so) On Sun Pictures. 455 
trees and shadows ought to be nearly as white as the colour 
of the paper. 
The picture, if carefully fixed according to the above direc- 
tions, will be quite unalterable by daylight. Care should be 
taken to keep the back free from spots and blots, as they 
would cause white blotches in the positive pictures, now to 
be described. 
7th Operation—The Positive Paper, or Printing 
Process. 
Dissolve 8 grains muriate of soda (common galt), in 
1 ounce of distilled water. Take a clean sheet of paper, 
and having, as before, marked one side, fix it on to a board 
and sponge it quickly and eyenly over with this solution. 
Dry it, and keep it for use. 
8th Operation—Sensitive, for Positive Paper. 
Dissolve 50 grains of nitrate of silver in 1 ounce of dis- 
tilled water. Drop into this solution as many drops of liquid 
ammonia as will cause the white precipitate which then forms 
nearly to clear—then stop; add to it 4 or 6 drops of acetic acid, 
and shake up the mixture, which will keep without change 
if closely shaded from daylight. Brush this into the posi- 
tive paper prepared in the above-mentioned manner; then 
dry it thoroughly (by candle-light only), and the paper will 
keep for twelye hours or so. 
9th Operation—In the Pressure Frame. 
Place the prepared paper and a negative picture face 
to face, and then put them into the pressure frame, with 
the back of the negative picture next the glass; so that 
when placed directly opposite the sun, its rays may pass 
through the negative picture to the positive paper placed 
