jjtJt On the Chemical Properties attrlbuteltg Light. 



iine linen, cotton, paper, &c. wetted in an aqueous folutlon of nitrate of filver ; with 

 this ditlerence, however, that the tinge produced by this metallic oxide, inflead of being 

 of a deep purple, inclining to crimfon, was of a very dark orange colour, or rather of a 

 yellowifii brown. 



In order to difcover whether the purple tinge, in the experiments with the oxide of gold, 

 was occafioned by the heat communicated by the afcending current of hot vapour, or by the 

 light of the candle, I made the following experiment, the rcfult of which I conceive to 

 Iiave been decifive. 



Experiment No. 4. A piece of riband was wetted with the aqueous folution of the oxide 

 of gold, and held vertically by the fide of the clear flame of -a burning wax candle, at the 

 diftance of kfs than half an inch from the flame. 



The riband was dried, but its colour was not in the fmallefl degree changed. 



When it was held a few feconds within about i of an inch of the flame, a tinge of a^ 

 mod beautiful crimfon colour, in the form of a narrow vertical ftripe, was produced. 



The heat which exifted at that diftance from the flame, on theftdeofit, where this co- 

 loured fliipe was produced, was fufliciently intenfe, as I found by experiment, to melt 

 V€ry fine filver wire, flatted, fuch as is ufed in making filver lace. 



:, The obje£ls I had in view in the following experiments are too evident to require any 

 paVticular explanation. 



Experiment No. 5. Two like pieces of riband were wetted at the fame time in the folution, 

 and fufpended, while wet, in two thin phials, A and B, of very tranfparent and colourlefs 

 glafs ; the mouths of the phials being left open. Both thefe phials were placed in a M'indow 

 which fronted the fouth ; that diftinguiflicd by the letter A being expofed naked to the 

 dire£1; rays of a bright fun ; while B was inclofed in a cylinder of paft:eboard, painted black 

 within and without, and clofed with a fit cover, and confequently remained in perfedb 

 darknefs. 



In a very few minutes, the riband in the phial A began fenfibly to change its colour, 

 and to take a purple hue ; and, at the end of five hours, it had acquired a deep crimfon 

 tint throughout. 



The phial B was expofed in the window, in its dark cylindrical cover, three days 5 but 

 ihere was not the fmalleft appearance of any change of colour in the filk. 



Experiment No. 6. Two fmall parcels of magnefta alba, in an impalpable powder, 

 (about half as much In each as could be made to lie on a fliilling,) were placed in heaps, 

 in two china plates, A and B, and thoroughly moiftened with the before-mentioned 

 aqueous folution of the oxide of gold. Both plates were placed in the fame window ; the 

 moiftened earth in the plate A being expofed naked to the fun's rays ; while that in the 

 plate B was exadly covered with a tea-cup, turned upfide down, which excluded all 



light. 



The magnefta alba In the plate A, which was expofed to the flirong light of the fun, 

 began almofl; immediately to change colour, taking a faint violet hue, which by degrees 

 became more and more intenfe, and in a few hours ended in a deep purple ; while that in 

 the plate B, which was kept in the dark, retained the yellowiih caft it had acquired from 

 the folution, without the fmalleft appearance of change. 



Experiment No, 7, A fmall parcel of magnefta alba, placed on a china plate, having been ' 



moiftened 



