1857.] of Gold (and other Metals) to Light. 429 



substance on which they are deposited. They have all the 

 chemical reactions of gold, being, though so finely divided, in- 

 soluble in the fluids that refuse to act on the massive metal, 

 and soluble in those that dissolve it, producing the same result. 

 Heat makes these divided particles assume a ruby tint, yet 

 such heat is not likely to take away their metallic character, 

 and when heated they still act with chemical agents as gold. 

 Pressure then confers the green colour, which heat takes away, 

 and pressure reconfers. All these changes occur with parti- 

 cles attached to the substances which support them by the 

 slightest possible mechanical force, just enough indeed to pre- 

 vent their coalescence and to keep them apart and in place, 

 and yet offering no resistance to any chemical action of test 

 agents, as the acids, &c., not allowing any supposition of che- 

 mical action between them and the body supporting them. 

 Still this gold, unexceptionable as to metallic state, presents 

 different colours when viewed by transmitted light. Ruby, 

 green, violet, blue, &c. occur, and the mere degree of division 

 appears to be the determining cause of many of these colours. 

 The deflagrations by the voltaic battery lead to the same con- 

 clusion. 



The gold films produced by phosphorus have every charac- 

 ter belonging to the metallic state. When thick, they are in 

 colour, lustre, weight, &c. equal to gold-leaf; but in the un- 

 pressed state, their transmitted colour is generally grey, or 

 violet-grey. The progression of their lustre and colour is 

 gradual from the thickest to the thinnest, and the same is 

 generally true, if thick films are gradually thinned and dis- 

 solved whilst floating on solvents ; the thick and the thin films 

 must both be accepted as having the same amount of evidence 

 for their metallic nature. When subjected to chemical agents, 

 both the thick and the thin films have the same relations as pure 

 metallic gold. These relations are not changed by the action 

 of heat, yet heat shows the same peculiar effect that it had 

 with preparations of gold obtained by beating, or by electric 

 deflagrations. The remarkable and characteristic effect of 

 pressure is here reproduced, and sometimes with extraordinary 

 results ; since from the favourable manner in which the par- 

 ticles are occasionally divided and then held in place on the 

 glass, the mere touch of a finger or card is enough to produce 



