PREPARATION OF THE IODIZED PAPER. 



Having selected paper of a close and even texture, and fine 

 surface, such as that recommended p. 4, and marked it on one 

 side with pencil, wash this side over carefully with a solution, con- 

 sisting of 30 grains nitrate silver, dissolved in one ounce distilled 

 water, which apply plentifully with a brush, thoroughly wetting 

 every part, but leaving no moisture unabsorbed ; this should be 

 done on a hard smooth board, and thoroughly dried in the dark. 

 Then take a solution of two hundred grains of iodide potassium in 

 half-a-pint of water, to which fifty grains of salt have been added ; 

 draw the paper over the surface of the liquid, letting it repose upon 

 it, when plastic, for a few seconds, never more than one minute. 

 After dipping, drain it, and lay it flat until about half dry, then 

 set it afloat in clean water for ten minutes, drawing it now and then 

 along the surface : hang it in the air to dry, and when dry smooth 

 it by pressure. It is of the utmost importance that all the soluble 

 salts should be got out of the paper, and this is readily effected by 

 leaving it floating for a time in water : a rougher washing would 

 loosen the iodide of silver. This paper will keep some time if 

 carefully laid by in a portfolio. 



APPLICATION OF THE GALLO-NITRATE OF SILVER. 



Dissolve fifty grains nitrate silver in two ounces of distilled 

 water, to which add one-fifth of its volume of strong acetic acid, 

 very pure. Dissolve also a small quantity of chrystalized gallic 

 acid in distilled water, about eight grains to the ounce.* When 

 about to use, mix one part of the latter solution with two parts of 

 the former, mixing however only a sufficient quantity for imme- 

 diate use, as the resulting liquid decomposes very rapidly. This, 

 and indeed all the operations connected with the calotype, should 

 be conducted in a room from which daylight is entirely excluded : 

 it is indeed preferable to surround any artificial light, which may 

 be used, with a screen of yellow glass, gauze, or paper, the rays 

 which pass through materials of this colour, having little or no 

 influence on the most sensitive preparations. The iodized paper 

 may now be washed evenly over on the prepared side, which may 



* A small quantity only of the gallic acid solution should be made at once, 

 as it soon undergoes a change, becoming of a yellow colour, and unfit for use. 



