50 
SELECTED ARTICLES. 
quantity of water which the plaster retains between its 
particles, and which, to be separated, exacts a long and trouble- 
some manipulation. 
In following the ancient method, it is possible to conduct 
the operation in a way that the water necessary to the boiling 
be entirely evaporated when the plaster is finished. 
By this means ulterior labor is much shortened, which, 
much as it may be necessary, ought to be taken into consider- 
ation, since it is indispensable. 
The solution of soap, even increasing the quantity of water 
prescribed, requires more time than is generally thought. 
The plaster prepared by double decomposition, is so friable 
that it cannot be employed alone for medicinal uses. This 
inconvenience you cannot avoid, either by substituting sub- 
acetate of lead for sacch. saturni, or by replacing the Mar- 
seilles soap by animal soap. 
The plaster of M. Gelis's process being harder than the 
ordinary one, it is natural to suppose that the mixtures, into 
which it is introduced, will also be of greater consistence. 
It is, however, certain that, by the addition of resins to this 
plaster, an inverse result is obtained; and even when the 
consistence is finally analogous, it is a longer time in manifest- 
ing itself; it is this which constitutes an inconvenience in the 
preparation of sparadrops, (adhesive plaster spread upon 
linen,) when they contain a noted quantity of resin. 
It is known that ether dissolves the stearate of lead. It 
would be well to observe whether the resins enjoy the same 
property by heat. It is, probably, the reason that a mixture 
composed of a brittle plaster and a friable resin, is always 
more or less soft. 
Journ. de Chimie. 
