296 DR. TURNER ON CHLORIDE OF BARIUM. 



potash. The equivalent of potash, deduced from that analysis, cannot be 

 i-elied 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 112.19 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 pai'ts 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 12.17, and in another 1 12.18, of sulphate from 100 

 parts of chloride of barium. According to Dr. Thomson, 100 parts of the 



