254 PROCEEDINGS OF THE AMERICAN ACADEMY 



The sodic carbonate was dissolved in water and poured into the 

 very dilute solution of sulphuric acid which had been formed by the 

 electrolysis. The lid of the crucible, as well as that vessel itself, 

 was very thoroughly washed with water. On account of the gieat 

 dilution of the liquid, carbonic anhydride was not at once set free, 

 but upon warming for six or eight hours upon the steam bath it was 

 easily expelled. During this operation the platinum flask was of 

 course suitably covered, a Gooch crucible being found most con- 

 venient for this purpose. 



When gas evolution had long ceased, the solution was wholly trans- 

 ferred to a large platinum dish, and was evaporated on the steam bath 

 to a volume of about fifty cubic centimeters. The very slight excess 

 of acid was then titrated by means of sodic hydroxide, using metiiyl 

 orange as an indicator, and was found to require 0.09 cubic centimeter 

 of a decinormal solution for neutralization. The probable error of 

 the end point was not greater than one drop, or one ten-thousandth 

 part of the sodic carbonate present. 



Grams. 



Sodic carbonate weighed out = 1.2988 



" " added in titration = 0.0005 



" " required (in vacuum) = 1.2993 



Cupric sulphate taken (CuSOi . 5 H2O) = 3.06006 



Copper found in " « = .77886 



Per cent of SO4 in CuSOi . 5 H2O = 38.439 

 Atomic weight of copper : 



NaaCOs : Cu = 106.108 : 63.606 



In transferring the sodic sulphate from the evaporating dish to the 

 capacious platinum crucible in which it was to be weighed, the pre- 

 caution of washing with water which liad been thoroughly boiled was 

 absolutely essential to prevent the possibility of subsequent mechan- 

 ical loss during evaporation. At best, the concentration of a solution 

 in an open crucible over the steam bath is an unsatisfactory operation, 

 and accordingly for the third series a new method was devised. The 

 water left the sodic sulphate very slowly ; but in the end it evaporated 

 so completely that after covering there was a scarcely audible decrepi- 

 tatiim on heating the crucible to redness. The pure white sodic 

 sulphate was finally fused at a bright red heat. During this last opera- 

 tion the salt occasionally became tinged with a slightly yellowish hue, 

 due probably to a trace of iron from the platinum vessels ; but the 

 purest specimens remained wholly colorless. The salt lost only one 



