68 J. A. EWING AND J. G. MACGREGOR ON THE 
supposing that each salt dissolved in the whole of the water, independently of 
the presence of the other salt, we could find first the density, and then the resist- 
ance of the two hypothetical solutions thus formed, by means of the curves on 
figs. 1, 2, and 3. We might expect that the conductivity of the mixture 
would be the sum of the two conductivities thus obtained. We calculated what 
would be the conductivity of several of the mixtures, if this supposition held 
good, but found that they did not agree with the experimental results, the 
amount of difference varying from 10 to 20 per cent. This difference is far too 
great to be explained as an error of experiment, and we may therefore say that 
the above hypothesis is erroneous, or at least imperfect. 
Since these experiments were made, we have found that the subject of 
mixed solutions had previously been touched upon by Paatzow (Pogg. Ann., 
CXxxvi., 1869), who noticed that in the case of the few solutions he examined, 
the resistance of the mixture was less than the mean of those of its com- 
ponents, as we also have found to be the case. 
The next salt tested was sulphate of potash, K,SO,, a salt which seems 
never to have been examined before. We chose it with a view to mixing its 
solutions with those of sulphate of copper and sulphate of zinc, because it forms 
a double salt with each of these. But we were unable to test these mixtures 
owing to the extreme insolubility of the double salt, which crystallised out in 
both cases shortly after the mixtures were made. This took place even when 
the component solutions were very weak. However, sulphate of potash itself 
turned out to be a most interesting salt, on account of its remarkably high con- 
ductivity. With the same amount of salt in solution, its resistance is about three 
times less than that of zincic or cupric sulphates. In spite of its sparingly 
soluble character, a saturated solution has a very much higher conductivity than 
any solution of the other two salts, or even any mixture of them. The following 
table shows this :-— 
SULPHATE oF PorasH. 







; Resistance in Specific ; Resistance in Specific 
ee of salt Density at | second tube Peeiuce at Havoion salt Density at | second tube beatae at 
(0) water in 10° Cc at 10° C 10°C to water in 10° G at 10° C 10° 
solution. ; cy me solution. ; =) “ 
B. A. Units. | B. A. Units. B. A. Units. | B. A. Units. 
1 to 100 1:0082 6860 118°7 lto 20 1:0394 1800 ol2 
Ig XO 1:0103 5540 95:9 Le aG 1:0482 1480 25°6 
1,, 40 1:0201 3150 54:5 ela 1:0697 1100 19:0 | 
Wy ail) 1:0265 2420 41°9 1 ,, 9488 ) | 
10801 960 16°6 | 
1s) 125 1a 130819 2070 358 Saturated | J | 




This table is given as a curve in fig. 3, the mode of representation being 
