232 Royal Society :— : 
When the temperature of the mixture had cooled down to 50° C., 
one sheet of Swedish filterimg-paper, torn up into small pieces, was 
completely immersed in the mixture, and allowed to remain therein for 
about half an hour. It was then thrown into a large pail of water, 
and the paper removed and placed on a sieve under a running tap 
for a quarter of an hour; after washing in very dilute solution of 
ammonia and then in plenty of water, the paper was pressed between 
the folds of a cloth, and then allowed to dry spontaneously in the 
air. 
The collodion was made with— 
Ether, sp. gr. *725 (previously freed from acid by 
rectification from dry caustic potassa) ...... 5 fluid ounces. 
Absolute el GOMOle te cera canescens tatwastyncuee 3 ss 
Soluble paper (dried at 100° C.) ............ 50 grains. 
Iodide of cadmium (pure)........ 0 see. ee ais} 1) ihn 
The alcohol and ether were mixed together, and then the paper 
and iodide of cadmium were added: they dissolved in a few minutes 
with a little shaking. As soon as the solution was complete, it was 
allowed to stand for twenty-four hours, and then half of the clear 
supernatant fluid was decanted carefully into a clean well-stoppered 
bottle for use. I believe that collodion prepared in this way will 
remain uniform from one year’s end to another. 
The nitrate of silver bath was made by dissolving 1 ounce of 
crystallized nitrate of silver, perfectly pure and neutral, in 2 ounces 
of water, then, with constant stirring, adding a solution of 4 grains 
of iodide of cadmium in 1 ounce of water, and a quarter of an ounce 
of the above iodized collodion, and water to make up the volume to 
10 ounces. This was allowed to stand for a few hours at a tempe- 
rature of about 25° C., and then filtered from the undissolved iodide 
of silver and precipitated paper. A glass bath was used in pre- 
ference to gutta percha, and, as above stated, it was heated to 30° C. 
when used. 
The developing solution consisted of— 
Pure pyrogallte acid... gsi.)s,ae wie oo 8 grains. 
Cryptallized clinic, AA 6. '<s0i6 pupal; mcieisyy pon ean 
BWV REET ice cia ny alle Paton Sek: faye aus ue nocauaEs 8 fluid ounces. 
ATeoh al eviccs ein timate nép Sank dee Se 5 Se 
This developing solution is very slow in its action, 15 to 20 
minutes being frequently required, but it ultimately produces nega- 
tives of such vigour and freedom from stains, that I much prefer it 
to the usual formula. 
The fixing solution employed was the ordinary nearly saturated 
solution of hyposulphite of soda. After its employment the pictures 
were well and carefully washed in warm water, dried before a fire, 
and, after scratching the description or name on a corner, varnished 
with the usual solution of amber in chloroform. 
The subsequent operation of printing is so easily performed, and 
has been so fully described by persons of more experience than 
myself, that any further allusion to it will be needless. 
