so Mr. Hunt on Actitio-Chemislry. 



phate of potash and chromium) no precipitate was formed in 

 eight hours. 



I have made one or two other experiments (particularly one 

 with a mixture of the bichromate of potash and the sulphate 

 of copper) in which precipitation appears retarded by solar 

 agency. I am rather inclined to think that it will eventually 

 be proved that the electric energy of the different bodies in 

 relation to each other will greatly modify the results we shall 

 obtain in these experiments, and I intend, if possible, to in- 

 vestigate this part of the subject with care. Since Becquerel 



/ has shown [Annales de Chimie, November 1843) that the 

 electrical excitation produced by the solar rays is different for 

 each ray, and that this power is at its maximum in the yellow 



' ray and also in the violet ray, the minimum force being be- 

 tween the green and blue rays; and since the mean maximum 

 of chemical energy has been shown to manifest itself in the 

 violet ray, and its minimum invariably to reside in the yellow 

 ray ; and as it is known that the negative and positive cur- 

 rents or sparks produce opposite effects, may we not reason- 

 ably conclude that the solar radiations are in some remarkable 

 manner involved in the production of electrical phgenomena? 

 To say, as has been said, that electricity is the agent pro- 

 ducing the effects I have been considering, is rushing much 

 too hastily to a conclusion ; indeed, cases will be found in 

 which, at the maximum of electrical power in the spectrum, 

 electrical phenomena which would occur in darkness or in 

 light, apart from heat or actinism, are entirely prevented. 



Colour of Precipitates. 



If a solution of bichromate of potash is exposed to sun- 

 shine, it acquires a property of precipitating several metals as 

 chromates, differing many shades in colour from the colours 

 produced by a similar solution prepared and kept in the dark. 

 If the actinized solution be poured into a solution of nitrate 

 of silver, the chromate of silver formed is of a much more 

 beautiful colour than that given by a solution which has not- 

 been exposed to the sun. A like effect will take place in pre- 

 cipitating chromate of mercury with actinized and non-acti- 

 nized solutions of the chrome salt. 



Solutions of sulphate of iron exposed to sunshine yield 

 a Prussian blue with the ferro-prussiate of potash, of a far 

 more beautiful colour than that produced by a solution which 

 has not been so exposed. If solutions of both the salts are 

 kept for many hours in good sunshine, the colour of the re- 

 sulting Prussian blue is still improved. 



I have long noticed in the process of darkening photo- 



