268 REPORT—1852. 
CuemIcat SErRIEs, No. 1. 
—— 
Chemical Spectra obtained after the Prismatic Spectrum has been analysed 
by the interposition of Transparent Coloured Screens. 
PHOTOGRAPHIC AGENT. 
Collodio-iodide of Silver on Glass Plates*. 
The numbers preceding the coloured glass employed, refer to the numbers attached to each 
particular medium in the previous series. No. 1. Those following the colour refer to the 
paragraph. 
(49). Normat Spectrum, formed by a very pure flint-glass prism.—Light 
admitted between two knife-edges, separated {th of an inch, and generally 
passed through a hole of the same diameter in an inner screen. The chro- 
matic image was received on a white tablet in a perfectly black box; its 
length, when most accurately adjusted, was 1 inch and j ths, but for con- 
venience this has been reduced to 1 inch and divided into 100 parts, and re- 
latively to this all the chemical spectra have been corrected (1:2). 
(50). Without any interposed medium, fig.19.—Chemical Fig. 19. 
action commences °40 above the lower end of red,and from 
this point extends to the length of 15 inch. Over the 
space covered by the red and orange rays are indications 
‘of a well-defined circle of protective action ; immediately 
above this a dusky brown commences, forming a kind of 
fringing which is extended to ‘60, and in a similar manner 
it bounds the whole of the spectrum. This is due to 
diffused light, which I always find bordering the spectrum. 
Over a space equal to *i0 a well-defined black space ap- 
pears, then the action weakens, but is still strong over °7, 
when it again increases just at the end of the violet, and 
is somewhat sharply cut off at 1-90 above 0, or lowest 
red, presenting an image similar to that represented in 
the margin. Placing the glass at a small angle, and ob- 
serving the spectrum by reflexion, the lower dark space 
comes out very strongly, and the whole space above it 
appears of a dark semi-metallic purple shaded by a dusky 
brown border. 

Glasses (A.) Yellow Media. Fig. 20. 
(51) 16. Deep yELLow (4), fig. 20.—Chemical ac- 
tion commencing over the region of the indigo and violet 
rays, the most intense action appearing to take place 
about the line H of Fraunhofer, It forms eventually a 
well-defined oval, the greatest amount of darkening going 
on in the centre of the impressed spectrum, a protected 
band, well-defined from the other parts of the surface, in 
* The collodion was made with gun-cotton which had been pre- 
pared with nitrate of potash and sulphuric acid. This being well 
washed was dissolved in ther. Iodide of potassium was dissolved in 
spirits of wine and iodide of silver added so long as it would take 
up any, and two drachms of this were mixed with one fluidounce of 
the collodion. The solution of silver employed was 30 grains to the 
fluidounce of distilled water. The image was always developed by 
pyrogallic acid. 

