ACTION OF ABSORBENT MEDIA AND IDEAL COLORATION. 133 



the means of effecting their separation. A remarkable observation, which appears to me 

 to be very much in point, was made many years ago by Professor SILLIMAN ; it has not 

 obtained that attention which it deserves ; he states, that on exposure of a mixture of 

 chlorine and hydrogen to the light of a fire, an explosion was produced. I quote the 

 fact, however, only from memory, and have endeavoured to substantiate it under a 

 variety of circumstances, but with a want of success probably due to the absorbing ac- 

 tion of the glass jars used, or to the nature of the light. It is desirable that this experi- 

 ment should be once more repeated ; it would settle an important point that chemical 

 rays of different characters exist. I have referred to this before, for it is more than 

 probable that there are chemical rays not absorbable by the chromates of potassa. 



Note added to the foregoing Chapter. 



(Being a Letter to the Editors of the London and Edinburgh Philosophical Magazine, inserted in thai Journal February, 1840.) 



AN ACCOUNT OF SOME EXPERIMENTS MADE IN THE SOUTH OF VIRGINIA ON THE LIGHT 



OF THE SUN. 



507. GENTLEMEN I have just seen in the Journals for the current month a letter 

 from Sir J. HERSCHEL to the British Association for the Advancement of Science, in 

 reference to some remarkable actions of the different colours of the solar spectrum. 



508. About five years ago, having the advantage of a bright and almost tropical sky, 

 I amused myself with attempting a repetition of MORICHINI'S experiment for the magnet- 

 izing of steel, and was led to some results in respect to the chemical action of the 

 sun's rays, which appear to bear very much on the subject of the letter above alluded 

 to. Most of these have been published in the Journal of the Franklin Institute of Phil- 

 adelphia ; but as they do not appear to have been noticed in England, I will ask the 

 favour of a page or two of your excellent Magazine, to give my testimony on a subject 

 which now appears to excite so much interest. 



509. If you pass a beam of the sun's light through a solution of chromate of po- 

 tassa, it can no longer blacken a piece of sensitive paper ; if you converge the light 

 which has thus passed through a stratum of this fluid, by means of a lens, chloride of 

 silver will remain for a long time, without much change, in the focus. 



510. The list which was published in the Journal above named of solutions pos 

 sessing this power, is as follows : 



Bichromate of potassa. Muriate of iron. 



Chromate of potassa. Chloride of gold. 



Yellow hydro-sulphuret of ammonia. Chloride of platinum. 

 Hydro- sulphuret of lime. 



511. It is to be remarked, that every one of these solutions is yellow, but I also found 

 that a great many vegetable coloured infusions would, in like manner, absorb the chem- 

 ical rays, especially those which have a yellow tint. 



612. When I exposed pieces of paper covered with a layer of chloride of silver 



