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SELECTED ARTICLES. 
ART. L V.— NOTICE OF A NEW SALT OF COPPER. 
By F. Wohler. 
I have found that the neutral acetate of copper can combine 
with a larger proportion of water, than that contained in the 
ordinary crystallized verdigris. The new salt is interesting 
in many points of view; it forms large, very beautiful trans- 
parent crystals, of the same blue colour as the sulphate of cop- 
per, which establishes at once a well marked difference be- 
tween it and the common neutral acetate. If a crystal is 
heated to 30° or 35° C, it becomes immediately opaque and 
green, like verdigris, without change of form, and can then 
be crumbled, by gentle pressure, into a mass composed of the 
minute crystals of verdigris. This transformation is more ap- 
parent, when the salt is thrown into warm water; moreover, 
the slower a crystal is heated, the larger and more distinct 
are the crystals into which it is subdivided. This phenomenon 
has a perfect analogy with such known modifications of form, 
as take place without a change of composition, and which have 
been noticed in sulphate of zinc, sulphate of magnesia, &c; 
and it is for this reason especially, that this salt of copper ap- 
pears to me worthy of some attention, for it shows that in 
phenomena of this kind, care should be taken to observe and dis- 
tinguish between the cases where a change of form occurs with 
out change of composition, and those in which one is the 
cause of the other. The phenomenon we have presented, be- 
longs to the last mentioned; as, to the alteration of colour and 
form is added, the separation of | of the water of crystalliza- 
tion of the salt, which last is not perceived while the crystal 
yet remains entire, although rendered pseudomorphous, be- 
cause the separated water remains enclosed between the mi- 
nute crystals of the new formation; and, for the same reason, 
immediate analysis shows that in it there is the same propor- 
tion of water as in the modified crystal. This circumstance 
might easily escape detection; for a similar crystal, upon be- 
coming green, may allow of the gradual evaporation of this 
