OXALATES, NITRATES, PHOSPHATES, SULPHATES, AND CHLORIDES. 
55 
One atom oxide of chromium, CrCr . . . 1003*6 16*28 
Three atoms potash, 3 K 1769*7 28*70 
Six atoms oxalic acid, 6 CC 27 1 7*4 44*07 
Six atoms water, 6 H 675* 10*95 
6165*7 100* 
The results in regard to the water and oxalic acid narrated above, agree completely 
with this view, and so does the determination of the oxide of chromium. 26*01 grains 
of the crystals left, when ignited, 14*08 grains of the mixed chromate and carbonate 
of potash, which were dissolved in water, and being acidulated with acetic acid, the 
chromic acid was precipitated by acetate of lead, and gave 17*45 grains chromate of 
lead, equivalent to 4*28 grains oxide of chromium. Hence by this experiment the 
crystals contain 16*46 per cent, of oxide of chromium, which approaches very nearly 
to the theoretical result. The fused residuary chromate and carbonate of potash 
amounted to 0*5425 of the weight of the crystals, which is so near the theoretical 
result, namely, 0*5433, that we may safely conclude that the quantity of potash in 
the salt agrees with our theoretical estimate. 
This salt is clearly, therefore, a compound of one atom oxalate of chromium, con- 
taining three atoms oxygen in the oxide and nine atoms oxygen in the acid, with 
three atoms oxalate of potash; and the salt has six atoms of water of crystallization. 
The oxygen in the oxide of chromium being 1, that in the potash is also 1, that in 
the water 2, and that in the oxalic acid 6. 
I made several attempts to crystallize the oxalate of chromium itself, but without 
success, so that I had no opportunity of studying its constitution in relation to the 
constitution of the preceding double salt. 
14. Oxalate of Peroxide of Iron and Potash. 
This salt, which has not hitherto been described, is formed by dissolving the 
hydrated peroxide of iron to saturation in binoxalate of potash. There is no effer- 
vescence, but a sap-green solution results, which, when concentrated, deposits the 
salt in question in tabular crystals, of which the form has no resemblance to that of 
the corresponding oxalate of chromium and potash, and which are of a beautiful 
grass-green colour. These crystals are permanent in the air, unless it is very dry, 
when they lose water by efflorescence and become brown and opake. The solution 
of the salt is decomposed by ammonia, and the peroxide of iron completely thrown 
down. The salt, when ignited, leaves peroxide of iron and carbonate of potash. It 
loses 10*56 per cent, of water at a temperature not exceeding 230° Fahr., but is par- 
tially decomposed at 300°. Below, the theoretical composition of this salt is placed 
in juxtaposition with the results of an analysis. 
