70 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(3.) 10.2107 grams of the solution gave 0.7804 gram of impure 

 baric sulphate, collected upon a washed filter and ignited after the 

 method of Bunsen. In the filtrate was found 0.001 1 gram of addi- 

 tional precipitate. Only 0.0007 gram of argentic chloride was ob- 

 tained from the whole of this substance. 



(4.) 10.2189 grams of the solution yielded 0.7821 gram of pre- 

 cipitate, collected and ignited in a Gooch crucible.* The filtrates 

 yielded 0.0017 more, and the whole of the baric sulphate gave 0.0024 

 gram of argentic chloride. 



If these two determinations are not corrected for the occluded baric 

 chloride, they give results for the strength of the acid solution which 

 respectively equal 3.215 and 3.221 per cent of HsSO^. When cor- 

 rected for this error, they are reduced to 3.213 and 3.215; and the 

 average of these corrected results, 3.214 per cent, is exactly equal to 

 that found by alkalimetry. 



It is evident that these experiments show clearly enough three 

 facts : — 



First, that, when the occlusion is small, the proposed method is 

 capable of yielding results which are both consistent and accurate. 



Second, that the solubility of baric sulphate may easily introduce an 

 error of as much as one fifth of a per cent, even when this solubility is 

 reduced to a minimum. 



Third, that the strength of the standard solution being analyzed 

 was very nearly 3.214 per cent. 



These experiments do not show that the method is capable of giving 

 a true result when the occlusion is large, nor do they show the circum- 

 stances which determine the amount of the intruding impurity. The 

 first of these additional questions, which is suggested by the fact that 

 pure baric chloride parts with some of its chlorine when heated in the 

 air, will be treated next. 



Throughout the following series of seventeen experiments the pre- 

 cipitation of the baric sulphate was conducted as usual very nearly at 

 the boiling point of the solutions. The precipitates were digested for 

 about an hour before filtering, and were each washed with nearly a 

 litre of boiling water. The baric sulphate was always ignited with its 

 filter paper ; if the whole mass of the paper is charred by gentle heat 

 before any active combustion is allowed, no trouble from reduction is 



* When good asbestos is used, — and this is not alwayseasy to obtain, — the 

 Gooch crucible answers admirably for tliis purpose. Compare Jannasch and 

 Eicliards, Mar, Browning, and Phinney, loc. cit. Ripper must have used a 

 poor quality of asbestos (Zeitschr. Anorg. Chem., II. 36). 



