OF ARTS AND SCIENCI-:S, 273 



tion scarcely influences the two most important results (II. and III.), 

 the figures have been allowed to stand uncorrected. 'Ihe final aver- 

 age would have remained essentially the same. The hi'diest and 

 lowest valut-s given in this table are in several cases much more 

 seriously in error than the actual experimental results. The reasons 

 for this widening of the limits will be sufllciently understood throu<di 

 a careful perusal of the matter which immediately precedes the table. 



Clianges in the atomic weights of the elements used as standards of 

 reference of course cause slight changes in the corresponding atomic 

 weights of cop{)er. Sulphur enters into a larger number of the ratios 

 than any other element, excepting of course oxygen and copper; but 

 a reasonable change in its assumed atomic weight, while slightly 

 affecting individual results, has no effect upon either of the averages. 

 Carbon and sodium are both determined with a hisih deirree of accu- 

 racy, and oxygen is our standard of reference. A fuller discussion of 

 these results will be found in the concluding summary. 



II. Synthesis of Cupric Sulphate. 



Parallel with the experiments which have just been described was 

 commenced a series of syntheses of cupric sulphate. It was hoped 

 that the results might furnish a valuable confirmation to the conclu- 

 sions based upon the analytical work, but the outcome of the series 

 was very disappointing. 



The method of experiment was as follows. A weighed amount of 

 pure electrolytic copper,* which had been ignited in hydrogen, was 

 dissolved in the purest nitric acid in a platinum flask provided with 

 bulb tubes for the condensation of spray. A slight excess of pure 

 sulphuric acid was then added, and the whole was evaporated to small 

 bulk in a platinum dish. After transferring to a small crucible en- 

 closed in a larg3r one, the remaining solution was evaporated to dry- 

 ness on the steam bath ; and the resi<lue was gradually raised to a 

 temperature of 400°. After some time the crucible was quickly 

 covered, placed in a phosphoric oxide desiccator, and allowed to cool 

 in a vacuum. Air having been admitted through suitable drying 

 tubes, the crucible was quickly weighed. The product of the experi- 

 ment soon reached constant weight upon reheating, but it was in- 

 variably found to contain a very j)erceptible amount of imprisoned 

 sulphuric acid, which rendered its solution strongly acid to methyl 

 orange. It is evident from the preceding section that this impurity is 



* For mode of preparation, see these Proceedings, XXV. I'JO, 206. 



VOL. XXVI. (n. S. XVIII.) 18 



