30 i THE HISTORY OF SOME DISCOVERIES OF PHOTOGRAPHY. 



solution of ffallic arid to 1 part of the solution of nitrate of sulvor 

 ordinarily used. It can then be dried without fear of spoiling, may 

 be kept a little time, and used without further preparation. 



5. The improvement of photographic drawings by exposing them 

 twice the usual time to the action of sunlight. The shadows are thus 

 rendered too dark and the lights are not sufficiently white. The 

 drawing is then washed and plunged into a bath of iodide of 

 potassium of the strength of 500 grains to each pint of w^ater and 

 allowed to remain in it for one or two minutes, which makes the 

 pictures brighter and its lights- assume a pale-yellow tint. After this 

 it is washed and immersed in a hot bath of hyposulphite of soda 

 until the pale-yellow tint is remoA'ed and the lights remain quite 

 white. The pictures thus finished have a pleasing and peculiar effect. 



6. The appearance of photographic pictures is improved by wax- 

 ing them and placing white or colored paper behind them. 



7. Enlarged copies of daguerreotypes and calotypes can be obtained 

 by throwing magnified images of them, by means of lenses, upon 

 caloty])e paper. 



8. Photographic printing. A few pages of letterpress are printed 

 on one side only of a sheet of paper, which is waxed if thought 

 necessary, and the letters are cut out and sorted; then, in order to 

 compose a new page, a sheet of white paper is ruled with straight 

 lines and the words are formed by cementing the separate letters in 

 their proper order along the lines. A negative photographic copy 

 is then taken, having white letters on a black ground; this is fixed, 

 and any number of positive copies can be obtained. Another method 

 proposed by the patentee is to take a copy by the camera obscura from 

 large letters painted on a white board. 



9. Photographic publication. This claim of the patentee consists 

 in making, first, good negative drawings on papers prepared with 

 salt and ammonio-nitrate of silver; secondly, fixing them by the 

 process above described; thirdly, the formation of positive drawings 

 from the negative copy, and fixing. 



These claims, taken from the specification as published in the 

 Repertory of Patent Inventions, are preserved in their original form 

 for the purpose of showing how much that is now fully accomplished 

 was foreseen by Mr. Talbot as the result of his discoveries. 



SECTION IV. PIC1TJRES ON PORCELAIN TABI.ETS. 



A third patent has been obtained by Mr. Talbot, mainly involving 

 the use of porcelain as a substitute for glass, and contains some useful 

 facts noticed by Mr. Malone. 



The first part of the patentee's invention consists in the use of 

 plates of unglazed porcelain to receive the photographic image. A 

 plate intended for pliotographic purposes should be made of the finest 



