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EXPERIMENTAL AND THEORETICAL.
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the character of the foundry whence it is procured, and the consequence is that butvery few brass compass boxes, that are in common use, are entirely free from mag-netic action.
42. The next alloy of importance that I have examined is German silver, in whichnickel is one of the principal constituents. In the best kind of German silver (con-stituted of copper eight parts, nickel six, and zinc three) a slight magnetic action hasbeen detected, but in the inferior kinds of German silver, into which only about threeparts of nickel enter, I have not detected any magnetic action whatever. Hence theMagnetism of that portion of nickel is obviously neutralized in that particular alloy.
43. The metallic salts that I have examined are some of those most frequent incommon use. The salts of iron were the sulphate, the yellow, and the red ferrocy-anuret of potassium, also Prussian blue. These, with the exception of the yellowprussiate, 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 pro-portions of iron are nearly alike (yellow 15 per cent, red 16 per cent.) should displaysuch a material difference in their magnetic characters; and it is still more singularthat Prussian blue, which contains more than 45 per cent, of iron, is less magneticthan 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 much of that of com-merce is highly magnetic, being, as I have ascertained, adulterated with sulphate ofiron. Hence the magnet would be a good and speedy test for ascertaining the qualityof the commercial salt.
45. The following salts appear to be perfectly neutral to magnetic forces:—Com-mon salt, saltpetre, borax, sulphate of magnesia, sulphate of soda, sulphate of potash,and carbonate of soda.
46. Thus far I have attempted to contribute to the list of facts previously known,and to correct some errors which, probably on account of the insufficient modes of in-vestigation, have crept into this particular branch of science. It is possible also, Ithink, that some of the facts which have now been pointed out may be an inducementto employ the magnet more extensively than hitherto in the laboratory of thechemist.
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