SOLUTIONS OF CERTAIN HYDROXIDES—MACGREGOR., 369 
gravities are referred. But on repeating some of his own calcu- 
lations I found their results to be consistent only with the sup- 
position that his standard was water at the temperature at: 
which the specific gravities of his solutions were determined. 
In all my calculations I have taken for the atomic weights of 
the elements the values given by Clarke,* and for the densities. 
of water at different temperatures, the values given by Volk- 
mann,* as quoted in both cases by Landolt and Bornstein.{ 
Sopium HyproxiprE.—NaOH. 
Thomsen’s data give the following table. The temperature 
of the solutions examined by him was about 18°C. The head- 
ings of the various columns will sufficiently explain their contents, 
except in the case of the last, which to avoid circumlocution is 
headed expansion, Expansion here means the excess of the 
volume of one gramme of a solution over the volume which at the 
same temperature and in the free state, the solvent water in one 
gramme of the solution would have. Possibly I should state 
also that by “ Percentage of a substance in solution,” I mean 
the mass of the substance contained in 100 units of mass of the 
solution. 
Volume of] |Volume at 18°C. 
Percentage of 2 ee at grm. of solu- of solvent fs ee ie 
ae ee Cas cu. ane ae bast be Pe sing (Ga cm.) 
¥ Rar acd (cu. cm.) 
1.1001 1.0111 0.9891 0.9903 —0.0012 
2.1762 1.0232 0.9773 0.9795 —0.0022 
4.2597 1.0472 0.9549 0.9587 —0,.0038 
6.9035 1.0768 0.9287 0.9322 —0.0035 
12.9154 1.1435 0.8745 0.8720 +0.0025 
22.8762 1.2559 0.7962 0.7723 + 0.02389 
The fifth column exhibits Thomsen’s result that for dilute 
solutions of this hydroxide, the expansion is negative; 7. e., the 
* Constants of Nature, V., Smithsonian Institution, Washington, 1882. 
+ Wiedemann’s Annalen, Bd. XIV (1881), p. 260, 
} Physikalisch-Chemische Iabellen, Berlin, 1883. 
