A Manual Of Photography

212 PRACTICE OF PHOTOGRAPHY. easily fixed. Well soaking these in water dissolves out the excess of nitrate of silver, and thus the sensibility is somewhat diminished ; indeed, they may he considered as half fixed, and may in this state he kept for any convenient opportunity of completing the operation. Muriate of soda (common salt) was recommended by Mr. Talbot as a fixing material, hut it seldom is perfectly successful: as a cheap and easy method, it may he occasionally adopted, when the picture to he preserved is not of any particular consequence. It may appear strange to many that the same material which is used to give sensitiveness to the paper should be applied to destroy it. This may be easily explained: In the first instance, it assists in the formation of the chloride of silver ; in the other, it dissolves out a large portion of that salt from the paper, the chloride being soluble in a strong solution of muriate of soda. When common salt is used, the solution of it should be tolerably strong. The picture being first washed in water, is to he placed in the brine, and allowed to remain in it for some little time ; then, being taken out, is to he well washed in water? and slowly dried. If the brine is used in a saturated state, the white parts of the photograph are changed to a pale blue—a tint which is not, in some cases, at all unpleasant. I have in my possession some pictures which have been pre- pared more than eight years, which were then fixed with a strong brine, and subsequently washed with warm water. They have become slightly blue in the white portions, but otherwise they are very permanent ; and they have lost but little of their original character. The chloride of silver being soluble in solution of ammonia and some of its salts, they have been recommended for fixing photographs. The ammonia, however, attacks the oxide, which forms the darkened parts in some preparations, so rapidly, that there is great risk of its destroying the picture, or, at least, of impairing it considerably. It matters not whether the liquid ammonia or its carbonate be used, but it must be a very diluted solution. The only photographs on which I have used it with any success are those prepared with the phosphate of silver; and to these it imparts a red tinge, which is fatal to their use for transfers. The ferrocyanate of potash, or, as it is more commonly called, the prussiate of potash, converts the chloride into a cyanide of silver, which is not susceptible of change by light ; consequently this cheap salt has been employed as a fixing agent, but, most unfortunately, photographs which have been subjected to this preparation are slowly, but surely, obliterated in the dark.