THE PHYSICAL PROPERTIES OF AQUEOUS SOLUTIONS. 
107 
combination as a sufficient and possibly the only cause of ionisation is dealt with, to 
some extent, in the former paper (see the revised version published in the ‘ Zeitschrift 
f. Pliys. Chem.,’ loc. cit.) and has also recently been considered by Lowry (“ An 
Application to Electrolytes of the Hydrate Theory of Solution,” ‘ Trans. Farad. 
Soc.,’ I., 197, 1905). 
Part II. —Experimental Determinations. 
(a) Density and Viscosity of NaCl Solutions at 18° C.—The material used for the 
earlier determinations was purest fused NaCl (obtained from Baird and Tatlock). 
A stock solution of a strength of 21’673 per cent, was prepared, the density of which 
at 15° C. was found to be U1638. Mendeleef (‘Principles of Chemistry,’ eel. 1905, 
vol. 1, p. 451) gives for the density of NaCl solutions at 15° C. the formula 
S 15 = 9991-6 + 7U17P + 0-214P- (water - 10,000). 
This formula gives for 21'673 per cent, the density 1T635. 
A further sample of material was purified by precipitation with HC1, recrystallised 
and fusefi (specially prepared by Merck). A stock solution of 20TOO per cent, was 
made from this sample, the density of which at 15° C. was IT502. Mendeleef’ s 
formula gives IT501. No substantial difference between these solutions manifested 
itself, but for any range of values the same solution was used. 
The densities were determined in all cases in duplicate, by means of a pair of 
pyknometers, each having a capacity of about 100 cub. centims. The viscosities were 
determined for the most part by means of the simpler type of viscosimeter described 
in the former paper. The results from this instrument are indicated in the diagram 
by black circles. A few determinations which were made with another instrument 
are indicated by open circles. 
The viscosities were calculated from a differential formula derived from the formula 
y = pt(A-B/t 2 ). 
By differentiating we have 
Sy = — S p + p ^A + St. 
For water, y is = 0'010514, p ls = 0'99866 ; and for the instrument chiefly used, 
A = 0'000017703, B = 0 - 28294, wi*th a small correction for variations when the time 
of flow of water at 18° C. varied from 621 seconds. 
These constants were determined by the time of flow of water at various tempera¬ 
tures, as derived from Thorpe and Bodgers’ determinations (‘ Phil. Trans.,’ A, 
vol. 185, p. 397, 1894), by means of the formula given in a former paper (Bousfield 
and Lowry, ‘ Boy. Soc. Proc.,’ vol. 71, p. 47, 1902), viz. 
= rj t [ 1 + 0-0251 (t—18) + 0'000115 (t—18) 2 ]. 
p 2 
