68 PHILOSOPHICAL TRA^fSACTIONS. [aNNO 1703. 



not SO much power over the copper, as to protrude out of its substance so many 

 air-babb!es, as it might otherwise have done, if there had not been so much 

 gold in it ; the water thereon assumed a greenish colour, and all the yellow 

 colour was turned into coagulated gold, insomuch that one might with the 

 naked eye distinguish the gold from the copper; particularly the extreme parts 

 of the little boughs formed by the coagulated gold; though the said gold con- 

 sisted of particles so very minute, that they did not appear larger with a good 

 microscope, than the smallest grains of sand to the naked eye. 



When I weakened with rain water the aqua regia, which had been impreg- 

 nated with a great deal of gold, and then put into it a bit of copper, 1 observed 

 that the gold in a short time was coagulated, or united with the copper, and 

 that the water was turned to a light green. I have also observed that the 

 small twigs of these coagulated particles were not of a fine gold colour ; from 

 whence I inferred, that there was copper blended together in them. The said 

 aqua regia, which had been impregnated with gold, having remained some days 

 in the glass, I perceived that where it was thickest, it was covered with a film 

 or skin, and that most of the salts, when the weather was not warm, nor the 

 sun shined, were dissolved, and much more in rainy weather. 



Moreover, I exposed the glass with the said water to such a heat of the fire, 

 that the salts evaporated in smoke, and that part of the glass where there lay 

 least of the aqua regia, assumed a colour that was somewhat reddish, but where 

 the said water lay thicker together we could not see the fine shining gold with 

 the naked eye; but when we raised that glass, where the gold lay higher to the 

 light than the microscope, I saw that the gold particles were not united with 

 the other, but now and then coagulated into branches ; and where the gold 

 particles were not thus coagulated, they were so very small, that how nicely 

 soever I viewed them, they escaped my sight ; and though there lay together 

 more than a thousand millions of these small particles, all of them did not 

 compose a body that was larger than one single grain of a large sand. Where 

 this matter lay thin and dispersed, I observed that its small particles were such 

 solid and compact bodies, as did not admit the least ray of light ; and where 

 they lay single, I saw other particles still smaller, whose bodies were more 

 loose; but I imagined these last to be some particles of that matter which the 

 aqua regia had left behind it. 



Now after the said aqua regia had remained on some of the glasses several 

 days, and the salt particles for the most part were changed into a fluid substance, 

 I observed among several of the coagulated branches small distinct particles, 

 which I fancy to be gold, though I could not for the sraallness perceive the 

 colour of them. To satisfy myself herein, I took a small glass bubble, with 



