It is necessary to prevent the liquid from flowing over the back of the paper, which it would cover with a 2 blue stain, and to prevent this the edges of the print are turned up all round. On lifting a corner, the progress of the development may be watched. As soon as the lines are sufficiently dark, or blue specks begin to show themselves in the white parts, the process must be immediately arrested by placing the sheet on a bath of pure water. If, as often happens, a blue tint then begins to spread all over the paper, it may be immersed in a mixture of 3 parts sulphuric or 8 of hydrochloric acid, to 100 of water. After leaving; it in this acidulated liquid for 10 or 15 minutes, the design will seem to clear, and the sheet may then be rinsed in a large basin of water, or under a faucet furnished with a sprinkling nozzle, and a soft brush used to clear away any remaining clouds of blue; and finally, the paper hung up to dry. The ferrocyanide bath is not subject to change, and may be used to the last drop. If it begins to crystallize by evaporation, a few drops of water may be added. The specks of blue which are formed in this bath, if not removed by the subsequent washings, may be taken out at any time by touching them with a weak solution of carbonate of soda or potash.

The prints may be coloured in the usual way.

(3) Blue figures on a white ground are changed into black by dipping the proof in a solution of 4 oz. common potash in 100 oz. water, when the blue colour gives place to a sort of rusty colour, produced by oxide of iron. The proof is then dipped in a solution of 5 oz. tannin in 100 oz. water. The iron oxide takes up the tannin, changing to a deep black colour; this is fixed by washing in pure water.

(4) Joltrain's. Black lines on white ground. The paper is immersed in the following solution: - 25 oz. gum, 3 oz. chloride of sodium, 10 oz. perchloride of iron (45° B.), 5 oz. sulphate of iron, 4 oz. tartaric acid, 47 oz. water. The developing bath is a solution of red or yellow prussiate of potash, neutral, alkaline, or acid. After being exposed, the positive is dipped in this bath, and the parts which did not receive the light take a dark green colour; the other parts do not change. It is then washed with water in order to remove the excess of prussiate, and dipped in a bath containing acetic, hydrochloric, or sulphuric acid, when all the substances which could affect the whiteness of the paper are removed. The lines have now an indigo black colour. Wash in water, and dry.

(5) Copies of drawings or designs in black and white may be produced upon paper and linen by giving the surface of the latter two coatings of: 217 gr. gum arabic, 70 gr. citric acid, 135 gr. iron chloride, 1/4 pint water. The prepared material is printed under the drawing, and then immersed in a bath of yellow prussiate of potash, or of nitrate of silver, the picture thus developed being -afterward put in water slightly acidified with sulphuric or hydrochloric acid.

(6) Benneden states that paper, prepared as follows, costs but 1/6 as much as the ordinary chloride of silver paper, is as well adapted to the multiplication of drawings, and is simpler in its manipulation. A solution of bichromate of potash and albumen or gum, to which carbon, or some pigment of any desired shade, has been added, is brushed, as uniformly as possible, upon well-sized paper by lamplight, and the paper is dried in the dark. The drawing, executed on fine transparent paper (or an engraving, or wood-cut, &c), is then placed beneath a flat glass upon the prepared paper, and exposed to the light for a length of time dependent upon the intensity of the light. The drawing is removed from the paper by lamplight, and after washing the latter with water, a negative of the drawing remains, since the portions of the coating acted on by the light become insoluble in water. From such a negative, any number of positives can be taken in the same way.

(7) Dieterich's copying-paper. The manufacture may be divided into 2 parts, viz. the production of the colour and its application to the paper. For blue paper, he used Paris blue, as covering better than any other mineral colours. 10 lb. of this colour are coarsely powdered, and mixed with 20 lb. ordinary olive oil; 1/4 lb. glycerine is then added. This mixture is, for a week, exposed in a drying-room to a temperature of 104° to 122° F. (40° to 50° C.) and then ground as fine as possible in a paint mill. The glycerine softens the hard paint, and tends to make it more easily diffusible. Melt 1/2 lb. yellow wax with 18 3/4 lb. ligroine, and add to this 7 1/2 lb. of the blue mixture, mixing slowly at a temperature of 86° to 104° F. (30° or 40o C). The mass is now of the consistence of honey. It is applied to the paper with a coarse brush, and afterward evenly divided and polished with a badgers' hair brush. The sheets are then dried on a table heated by steam. This is done in a few minutes, and the paper is then ready for the market. The quantities mentioned will be sufficient for about 1000 sheets of 36 in. by 20, being a day's work for 2 girls. For black paper, aniline black is used in the same proportion.

The operation must be carried on in well - ventilated rooms protected from fire, on account of the combustibility of the material and the narcotic effects of the ligroine. The paper is used between two sheets of paper, the upper one receiving the original, the lower one the copy.

(8) A process similar to autoscopy. The pad is prepared with glue, glycerine, and water, in the same manner as for the well-known hectograph, but with a larger proportion of glue. For writing or drawing, a concentrated solution of alum is used, coloured with a little aniline to render the writing visible. Before using, the pad is damped by means of a wet sponge, and the moisture is permitted to remain a few minutes. The writing may now be applied, and upon removing it, after a short time, the lines will be transferred to the pad. A small quantity of printers' ink is applied with a rubber roller, and will be taken up by the etched lines only. An impression is obtained by pressing moistened paper over the lines with the palm of the hand. The pad must be inked for each copy, bat a great number may be made from the same etching or transfer.