mutual induction of the primary on the secondary of a solenoid arising from the presence of a liquid in the solenoid against known small inductances* Thus, if the sum of the inductances be reduced to zero, as shown by the galvanometer in the secondary giving no deflection, the balance will be disturbed to the extent AnrkM, due to the insertion of a liquid into the solenoid whose coefficient of magnetisation is Jc, and the galvanometer in the secondary circuit will give a deflection when the commutator revolves. An adjustable inductance is then reduced by a known amount, m, till the deflection disappears; so that we get
4 irkM.= m .'. k = m / 4 7 r M ,
where m and M are quantities easily calculated.
Since the formula does not contain either the rate of the rotation of the commutator nor the value of the primary current, no particular precautions are necessary to keep these quantities constant.
In all the determinations the magnetising force was varied from 1 to 9 centigram units, and in no case was there any variation in k. The densities of the salt§ in solution were also varied over large ranges, and showed that the coefficient of magnetisation for ferric salts in solution depended only on the quantity of iron per c.c. that was present, giving the formula 107& = 2660 W —
for ferric salts, where W is the weight of iron per c.c., the quantity — 7‘7 arising from the diamagnetism of the water of solution. A similar result was obtained for ferrous salts, the corresponding formula being 107& = 2060 W —7‘7, the temperature being 10° C.
The following table shows the coefficient of magnetisation for the different salts examined, w being the weight of the salt per c.c. of the
Magnetisation of Liquids. 187 Fe2Cl6 ............. 916 w—7*7 Fe2(S04)3 .... 745 Fe2(N03)6. . . . 615w-7-7 FeCl2.... 908 7-7 FeS04-------- 749 w - 7-7
The effect of temperature was also estimated, the results of the experiments being shown by means of a curve (fig. 1), the x ordinates of which denote the temperature, and the y ordinates are proportional to the coefficient of magnetisation, a length corresponding to 50 being subtracted from each for convenience of representation
