Mr. Hunt on Actino-Chemistry, 27 



dri-sulphuret of lime and the solution of the bichromate of] 

 potash, as Adiactinic, whilst media admitting the free per- ' 

 meation of this power, as colourless glass, or a solution of the 

 ammoniuret of copper, would be distinguished as Diactinic*. 

 Any instrument used for measuring the amount of chemical 

 disturbance effected by the solar rays, would be called, as was 

 proposed by Sir John Herschel, an Actinograph. With 

 these preliminary observations I do not think any difficulty 

 will arise from the terms made use of in this paper. 



Influence of the Solar Rays on Precipitation. 



In 1832 Sir John Herschel communicated the remark- 

 able fact, that when a solution of platinum in nitro-muriatic 

 acid, which has been neutralized by the addition of lime, and 

 has been well-cleared by filtration, is mixed with lime-water 

 in the dark, no precipitation, or scarcely any, takes place, but 

 when (being thoroughly cleared of any sediment) this mixture 

 is exposed to sunshine it instantly becomes milky, and a white 

 or yellowish-white precipitate speedily falls. 



By exposing this mixture behind coloured media, Sir John 

 Herschel found that the effect was due to the influence of the 

 most refrangible rays. I have placed this mixture in small 

 glass tubes, and so arranged them that they were individually 

 exposed to a separate ray of the spectrum. After an exposure 

 of one hour the following results were obtained, the precipi- 

 tates having been carefully washed and dried in the tubes in 

 which they were formed. 



Most refrangible rays beyond the visible spectrum 0*07 gr. 



Violet rays 1'05 ... 



Indigo rays 0'60 ... 



Blue rays 0*45 ... 



Green rays 0*10 ... 



Yellow and orange rays 



Red rays 0*05 ... 



It is a fact worthy of especial notice, that this precipitation 

 is so dependent upon the amount of sunshine, that precipitates 

 obtained in the same time, being carefully weighed off, will 

 show the relative amounts of actinic influence to which they 

 have been exposed. 



Maiiganate of Potash. — A solution of this body having been 

 made in the dark, was placed in two glass vessels and set 

 aside. After having been kept in darkness for two hours, the 



* These terms are formed from those proposed by M. Melloni in his 

 *' New Nomenclature for the Science of Calorific Radiations," a slight 

 liberty being taken with them for the sake of euphony. 



