Scientific Intelligence.— Chemistry. 371 
SCIENTIFIC INTELLIGENCE. 
Translated and Extracted by Prof. G. Griscom. 
CHEMISTRY. 
1. On the Setting of Plaster, by M. Gay Lussac.—The property 
which plaster of Paris possesses, when deprived of its water by heat, 
of setting into a firm mass by combining with additional water, is well 
known to most persons. The consistency which it acquires is very 
variable, and it is the purest plaster that acquires the least. ‘The 
solidification has been attributed to the presence of some hundredth 
parts of carbonate of lime ; but doubtless erroneously, for the heat 
necessary to bake plaster, and which in the small way does not rise 
to 150° cent. is not sufficient to decompose carbonate of lime. Be- 
sides, baked plaster does not ordinarily contain quick lime, and the 
addition of this base to plasters of feeble consistency does not sensi- 
bly improve them. _ I think that the difference observable in the con- 
sistency of baked plasters, is to be ascribed to their hardness in ina 
crude state. I conceive that hard stone plaster, after Tosing i its wa- 
ter, will resume a firmer consistency, in returning to its former ¢ con- 
dition than that which is more tender. The primitive molecular ar- 
rangement is in some sort regained. On the same principle, it is, 
that good cast steel, the carbon of which has been removed by ce- 
menting it with oxide of iron, produces by a fresh’ cementation. 
carbon, a steel much more homogeneous and perfect than ‘that ob- 
_ tained under the same circumstances, by the cementation of i iron.— 
Quar. Jour. July—Sept. 1829. 
2. Braconnot’s Indelible Ink.—The_ inventor amanatdl aie 
in ascribing indelibility to this ink, he was much too hasty, (beau- 
coup trop.empressé.) For, having subjected it, recently, to fresh tri- 
al, he has convinced himself. that it.does not deserve: the title of in- 
delible, since its characters disappear aa successive macerations in 
chlorine and potash.—Jdem. i 
Admitting the correctness as well as candor of this retraction, we 
have assured ourselves by a hasty trial of Braconnot’s ink, that che 
not absolutely indelible, it is much more durable, or much less moots 
destroyed, than common ink.— Trans. 
