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 alcohol 3 



Soluble paper (dried at 100 0.) 50 grains. 



Iodide of cadmium (pure) 30 



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 pyrogallic acid 8 grains. 



Crystallized citric acid 16 ,, 



Water 8 fluid ounces. 



Alcohol i 



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 



