206 
SIR J. F. W. HERSCHEL ON THE ACTION OF THE RAYS 
leaving - a white oval, as in the specimen annexed ; precisely the same phenomenon, in 
short, as would have been produced under the spectrum had the two liquids acted in 
conjunction. And this white portion comports itself under the influence of water or 
air, just as it would have done had it been produced under such joint action ; i. e. it 
gradually turns blue till it is no longer distinguishable from the rest of the spectrum. 
It is also blued by ammonia, just as the positive paper of Art. 210, after bleaching, 
would be, &c. In short, it is evident that we have succeeded in separating the final 
action described in that article into two distinct steps or stages, the photographic in- 
fluence being confined to the first, and the ferrosesquicyanate acting as a mere pre- 
cipitant on the nascent compounds resulting from that influence. 
212. In order to ascertain whether any portion of the iron in the double amrao- 
niacal salt employed had really undergone deoxidation, and become reduced to the 
state of protoxide as supposed, I had recourse to a solution of gold, exactly neu- 
tralized by carbonate of soda. The proto-salts of iron, as is well known to chemists, 
precipitate gold in the metallic state. The effect proved exceedingly striking, issuing 
in a process nowise inferior in the almost magical beauty of its effect to the calotype 
process of Mr. Talbot, which in some respects it nearly resembles, with this advan- 
tage, as a matter of experimental exhibition, that the disclosure of the dormant image 
does not require to be performed in the dark, being not interfered with by moderate 
daylight. As the experiment will probably be repeated by others, I shall here describe 
it ah initio. Paper is to be washed with a moderately concentrated solution of am- 
monio-citrate of iron, and dried. The strength of the solution should be such as to 
dry into a good yellow colour, not at all brown. In this state it is ready to receive 
a photographic image, which maybe impressed on it either from nature in the camera- 
obscura, or from an engraving on a frame in sunshine. The image so impressed, 
however, is very faint, and sometimes hardly perceptible. The moment it is removed 
from the frame or camera, it must be washed over with a neutral solution of gold of 
such strength as to have about the colour of sherry wine. Instantly the picture ap- 
pears, not indeed at once of its full intensity, but darkening with great rapidity up 
to a certain point, depending on the strength of the solutions used, &c. At this point 
nothing can surpass the sharpness and perfection of detail of the resulting photo- 
graph. To arrest this process and to fix the picture (so far at least as the further 
agency of light is concerned), it is to be thrown into water very slightly acidulated 
with sulphuric acid and well soaked, dried, washed with hydrobromate of potash, 
rinsed, and dried again. 
213 . Such is the outline of a process to which I propose applying the name of 
Chrysotype , in order to recal by similarity of structure and termination the Calotype 
process of Mr. Talbot, to which in its general effect it affords so close a parallel. 
Being very recent, I have not yet (June 10 , 1842 ) obtained a complete command 
over all its details, but the termination of the Session of the Society being close at 
hand, I have not thought it advisable to suppress its mention. In point of direct 
