Chap. 32.] Beautiful Green Paint. 197 



A beautiful green paint may be precipitated from 

 blue vitriol, by means of white arfenic diflblved in 

 water together with vegetable a4kali. 



The nitrous acid diflblves copper with great rapi- 

 dity, without the afiiftance of heat, with the production 

 of a large quantity of nitrous gas. Part of the metal 

 falls down in the form of a calx, and the filtrated folu- 

 tion, which is of a much deeper blue colour than the 

 vitriolic folution, affords cryftals by flow evaporation. 

 This fait is more corrofive than vitriolated copper; 

 it fo powerfully attracts the humidity of the atmo- 

 Iphere that it deliquefces, unlefs kept in clofe vefTels or 

 in a very dry place. When melted in a crucible it 

 emits large quantities of nitrous vapour and becomes 

 brown, in which ftate it is merely a calx of copper. 

 In a dry and hot air this fait becomes covered with 

 a green efflorefcence. It detonates lightly on burning 

 coals . 



The muriatic acid acts with great difficulty on. cop- 

 per in its metallic ftate, but diflblves its calces with 

 conflderable rapidity. This may be eafily accounted 

 for from the ftrong attraction which the bafis of 

 the muriatic acid has for oxygen, fo that it will not 

 part with any of it to oxygenate the metal, and no 

 metal is foluble in acids without being oxygenated. 

 "When, however, the metal -has been prepared for 

 folution by an union with oxygen, that is by being cal- 

 cined, the acicl then diflblves it, ,and adheres very 

 clofely, fo that it is with great difficulty feparated by 

 heat. The muriatic folution of copper is of an 

 agreeable green colour, and affords cryftals of the fame, 

 and in this particular differs remarkably from the vi- 

 triolic and nitrous combinations of copper, which are 

 of a deep blue. 



The vegetable acids diflblve copper when caic : 



O 2 but 



