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 proportions with the lighter through imperfect rectification, are mischievous. Second, the proportion of caoutchouc in the solution and on the paper, should not be too small. Third, heavy pressure must be applied after the tissue is laid down on the caoutchouc paper: this is most important; that is to say, if the tissue and paper are laid together dry, if I may use the term. Of course, if the caoutchouc solution, or the tissue, or paper, is fluid when they are brought into contact, air can be excluded, and perfect cohesion obtained without pressure, but then a long time must be allowed for evaporation of the caoutchouc solvent. But probably the dry method will be preferred, and with that method strong pressure is indispensable, in order to avoid blisters. Fourth, in developing the prints, the paper on which they rest must be carefully handled, so as to avoid creases and rumples. Wherever a crease or incipient break in the paper occurs, there will be a blister. Fifth, avoid the use of very hot water. To that end, use tissue easily soluble; that is to say, tissue which is fresh, and that has been so quickly dried as to retain the normal solubility of the gelatine almost unimpaired.

When removed from the bichromate solution, if the back of the tissue be drawn over a glass rod the superfluous solution will be removed, and prevent insoluble spots in the print.

Never be in too great haste. Follow the given rules, and you will succeed. Cleanliness and care are quite as essential in this as in the silver process.

Remember that bichromate of potash is quite as poisonous as cyanide, and, getting it into cuts and abrasions of the skin, should be avoided.

Bubbles and blisters, in the tissue, arise from the presence of air in the pores, which suddenly expands when