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374 THE PHOTOGRAPHIC NEWS. [August 7, 1863. is exhaled which is sensibly different from pure chlorine. The compound is generally regarded as consisting of hypo chlorite of lime, chloride of calcium, free chlorine, and lime. Chloride of lime is said to be soluble in ten parts of water, which is equivalent to forty-eight grains to the ounce. It appears to be, however, more probably decomposed by water, as on adding this proportion to form a saturated solution a bulky precipitate is formed, which consists simply of hydrate of lime deprived of its chlorine. It will be seen from this that formul containing what is termed a satu rated solution are apt to be misleading, as the manipulator is very apt to suppose he has obtained a saturated solution as soon as he sees a permanent precipitate, which will occur, however, long before he has obtained a really saturated solution. Again, chloride of lime is constantly changing in composition. In a vessel exposed in any degree to atmospheric action it is destroyed by the absorption of carbonic acid. Even when kept carefully stoppered a slow change is taking place, by which it is eventually converted into chlorate of lime and chloride of calcium. If a really saturated solution of freshly made chloride of lime be made by dissolving about forty-eight grains in an ounce of water, a drachm will contain six grains ; sufficient, and sometimes too much, for two or three grains of gold. Carbonate of lime is very sparingly soluble in ordinary water, which rarely dissolves more than half a grain to the ounce. In Parkinson’s formula, it will be seen that if the chloride of lime have been freshly prepared, and great care have been used to secure a saturated solution nearly four grains would be used to each grain of gold. Such a propor tion would probably, in many cases, especially when newly made, give excessive bleaching and mealiness. In many cases it is probable that the chloride of lime used is not freshly prepared, and possibly the solution is not really saturated, the presence of undissolved hydrate of lime mis leading the manipulator in this respect. It is quite possible that the difference between an old and a new sample of chloride of lime, and the difference between real and appa rent saturation may account for the varying experiences of some careful manipulators, and may* account for success and failure. The remedy for failure in such a case is to adopt the suggestion of Mr. Hughes in our last: where bleaching and mealiness exist, decrease the amount of chloride of lime; when it is difficult to get a sufficiently black tone increase the amount. There is another point which may be worthy of notice, it is this :—Experimentalists, when trying a new bath, very naturally commence by im mersing one or two prints. Now, if the quantity of solution be sufficient for many prints, and it contain free chlorine, it follows from the great affinity of that element for silver that the prints are at once attacked, all the free chlorine in the solution sufficient for a score of prints, it may be, is at liberty to act upon one or two, and considerable bleaching ensues, sometimes to the entire destruction of the print. Mr. Parkinson, in a recent letter, speaks of putting two hundred prints at once into a sufficient quantity of solution to tone them, and leaving them, with occasional turning over, for an hour, when the toning was completed. In trying this bath, then, it is probably desirable to use no more of the solution than is required for toning the prints immersed in in it, so that there may not be the free chlorine of a larger quantity of solution to act upon a small number of prints. Although the method of preparing the bath adopted by Mr. Parkinson is very convenient, and gives such excellent results in some hands, possibly more certainty may be ob tained by weighing a definite proportion of chloride of lime than in using a saturated solution. A method we have re peatedly tried, and always with success, is to make a solution of chloride of gold one grain to the ounce, to this add excess of carbonate of lime, agitating well, and leaving the excess at the bottom of the bottle ; to each ounce of this add from one to two grains of chloride of lime if freshly made, and from two to three grains if it have been kept some time. When required for use dilute the solution by the addition of seven or eight ounces of water. This should be ready for use in a few hours, or keep for weeks. We subjoin Herr Liesegang's modification of a similar formula, and his comments thereon, given some time ago in the Photographisches Archiv. Take any chloride of gold in the market, dissolve it in rain water; then add to this solution common chalk in quantity of about one-sixth the weight of the chloride of gold dissolved; the chalk must be finely pulverized before it is mixed with the gold solution. The free acid of the gold combines with the lime and forms chloride of calcium, leaving probably a small quantity of carbonate of lime. After standing for an hour or two, shaking frequently in the meanwhile, the solution is filtered through broken glass and kept for use; it is a solution of the double chloride of gold and of calcium. If 15 grains of ordinary acid chloride of gold were used in the solution, then, to form the toning bath, take 45 ounces of rain water with which mix the solution of the double chloride ; to this mixture add of a solution of chloride of lime until the whole assumes an alkaline reaction. Of the value of the bath so made he speaks in the highest terms. This description of gold bath, we are inclined to believe from experience, will last for a long time ; at least, the qualities of a solution that has been prepared for more than a month have not undergone the slightest alteration ; hence it may be argued that they will bo retained much longer—a great advantage for amateurs, who only occasionally take a small quantity of the solution, dilute it with water, and thus can apply it. This gold-toning bath for albumen paper is an important improvement. In the first place it is a clear and colourless solution, quite permanent, and immediately ready for use. Besides this, it does not bleach the prints, nor render them mealy like other gold baths. It is a solution of the double chloride of gold and of calcium, with a small addition of chlo ride of lime to neutralize the acid, and to give the solution a slightly alkaline reaction. The advantages of this solution over the gold bath, containing carbonate of soda, acetate of soda, and phosphate of soda, can easily be comprehended. All these baths are liable to change and precipitate the gold: the soda giving up the acid with which it is combined, enters into combination with the chlorine of the gold. But in our new bath the alkali is already in combination with chlorine, and thus neither withdraws chlorine from the gold salt nor preci pitates the gold. When the excess of the alkaline salt is either a carbonate, acetate, or phosphate, the base gives up the weak acid with which it is in combination, and robs the chloride of gold of its chlorine; but when the excess of the alkaline salt is a chloride, such an effect is not produced, and the solution is perfect. In the preparation of this toning bath, it is necessary to be very careful to add neither too little nor too much of the chloride of calcium to the chloride of gold; a definite formula cannot be given, from the fact that commercial chloride of gold is very variable as to the quantity of free acid which it contains. It is better to use the gold bath not too concentrated, the slower the process of toning, the more brilliant the picture remains. The bath loses strength with each print that is toned, but it remains clear and colourless, and can be strengthened by the addition of fresh solution. Before toning, the prints have to bo thoroughly washed. We have treated this subject at some length, because, having recommended the lime bath as possessing certain specific good qualities, we are anxious to give such informa tion on the subject as will enable any of our readers to use it with satisfaction, and because for certain subjects requiring pure blacks and warm neutral tints, it gives better results than any bath we know. PHOTOGRAPHY AT THE ASSIZES. A case was heard on Tuesday last, before Mr. Baron Erani well and a common jury, at Croydon Assizes, which wi interest photographers, and points a moral as to the im portance of having contracts relating to photography, well as other matters, properly drawn and duly stamped.
