PREPARATION OF SIMPLE PLASTER. 49 
product will be four pounds. In following exactly this for- 
mula, a very white plaster is obtained, but of a consistence too 
hard. Messrs. Chevallier, Lecanea, and Boudit announced 
the chemical proportions of this stearate to be about the 
same as that in the Codex, and not dearer. 
Additional Plaster. 
Take of plaster as above, 4 lbs. 
Fatty acid, separated from soap, 8 oz. 
Melt and mix exactly. 
This addition, which has been recommended by M. Gelis, 
seems to have for its object, the giving to the plaster obtained 
by double decomposition the consistence and malleableness 
of the common plaster. 
Fatty Jicid. 
Take of white Marseilles soap, 16 oz. 
Water, 32 oz. 
Dissolve and decompose the soap by the following mix- 
ture: 
Sulphuric acid, 2 oz. 
Water, 16 oz. 
Observations. — The mode proposed by M. Gelis for the 
preparation of simple plaster,is distinguished from the ordinary 
process, not only by an easier and more certain execution, but 
likewise by the nature of the product, which is always iden- 
tical and of greater whiteness. 
These facts, the merits of which we have not heard con- 
tested through any scientific report, do not appear to us 
sufficient for the definite adoption of M. Gelis's process in 
practice. This may be judged by the following: 
This process, though more prompt than the old one, when 
operating in a small way, requires, on the contrary, longer 
time when treating twenty or twenty-five pounds of soap at 
once. This circumstance depends altogether upon the large 
VOL, iv. — no. i. 7 
