NATURAL PHILOSOPHY. 161 



1,000 parts of rice water, 

 40 " sugar of milk, 



15 u u iodide of potassium, 



0.80 " " cyanide of potassium, 



0.50 " " fluoride of potassium. 



The sheet of paper should be laid in this solution for half an hour, 

 and it may then be withdrawn, and hung up to dry. 



The paper is then immersed in a clear solution of aceto-nitrate of 

 silver, which is thus formed : 



300 parts of distilled water, 

 20 " " acetate of silver, 

 24 u u crystallizable acetic acid, 

 5 " " animal charcoal. 



The animal charcoal serves to render the paper more susceptible to 

 receive impressions, and decolorizes the solutions when they have 

 been previously used. The paper should remain three minutes in this 

 solution, and in order to insure contact with the liquid, the two sides 

 of the sheet should be rubbed over with a brush. The paper is then 

 washed several times with distilled water, and well dried between 

 pieces of blotting paper. Paper thus prepared may be taken imme- 

 diately into the dark chamber, and it is not necessary to subject the 

 image to the action of gallic acid on its removal from the camera ; 

 this may be deferred till the evening, or even the next day, or the 

 day following. 



The paper may be kept in a dark place for more than a fortnight, 

 without undergoing any alteration ; and in this respect offers greater 

 advantages than any of the photographic papers hitherto known. 

 The solution of gallic acid is composed of one part of gallic acid, half 

 part (0.5) of nitrate of silver, and 200 parts distilled water. The 

 image is fixed, as usual, by the hyposulphite of soda. 



Whipple's Chrystalotype. The following is the outline of a process 

 discovered by Mr. J. A. Whipple, of Boston, for the production of a 

 picture on paper, to which the name chrystalotype has been given. 

 A glass plate is first prepared with a sensitive coating, and on this the 

 picture is taken. As in all such pictures, when prepared after Tal- 

 bot's process on paper, the light objects are here represented the 

 darkest, and the dark ones the lightest. A black man with a white 

 hat becomes a white man with a black one. The lights in this glass 

 picture are transparent. The shades are opaque. In the preparation 

 of this plate, we presume, is Mr. Whipple's invention. Xow, take 

 this plate, place under it a sheet of paper prepared with one of the 

 photographic solutions, and let the sun strike through. The light 

 parts of the plate are copied dark, and vice versa. Of course, the 

 black man gets a black face again, and a white hat. 



The pictures taken by this process upon paper are of marvellous 

 delicacy and finish, and surpass anything of the kind we have here- 

 tofore examined. 



