COPPER. 413 



lected without loss, it will weigh exactly five 

 grains. This experiment is not easily made, be- 

 cause we have no good precipitant of oxide of 

 copper. But I have accomplished it in various 

 ways. If we throw down the oxide of copper by 

 caustic potash, we obtain very nearly five grains, 

 though I have never got the exact amount in 

 this way. In general, the oxide of copper thus 

 procured weighs about 4-9 or 4'95 grains. 

 When the copper is thrown down by sulphuret- 

 ted hydrogen, or by hydrosulphuret of ammonia, 

 the precipitate, when collected without loss, and 

 sufficiently dried, weighs 8 grains, and when dis- 

 solved in aqua regia, and precipitated by muriate 

 of barytes, the sulphate of barytes obtained 

 weighs 29*5 grains, indicating 10 grains of sul- 

 phuric acid, equivalent to 4 grains of sulphur ; 

 consequently, the copper in 15 '625 grains of 

 blue vitriol weighs exactly 4 grains.* This, 

 coupled with the amount of the precipitate by 

 means of caustic potash, leaves no doubt that 

 the true weight of the oxide of copper in 15*625 

 grains of blue vitriol is 5 grains ; and that it is 

 a compound of 



* If we precipitate the copper from 15-625 grains of sulphate of copper 

 by means of a plate of zinc, taking care in the first place, to acidulate the 

 solution of the salt with a little sulphuric acid, to prevent the copper from 

 adhering to the zinc ; the precipitated copper, if it be dried without allow- 

 ing it to absorb oxygen, will weigh exactly four grains. This experiment 

 is not easily made, because the copper while drying has a tendency to 

 absorb oxygen. But it is easy in this way to obtain a very near approxi- 

 mation. 



9 



