l'*2 The Process followed at Montpellier in 
saline solution;, and afterwards to expose them to the air 
to dry. 
Those acids which oxydate the copper by their decom- 
position^ produce an effect like that of neutral salts. The 
oxyde is of a soft blueish-green colour; their action is so 
speedy, that if the copper be exposed to the vapour of 
them for some minutes, its surface will be immediately 
oxydated. The oxygenated muriatic acid produces that 
effect as well as the vapour of the nitric acid, and even 
those of the sulphuric acid. A phenomenon which can- 
not escape the eye of an observer is, that the oxydes of 
copper obtained by tire are very different from those pro- 
duced by the decomposition of acids on that metal. The 
colour of them is grey, instead of being green; and when 
the calcination is continued a long time at a violent heat, 
they may be concentrated to a red oxyde of a blood co- 
lour. This phenomenon was observed by Kunekel in 
his chemical laboratory. 
Saline substances are not the only ones capable of 
oxydating copper green. All oils and fat matters pro- 
duce the same effect. Even water, when left for a con- 
siderable time in copper vessels, causes an oxydation. 
But what will appear very extraordinary is, that the 
greater part of these substances have no sensible effect 
upon copper, except when cold. Those salts even which 
corrode that metal w hen left at rest in vessels, do not 
attack it in so sensible a manner w hen in a state of ebul- 
lition. 
Of all the preparations of copper by oxydation, there 
is none more valuable than that made by vinegar. All 
the verdigrise used in commerce is prepared by that acid, 
and it is at Montpellier in particular and in the neigh- 
bourhood, that the manufactories of it are established. 
In the Memoirs of the Academy of Paris for 1750 and 
1758, may be seen a very exact description of the pro- 
