ae 
the: 
W. Crookes on the Wax-paper Photographic Process. 167 
any empyreumatic odor, and must cause no turbidity when 
mixed with a solution of nitrate of silver, e. g.in making the 
exciting bath (42). 
_ The gallic acid should be as nearly white in color as possible. 
Especial care should be taken to have the alcohol ood ; it 
should be 60° over proof, and of ney gravity 0°83. On evap- 
orating a few drops on the palm of the hand, no smell should be 
left behind, nor should it, under the same circumstances, leave 
any stain on a sheet of white spree 
_ 26. The hyposulphite of soda will be found one of the articles 
most difficult to obtain pure; there is a large quantity at present. 
in the market, having little else of the salt but the name, and is 
of course totally unfit for use; if there be the least doubt about 
its purity, it should be tested in the following manner :— 
eigh out accurately 10 grains of, nitrate of silver, dissolve 
this in half an ounce of distilled water; then add 4 grains of 
ehlorid of sodium (common salt) also dissolved in water. On 
mixing these two solutions together, a white curdy precipitate of. 
chlorid of silver will fall down. .N ext add 22 grains of the hy- 
posulphite of soda, and allow it to stand for about ten minutes, 
stir : 
less amount of residue will 
urity. 
nerally all the sheets lie in the same direction, therefore it is 
only necessary to ascertain that the smooth side of one of them 
is uppermost, and then draw a pencil once or twice along the 
exposed edges. : , 
28. The paper has now to be saturated with white wax.. The 
apparatus br this purpose has been previously described (11.) 
ne eax is to be made perfectly liquid, and then the sheets of 
‘Paper, taken up singly and held by one end, are gradually low- 
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