On some Compounds of Chrome. 127 
nution of the number of deaths from small pox may fairly be at- 
tributed to the wider diffusion of vaccination. 
(Signed) Henry Hatrorp, President. 
ALGN. FRAMPTON, 
THo. Hume, 
Cuarues Bapnam, 
Rosert Lioyp, 
Everarp Home, Master of the Royal College of Surgeons. 
Wi.iiaM neta Governors of the Royal College of 
Censors of the 
Royal College 
of Physicians. 
Henry Cine, Surgeons. 
By order of the Board, 
James Hervey, M.D., Registrar. 
XXXV. On some Compounds of Chrome. By M. GRovvEts*. 
Acid Chromate of Potash. 
Aci chromate of potash is anhydrous: I obtained it by di- 
gesting the neutral chromate of potash with nitric acid, separat- 
ing from the first crop of erystals all those of nitre, and then re- 
dissolving and again crystallizing the chromate. When this salt 
is strongly calcined it melts, and passes to the state of neutral 
chromate, giving up half its acid, which is decomposed, and 
leaving an oxide of chrome crystallized in brilliant green scales. 
The neutral chromate thus obtained was analysed by a solution 
of sulphurous acid, which changed it instantaneously into sul- 
phate of potash, sulphate and sulphite of chrome. The me- 
tallic oxide was precipitated by ammonia, and the sulphate of 
potash evaporated. The super-chromate, therefore, contains 
twice as much acid as the neutral chromate, and is composed of 
Chromic acid (two atoms) ....... 68°846 
Potash (one atom) ........ee.00+ S154 
100-000: 
Carbonate of Chrome. 
On pouring sulphurous acid and potash into liquid chromic 
acid, M.Vauquelin obtained a brown precipitate, which he thinks 
is an oxide more oxygenated than the green oxide of chrome. 
. This, however, is not an oxide, but a carbonate of chrome. It 
dissolves without effervescence in diluted acids. When boiled in 
distilled water it is decomposed, and the green oxide and car- 
bonic acid gas are obtained, on which account care should be 
taken not to wash it with hot. water. This salt may also be 
procured in another way, that is, by passing a current of nitrous 
* From the Annales de Chimic et de Physique. 
gis 
