184 Dr. Turner on the Composition of Chloride of Barium. 



of baryta; the insoluble sulphate was edulcorated until the 

 washings ceased to contain a trace of baryta, and was then 

 collected on a filter, and ignited. On boiling it in powder 

 with water, sulphate of potash was dissolved. The experiment 

 was varied by mixing the solutions at a boiling temperature, 

 and continuing the ebullition for some minutes; but the result 

 was the same as before. On edulcorating the precipitate with 

 boiling water, sulphate of potash begins to make its appearance 

 in the washings as soon as the excess of muriate of baryta has 

 been removed; but neither by this means, nor by boiling the 

 recent precipitate for hours in successive portions of distilled 

 water, have I succeeded in removing all the sulphate of potash. 

 The adhesion of this salt ensues even in a dilute solution ; and 

 it is not prevented by the presence of other salts, such as nitre, 

 and nitrate or muriate of ammonia, nor by free muriatic acid. 

 The quantity of adhering sulphate of potash is variable, de- 

 pending apparently as well on the relative quantity of the two 

 salts, and the strength of the solution, as on the manner and 

 extent of edulcoration. I have known it to increase the weight 

 of the sulphate of baryta by one per cent. 



The foregoing observations, unless I am much deceived, 

 will fully justify the statement, that Dr. Thomson's method of 

 analysing chloride of barium is radically defective. For if 

 chloride of barium and sulphate of potash be mixed in the 

 proportion to make a perfect interchange, some of the former 

 will remain in the liquid, proportional to the quantity of the 

 latter which escapes decomposition; whereas the absence both 

 of sulphuric acid and baryta from the liquid can only occur, 

 when the quantity of chloride of barium is insufficient for 

 effecting complete double decomposition with the sulphate of 

 potash. So that when the proportions appear to be right, 

 they are certainly wrong ; and they may be right, when they 

 appear to be wrong. It is obvious, too, that Dr. Thomson's 

 analysis of sulphate of potash by means of chloride of barium, 

 is not more satisfactory than his analysis of chloride of barium 

 by sulphate of 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 sul- 

 phuric acid, mav also be suspected of slight inaccuracy. 



The 



