W. Crookes on the Wax-paper Photographic Process. 171 



room, and hooking the papers on to this by means of a pin bent 

 into the shape of the letter S. After a sheet has been hung up 

 for a few minutes, a piece of blotting paper, about one inch 

 square, should be stuck to the bottom corner to absorb the drop, 

 and prevent its drying on the sheet, or it would cause a stain in 

 the picture. 



39. While the sheets are drying, they should be looked at 

 occasionally, and the way in which the liquid on the surface 

 dries, noticed; if it collect in drops all over the surface, it is 

 a sign that the sheets have not been sufficiently acted on by the 

 iodizing bath, owing to their having been removed from the 

 latter too soon. The sheets will usually during drying assume a 

 dirty pink appearance, owing probably to the liberation of iodine 

 by ozone in the air, and its subsequent combination with the 

 starch and wax in the paper. This is by no means a bad sign, 

 if the color be at all uniform ; but if it appear in patches and 

 spots, it shows that there has been some irregular absorption of 

 the wax, or defect in the iodizing, and it will be as well to reject 

 sheets so marked. 



40. As soon as the sheets are quite dry, they can be put aside » 

 in a box for use at a future time. There is a great deal of un- 

 certainty as regards the length of time the sheets may be kept 



in this state without spoiling; I can speak from experience as to 

 there being no sensible deterioration after a lapse of ten months, 

 but further than this I have not tried. 



Up to this stage, it is immaterial whether the operations have 

 been performed by daylight or not; but the subsequent treat- 

 ment, until the fixing of the picture, must be done by yellow 

 light (51 



41. The next step consists in rendering the iodized paper sen- 

 sitive to light. Although, when extreme care is taken in this 

 operation, it is hardly of any consequence when this is performed; 

 yet in practice, it will not be found convenient to excite the paper 

 earlier than about a fortnight before its being required for use. 

 The materials for the exciting bath are nitrate of silver, glacial 

 acetic acid, and water. Some operators replace the acetic acid 

 by tartaric acid ; but as I cannot perceive the effect of this 

 change except in a diminution of sensitiveness, I have not adopted 

 it. It is of little importance what be the strength of the solu- 

 tion of nitrate of silver;, the disadvantages of a weak solution 

 are, that the sheets require to remain in contact with it for a con- 

 siderable time before the decomposition is effected, and the bath 

 requires oftener renewing ; while with a bath which is too strong, 

 time is equally lost in the long-continued washing requisite to 

 enable the paper to keep good for any length of time. The 

 quantity of acetic acid is also of little consequence. 



