Albumen prepare the albumen solution take the white of a fresh egg, careful that none of the yolk or the germ is accidentally admitted. Break this into a froth with an ordinary egg-beater, and mix with forty-eight ounces of water. This should be the purest procurable, distilled, or from melted transparent ice, and filtered before use. Thoroughly mix by beating again with the egg-beater ; neutralize by adding five or six drops of acetic acid, and let stand over night. Before using, it must be frequently filtered through absorbent cotton until it is seen to be thoroughly clear and limpid, and with no shreds of albumen visible. To get it to this condition will necessitate filtering three or four times, and it will be found most con venient to take several graduates of varying sizes with a funnel containing the cotton in each, and pass from one to another, till the last be found in condition of sufficient purity to be flowed over the plate.
Flowing the the glass perfectly clean, immediately after rinsing in pure water, as above recommended, take the graduate containing the last filtered albumen solution in the right hand, while the glass is held in the left by the lower left-hand corner ; pour the solution copiously on the plate at the upper right-hand corner, and allow to flow gradually over it and run off at bottom. Flow at least twice, as much as possible preventing any from reaching the back, because of its not being necessary there, and of the injury it may afterward inflict on the silver sensitizing bath. After flowing twice, set up the plates on a rack to dry spontaneously, being careful to arrange them with the albumen side turned one way, as it is hardly possible to discern after drying which side has been albumenized. After drying, they may be stored in some convenient cupboard or shelf, and protected from dust by a cover being kept over them. Any number may be thus prepared at once, as they will keep for any length of time.
The next further stage in the process is the preparation of the collodion. This may be purchased ready prepared, but no work on the subject would be complete without the formula for making, and its preparation presents no great difficulty. There are many recipes, varying somewhat with the fancy which some operators think they have discovered in a few grains less or more of some one or other bromide or iodide salt, but all practically bringing out the same re sult ; the supposed excellence of one more than another probably resulting from the methods of handling the after operations. The following will be found to be one of the best : Alcohol, 95 per cent 8 ounces Iodide of ammonium 48 grains Iodide of cadmium 24 grains Bromide of cadmium r6 grains Pyroxyline 120 grains Sulphuric ether 8 ounces Dissolve the salts by grinding each separately in a mortar with a portion of the alcohol in the above order; add the pyroxyline and shake well; last, add the ether, and, after shaking, the whole will be seen to dissolve into a clear liquid of amber color. It will be sufficiently ripened
to work in a few hours, but will improve as it gets older. The ether being very volatile, it should be kept in glass-stoppered bottles. There are bottles manufactured for the purpose —" collodion pourers "—but in the absence of these an ordinary wide-mouthed bottle with glass stopper is an excellent substitute. The most convenient shape is that shown in Fig. 361. It allows all impurities to settle in the bottom, so that the collodion may be poured out without disturbing them, and the formation of the bottle is also such that air bubbles are not formed when pouring out the solution.
Flowing the so flow the collodion over the plate as to give a uniform coating requires a little dexterity that can only be acquired by practice. Take hold of the glass by the lower corner in the left hand, stretch ing the forefinger along the edge so as to give support at that point, while the thumb and middle finer support the bottom (see Fig. 362). Now, holding it as level as the eye can judge, pour a pool of collodion about the center, or nearer the top, of the plate with a steady, even flow, and of sufficient quantity to cover it. Incline the glass so as to make the collodion flow first to the upper right-hand corner (to No. 1), then over to the left (to No. 2), and then down to the bottom (to No. 3), allowing the surplus to flow off at the lower right-hand corner (at No. 4), into a wide-mouthed bottle, kept for the purpose, and fitted with a stopper or cork. This can be afterward utilized by filtering, and adding to the stock bottle.
The important object is to have a regular coating all over the plate; and to attain this there must be no hesitation in the pouring and flowing over the whole surface, and then, by raising it into a perpendicular position, allow the surplus to drain, at the same time giving it a to-and-fro motion sideways, but by no means such as would send it back over the plate. Having an eye to the careful preservation of the silver bath, wipe off all superfluous collodion that may have got on the back of the glass. It would set in a few seconds, indicated by its drying or thickening so as take the impress of the thumb at the lower corner where last poured off. Whenever this is noticed it is ready to be lowered into the sensitizing bath, which should be done without delay.