744 PLUCKER ON THE DETERMINATION OF THE 



46. The deportment of the ferrocyanogen salts is most re- 

 markable. In the 46th paragraph of my memoh- upon the action 

 of the magnet upon vapours and liquids, I have denoted both of 

 them as diamagnetic ; which Faraday, by allowing crystals of the 

 two salts to oscillate, had also found them to be. The fact is un- 

 doubted in the case of the ferrocyanide, though I must withdraw 

 my assertion, that a saturated solution of this salt is more strongly 

 diamagnetic than water. It was based upon the observed mo- 

 tion which this solution, contained in a watch-glass and placed 

 upon the approximated poles of a magnet, assumes on closing 

 the circuit ; an indefinite mode of estimation, which, probably 

 on account of the slight transparence, preponderated in favour 

 of the solution of the ferrocyanide. But the case is quite 

 different as regards the assertion that the ferridcyanide is 

 diamagnetic; on the contrary, it is decidedly magnetic. My 

 former statement refers to a period at which I was unacquainted 

 with the results contained in my memoir on the repulsion of 

 the optic axes of crystals by the poles of a magnet, and arose from 

 giving a false interpretation to a correct observation. 



In the first series of experiments, a tolerably concentrated 

 solution of the ferridcyanide, obtained from a chemist's shop, was 

 found to be decidedly magnetic. Its magnetic attraction amounted 

 to 164, placing the diamagnetic repulsion of water at 100. To 

 control this result, in the second series of experiments I exa- 

 mined crystals of the ferridcyanide, procured from a chemical 

 manufactory ; these were finely powdered, and the watch-glass 

 then filled with them. They were strongly magnetic ; for the 

 same weight, they were 7*4 times as strongly magnetically at- 

 tracted as water was diamagnetically repulsed. I immediately 

 supposed that the contrary assertion might have arisen from a 

 magnetic axial action. To decide this point, I selected two cry- 

 stals, one a small one, which Prof. Bergemann gave me as che- 

 mically pure ; and a larger one, which I had long had in my 

 possession, and which came from the Schonebeck manufactory. 

 Both crystals, when suspended so as to oscillate horizontally be- 

 tween the approximated apices of the poles, on closing the circuit 

 flew to the neai est of the apices of the poles ; this occurred even 

 when the current was excited by a single cell instead of ten. 

 But when the crystals, by shortening or elongating the silkworm- 

 thread by which they were suspended, were sUghtly raised above 



