*296 
DR. TURNER ON CHLORIDE OF BARIUM. 
potash. The equivalent of potash, deduced from that analysis, cannot be 
relied on ; and his proof of 40 being the exact equivalent of sulphuric acid is 
also liable to objection. But the error upon which Dr. Thomson has so 
unhappily fallen, has been also committed by other chemists. Every analysis 
of sulphate of potash, or of salts containing this alkali and sulphuric acid, 
must be regarded with suspicion. Thus the analysis of common alum by 
Dr. Thomson and Berzelius can scarcely be quite exact ; and the analysis 
of potash-minerals, in which baryta has been separated by sulphuric acid, 
may also be suspected of slight inaccuracy. 
The process by which I have endeavoured to analyze chloride of barium 
consists of two parts. In the first, a given quantity of the chloride was dis- 
solved in water, and the baryta thrown down as sulphate by sulphuric acid. 
In the second, a similar solution was precipitated by nitrate of silver, and the 
chlorine inferred from the quantity of fused hornsilver which was produced. 
The quantity of chloride of barium employed in each experiment varied from 
30 to 40 or 45 grains. The sulphuric acid had of course been purified by 
distillation, and left no residue when evaporated on platinum. 
The process by sulphuric acid was varied : one while the solution and pre- 
cipitate were evaporated to dryness in a platinum capsule ; and at another, the 
insoluble sulphate was collected on a double filter. Both methods were fre- 
quently repeated, and the sulphate of baryta was always dried by exposure to 
a red heat. The quantity of sulphate of baryta obtained by the first method 
from 100 parts of the chloride ranged from 112.17 to 112.2, being more fre- 
quently the latter than the former ; and 1 12.19 may be adopted as a mean of 
the most successful experiments. The quantity obtained by filtration fell 
rather short of this, varying in the best experiments from 112.08 to 112.12. 
The difference is referable to a trace of sulphate of baryta being retained by 
the acid solution, in which it may really be detected by evaporation. The 
first series of experiments may therefore be considered the more accurate, and 
it may be inferred that 100 parts of pure chloride of barium are capable of 
yielding 112.19 parts of sulphate of baryta. This result agrees very closely 
with that stated by Berzelius in the last edition of his System of Chemistry, 
who in one experiment got 1 12.1 7 , and in another 1 12.18, of sulphate from 100 
parts of chloride of barium. According to Dr. Thomson, 100 parts of the 
