Carbonates of alumina, glucina, iron, chromium, . 



Art. XXVIII. — On the Carbonates of Alumina, Oluctna and the 

 sesquioxyds of Iron, Chromium and Uranium; by Theodore 

 Parkman, Ph.D. 



The precipitates, prodaced by the alkaline carbonates in so- 

 lutions of alumina, glucina and the sesquioxyds of iron, chro- 

 mium and uranium, have been investigated by a large number 

 of observers; but their results are so discordant, that the true 

 composition of the substances in question is still in doubt. The 

 following investigation was undertaken at the suggestion of Prof. 

 Charles W. Eliot, under the idea that the contradictory results, 

 obtained by previous writers, may have been owing to a loss of 

 carbonic acid, during the processes of washing and drying. This 

 would be probable enough in itself, from the weak affinities of 

 ooth acid and base, in each case, and is, I think, fully confirmed 

 by the analyses which follow. 



1. Carbonate of the sesquioxyd of iron. 

 FejOs, GOa. 



.The precipitate, formed by mixing carbonate of potash with 

 nitrate of the sesquioxyd of iron, after washing with cold water, 

 consists, according to Gmelin,* of hydrated sesquioxyd of iron, 

 free from carbonic acid. Berzeliusf considers that the compound 

 Je.Oj, 3C0^ is formed, but that - • ' 



Langlois:j: gives an analysis of a precipitate, produced by carbon- 

 ated alkali in a sesqui-salt of iron, perfectly freed from alkali 

 by washing and dried at 100° C. His results were 88-47 p. c. 

 Je^Oj, 10-17 HO, 1-36 CO3, from which he does not deduce any 

 formula. Wallace§ finds the precipitate by carbonate of soda in 

 sesquichlorid of iron, after drying over sulphuric acid, to be 

 ^Fe,03, CO,, 6H0 : in the nitrate, 9Fe,03, CO,, 12H0. Ac- 

 cording to Barratt,! the precipitate produced by carbonate of 

 soda in sesquichlori'd of iron, when dried in the air, has the for- 

 mula 3Pe,0„ C0,-f8H0: when dried at 100°, SFe^O,, 

 C03+4Hd 



The carbonate of iron which I have examined was precipi- 

 ^ted. at t.liP nrrJinavtr tcmpcraturc, from pure crystallized iron- 

 " ' ■ light excess. The precipi- 

 ly pressed between folds of 

 _ , for about twelve hours, 

 ^^d whife stTli m'oi^t,^ introduced int'o a bulbed tube of hard glass, 

 ^^d the whole weighed. It was then ignited in a slow stream of 



* Handbook of Chem., y, 222. t ^ehrb. der Chem., iii, 626. 



I Ann. Chim. et Phys., xlviii, 602. 



I Chem, News. i. 110. in J. nr. Chem.. Ixxsii, 61. 



potash-alum by carbonate of soda 

 ^te was not washed or dried, but s 

 paper, under a heavy wei 



