482 DENSITY OF SOLUTIONS 
the calculation of the percentages of anhydrous salt in the 
various solutions, the atomic weights given in Clarke’s “ Con- 
stants of Nature” were employed. 
All the density determinations were made for 20° C. by means 
of a specific-gravity bottle of about 50 cu. cm. capacity. This 
was light, of thin, hard glass, and not easily deformable, and was 
provided with an accurately-fitting, perforated ground glass 
stopper. When a determination was to be made this bottle was 
filled with the solution slightly below 20° and, held by its neck, 
was plunged, up to the neck, in a bath of water kept constantly 
stirred and at a temperature of 20° C. The solution, being in- 
creased in volume by being thus raised in temperature, oozed 
out through the perforation in the stopper, whence it was re- 
moved by means of a bit of lintless blotting-paper. When the 
oozing ceased the solution had acquired the temperature of the 
bath, and the bottle containing it was taken out and wiped dry 
with a clean, lintless rag,—care being taken to exert very little 
pressure and to avoid direct contact of the hand with the glass. 
These precautions were necessary to prevent deformation and 
heating of the bottle and consequent expulsion of the liquid 
through the perforation in the stopper. The temperature of 20° 
C. was chosen as it is some degrees above the usual laboratory 
temperature, so that, when the solution is removed from the bath, 
it contracts, and thus loss from running over and evaporation is 
avoided. 
As the result of these experiments, it was found that the con- 
centration and density of solutions containing not more than 
2.5 per cent. of anhydrous Cobalt Sulphate are connected by the 
equation— 
Dx = .99827* + .01116 p. © 
The following table contains, in the first column, the percent- 
ages of anhydrous salt in solution; in the second column, the 
corresponding densities observed at 20°; in the third column, the 
densities calculated from the above formula, and, in the fourth 
*The density of water at 20° C., according to Volkmann, Wied. Ann,, XIV (1881), p. 260. 
