and Maximum of Magnetism of Nickel and Cobalt, 325 



again read with the needle on the other side of the zero-point. 

 The pressure of outside duties at present precludes me from 

 putting this in practice. But the results which I have obtained, 

 though probably influenced in the higher magnetizing-forces by 

 this heating, are still so novel that they must possess value not- 

 withstanding this defect ; for they contain the only experiments 

 yet made on the permeability of cobalt at ordinary temperatures, 

 and of iron, nickel, and cobalt at high temperatures. 



The rings of nickel and cobalt which I have used in the expe- 

 riments of this paper were all turned from buttons of metal ob- 

 tained by fusing under glass in a French crucible, it having 

 been found that a Hessian crucible was very much attacked by 

 the metal. The crucibles were in the fire three or four hours, 

 and when taken out were very soft from the intense heat. As 

 soon as taken out, the outside of the crucible was wet with water, 

 so as to cool the metal rapidly and prevent crystallization ; but 

 even then the cooling inside went on very slowly. As the phy- 

 sical and chemical properties of these metals exercise great in- 

 fluence on their magnetic properties, I will give them briefly. A 

 piece of nickel before melting was dissolved in HC1 ; it gave no 

 precipitate with H 2 S, and there were no indications of either 

 iron or cobalt. A solution of the cobalt gave no precipitate 

 with H 2 S, but contained small traces of iron and nickel. After 

 melting the metals no tests have been made up to the present 

 time ; but it is to be expected that the metals absorbed some 

 impurities from the crucibles. They probably did not contain 

 any carbon. One button of each metal was obtained, from each 

 of which two rings were turned. The cobalt was quite hard, 

 but turned well in the lathe, long shavings of metal coming off 

 and leaving the metal beautifully polished. The metal was 

 slightly malleable, but finally broke with a fine granular frac- 

 ture. The rings when made were slightly sonorous when struck ; 

 and the colour was of a brilliant white slightly inclined to steel- 

 colour, but a little more red than steel. The nickel was about 

 as hard as wrought iron, and was tough and difficult to turn in 

 the lathe, a constant application of oil being necessary, and the 

 turned surface was left very rough ; the metal was quite mal- 

 leable, but would become hard, and finally fly apart when 

 pounded down thin if not annealed. When the rings were 

 struck, they gave a dead sound as if made of copper. In both 

 cases the specific gravity was Considerably higher than that gene- 

 rally given for cast metal ; but it may be that the metal to which 

 they refer contained carbon, in which case it would be more 

 easily melted. There is great liability to error in taking the 

 specific gravity of these metals, because they contract so much 

 on cooling, and unless this is carried on rapidly crystals may 



