480

SCIENTIFIC RESEARCHES,

(TWENTY-SIXTH MEMOIR.)

30. Silver articles for domestic purposes, such as spoons, prongs, fruit knives, &c.were, in many specimens, found to be much more magnetic than any of the silvercoins that I have examined. I have tested several sets of silver tea spoons, belong-ing to neighbouring families, and, with the exception of one half-dozen of Scotchspoons, of very old date, all of them have displayed high magnetic powers, though ofvery different degrees in different sets. But what is very remarkable, if one indi-vidual spoon was found to be highly magnetic, the whole of that particular set,whether it consisted of half-a-dozen or a dozen spoons, were highly magnetic also.And generally, whatever might he the magnetic condition of any individual spoon,the whole number of the set to which that spoon belonged were magnetic alike, ornearly so. Hence if the quantity of magnetic action of any individual spoon wereto be denoted by q, and the number of spoons in the set denoted by n, the sum total ofmagnetic action in that set of spoons would be nq nearly. Of course this reasoningapplies only to individual sets of spoons which are of uniform make, composition,and structure of metal. It appears also, as far as my experience has extended, thatthe same mode of reasoning would give the sum total of all the magnetic action thatany individual coinage would display. Suppose, for instance, the Magnetism dis-played by a half-crown piece were to he taken as the unit of quantity equal to q ,then the number of pieces being n, the sum total of Magnetism which the whole ofthat coinage would display would be n q nearly, and similarly for any other indi-vidual coinage of silver.

31. The difference of magnetic action displayed in the silver coinage and domesticarticles of that metal (29-30), led to the supposition that minute portions of ironmight accidently have got introduced to the alloys, whilst in a state of fusion, whichhad some probability in its favour, from the fact that the metal for silver coinage isfused in cast iron pots,* and therefore liable to take up portions of those vessels;but on the other hand, if that were always the practice, it would lead to the infer-ence that in all the silver coins the iron would be nearly in the same proportion, an dthe extent of magnetic action almost the same in all; whereas, by the tests alreadydescribed, this is not the case.

32. The current silver coinage of William and Mary became so base that, in theyear 1694, it was all called in and a new coinage issued. From this fact it occurredto me that there was a possibility, at least, that the high degree of magnetic actiondisplayed by the half-crown of 1691 (29), was owing to an undue proportion of cop-per, or of some other inferior metal. This idea led to the selection of a shilling, inwhich scarcely a trace of Magnetism could be detected, for fusion, with an additionalportion of copper, also non-magnetic, having been obtained by the electro-type process.These, together with a piece of pure silver, were fused in an earthenware crucible, and

* Ure’s Dictionary of Arts and Manufactures, also Brand’s Chemistry, 1037.