RICHARDS AND PARKER. — BARIC SULPHATE. 71 



encountered. In order to prove this, two portions of baric sulphate 

 ignited with their respective filters were treated with a little sulphuric 

 acid and ignited again. In neither case was a gain in weight observed. 

 A comparison of experiment No. 3 with No. 4 shows the same fact ; for 

 in one of these experiments the precipitate was collected in the usual 

 way, while in the other it was ignited in a capped Gooch crucible, 

 where there was no chance of reduction.* 



After the precipitate had been weighed, the chlorine present was 

 determined in the manner used in Nos. 3 and 4. The results are 

 given on the next page. 



The reasons for the varied amounts of occlusion noticed in this 

 table will be discussed later. At present it concerns us only to note 

 that, while the variation in the uncorrected column is from 0.3198 

 gram (experiment No. 5) to 0.3247 gram (experiment No. 11), or 1.77 

 per cent, the corrected column shows an extreme difference of only 

 0.53 per cent (0.3192 in Nos. 5 and 12, to 0.3209 in No. 15). 

 The seventeen experiments may be grouped into two series ; one, 

 where the occlusion is large, giving a corrected average of 0.3199 

 (Nos. 7, 8, 9, 10, 11, 12, 13); the other, where the occlusion is 

 small, giving a corrected average of 0.3201 (Nos. 5, 6, 14, 15, 16, 17, 

 18, 19, 20, and 21). The close agreement of these averages is suffi- 

 cient proof that the method is capable of giving satisfactory results 

 even when the occlusion is very large, and hence that no essential 

 amount of the occluded chlorine in baric sulphate is liberated upon 

 ignition. 



The individual variations are no doubt chiefly caused by the solu- 

 bility of baric sulphate in the acid solution from which it came, as is 

 the deficiency of nearly 0.5 per cent in the final average. It is to 

 be noted that in Nos. 14, 15, 16, and 17, where the average is higher 

 than the others, a large escess of baric chloride, which must diminish 

 the solubility of the sulphate, was used. The amount dissolved was 

 not determined in any case, as the results were intended to represent 

 the usual method of analysis, and were rather to be compared with one 

 another than with an absolute standard. 



It is interesting to note, however, that when the precipitation is 

 conducted with reasonable care — as in Nos. 14 to 21, — the 



* This observation does not agree with that of M. Ripper (Zeitschr. Anorg. 

 Chem., II. .36). It is possible that Ripper conducted his combustion at too high 

 a temperature ; at any rate, it is true, as he observes, that a slight reduction 

 would make much more diflference in his work than in such as ours. 



