ACETATE OF ALUMINE PRECIPITATEt> BlT «EAT* $5 



ceive the reasons of the copious precipitation, that some- 

 times takes place in solution of acetate of alumine. The 

 precipitate retains some acid as well as that obtained by 

 the heat of ebullition ; for water dissolves a part of it, and 

 sulphuric acid expels acetic acid from it: however, it may 

 be completely removed by repeated washings with hot 

 watei-. 



The precipitation of alumine bv heat, and its solution at The pracipita- 

 , /. , ' ^' i 1 1 tion is not 



a lower temperature, are tacts interesting to the general ^j^^ii^g to vola- 



theory of chemistry, and have very few analogous to tilizationof the 

 them. If this precipitation vere owing to the volatiliza- 

 tion of acetic acid, the alumine could not redissolve by 

 cooling : besides, we observe the same phenomena with a 

 very acid acetate, and also in vessels hermetically closed. 

 Since then it is not owing to the volatilization of the acid. Attempts to 

 it is clear, that it must be occasioned by the heat : *'^"^°""* *^^"'' 

 which, separating the particles of alumine and acid to a 

 greater distance, carries them beyond the sphere of their 

 action on each other, and occasions their separation : but, 

 if the heat be diminished, these same particles enter again 

 within their sphere of activity, and combine. This decom- 

 position appears to me analogous to that of a neutral solution Supposed ana* 

 of carbonate of potash, or of soda, by heat; with this differ- jj°g^^.o"^°ijiQ^ 

 ence only, that the carbonic acid, being separated from of the neutral 

 its base, immediately flies off on account of its elasticity, ^^j^^^^^g^ *^*^* 

 and its little solubility in water ; while the acetic acid re- 

 mains still in presence of the alumine, because it is not 

 volatilized by the temperature that occasions its se- 

 paration. 



It appears to me also, that this decomposition has con- an^ the coagu- 

 siderable analogy with the coagulation of albumen hy heat : Jf Lg 

 for, according to the explanation, which Mr. Thenard has 

 given of this phenomenon, it is owing to the tendency 

 water has to evaporate. Thus it happens in like manner, 

 that the particles of water and albumen are carried by the 

 heat out of their sphere of activity, and separate. No doubt 

 they would combine again on cooling, in the same manner 

 as the elements of the acetate of alumine ; but water is too 

 feeble a solvent, and the coherence the albumen has ac- 

 quired too great, for the solution to take place. 



D 2 VIIL 



