40 PHILOSOPHICAL TRANSACTIONS. [aNNO 1776. 



within the mouth of the phial, clapping his hand fast to the orifice of the phial, 

 the loose part of the elastic bottle, so that the nitrous air, rising from the phial, 

 must take its course through the tube. When the whole tube is filled with red 

 fumes, he takes it out, and shuts the two extremities with his two fore-fingers. 

 He then puts one end of the tube in a vessel with quicksilver, and withdraws 

 both fingers for an instant to make the colunm of quicksilver rise within the 

 tube. He applies immediately both fingers ; and holding the tube nearly in a 

 horizontal direction, so that the extremity where the quicksilver is may be rather 

 the highest, he opens and shuts at the same time both extremities, so that the 

 column of quicksilver gradually advances towards the middle. Tlie quicksilver 

 advancing towards the middle, as much common air follows the quicksilver as it 

 forces out nitrous air from the other extremity. As soon as the column of 

 quicksilver is in the middle, he keeps both extremities well shut with his fingers, 

 and moving the tube in various ways, he forces the two airs to come into mutual 

 contact, and to mix intimately together. He then puts one extremity into a 

 vessel filled with quicksilver, withdraws the finger from within the quicksilver, 

 and observes to what height the quicksilver rises. It requires some practice to 

 perform this experiment with dexterity. 



Some time ago Dr. I. got some ounces of fine platina from Spain, with which 

 he made some experiments. Most writers assert, that a considerable part of 

 the platina is attracted by the magnet, but not the whole of it : but by a nice 

 inquiry he found, that every one of tiie particles obeyed the magnet more or 

 less, except some transparent stony particles ; and that even these were all 

 magnets in themselves ; or that each particle had 2 poles, which he could change 

 at pleasure by the application of magnetical bars. Though their magnetical 

 virtue is always much less than that of particles of iron, yet every one had 

 more or less of it ; but some so little as not to be perceived but by applying a 

 strong magnet to them when floating on water. Besides the flat, smooth, and 

 shining bright particles, which are alone the true platina, he found 2 other kind 

 of particles among them ; viz. some very small black particles, most of which 

 are of an irregular figure, resembling the iron sand found in some parts of North 

 America ; at Teneriff'e ; near some lakes in Italy ; in some rivers in Transyl- 

 vania, among the gold dust which is taken out of them ; and in many other 

 places. Some of these black particles, though few in comparison with the 

 number of the irregular particles, are of a very regular figure, and when seen 

 through a good magnifier, somewhat resemble the figure of a melon. These 

 black particles of both sorts are attracted by the loadstone, and have eacli of 

 them 2 poles, though tliose of an irregular figure have them more manifestly. 

 The other i)articles are of a gold colour ; having, in general, more or less of a 

 paleness approaching to the colour of platina. Some of these gold particles 



