216 
Dr. Thomson on some of 
hydrated oxide (containing 23*58 grains of green oxide), 
were digested in a flask with 40*2 grains of crystallized 
tartaric acid, previously dissolved in water. This quantity 
contains 35‘55 grains of real tartaric acid. After several 
weeks digestion the liquid was filtered. There was separated 
a light-blue powder, weighing after edulcoration and drying 
on the filter 24*52 grains. When heated it glowed, and its 
weight was reduced to 16*64 grains. Thus, 35*55 grains of 
tartaric acid had dissolved 16*64 grains of green oxide. The 
weight of the salt was 58*8 grains. Consequently, its con¬ 
stituents were. 
Tartaric acid - - 35‘55 or io*68 or 1^ atom. 
Green oxide - - 16*64 or 5 - or 1 atom. 
Water _ > _ 6*61 or 1*99 or 2 atoms nearly. 
58*80 
This salt, like most of the others, contains an excess of 
acid. My attempts to obtain a neutral tartrate were not 
successful. 
11. Potash-tartrate of Chromium. 
This salt was accidentally formed in one of my processes 
to reduce the chromic acid in bichromate of potash to green 
oxide by means of tartaric acid. The liquid had assumed a 
deep green colour ; but I was surprized that no precipitate 
could be obtained when ammonia was poured into it; though 
in a process of the same kind, which I had performed the day 
before, the green oxide had been readily thrown down by 
that alkali. On investigating the cause of this anomaly, I 
found that it depended upon the quantity of tartaric acid 
employed. If just the proportion requisite for decomposing 
