32 Mr., Huat on Actino-Chmistm, 



two or three hours a coating of white metal was formed in 

 two well-defined stripes along the tube which had been undeV 

 solar influence ; one on the side directly facing the sun, an4 

 the other on the other side of the tube, but along a line, upor\ 

 which I found by subsequent experiment the rays were con- 

 centrated, by the form and refractive power of the media — 

 glass and metallic solution — through which they had to pass. 

 That these lines were due to the action of the solar rays was 

 proved by placing a piece of blackened paper around a tube,; 

 as marked in the figure, which effectually prevented the me- 

 tallic deposit over the space it covered. This deposit is some- 

 what capricious in its formation. The experiment has been 

 often repeated, but although the precipitation was invariably 

 as described, it frequently happened that no metal was de- 

 posited along the glass. ■^'!:i^'^ ■"'■^j V' '^•^^'^ "^,11 



Sulphate of iron in solution ^yas ' foUrtd io £S^\me the 

 same property by exposure as the other salts above-named. 

 30 grs. of this protosalt were dissolved in an ounce and a half 

 of water. It was then divided into two portions, one of which 

 was exposed for an hour to sunshine. 100 grs. of each solu- 

 tion were carefully weighed into test-tubes, and the same 

 weight of a solution of nitrate of silver made in the dark, was 

 added to each. As quickly as possible the precipitates were 

 collected, washed, dried and weighed. The precipitate pro- 

 duced immediately by the iron solution which had been acti- 

 nized weighed 2'8 grains, whereas the precipitate by the un- 

 exposed solution weighed 0*7 grain. These results ard the 

 mean of six experiments. 



Two test-tubes had 120 grains of an actinized solution of 

 nitrate of silver weighed into them, and into two others was 

 put the same quantity of a like solution which had not been 

 actinized. Four other tubes held the same weights of solutions 

 of the protosulphate of iron, two of them actinized, the others 

 not so. They were mixed in the following order, and the 

 precipitates collected immediately from each were as stated: — 



1. Actinized silver with actinized iron . 0*5 gr. 



2. Unactinized silver with unactinized iron 0*7 ... 



3. Actinized silver with unactinized iron I'O ... 



4. Unactinized silver with actinized iron 1'5 ... 

 Considerable difficulty arises from the length of time which 

 must necessarily elapse before the precipitates can be re- 

 moved from the solutions. In all cases I find that after some 

 little time the conditions required to effect a precipitation are 

 established, and in both kinds of solutions it then proceeds 

 without any apparent difference. It would appear from the 

 above results, which are the mean of many experiments, that 



