394 Mr. H. Tomlinson on the Villari 



The effect on the conductivity, even after heating to and at 

 the temperature of 100° C, was nothing. A drop of water 

 added to the double chloride before adding it to the stannic 

 chloride was powerless to promote conductivity. 



The fact, then, is that neither the crystalline hydrate, nor 

 sulphydrate, nor moist nor dry sodium chloride, nor the moist 

 nor dry ammonium stannic chloride have any influence on the 

 conductivity of the stannic chloride. The solids remain out- 

 side the sphere of action : and, like the drop of strong hydro- 

 chloric acid as long as it was unmixed with the stannic 

 chloride, and like the perfectly dissolved chloroform and the 

 gases chlorine and sulphuretted hydrogen, having produced 

 no effect on the chemical homogeneity of the stannic chloride, 

 which remains stannic chloride, they were without influence 

 on its electrical conductivity. 



[To be continued.] 



XLIII. The Villari Critical Points of Nickel and Iron*. 

 By Herbert Tomlinson, F.R.S4 



WE owe to Villari the discovery that the magnetic per- 

 meability of iron is increased by longitudinal traction 

 provided that the magnetizing force does not exceed a certain 

 limit, but beyond this limit the traction produces decrease of 

 permeability so that for a certain value of magnetizing force, 

 known as the Villari's Critical Point, longitudinal traction has 

 no effect in either direction. Several experimenters have 

 verified and extended Villari's discovery, notably Sir William 

 Thomson and Prof. Ewing, but, as far as the author is aware, 

 no observer has been as yet able to find a similar critical 

 point for nickel. If, however, we confine ourselves to the 

 consideration of the temporary magnetization J, aVillari critical 

 point in nickel can be detected with comparative ease. In the 

 present investigation the ballistic method of observation has 

 been employed, the arrangements of which have been already 

 described §. The nickel wire used contains nearly 98 per 

 cent, of nickel and only 0*7 per cent, of iron ; the iron wire 

 is also, judging from its small specific resistance, nearly pure. 

 The mode of conducting the experiments may be illustrated 

 by the aid of fig. 1 ; this figure refers to a piece of well- 



* Communicated by the Physical Society : read March 21, 1890. 



t The author begs to acknowledge with thanks the assistance which he 

 has received in this investigation from the Elizabeth Thompson Science 

 Fund, U.S.A. 



\ The magnetization which disappears on the removal of the magneti- 

 zing force. 



§ Phil. Mag. xxv. p. 372. 



