MAGNETIC CHARACTERS OF METALS, &c. 657 
43. The metallic salts that I have examined, 
are some of those most frequent in common use. 
The salts of iron were the sulphate, the yellow 
and the red ferrocyanuret of potassium, also 
Prussian blue. ‘These, with the exception of the 
yellow prussiate, are magnetic; the sulphate of 
iron in the highest degree of any of them. It 
is somewhat remarkable that the two kinds of 
prussiate of potash, where the proportions of iron 
are so nearly alike, (yellow 15 per cent, red 16 
per cent,) should display such a material differ- 
ence in their magnetic characters. And it is still 
more singular that Prussian blue, which contains 
more than 45 per cent of iron, is less magnetic 
than the red prussiate of potash. The sulphate 
contains about 33 per cent of iron, and is the 
most magnetic of the whole. 
44, Pure sulphate of copper shows no magnetic 
action, but that of commerce is highly magnetic, 
being, as I have ascertained, adulterated with 
sulphate of iron. Hence, the magnet would be a 
good and speedy test for the quality of the com- 
mercial salt. 
45. The following salts appear to be perfectly 
neutral to magnetic forces :—Common salt, salt- 
