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 a 

 crude state. I conceive that hard stone plaster, after losing its wa- 

 ter, will resume a firmer consistency, in returning to its former con- 

 dition tlian 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 with 

 carbon, a steel much more homogeneous and perfect than that ob- 

 tained under the same circumstances, by the cementation of iron.— r. 

 (^uar. Jour. July — Sept. 1829. 



2. Braconnofs Indelible Ink. — The inventor acknowledges, that 

 in ascribing indelibility to this ink, he was much too hasty, (beau- 

 coup trop empresse.) 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 by successive macerations in 

 chlorine and potash. — Idem. 



Admitting the correctness as well as candor of this retraction, we 

 have assured ourselves by a hasty trial of Braconnot's ink, that though 

 not absolutely indelible, it is much more durable, or much less easily 

 destroyed, than common ink. — Trans. 



