66 REPORT—1850. 
general result of the inquiry was, that a few weeks sufficed for the bleaching of a body 
by chlorine in sunlight, where months, and I may even say years, would not avail in 
darkness. I had not been able, however, to watch the stages of the actinic bleaching 
by chlorine, and I returned to the inquiry this summer, with a view to ascertain this, 
and subjected at the same time all the gases upon which I had previously experi- 
mented to the influence of sunlight. The results of this inquiry I shall now briefly 
state to the Section, and the method of procedure may be best illustrated by a special 
reference to the most important of the bleaching gases, chlorine. Four tubes were con- 
nected together so as to form a continuous canal, through which a current of gas could 
be sent. Each tube contained a small glass rod, on which seven pieces of differently 
coloured paper were spiked or impaled. Three of those papers were tinged with the 
colouring matter of the wallflower, which I expected to prove very sensitive to actinic 
action. This colouring matter, as extracted from the petals by diluted alcohol, colours 
paper of a grayish blue or slate colour; this formed one tint. The same colouring 
matter reddened by an acid, gives a bright crimson, much more vivid than the tint 
of reddened litmus; and when treated by ammonia, gives a pure bright green. Each 
of those wallflower-tinted papers was introduced into every tube, and, in addition, a 
piece of blue litmus paper, a piece of red litmus paper, a piece of alkaline or brown 
rhubarb paper, and a piece of yellow rhubarb paper. All the tubes thus contained 
seven different coloured papers, of different origins, and easily distinguished by the 
eye. They were arranged in the same order in each tube, and were prepared as 
nearly as possible of the same shade. 
The papers were first dried in a current of desiccated air, passed over them for some 
hours, and a current of the gas to be experimented on was then passed through the 
tubes for five minutes, after which they were sealed hermetically, whilst full of the 
gas. One of the four tubes was placed aside in darkness, the other three were ex- 
posed to sunlight. This exposure was not commenced till the Ist of last June, when 
four tubes having been filled with each of the gases to be experimented on, three in 
each case were exposed to sunlight. Two of the tubes were hung up on the inner 
side of a window having a western exposure ; the third tube was attached to a frame 
and exposed in the open air on a wall looking directly south. ‘The exposed tubes 
were in this way subjected to the light of the sun, as well as to that of the other 
heavenly bodies, so far as they could influence them, from the 1st of June to the 27th of 
July, a period of eight weeks. I have now arranged the four tubes, which were filled 
with each gas, on one sheet of pasteboard; the upper tube was that left in darkness ; ~ 
the two middle tubes were placed in a western exposure behind glass, and the lowest 
was turned to the south in the open air. 
I shall now describe the effect of sunlight in each of the gases. In the dark chlorine 
tube, the colours are very little altered, and would probably have been altered less, 
had the tube not been frequently exposed to light for the sake of examination. In 
the western tubes, the originally gray and green wallflower papers have become 
bright crimson; the blue litmus is bright red, and the brown rhubarb has become 
yellow. The whole chlorine has apparently entered into combination with the co- 
louring matters, for the yellow tint of the gas has totally disappeared. Inthe southern 
tube, on the other hand, the colour of chlorine can yet be seen, and the reddening 
action is less decided, whilst the bleaching action is much more powerfully evidenced. 
1 was led, from the appearances in the western tubes, to infer that I had employed too 
small a volume of chlorine, and I began a new set of experiments on the Ist of July, 
with a larger quantity of the gas, the results of which I now exhibit to the Section. 
A month’s exposure to direct sunlight has not sufficed to effect the full bleaching of the 
colours, nor have those which have paled in tint changed in the way they should have 
done if an acid had been developed. This, I confess, has surprised me; for theory 
would lead us to expect that when chlorine bleaches, it should form hydrochloric acid, 
and the reddening observed in the exposed tubes seemed entirely to confirm what 
theory indicated. The general result, however, of my inquiry has been, that the 
action of sunlight in increasing the bleaching power of chlorine is Jess uniform than 
might have been expected ; for whilst some tints have rapidly disappeared under its 
action, these colours have remained unaffected in apparently the very same cireum- 
stances. I propose accordingly to continue this inquiry. I shall describe much more 
briefly the effect of the other gases. 
