2oS Red Precipitate, 6V. [Book VI . 



added to this folution, precipitates a pure calx ; mild 

 alkali, a calx combined with carbonic acid. The 

 volatile alkali precipitates the mercury in the form 

 of a dark grey powder. When this precipitate is 

 examined, it is found to contain a quantity of uncal- 

 cined mercury. For if this matter is dried and rubbed 

 on pure gold, it turns white, by which we may dif-^ 

 cover (mail quantities of mercury in the metallic ftate. 

 The near approach to the metallic ftate, obferved in 

 the precipitate afforded by the volatile alkali, feems to 

 be owing to the prefence of hydrogen, which is one of 

 the conftitucnt principles of volatile alkali, and which 

 has a ftrong attraction for oxygen. 



The precipitates of mercury, formed by alkaline 

 intermediums, have a property difcovered by M. 

 Bayen, which muft not be paflfed over in filence. They 

 detonate like gun-powder, when expofed in an iron 

 fpoon to a gradual heat, after having been triturated 

 in the quantity of half a drachm, with fix grains of 

 flowers of fulphur : after the detonation, a violet powder 

 remains, which may be fublimed into cinnabar. 



The nitrous acid may be feparated from mercury 

 by heat alone. Its firft effecl: is to evaporate the 

 watery parts ; after this the acid flies off in deep co- 

 loured fumes ; as the acid evaporates the calx becomes 

 yellow, then of a deep red, but when removed fome 

 time, orange. This is the red precipitate of the 

 fhops. The nitrous acid, therefore, as in the cafe of 

 other metals, though it ads with more rapidity, ad- 

 heres with lefs force to the mercury than the vitriolic 

 acid, which ads flowly and with difficulty. This 

 proceeds, as was before mentioned, from the eafe with 

 which the nitrous acid is decompofed, fo as to afford 

 to metals the oxygen which is neceilary to render them 

 foluble. 



The 



