244 Dr.Thomson's Experiments to determine the Weight [April, 



of copper as a compound of one atom copper -f one atom oxy- 

 gen, and the protoxide as a compound of two atoms copper + 

 one atom oxygen ; so that their constitution, according to this 

 view of the subject, is as follows : 



Protoxide 8 copper + 1 oxygen 



Peroxide 4 +1 



I consider my view Qf the subject as more simple and more 

 conformable to the analogy of other metals. 



(2.) Blue vitriol, how frequently soever we crystallize it, or 

 how carefully soever we wash it, always reddens vegetable blues, 

 and of course contains an excess of acid. "Now most of the salts 

 containing two atoms of acid united to one atom of base that I 

 am acquamted with, have the property of reddening vegetable 

 blues. This is the case with 



Bisulphate of potash, 

 Bisulphate of soda, 

 Bitartrate of potash, 

 Binoxalate of potash, 

 Alum, 



and various other bisalts which will readily occur to the recol- 

 lection of the practical chemist. Blue vitriol then possesses the 

 characters of a bisalt. Hence it is reasonable to conclude that 

 it is a compound of two atoms of acid and one atom of peroxide. 



(3.) There exist other two sulphates of copper besides blue 

 vitriol, both of which I have repeatedly obtained. 



If you dissolve 31 '25 grs. of the crystals of blue vitriol ia 

 water, put into the solution 10 grains of peroxide of copper in 

 the state of a fine powder, and digest the whole in a retort on a 

 sand-bath for two months, the whole of the oxide gradually dis- 

 appears, the solution becomes colourless, and a green coloured 

 powder is deposited, which is a neutral sulphate of copper; for 

 it contains, as is obvious, twice as much peroxide of copper as 

 blue vitriol. This neutral sulphate has no effect on vegetable 

 blues, and is insoluble in water ; but it dissolves easily in 

 muriatic acid. If we analyze it, vve shall find it to consist of 

 one sulphuric acid + two peroxide of copper by weight, and a 

 certain quantity of water, which I have not determined with 

 accuracy. 



If into a solution of blue vitriol you pour a quantity of sulphu- 

 ric acid, and evaporate the liquid sufficiently in a Wedgewood 

 dish, a salt is deposited in small irregular crystals having a much 

 lighter blue colour than blue vitriol, a much more acid and acrid 

 taste, and acting more powerfully on vegetable blues. This salt 

 is slowly deliquescent, and from the few trials to which I have 

 subjected it, I have reason to consider it as a perquadrisulphate 

 of copper, or a compound of four atoms of sulphuric acid and 

 one atom of peroxide of copper. 



