Mr. Hunt oji Actino-Chemistry. SI 



graphic papers and Daguerreotype plates, that the colours pro- 

 duced varied in richness of tint and in shade with the bright- 

 ness of the sun and the clearness of the atmosphere at the time 

 of exposure. In some positive processes, in which a darkened 

 paper was bleached under the influence of actinic radiations 

 (if this expression be permitted), the effects of colour were 

 often very striking and beautiful, whereas in winter, or when 

 a slight haze existed, a dull dun-brown almost invariably re- 

 sulted. It appears that dyers and the manufacturers of some 

 of the fine pigments are not unacquainted with these facts ; 

 they are certainly curious, and deserve attentive investigation 

 at the present time. I regret that I am only in a position to 

 record the facts I have noticed, not having as yet determined 

 even the influence of the various independent rays upon these 

 coloured precipitations. 



Actinic Influence on Chemical Combination. 



Two phials were filled with a solution of acetate of sil- 

 ver and carefully corked. One was exposed for an hour to 

 good sunshine, whilst the other was carefully kept in the dark. 

 At the end of this time, a solution of the protosulphate of iron 

 having been made in the dark, ten drops of it were added to 

 each solution of silver. The one which had been exposed 

 gave immediately a copious precipitate of silver, whereas the 

 other was only rendered slightly turbid, and was some mi- 

 nutes before it precipitated. Alter having stood eight or ten 

 minutes no difference could be detected in the quantity of sil- 

 ver precipitated in either phial. 



Acetate of mercury was used in the place of the acetate of 

 silver, and the difference between the actinized solution and 

 the other, on the addition of the iron salt, was very striking. 



The two salts, acetates of silver and mercury, were mixed 

 (they had been used, combined rather successfully, in a pho- 

 tographic process of some interest). One portion was ex- 

 posed in a large test-tube carefully corked, and another por- 

 tion was protected from all light in a bottle. The exposure 

 in this case was from two to three hours, but during that 

 time there was not more than half an hour's good sunshine. 

 By the light of a taper an equal quantity of the sulphate of 

 iron was added to each. In about three minutes the solution 

 which had been exposed appeared a little disturbed, small 

 specks were seen to form in various parts of the fluid, and 

 these rapidly increasing in size and assuming star-like shapes, 

 fell heavily. At the expiration of an hour a dark and bulky 

 precipitation was formed, but in the unexposed solution the 

 precipitate was but little and of a light gray colour. In about 



