138 
MESSRS. W. R. BOUSFIELD AND C. ELSPETH BOUSFIELD 
temperature will be taken, because certain other data for NaCl at this temperature 
are available which are necessary for the complete explanation of the phenomena. 
Let 
0 = (E + H)v-Hw, 
^ = (E + H) s—Hs w , 
where 
w = specific volume of pure water at the given temperature, 
s w — specific heat of pure water at the same temperature, and 
IL = he, the weight of water in which E grammes of the solute are 
dissolved. The symbol H is more convenient than he in some 
cases. 
The quantities 0 and \fs correspond to those between which Thomsen found a 
notable parallelism. 0 is sometimes called the “ molecular volume ” of the solute—a 
somewhat misleading term, especially when <p happens to be a negative quantity. 
It is really the difference between the volume of the solution containing the gramme 
molecular weight E of the solute and the volume of the original water. \p- is the 
corresponding function substituting specific heat for specific volume, and is described 
by Thomsen as the difference between the “ caloric equivalent ” of the solution and 
that of the water. It should be noted that 
0 = E w- x , 
and 
\Jr —- E.s —H As. 
In Table XIII. are set out the values of 0 and - 0 - for NaCl solutions at 20 ° C. and 
also the values of H As. Fig. 4 shows the values of 0 - plotted on the 0 values and 
also the values of H As plotted on the 0 values. 
Table XIII.—NaCl Solutions at 20" C. 
No. of 
solution. 
1J - 
H. 
0- 
0. 
H As. 
I. 
25•000 
175-38 
38-06 
21-01 
154-5 
II. 
18-945 
250-12 
17-27 
20-23 
183-8 
III. 
13-519 
373-98 
4-59 
19-40 
215-1 
IV. 
10-005 
525-87 
- 18-30 
18-82 
236-1 
V. 
5 ■ 625 
980-83 
- 34-46 
18-12 
262-9 
VI. 
2-8669 
1980-7 
-51-61 
17-45 
287-2 
VII. 
1-4476 
3979-9 
-62-84 
17-05 
302-5 
Both appear to be good straight lines, but they cannot both be absolutely straight 
unless there is a straight-line law between s and y. This is nearly but not quite the 
