196 Blue Vitriol, &V. [Book VI. 



are moiftened with a folution of blue vitriol, which dif- 

 folves the iron to a very inconfiderable depth, and de- 

 pofits in its place a thin lamina of copper. 



Blue vitriol has' a ilrong ftyptic tafte, and is in fome 

 degree cauftic. Expofed to heat it parts with its water 

 of crystallization, melts, and becomes of a pale blue 

 colour. A ilrong heat is required to feparate from it 

 the vitriolic acid, which adheres more firmly to copper 

 than iron! Blue vitriol is decompofed by magnefia 

 and by lime. If the mild vegetable alkali is poured 

 into a folution of blue vitriol, a precipitate is formed 

 of a pale blue colour, which, however, becomes green 

 by expofure to air : in this experiment no effervefcence 

 takes place, and we may therefore conclude that the 

 carbonic acid of the mild alkali unites with the calx 

 of copper. Volatile alkali precipitates the folution of 

 blue vitriol, in the fame manner, of a blueilh. white 

 colour; but the mixture very foon becomes of a deep 

 blue colour, which happens from the alkali re-diiTolving 

 the precipitate. In order to obtain the cuprum ammo- 

 macum, which has been recommended as a remedy for 

 epilepfy, add volatile alkali till the whole precipitate 

 of copper is re-difiblved, then fet the folution before 

 a fire in a flat vefiel, and let it gradually evaporate, 

 which mould be done with a heat not exceeding that 

 of the human body; the matter which remains at the 

 bottom, in the form of a cruft, muft be rubbed in a 

 mortar, that it may be intimately mixed. 



. The blue vitriol of the (hops is made by means of 

 the action of fulphur upon copper ; thefe are gently 

 calcined together : the fulphur attracts the oxygen of 

 the atmofphere, and unites with the copper into a fo- 

 luble powder, which is afterwards cryftallized into blue 

 vitriol. 



A beautiful 



