Mr. Hunt on Adino-Chemistry. 29 



place in the arrangement of the elements of the salts em- 

 ployed. 



100 grains of the protosulphate of iron were dissolved 

 in 2 oz. of distilled water ; 30 grs. of the bichromate of potash 

 were dissolved in 4 oz. of distilled water; 1 oz. of the iron 

 solution was weighed into two large test-tubes, and 6 drachms 

 of the solution of the bichromate of potash added to each, 

 which formed a fine red- brown clear solution. One tube was 

 kept from all light, and the other exposed to good sunshine 

 for an hour ; in both tubes there was a precipitation of the 

 chromate of iron, described by Dr. Thomson in his memoir 

 on the Salts of Chromium, published in the Philosophical 

 Transactions. The solutions, which were perfectly clear, were 

 poured off from the precipitates; these were washed and 

 weighed. The precipitate formed in the dark was found to 

 weigh three grains more than that formed in the sunshine. 

 This result was different from what my previous experiments 

 had led me to expect, and it was several times repeated with 

 the most scrupulous care. In every instance the precipitation 

 which took place during thejirst exposure to sunshine was less 

 than that formed in darkness. 



The clear actinized solution poured oflF from the chromate 

 of iron, being again exposed to solar influence, the other 

 being carefully guarded from the slightest radiation, it was 

 found that the precipitation went on much quicker in sunshine 

 than in the dark ; the side of the tube facing the sun was al- 

 ways thickly coated with chromate of iron, whilst the other 

 side of it was perfectly free from any precipitation. Dr. 

 Thomson has shown that this precipitation is produced by 

 heat ; it became interesting to know what part solar heat had 

 in the phaenomena. As I experienced some difficulty in ar- 

 ranging in a satisfactory manner many tubes along the pris- 

 matic spectrum, I used only three. One was placed in the 

 mean indigo ray, another in the mean yellow ray, and the 

 third in the least refrangible red ray. After an exposure of 

 four hours, the precipitation formed in the tubes in the differ- 

 ent rays was as follows : — 



Indigo ray 5*25 



Yellow ray 0*50 



Red ray 2-15 



Similar results were obtained by placing the solutions behind 

 blue, yellow and red glasses, proving that although the calo- 

 rific rays were not without action, the principal effect was 

 due to the chemical rays. The half grain formed in the 

 yellow ray I still regard as due to the thermic or actinic power 

 of the beam, as behind a deep-coloured yellow solution (sul- 



