RAYS OF THE SOLAR SPECTRUM ON PREPARATIONS OF SILVER, ETC. 
33 
The colours of the impression are smoke-grey or lead colour over the first twenty-four 
or twenty-five parts, and a purplish grey passing into a shade of dull pink over the 
more refracted portion. 
87. Among the most remarkable spectra are some of those impressed on papers 
prepared with precipitates from liquids abounding in animal matter (such as are ob- 
tained by precipitating lead or other bodies from such liquids) applied as described 
in Art. 28. The paper described in the latter part of that article, Avhen subjected 
to the solar spectrum, exhibited an impression whose coordinates and tints were as 
follows : 
First sensible commencement of action at the least refracted end — White 
White. 
Termination of white, commencement of faint brick red 
Faint brick red. 
Termination of red, passing into a smoky brown 
Smoky dull brown. 
Commencement of a fine rich purple brown 
Gradually increasing in intensity to a maximum about 
Thence gradually declining, without change of tint, to the sensible ter- 
mination of the impression at 
Consequently the total extent of chemical action on this paper, including 'j 
the whitening or conservative action, which in this instance is marked ; 
with uncommon distinctness ' 
Total length of the white portion 
- 23-0 
- 5-0 
+ i-o 
+ 6-0 
+ 26-0 
j + 91-3 
1= 114-3 
= 18-0 
88. A precipitate consisting chiefly of phosphate of lime, but containing animal 
matter in combination, applied in mixture with a pretty strong solution of common 
salt, gave a spectrum not a little remarkable, being throughout of a uniform and very 
delicate lilac tint, with the slight exception of having the middle a little more verging 
to pink than the extremities. Its total length was ninety parts, commencing pre- 
cisely at the fiducial point, and its maximum of intensity rather beyond the middle, 
towards the more refrangible end, viz. at + 60. When the same precipitate was ap- 
plied intermediately between two washes of nitrate of silver, omitting the muriate of 
soda, a much more intense spectrum was produced, of a nearly uniform smoky brown 
or very dark grey, but peculiarly rich and velvety, barely attaining the fiducial point, 
and from thence, for a considerable distance, continuing extremely faint, and increas- 
ing by very gradual progress to a maximum about + 45, and decaying as gradually, 
but assuming at the more refrangible extremity a somewhat more ruddy hue, while 
at the less its tint inclined rather to a blueish or lead colour. 
Effect of the Spectrum on certain Vegetable Colours. 
89. The evidence we have obtained by the foregoing experiments of the existence 
of chemical actions of very different, and to a certain extent opposite characters at 
MDCCCXL. f 
