the compounds of chromium. 217 
the chromic acid be used, we can always throw down the 
green oxide of chromium by ammonia ; but when such a 
quantity of tartaric acid had been employed that a notable 
portion of it remained undecomposed in the liquid, then no 
green oxide could be thrown down by ammonia, or by any 
other alkali. Knowing that the compound metalline tartrates 
are not precipitable by alkalies, I was naturally led to suspect 
that I had formed potash-tartrate of chromium. To verify 
this suspicion, I put bitartrate of potash and protoxide of 
chromium in the atomic proportions into a flask, with the 
requisite quantity of water, and digested the mixture for some 
days. By degrees the oxide entered into combination with 
the salt, and formed a deep-blue liquid, having a sweet 
acidulous taste. When evaporated to dryness, there remained 
a powder almost black and tasteless. It was still soluble 
in water, unless too much heat had been employed, and 
possessed exactly the characters of the substance obtained 
by digesting bichromate of potash with tartaric acid in 
such quantity as to form the compound not precipitable by 
ammonia. 
This compound salt was subjected to analysis, and its con- 
stituents found to be, 
2 atoms tartaric acid - - 16.5 
1 atom potash - 6 
1 atom protoxide of chromium 5 
2 atoms water - - - 2-25 
29T5 
The three first constituents are given exactly as they came 
out in the analysis. The water actually procured was only 
MDCCCXXVII. F f 
