wine undergoes no change, 

 whether it be digested or distilled with arsenical acid. (0) 

 Six parts of the acid, digested with one of sulphur, suffer no 

 change ; but when the mixture is evaporated to dryness, and 

 distilled from a glass retort provided with a receiver, a 

 violent combination takes place, as soon as the mixture is 

 heated to that degree at which sulphur melts. The whole 

 mass rises almost at the same instant, in the form of a red 



