572 PLUCKEB OX THE ACTION OF THE MAGNET 



acid, hydrochloric acid, solution of ammonia, sulphuret of car- 

 bon, fatty and volatile oils, wax in a state of fusion, saturated 

 solutions of nitrate of bismuth, chloride of sodium, nitre, sul- 

 phate of soda, and especially ferrocyanide of potassium, milk and 

 blood. 



45. Mercury placed in the watch-glass was found to be indif- 

 ferent to the magnet, which at once gave rise to the supposition 

 that this depended upon its slight amount of mobility ; and that 

 this again might be explained by the fact, that it did not moisten 

 the surface of the glass. But when the mercury was placed in 

 a small brass cup which had been recently amalgamated, it ex- 

 hibited its diamagnetic reaction distinctly. 



46. The diamagnetic reaction of ferrocyanide of potassium, 

 which Dr. Faraday also observed on allowing the crystals of this 

 salt to oscillate, was least to be anticipated. A saturated solution 

 of the ferrocyanide in water was more powerfully diamagnetic 

 than pure water. Hence it was at least to be anticipated, that 

 together with the large amount of iron it contained, unusually 

 powerful diamagnetic matters must be present in the double 

 salt, and that the same would be found to exist in the cyanide 

 of potassium, which, when combined with cyanide of iron, 

 would overpower the magnetism of the latter, and have rendered 

 it decidedly diamagnetic. But cyanide of potassium, when dis- 

 solved in water, did not appear to render it more diamagnetic. 



47. The preceding method of observation appeared to me 

 worthy of further application for two reasons, — on the one 

 hand, for enabling us to detect the presence of even the slightest 

 trace of magnetism or diamagnetism in any liquid ; and on the 

 other, for measuring the intensity of both. With regard to 

 the first point, it might be expected that the action of the 

 magnet upon the liquid would increase considerably, when the 

 latter, instead of being put into a watch-glass, was placed upon 

 a thin lamina of mica lying upon the two halves of the keeper 

 (C), a short distance only apart. A strongly diamagnetic liquid 

 under these circumstances formed two double elevated ridges, 

 several milUmetres in height, which following exactly the two 

 semicircular edges, ascended highest at that part where the 

 distance between tlie two halves of the keeper was least. 



The action of the magnet was strongest when the same two 

 halves of the keeper were applied in such a manner that as 

 before they were about 3 millims. apart, with their planed 



