On the Magnet, by William Gilbert

Chap. xxxvii. Use of a Loadstone as it affects iron.

B y magnetick coition we test iron ore in a blacksmith’s forge. It is burnt, broken in pieces, washed and dried, in which way it lays down its alien humours; in the bits collected from the washing is placed a loadstone, which attracts the iron dust to itself; this, being brushed off with feathers, is received in a crucible, and the loadstone is again placed in the bits collected from the washing, and the dust wiped off, as long as any remains which it will attract to itself. This is then heated in the crucible along with sal nitri187 until it is liquid, and from this a small mass of iron is cast. But if the loadstone draws the dust to itself quickly and readily, we conjecture that the iron ore is rich; if slowly, poor; if it seems altogether to reject it, there is very little iron in it or none at all. In like manner iron dust can be separated from another metal. Many tricks there are also, when iron is secretly applied to lighter bodies, and, being attracted by the motion of a loadstone which is kept out of sight, causes movements which are amazing to those who do not know the cause. Very many such indeed every ingenious mechanician will perform by sleight of hand, as if by incantations and jugglery188.

187 Page 109, line 11. Page 109, line 13. halinitro.— Either native carbonate of soda or native carbonate of potash might be meant, but not saltpetre. Scaliger, in his De Subtilitate ad Cardanum (Lutet., 1557, p. 164), Exercitatio CIII., 15, under the title, Nitrum non est Salpetræ, says: “More tuo te, tuaque confundis. Salpetræ inter salis fossilis ponis hîc. Mox Halinitrum inter salis, & nitri naturam, speciem obtinere.”

Sal nitrum is salt which is boiled out of the earth, especially fat earth, as in stables, or any place of excrements.” (A Chymicall Dictionary explaining Hard Places and Words met withall in the Writings of Paracelsus . . ., Lond., 1650.)

188 Page 109, line 20. Page 109, line 23. arte ioculatoriâ.— Edition 1628, joculatoriâ; edition 1633, jaculatoriâ.


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