326 Carbonates of alumina, glucina, iron, chromium^ etc. 



Preparation I. was analyzed in April : Preps. 11. and TIL in 

 summer: Prep. IV. also in summer ; but, to avoid a possible loss 

 of carbonic acid in hot weather, it was precipitated from cooled 

 solutions of alum and carbonate of soda, washed with ice-water 

 saturated with carbonic acid, and pressed in a refrigerator. The 

 variable composition of the substance led me to suppose that ii 

 was a mixture of more than one substance, and, for the same 

 reasons as in the case of the carbonate of chromium, led me 

 to make the following analyses of precipitates, produced by 

 pouring alum into carbonate of soda, until the alkaline renction 

 became weak. Both were prepared in hot weather, but with the 

 precautions above mentioned. 



The composition of the first preparation comes pretty near the 

 formula, while that of the second is very much like that of the 

 substances, precipitated in the other way. Possibly in this last 

 precipitate, the alum may have been "poured in too rapidly, 

 without agitation of the liquid, and thus caused, at the point 

 where it fell, temporary excess of alum, thus affording the same 

 probable cause for error as in the other mode of precipitation. 

 The above results lead to this, I think, as the most probable con- 

 clusion : viz., that the normal carbonate of alumina possesses the 

 composition Al^Og, CO3, analogous to that of tlie carbonates ot 

 iron and glucina and one of the carbonates of chromium; «ina 

 that the precipitate, produced by the alkaline carbonates in solu- 

 tions of alumina, consists chiefly of this normal carbonate, gen- 

 erally mixed, however, with more or less of a more basic salt or 

 of hj^drate of alumina. 



4. Carbonate of Glueina. 

 G2O3, CO,. 

 Schaffgotsch* gives an analysis of a carbonate of glucinn, pre- 

 cipitated by boiling a solution of glucina in carbonate of ammo- 

 nia. He finds the percentages, 47 53 G.O^, 17-57 CO, a"^ 

 34-90 HO, corresponding most nearly to the formula, SG.}Jv 

 2C0, +9H0. Weerenf gives analyses of precipitates, obtained 

 by boiling solutions of glucina in carbonate of ammonia, xmaer 

 somewhat different circumstances, and obtains the iornju^^r 

 40,03+400, + imO: 3G3O3+2CO, + 10HO: lG,0,+^^y' 

 -I-14H0. For a precipitate by carbonate of ammonia, not m 

 excess, from a neutral solution of glucina in hydrochloric acio, 

 he obtaias the formula, llGaO,+6C03-i-26HO. 



