PHOTOGRAPHIC PAPER. 87 



Daguerreotype. — According to Belfield Lefevre, and Fou- 

 cault, an ordinary iodized silver plate, exposed to bromine vapor, 

 until it assumes a dark purple tint, is less susceptible, but 

 produces the lightest and darkest parts of the picture in com- 

 plete detail. (Phil. Mag. xxx. 213.) 



For various improvements in the Talbotjpe process, see 

 Kep. Pat. Inv. for Aug. 1850. 



Photographic Paper. — Blanquart-Evrard's method of pre- 

 paring this paper is as follows (An. de Chim. et de Phys. xx.) 

 To produce the negative picture, the best smooth letter-paper 

 is laid for 1 minute upon the surface of a solution of 1 pt. 

 nitrate of silver in 30 pts. water, taking care that no air-bubbles 

 intervene. It is now removed, suffered to drain off, laid on a 

 glass plate and suffered to dry. It is then passed into a 

 solution of 25 pts. iodide of potassium, and 1 pt. bromide of 

 potassium, in 560 pts. water, so that the surface covered with 

 silver-salt is uppermost, and after remaining in it for l|-2 

 minutes, it is taken out, washed in a large quantity of water, 

 drained, laid on glass and dried. Before putting it into the 

 camera,, it is moistened on the first side with a solution of 6 

 pts. nitrate of silver, in 11 pts. crystallizable acetic acid, and 

 64 pts. water, and, after the action of light, with a saturated 

 solution of gallic acid. The negative picture then appears. 



The paper for the positive picture is laid for 2-3 minutes 

 upon the surface of a solution of 3 pts. common salt in 10 pts. 

 distilled water, carefully dried between blotting-paper, then 

 passed for a few minutes through a solution of 1 pt. nitrate 

 of silver in 6 pts. water, dried, and protected from light. The 

 negative picture and the positive paper are laid together be- 

 tween two glass plates, exposed for some 20 minutes to sun- 

 light, laid in water for some 15 minutes in a dark room, and 

 then passed through a solution of 1 pt. hyposulphite of soda 

 in 8 pts. water (containing also a little nitrate of silver). By 

 the latter action, the white ground becomes clearer, and the 

 red tints pass into a brown and lastly into black. 



Horlsley prepares it thus. Fine paper is passed through a 

 solution of 4 grm. common salt or salammoniac in 25 centi- 



