Uefearches nn Alumine, 29 



acid gas which is fepa rated from the alkali joins the precipi- 

 tated alumine and the other part the liquor, which then 

 holds in (blution real carbonat of alumine, which may be 

 obtained by volatilifmg the acid gas. He then fays, that 

 natural aluminous earths are very frequently found combined 

 with carbonic acid, which may be icparated by a ftronger 

 acid. 



Gren announces *, that alumine has no affinity for car- 

 bonic acid. This author enters into no detail on this fubjecl, 

 and he feems to fupport his opinion on the efTervefcence pro- 

 duced during the decompofition of the fulphat of alumine by 

 the alkaline carbonats. 



C. Haflenfratz has fince that time given the fpeciflc gra- 

 vities of alumine and the carbonat of alumine. Several other 

 authors have admitted, and Hill admit, aluminous carbonats, 

 both artificial and natural. 



IV. I mail now give the refult of my refearches on this 

 combination. I diuolved fulphat of alumine, known under 

 the name of Roman alumf , in water, and precipitated it from, 

 the liquor cold by a faturated folution of the carbonat of pot- 

 ato. Little or no efTervefcence was produced, as wasobferved 

 by Fourcroy (III). This effecl:, however, does not take place 

 but when the folution is diluted with a certain quantity of 

 water. The alumine obtained by this operation, after having 

 been warned feveral times while ftill moift, and dried at the 

 temperature of the atmofphere, was equal in weight to the 

 twenty-nine hundredths of the fulphat of alumine employed : 

 it diflfolved in nitric acid with a ftrong efTervefcence, and loil 

 about kvtn hundredths of its weight of carbonic acid gas. 

 The precipitation of the fulphat of alumine by the carbonat 

 of foda exhibited rcfults nearly fimilar. I (hall here add, 



* Manuel de Chimie, § 449 and 516. 



f For thcfe experiments 1 made choice of a fulphat of alumine which 

 contained but a very fmall quantity of the oxyd of iron, and I afcertained, 

 by comparative experiments on alumine, as pure as it poffibly couki b~, 

 that this fmall dole of oxyd had no fenfible influence on the refults which. 

 I am about to give. The iron in the common fulphat of alumine is at its 

 minimum of oxydation. None of it was precipitated by the alkaline pruf- 

 fiats till «fter the mixture had been expofed to the free air and the heat; 

 and it may be cahly proved that, if alumine extracted from alum was em- 

 ployed in the repetition of Humboldt's experiments, it was by the prefence 

 of the oxyd of iron that feveral chemifts have been led into an error re- 

 fpefting the abforption of the oxygen gas of the atmofphere by an earth 

 luppoftd to be pure, and which was not fo. For alumine, purified by 

 repeated folutions in potafli, never, when moiftened, exercifed any other 

 action on the oxygen gas of the atmofphere in the experiments I made on 

 this fubjefir. Common alum, fufficiently pure for the alumine extracted 

 from it to give the fame refults in its purifications, may be often found. 



that 



