178 Mr. Faraday on the general Magnetic Relations 
fine platinum wires, and then cooled to a very low degree by the 
evaporation of sulphurous acid. They were then brought 
close to one end of one of the needles of a delicate astatic ar- 
rangement, and the magnetic state judged of by the absence or 
presence of attractive ferces. ‘The whole apparatus was in an 
atmosphere of about 25° Fahr.: the pieces of metal when 
tried were always far below the freezing-point of mercury, and 
as judged, generally at from 60° to 70° Fahr. below zero. 
The metals tried were, 
Arsenic, Lead, 
Antimony, Mercury, 
Bismuth, Palladium, 
Cadmium, Platinum, 
Cobalt, Silver, 
Chromium, Tin, 
Copper, Zinc, 
Gold, 
and also Plumbago; but in none of these cases could I obtain 
the least indication of magnetism. 
Cobalt and chromium are said to be both magnetic metals. 
I cannot find that either of them is so, in its pure state, at 
any temperatures. When the property was present in speci- 
mens supposed to be pure, I have traced it to iron or nickel. 
The step which we can make downwards in temperature 
is, however, so small as compared to the changes we can pro- 
duce in the opposite direction, that negative results of the 
kind here stated could scarcely be allowed to have much weight 
in deciding the question under examination, although, unfor- 
tunately, they cut off all but two metals from actual compari- 
son. Still, as the only experimental course left open, I pro- 
ceeded to compare, roughly, iron and nickel with respect to 
the points of temperature at which they ceased to be magnetic. 
In this respect iron is well known*. It loses all magnetic pro- 
perties at an orange heat, and is then, to a magnet, just like a 
piece of copper, silver, or any other unmagnetic metal. It does 
not intercept the magnetic influence between a magnet and 
a piece of cold iron or a needle. If moved across magnetic 
curves, a magneto-electric current is produced within it exactly 
as in other cases. The point at which iron loses and gains 
its magnetic force appears to be very definite, for the power 
comes on suddenly and fully in small masses by a’small di- 
minution of temperature; and as suddenly disappears upon 
a small elevation, at that degree. 
With nickel I found, as I expected, that the point at which 
it lost its magnetic relations was very much lower than with 
* See Barlow on the Magnetic Condition of Hot Iron. Phil. Trans. 
1822, p. 117, &c. 
