66 J. A. EWING AND J. G. MACGREGOR ON THE 
inclined than in the case of sulphate of zinc, tan @ (see fig. on page 62) being 
in this case 23, while 4, the intercept on the axis of y, is now smaller, being only 
12:2. Substituting these values in the general equation given before, and find- 
ing ¢ from a known point, we have 
: 27 
y = 122 + 23% + 
a 
Curiously, ¢ is here very nearly the same as for sulphate of zinc. If we write, 
as before, D for the density, and R for the specific resistance at 10° C., we have 
2-7 
RS oo) eee ee 
jee 
The resistances given by this formula are compared with experimental ones in 
the following table :— 

Specific Resistance. | Specific Resistance. 
| —————————E—~ 
Onsered Caleiaed oy} Obaarved ee 
164°4 : ; ; 174:2 35°0 : : : 34°9 
134°8 : : ‘ 137-7 34°1 : ‘ : 34°3 
98°7 : : : 99-1 31:7 : : 32:1 
59:0 : : é 57:0 30°6 : : : 31:2 
47:3 : ‘ ; 46°7 29°3 : t : 30°0 
S81 & 37-9 | 

The remarks which follow the similar table for sulphate of zinc (page 64) apply 
to this table also. 
The next part of our experiments consisted in testing the resistance of 
mixtures of the above sulphates.. We selected three solutions of sulphate of 
copper: one pretty dense (2875 to 1), which we may call A; the next, 1 to 
7, B; and the third, a very weak one, 1 to 20,C. Five solutions of sulphate of 
zinc were selected : L, saturated ; M, that of maximum conductivity (735 to 1) ; 
N, one whose resistance is very nearly equal to that of the saturated solu- 
tion, and the constitution of which is ‘337 to 1. This solution corresponds (in 
density) pretty nearly to the solution of sulphate of copper, A. Also, O corre- 
sponding to B—constitution, 1 in 7; and P corresponding to C—constitution, 
1 in 20. Each of the zinc solutions was mixed with each of the copper ones, 
equal volumes of the two solutions being in all cases taken. The following 
table shows the resistance of each solution separately, and the resistances 
of the mixtures :— 
