The collodion to be used in this process must be one yielding good _negative_ pictures--that supplied by Home & Thornthwaite under the name of negative collodion answers admirably. This is supplied either ready iodized, or the collodion and iodizing in separate bottles. As this collodion becomes less sensitive after being iodized a fortnight, it is advisable to iodize no more than will be used in that time--therefore, obtain the collodion and the iodizing solution separate, as the mode of iodizing this collodion is very simple. Half an ounce of the iodizing solution is mixed with one ounce and a half of collodion, and the mixture allowed to settle twelve hours before being used; and it is even advisable to pour off the clear solution into a perfectly clean bottle, in order to get rid of any insoluble matter which may fall to the bottom. _Iodized Albumen._ White of egg (free from yelk) 10 ounces. Honey 1 ounce. Iodide of calcium 2 scruples. Yeast 1 tablespoonful. Mix these together in a tall glass jar, or wide-mouthed bottle of at least one pint capacity; tie a piece of paper, pierce with small holes over the top to keep out dust; then place the whole near a fire or other warm situation, where the temperature is not lower than seventy degrees, or higher than ninety degrees. In a few hours fermentation commences, which is evident by the formation of bubbles of gas, rising through the liquid. This action continues for five or six days; when it ceases, pour the whole on a paper-filter contained in a funnel, underneath which must be placed a bottle to receive the liquid as it passes through. The fluid being of a viscid nature filters slowly, generally occupying twelve hours. The filtered liquid is the "iodized albumen," which is said by Dr. Taupenot to keep good for years. It must be carefully preserved from dust or contact with any substance, as the success of the picture depends materially on the condition of this albumen. _Albumen Bath Solution._ Nitrate of silver 1 ounce and a half. Acetic acid, glacial 1 ounce. Distilled water 16 ounces. Animal charcoal 2 drachms. Dissolve the nitrate of silver in the distilled water, then add the acetic acid and animal charcoal, and keep in a closely stoppered bottle for use. _Pyrogallic Solution._ Pyrogallic acid 15 grains. Glacial acetic acid 2 drachms. Alcohol 2 drachms. Distilled water 7 ounces. Dissolve the pyrogallic acid in the distilled water, and then add the acetic acid and alcohol. _Silver Developing Solution._