I have said that the above solutions comprise all that are necessary for the development of the negative, but it will be convenient to describe here the preparation of the solutions which will be required when we come to the sub sequent operation of printing from it.
For the process known as " silver printing" we shall only require one additional solution, namely, a toning bath, the basis of which is a salt of gold. Before we prepare this wo had better take the hermetically sealed tube of chloride of gold, carefully break it, and dissolve the contents in a clean stoppered bottle containing 15 drm. of distilled water. The reason for so doing is that chloride of gold being very deliquescent—that is, prone to absorb moisture from the air —we should lose a great deal of the costly chemical in attempting to weigh out small quantities, whereas, if we make it into a solution of the above definite strength, we shall know that each drachm of it will contain 1 gr. of gold. To make the toning bath, place 4 drm, of acetate of soda in a large bottle, add 2 pints of distilled water, agitate until the crystals are dissolved, and then add 8 drm. (fluid measure) of the gold solution. This solution may be used over and over again until exhausted, when it will refuse to tone ; it improves by keeping, and should never be used until after twenty-four hours from the time of mixing.
For the other printing process, which I shall hereafter describe, we shall require a distinct set of solutions, which, as they will keep indefinitely, we may as well now make up. The process I refer to is known as the " bromide pro cess," and prints produced by it are developed in the same way as is an ordinary negative, but the solutions used are different, the particular form of developer known as " ferrous oxalate" being employed. This consists of two stock solutions : one a saturated solution of oxalate of potash, the other a saturated solution of sulphate of iron. By " saturated solution " is meant a solution in which is dissolved as much of the chemical substance as the water is capable of taking up. To make the first, put into a clean jug (the vessel employed should be retained for the purpose, and not returned to the kitchen for future domestic use) half a pound of the crystals of oxalate of potash, and pour over them about 12 oz. of water, stir vigorously, and if after a few hours some crystals remain undissolved, it may be assumed that the solution is a saturated one. The solution will probably present a turbid or milky appearance, due to the presence of oxalate of lime. It should be poured into a large funnel, in which a filter paper has been placed, and filtered into a clean bottle. In this condition it will keep indefinitely. It may then be labelled " Saturated solution of oxalate of potash, No. 1." No. 2 consists of a saturated solution of sulphate of iron, and to make it proceed in the same way, put half a pound of the sulphate of iron crystals in a clean jug, pour about 10 oz. of water upon it, and stir well. Filter and bottle off, labelling it, " Saturated solution of sulphate of iron, No. 2." Finally, add 10 minims of strong sulphuric acid.
The " alum bath " used for clearing negatives from stain consists of a saturated solution of alum, and is made by dissolving as much of the salt in warm water as it will take up. This solution must also be filtered and labelled
" Clearing bath." The next solution is one that we must both prepare and use with the greatest care, as it contains one of the most active poisons known. It is called " the intensifying solu tion," and it consists of a saturated solution of bichloride of mercury. It is made by carefully dissolving in 5 oz. of distilled water, -1 oz. of the salt. It should be plainly labelled "Solution of bichloride of mercury," and a "poison" label should also be affixed to the bottle. Its use will be fully explained when we come to deal with the intensifica tion and reduction of negatives.
When we have prepared the next two solutions, we may consider our laboratory arrangements fairly complete. To make them we place in a 10-oz. stoppered bottle 9,1 oz. of distilled water ; to this we add 160 gr. of hydroquinone. This substance is not very soluble, but constant agitation will effect solution. When it has entirely dissolved, add 2 oz. of sulphite of soda, 60 gr. of citric acid, and 30 gr. of bromide of potassium. Label this " Hydroquinone developer, No. 1." Then, in another clean 10-oz. bottle, dissolve 160 gr. of soda hydrate in 9 oz. of distilled water. Filter, and label " Hydroquinone developer, No. 2." I have already pointed out the necessity of avoiding any chance of mistaking one solution for another by carefully labelling all bottles. Convenient books of printed labels, containing the names of all chemicals, developers, and solutions in ordinary use, are now to be obtained from most dealers in photographic apparatus. One of there should be purchased, and a,11 our bottles labelled. But if we content ourselves with simply a,ffixing the labels to the bottles by means of the mucilage at their back, we shall probably find that, be we as careful as we ma,y, the labels will sooner or later be affected by a portion of the solution running down from the necks of the bottles after they have been in use, and the effect of this will be that in a very short space of time the labels will become illegible, if, indeed, they do not entirely detach themselves from the glass. This state of affairs can, however, be remedied with very little extra trouble. Dissolve by means of gentle heat about 20 gr. of gelatine in 1 oz. of water, and with a small brush paint over each label, carrying the brush well over the margin of the label 011 to the glass. Obtain at the oll-shop some hard oak varnish, and, when the labels have become thoroughly dry, paint them over with the varnish in a precisely similar manner with a stiff hog-hair brush. Labels so treated will rema,in firmly attached to bottles for a, very long while, and if at any time they should become discoloured, they may oe washed or wiped with a damp cloth.
The photographer should always have by him a sufficient quantity of distilled water—it can be purchased in quantity at a very low rate—and all the solutions should be made up with it. Ordinary tap water is generally contaminated with foreign substances, more or less—many samples of London water being rich in carbonates, while in some country districts organic matter is found suspended in large quantities. By using distilled water difficulties of this kind will be avoided.