TOOM.
In this state the paper is bibulous, or blotting-paper, and the next operation is to size it.
English papers are in general sized with a mixture of gelatine and alum, to which sometimes flour, resin, and yellow soap are added. French papers are sized with a less soluble size, consisting for the most part of starch, with a little potass.* The sheets of bibulous paper are placed, one at a time, in a vertical position in the tub of size, and pressed into close contact. After a time the papers are taken out, scraped, and pressed to remove the superfluous size, then parted, and pressed again, and • afterwards hung up to dry, a process which occupies two or three days, and must not be done too quickly. The paper is then pressed again.
The paper has now to be glazed or hot-pressed. This is done by • With respect to the sizing of French papers. The follovring recipe was given some years ago by the Societe d'Encouragement of Paris :— 100 kilogrammes of dry paper stuff, 12 „ starch, 1 ID reain, previously dissolved in 500 kilogrammes of carbonate of soda.
18 pails of water.
This size evidently renders the paper alkaline.
The following formula is given by M. Braconnot, in the " Annales de Chimie," Vol. 23 :— " To 100 parts of dry stuff', properly diffused through water, add a boiling uniform solution of 8 parts flour, vrith as much caustic potass as will render the liquid clear. Add to it 1 part of white soap previously dissolved in hot water. At the same time, heat half a part of resin with the requisite quantity of weak potass lye for dissolving the resin, mix both solutions together, and pour into them 1 part of alum dissolved in a little water.
This size also renders the paper alkaline. Alum has an acid reaction, and there fore English paper sized with alum and gelatine is acid and not alkaline.
placing a sheet of paper between two glazed pasteboards, alternately in a pile, and between every fifty pasteboards a hot iron plate, then subjecting the pile to the press. Or a pile of sheets of paper placed between pasteboards, may be rolled backwards and forwards upon a plate between cold iron cylinders. This communicates a glaze to the surface of the paper.
The paper is now finished, and has merely to be trimmed, and the sheets counted and sorted, and tied up in reams each containing 480 sheets.
The above operations of making paper by hand may be success fully imitated by machinery ; the paper is then said to be " machine made." It may be made in sheets of indefinite length.
Paper frequently contains metallic spots, consisting of particles of iron, brass, or zinc, detached from the machinery, or introduced through carelessness in sorting the rags. The roughness of the felts between which the paper is pressed also occasions inequalities of texture. It is highly desirable to remove these imperfections from paper which is to be used in photography. The practice employed by the French paper-makers of colouring their paper with artificial ultramarine, (sulphide of sodium,) is also highly objection able for photographic purposes, both as regards the appearance of the paper, and from the probability that the introduction of an alkaline sulphide into it might assist the process of fading of positive proofs.
Should the process of printing positives in carbon ever come into general use, (which it is tolerably certain that it will,) the imperfections now existing in paper for positives will be of less moment.