324 Carbonates of alumina, glucina, iron, chromium, etc. 



alum slowly into carbonate of soda, with constant agitation, tin- 

 til the alkaline reaction became eomparativelj feeble. In this 

 way there would be always an excess of carbonate of soda pres- 

 ent. Two analyses were made of the same preparation. 



Cr^O^. "esVe ^' 65-03 64-96 



2CO2. 36-24 84-97 35-04 



Tocnio 100-00 10000 



This seems to prove pretty conclusively that there is a carbon- 

 ate of chromium, possessing the above formula, and that the 

 precipitate produced by the alkaline carbonates consists chieflv 

 of it, generally mixed, however, with variable quantities of a 

 more basic compound. This latter may very probably be a car- 

 bonate of chromium, which will be described further on. 



As already mentioned, Lefort asserts that the precipitate, 

 produced by the alkaline carbonates in solutions of the green 

 modification of sesquioxyd of chromium, is hydrated oxyd, con- 

 taining no carbonic acid. The following is the result of an 

 analysis, made by myself, of such a precipitate. The chromium 

 solution used was prepared by boiling the violet chrome-alum 

 for about an hour, and cooling the solution before precipitation. 

 The percentages obtained were 59-38 CrgO, and 40-62 CO,- 

 The carbonic acid is probably too high, and I regret that I did 

 not have time to repeat the analysis. It is, however, sufficient 

 to show that the substance contains carbonic acid, and that its 

 composition is probably the same as that of the precipitate ob- 

 tained in the violet modification. 



The agreement of the results of Lefort, Wallace and Barratt, 

 who all make the carbonate of chromium to be CrjOj, C0a4- 

 4H0, makes it probable that the bicarbonate, above described, 

 loses its second atom of carbonic acid more readily than the 

 other and is converted by washing and drying into a more stable 

 monocarbonate. This latter is also formed, when a boiling solu- 

 tion of chrome alum is precipitated by carbonate of soda, as is 

 shown by the following analysis of a precipitate thus prepared • 



Cr,03 nn-4: ""'''"■ ^^.86 78-63 



CO3 22- • 22-14 21-32 



3. Carbonate of Alumina. 



Saussure* considers the precipitate, produced by alkaline car- 

 bonates in the solutions of alumina, to be a compound of alumina 

 with a little alkal" ' " ■ ^ ^ -^ . ^1 -im- 



itate by carbonate 



* Jour. Phya, Ui, 290. l Chem. Soc, Qa J 



the solutions of alumina, to be a compound ot aiu.i^'- 

 3 alkaline carbonate. Musprattf finds that the precip- 

 bonate of ammonia in alum is SAl^Og, 200^ +loii^' 



