20 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(2) That time is required for the formation of this complex sulphate, 

 especially at low temperatures. 



These reasonable conclusions are entirely in accord with the outcome 

 of our previous work. It became now possible to determine by analysis 

 the basic nature of the occluded body. 



In order to attain this end, the occlusion was made as marked as pos- 

 sible by allowing plenty of time for the formation of the complex sul- 

 phate. Four portions of several grams each of baric sulphate thus 

 badly contaminated with chromium were precipitated from a solution, 

 which had been made strongly acid with hydrochloric acid in order to 

 prevent excessive hydrolysis. Each portion of precipitate was analyzed 

 twice, making eight analyses in all. Every analysis indicated a de- 

 ficiency of sulphuric acid in proportion to barium and chromium (a de- 

 ficiency at least as great as that demanded by Recoura's formula), although 

 the extent of the deficiency was not exactly the same in every case. 

 The variations are inessential, and the average result will serve for the 

 present purpose- The precipitate was found to contain 57.24 per cent of 

 barium, 0.39 per cent of chromium, and 40.84 per cent of the sulphuric 

 radical. This quantity of barium should correspond to 40.01 per cent of 

 the sulphuric radical ; an amount which leaves 0.83 per cent to be asso- 

 ciated with the chromium. This is a considerable deficiency, since 0.39 

 parts of chromium corresponds to 1.16 parts of the sulphuric radical in 

 the normal sulphates. 



Yet a greater amount of occlusion might obviously be obtained by 

 causing the formation of more of the complex sulphate by neutralization 

 of the acid before precipitation, but such a basic solution cannot be heated 

 without the obvious deposition of chromic hydroxide, as has been already 

 stated. Hence experiments were made with a cold green solution, satu- 

 rated with chromic hydroxide. From the clear solution baric sulphate was 

 precipitated, and allowed to stand for a long time. The baric sulphate 

 thus formed was washed with cold water to prevent the accidental hydrol- 

 ysis of the adhering filtrate. In four successive analyses of two separate 

 specimens of gently dried baric sulphate thus made, the following per- 

 centages were found: barium, 55.46, 55.50; 55.14, 55.29; chromium, 

 0.64, 0.64; 0.65, 0.80; sulphuric radical, 39.67, 40.07; 39.53, 39.50. 

 The averages of all these values are 55.35. 0.68, and 39.69. This quan- 

 tity of barium corresponds to exactly one per cent less of sulphuric acid 

 than the figure actually found, hence this 1.00 part may be supposed 

 to be associated with 0.68 part of chromium. But this quantity of 

 chromium should be associated with nearly twice as much sulphuric acid 



