302 THE HISTORY OF SOME DISCOVERIES OF PHOTOGRAPHY. 



of a communication to the Academy of Sciences in Paris. His re- 

 marks were printed in extenso in the Comptes Rendus. 



Mr. Talbot's description of his process, the patent for which is 

 dated 1841, is as follows:" 



Take a sheet of the best writing paper, having a smooth surface 

 and a close and even texture. The watermark, if any, should be 

 cut off lest it should injure the appearance of the picture. Dis- 

 solve 100 grains of crystallized nitrate of silver in G ounces of dis- 

 tilled water. AA^ash the paper with this solution with a soft brush 

 on one side, and put a mark on that side, whereby to know it again. 

 Dry the paper cautiously at a distance from the fire, or else let 

 it dry spontaneously in a dark room. AVhen dry, or nearly so, dip 

 it into a solution of iodide of potassium, containing 500 grains of 

 that salt dissolved in one pint of water, and let it stay two or three 

 minutes in the solution. Then dip the ])aper into a vessel of water, 

 dry it lightly with blotting paper, and finish drying it at a fire, 

 which will not injure it even if held pretty near; or else it may be 

 left to dry spontaneously. All this is best done in the evening by 

 candlelight. The ])aper, so far prepared, is called iodized paper, 

 because it has a uniform pale-yellow coating of iodide of silver. It 

 is scarcely sensitive to light, but nevertheless it ought to be kept 

 in a portfolio or drawer until wanted for use. It may be kept for 

 any length of time without spoiling or undergoing any change, if 

 protected from sunshine. AVhen the paper is required for use take a 

 sheet of it and wash it with a liquid prepared in the following manner : 



Dissolve 100 grains of crystallized nitrate of silver in 2 ounces of 

 distilled water; add to this solution one-sixth of its volume of strong 

 acetic acid. Let this be called mixture A. 



Make a saturated solution of crystallized gallic acid in cold dis- 

 tilled water. The quantity dissolved is verj^ small. Call this solu- 

 tion B. 



Mix together the liquids A and B in equal volumes, but only a 

 small quantity of them at a time, because the mixture does not keep 

 long Avithout spoiling. This mixture Mr. Talbot calls the gallo- 

 nitrate of silver. This solution must be washed over the iodized 

 paper on the side marked, and being allowed to remain upon it for 

 half a minute, it must be dipped into water, and then lightly dried 

 with blotting paper. Tliis operation in particular requires the exclu- 

 sion of daylight ; and although the paper thus prepared has been found 

 to keep for two or three months, it is advisable to use it within a few 

 hours, as it is often rendered useless by spontaneous change in the dark. 



o Mr. Talbot, by a letter in the Times of August 13, 1852, gives to the public 

 the right of using any of his patents for any purpose not involving the produc- 

 tion of portraits from life. 



