42 PHILOSOPHICAL TRANSACTIONS. [aNNO 1776. 



through it, in order to compare the effect of electricity on it with what hap- 

 pened to the platina. He found, by looking at the outside, somewhat of the 

 same appearance, of being melted. By cutting this tube in small hits, he could 

 easily push out the filings with a pin, which he could not do in the other case 

 but with great force. The filings stuck together, as the particles of platina had 

 done ; but with less force. 



By this experiment it should seem as if platina, wliich hitherto could never 

 be melted by common fire by itself, but only in the focus of a very strong 

 burning glass, were equally fusible, if not more so than iron, by electrical fire. 

 The particles of platina taken out of the aforesaid tube, had got a remarkably 

 stronger magnetical force, being attracted by a loadstone at a greater distance, 

 and turning their poles more briskly on the water than before, though the 

 whole cylinder of these particles, still inclosed in the tube, gave no signs of 

 having acquired polarity. Thus it appears, that common fire diminishes the 

 magnetical virtue of platina, and that electrical fire increases it. Platina mixed 

 with lead was put on an ordinary cupel in a docimastic furnace strongly heated. 

 When the metal came to a solid state, it was a fiat rough lump, much heavier 

 than the crude platina. He put fresh lead to it, and cupelled it again as before.; 

 He repeated it 10 times, when he obtained a large lump, somewhat less fiat, 

 pretty smooth, but not bright ; of about the same weight as after the first 

 cupellation. This lump did not give the least sign of magnetism, and even 

 would not receive any by being applied to strong magnetical bars ; and the 

 substance was very brittle, nearly of the same colour as platina, and took a fine 

 polish. 



Though a piece of soft iron attracts the 2 poles of a compass indiscrimi- 

 nately, and is incapable of acquiring polarity itself, yet Dr. I. has never been 

 able to separate a single particle of the softest iron, even when he separated it 

 carefully with a flint, or other body containing no steel or iron, without its 

 o-iving evident signs of 1 distinct poles when floating on water, nay even on 

 paper. Dr. I. could also never find iron filings of ever so soft a substance, but 

 each particle separately had evidently 2 poles. Such iron filings mixed with bees 

 wax, as mucli as is sufficient to keep them together, got a strong polarity by 

 being touched with magnetical bars, and had all the qualities of a magnet : the 

 mass is easily cut with a warm knife, and is very convenient for magnetical 

 experiments, such as Dr. Knight made with similar loadstones made of pounded 

 magnets. He found also, that each part of those granulated iron ores of 

 Sweden, which are placed among the minerae ferri retractoriae, separated iron 

 from stone, and had 2, distant poles, and that a piece of the ore itself became a 

 tolerable magnet by being touched with the bars. 



