After the picture is fully brought out, wash in cold, and subsequently in warm water, to remove the Gallic Acid, which, if allowed to remain, would discolour the Hyposulphite Bath. Then fix the Print in a solution of Hyposulphite of Soda, one part to two of water, continuing the action until the yellow colour of the Iodide disappears. The fixing Bath ought not to produce much change in the tint. If the Positive loses its dark colour on immersion in the Hyposulphite, and becomes pale and red, it has been insufficiently developed. The theory of this part of the process should be understood:--It is particularly the _second stage_ of the development of a Photograph (see p. 144) on which the fixing Bath produces no effect; and therefore a considerable change of colour in the Hyposulphite indicates that too little Silver has been deposited, and the remedy will be to push the development, adding a little Aceto-Nitrate to the Gallic Acid if the strength of the Bath be found insufficient to yield dark tones. The colour of Positives developed upon Iodide of Silver is not agreeable, and they become blue and inky when toned with gold. By fixing the proof in Hyposulphite of Soda which has been long used and has acquired sulphuretting properties, the tint is much improved; but the permanency of the Print under unfavourable conditions is lessened by adopting that mode of toning. A NEGATIVE PRINTING PROCESS UPON BROMIDE OF SILVER. By substituting the Bromide for the Iodide of Silver in the above process, the proportions and details of manipulation being in other respects the same, a more agreeable colour is obtained. Paper prepared with Bromide of Silver is less sensitive than the Iodide, but an exposure of one minute (in the printing frame) will usually be sufficient even on a dull day. The image is nearly latent, but sometimes a very faint outline of the darkest shadows can be seen. The proportion of Bromide used is likely to influence this point; the sensitiveness being diminished, but the image showing more of the details before development, when the quantity of the Silver Salt is reduced to a minimum. Either English or French papers may be used, but in the latter case the Bromide should be dissolved in Serum of Milk (p. 262), or it will be difficult to obtain a good surface picture. The proportion of Bromide may be five grains to the ounce of Serum. These proofs, even when simply fixed in plain Hyposulphite of Soda, are superior in colour to the Positives printed by the last formula upon Iodide of Silver; and the permanency is very great if the development be sufficiently pushed. The use of the Serum of Milk gives an advantage in resisting the oxidizing influences to which Positives are liable to be exposed (p. 150). GENERAL REMARKS ON NEGATIVE PRINTING. Printing by development should not be attempted until the manipulation of the ordinary process by direct exposure to light has been acquired.