PHOTOGRAPHY. 



saturated solution of gallic acid (i grain of pyro- 

 gallic acid to 4 ounces of solution, seems to render 

 the action more rapid) ; allow it to rest for four or 

 five minutes ; then add twelve drops of aceto- 

 nitrate, agitating the bath to secure complete 

 mixture. A few drops must be added from time 

 to time. The development will now proceed very 

 beautifully, and will require from twenty minutes 

 to several hours. When it is completed, the 

 sheet is washed in water, which must be changed 

 two or three times during an hour, after which it 

 is fixed in a solution of hyposulphite of soda, of 

 the same strength as that employed for a plain 

 calotype. 



THE ALBUMEN PROCESS. 



This process succeeded those on paper for 

 landscapes, and some kinds of architecture. The 

 results sometimes obtained by it can hardly be 

 excelled by those of any other process. It was 

 first suggested by M. Niepce, and shortly after- 

 wards, Messrs Ross and Thomson of Edinburgh 

 attained great success in the practice of it. From 

 the difficulty of conducting the process with the 

 required nicety, it has been little followed by 

 amateurs. A plate of glass, perfectly flat, is 

 thoroughly cleaned. A mixture of albumen (white 

 of egg) and water, containing iodide of potassium 

 in solution, is beaten into a froth, and after having 

 subsided, is poured upon the plate, which requires 

 to be kept in a horizontal position until the albu- 

 men has been dried by exposure to a considerable 

 degree of heat. In this state, it is insensitive to 

 light, and will keep good for some time. To 

 render sensitive, it is placed for a short time in a 

 solution of nitrate of silver, to which acetic acid 

 has been added, and then washed with two or 

 three changes of water. When dry, it is ready 

 for the camera. These plates may be made to 

 keep good for some hours or weeks, according to 

 the amount of washing given on removal from the 

 aceto-nitrate bath. The exposure is somewhat 

 long compared with dry processes by collodion, 

 and may extend from three minutes to one or two 

 hours, according to circumstances. The develop- 

 ment is accomplished by immersion in a solution 

 of gallic acid, to which a small quantity of nitrate 

 of silver solution has been added. The image is 

 fixed by hyposulphite of soda. 



COLLODION NEGATIVE PROCESS. 



This is the most beautiful of all photographic 

 processes, and is the one which seems, more than 

 any other, to be capable of almost indefinite 

 improvement. Pictures are taken by it almost 

 instantaneously, with a minuteness of detail and a 

 delicacy of expression which give results no less 

 wonderful than beautiful. 



The plates used are of glass : the medium or 

 which the pictures are received is a thin film 

 deposited on its surface from a solution of gun- 

 cotton (pyroxyline) in ether and alcohol This 

 solution is called collodion. 



The glass plates must be very carefully cleaned 

 by washing under a tap, and drying with a per- 

 fectly clean cloth. A few drops of a plate-c 

 solution, consisting of rouge, ounce ; alcohol, 6 

 ounces ; and water, 2 ounces, are then poured on 

 the plate, and briskly rubbed with a tuft of cotton 



wool on both sides. This is then rubbed off" with 

 a cloth, and a final polish given with a third cloth, 

 and the plate is ready for the collodion. The 

 cloths should be kept each for its special purpose, 

 and numbered I, 2, and 3. Plates which have 

 been used should be soaked in a strong hot 

 solution of potash, contained in a shallow tub or 

 earthenware foot-bath. In a short time the old 

 Sim becomes easily detached ; they are then 

 treated as before. 



When large plates are used, it will be found 

 advantageous to give them a coat of dilute 

 albumen, made of the white of one egg, and 

 2 drachms of strong ammonia, to 20 ounces of 

 water. This may be applied to the cleaned 

 plate in the same way as collodion, and insures 

 both a chemically clean surface, and perfect adhe- 

 sion of the collodion film. Good flattened crown- 

 glass is suitable for all ordinary purposes. 



To coat a plate, it is held by one corner between 

 the forefinger and thumb of the left hand, and in 

 a nearly horizontal position. The collodion is 

 poured on at the opposite corner, allowed to flow 

 round the plate, and back into the bottle. In 

 pouring off the collodion, the plate should be 

 tilted just enough to let it run freely, and as the 

 last drops run into the bottle, it should be gently 

 rocked, to prevent the formation of lines. It 

 must now be allowed to set for from thirty 

 to sixty seconds, according to the temperature, 

 c., and then slipped quietly and continuously 

 into the nitrate of silver bath by means of a 

 dipper, upon which the plate is laid, and which 

 is usually made of a slip of fluted glass, one end 

 of which has been fused and turned up to form 

 a groove on which the plate may rest. This 

 operation must be performed in what is called 

 the 'dark room,' but which is in reality a room 

 lighted by a deep yellow or orange light. The 

 following is the for- 

 mula for the nitrate 

 bath : Nitrate of 

 silver, 13 drachms; 

 pure water, 8 

 ounces : dissolve, 

 and add iodide 

 of potassium, 5 

 grains. Shake well, 

 to dissolve the yel- 

 low iodide of sil- 

 ver, which will be 

 precipitated ; then 

 add water, 16 

 ounces. After 



being filtered, it 

 is fit for use. In 



fig- 13, M represents the most convenient f 

 bath-dish, usually made of glass or porcelain. 

 N is the top of the dipper projecting from the 

 dish. 



Immediately after insertion m the bath, tl 

 plate should be moved about for a few seconds, 

 and then left undisturbed for from two to three 

 minutes. It should then be lifted up and down 

 several times ; and when the solution flows freely 

 over the surface, and leaves no oily-looking 

 streaks, it is drained for a little, and placed face 

 downward in the slide, and exposed as soon as 

 possible in the camera. The period of cxposui 

 depends upon many circumstances, and may vary 

 from i to 50 seconds. The next stage m the 



