Miscella nies. 181 



ally becomes darker and darker, and is ultimately destroyed, owing to 

 the action of the light on it. The method I now follow is to put°the 

 paper into a diluted solution of water of ammonia (one of the spirit of 

 hartshorn to about six of water,) and leave it there till the yellow 

 parts become white, showing that the phosphate is dissolved, after 

 which it is washed with water to carry off the whole of the ammoni- 

 acal solution. It should then, when nearly dry, be subjected to pres- 

 sure till dried, by which it is prevented from wrinkling, and the im- 

 pression retains its original sharpness, which, unless this is done, it is 

 apt to lose, by the fibre of the paper being raised by the repeated 

 moistcninff. 



o 



t 



Thoiigli the phosphate specimens may be preserved in this way, 

 yet they do not retain exactly their original appearance- Those parts 

 whitened by the ammonia, owing to part of the silver being united 

 with the paper, gradually acquire a faint reddish tinge,— but, though 

 altering the appearance, it does not affect the brilliancy; indeed, in 

 some cases it rather improves it, by giving a pleasing tint, which con- 

 trasts well with the darker parts, and gives the appearance of color- 

 ing. I have also found that carbonate of ammonia answers equally 

 well, and, being much cheaper, it will of course be preferred. I gen- 

 erally employ a solution, prepared by dissolving one part of salt in 

 about four of water, in which the paper is kept for a minute or so, and 

 then afterwards washed, and subjected to pressure, as already noticed. 

 Impressions thus preserved acquire the same reddish tinge as those 

 acted on by anjmonia. 



I have before stated that the paper maybe prepared by washing it 

 over with a solution, procured by adding nitrate of silver to carbonate 

 of ammonia. The impressions taken with that paper are easily pre- 

 served by merely washing them with water, to carry off the part not 

 acted on by the light, which is another advantage, in addition to those 

 stated, for using the carbonate solution. Like the phosphate speci- 

 mens, they also acquire a reddish tint. 



Odier preservative methods have been recommended, as, by cover- 

 ing the impressions with a yellow color, to prevent, as much as possi- 

 ble, the transmission of the chemical ray of the light ; but those above 

 stated, particularly when the phosphate or carbonate is used, are so 

 simple and efficacious that it is unnecessary to allude to them. 



Before finishing this part of the subject, I may here allude to a val- 

 uable practical application of photography, in diminishing the labors 

 of the lithographer. In communicating the impression of any object 

 to the stone, as of a dried plant, or in copying an engraving, it is ne- 

 cessary to trace them on paper, and after again tracing ihem with the 

 transfer ink, transfer them to the stone. Now, by receiving the im- 

 pression on paper by the photographic process, all the labor of the 



