34 REPORT—1843. 
to the conclusion, that the decomposition in question was due to the ray of light, a 
result obtained by the agency of coloured glasses, but which does not appear to have 
been accepted by later authors, who have attributed it to the chemical rays. There 
is but one way by which the question can be finally settled, and that is by conducting 
the experiment in the prismatic spectrum itself. When we consider the feebleness 
of effect which takes place, by reason of the dispersion of the incident beam through 
the action of the prism, and the great loss of light through reflexion from its surface, 
it would appear a difficult operation to effect the determination in this way. Encou- 
raged, however, by the purity of the skies in America, I made the trial, and met with 
complete success. A series of tubes, halfan inch in diameter and six inches long, were 
arranged so that the coloured spaces uf the spectrum fellon them. In these tubes, 
water, impregnated with carbonic acid gas, and containing a few green leaves (Poa 
annua), was placed. It was expected that if the decomposition be due to the radiant 
heat, the tube occupying the red space, or even the one in the extra-spectral red space, 
would, at the close of the experiment, contain most gas. If it were the ‘‘ chemical 
rays,” in the common acceptation of the term, we might look for the effect in the blue, 
violet, or indigo spaces ; but if it were the Licut, the gas should make its appear- 
ance in the yellow, with some in the green, and some in the orange. I made the trial 
several times, and found it much more easy to accomplish than I had-expected. 
The results were briefly as follows: —In the tube that was in the red space a minute 
bubble was sometimes found, but sometimes none at all. That in the orange con- 
tained a more considerable quantity ; in the yellow ray a very large amount, compa- 
ratively speaking; in the green a much smaller quantity ; in the blue, the indigo, the 
violet, and the extra-spectral space at that end, not a solitary bubble. From these 
facts, in connexion with some results obtained by the use of bichromate of potash as 
an absorptive medium, I conclude that it is the rays of light which effect the decom- 
position, and that the rays of heat and the tithonic rays have nothing to do with the 
phenomenon. The alkaline bicarbonates are easily decomposed by elevation of tem- 
perature, yielding a portion of their acid at the boiling point of water. Instead of 
using a solution cf carbonic acid, I endeavoured to effect the decomposition of these 
salts by leaves in the sunlight, and found that it tock place with facility. Nor is the 
effect limited to the removal and decomposition of the second atom of the acid. It 
passes on to the first; the neutral carbonate of soda itself decomposing and yielding 
oxygen gas. In like manner the sesquicarbonate of ammonia may be made to yield 
a very pure oxygen gas. Dr. Draper, in concluding this communication, alludes to 
his method of multiplying the Daguerréotype pictures, as published in the Philosophi- 
cal Magazine, and then mentions a process of precipitating copper, after the picture 
has been fixed by gold, by the electrotype process, on the plate, which, as he states, 
gives a very perfect copy. “It is difficult,” says the Professor, “ to describe in words 
the beauty and perfection of these ‘ copper-tithonotypes.’ The problem of multi- 
plying the Daguerréotype may be now regarded as completely solved.” 

On Chromatype, a new Photographie Process. By R. Hunt. 
We are indebted to Mr. M. Ponton for the discovery of the first photographie 
process in which chromic acid was the active agent. He used a paper saturated 
with the bichromate of potash, which, on exposure to sunshine, speedily passed from 
a fine yellow colour iato a dull brown, giving, consequently, a negative picture. HE. 
Becquerel improved upon this process, by sizing the paper with starch previously to the — 
application of the bichromate of potash, which enabled him to convert the negative 
picture into a positive one by the use of a solution of iodine, which combined with 
the starch in those parts on which the light had not acted, or acted but slightly, forming 
the blue iodide of starch. These pictures are, however, tediously produced ; they — 
are seldom clear and distinct, and failure too frequently follows the utmost care, 
While the author was pursuing an extensive series of researches on the influence of 
the solar rays on the salts of different metals, he was led to the discovery of a pro- 
cess by which positive photographs are very easily produced. Several of the chro- 
mates may be used in this process; but the author prefers those of mercury or cop- 
per, the most certain effects being produced by the chromate of copper, and, indeed, 
in a much shorter time than with any of the other chromates, The papers are thus 
