258 PROCEEDINGS OP THE AMERICAN ACADEMY 



many refinements of manipulation were employed, too numerous to be 

 fully described. For example, pbospliorous pentoxide was used as a 

 drying agent in the desiccator, and immediately after the introduction 

 of a hot crucible the air was exhausted with a good air-pump and 

 readmitted through a series of drying tubes. This method of course 

 absolutely prevents the absorption of moisture by the contents of the 

 crucible, while cooling. 



Again, in the ninth experiment, the solution of the perfectly neutral 

 sodic sulphate was transferred to a small flask, heated to 103°, and 

 evaporated by means of a current of pure dry air. When dry, the 

 sulphate was gently ignited and weighed in the flask, and subsequently 

 fused in a platinum crucible. The flask lost 0.00010 gram during the 

 operations, and the sodic sulphate lost 0.0003 gram upon fusion. 

 With the exception of the small flask, all the apparatus was of plati- 

 num. The sodic sulphate formed in the second experiment, and the 

 sodic carbonate required in the third, were not determined. 



The last experiment of the series was not of the same grade of 

 refinement with the others. It is only included here because the 

 same preparation of cupric sulphate was used in its execution. 



The determination of the sulphuric acid by still another method was 

 the object of this experiment. Baric sulphate was precipitated from a 

 boiling solution of cupric sulphate strongly acidified with hydrochloric 

 acid. After weighing as usual, the perfectly white precipitate was 

 fused with pure sodic carbonate, and the resulting cake thoroughly 

 lixiviated with boiling water and dilute sodic carbonate solution. In 

 the filtrate, the chlorine, which had been originally present as baric 

 chloride occluded in the sulphate, was determined in the usual manner. 

 Traces of baric sulphate and argentic chloride must have been dis- 

 solved in the wash water, but these errors tend to counterbalance one 

 another, and hence no correction was made for them. Finally, the 

 weight of baric chloride, calculated from the amount of chlorine found, 

 was subtracted from the weight of baric sulphate ; and from the cor- 

 rected weight thus obtained the percentage of sulphuric acid in cupric 

 sulphate was calculated. The astounding agreement of this experi- 

 ment with the others may be nothing more than accident. In any 

 case, the uncertainty of the atomic weight of barium, and the very 

 unsatisfactory nature of baric sulphate, combine to make a repeti- 

 tion of the experiment of little value for the present purpose ; but the 

 method seems to be of value, and will form a subject of future inves- 

 tigation in this Laboratory. It is well known that baric sulphate has 



