I generally pour all waste solution of silver into a jar of iodide of potassium solution; and last year, having washed some of the precipitated iodide of silver, I redissolved it in a solution of iodide of potassium of an unknown strength. Paper prepared with this solution answered very satisfactorily, kept well after excitation, and was very clear and intense; but this was purely accidental: and if you can tell me how to insure like success this summer, without a series of experiments, for which I have but little time just now, the information will be very acceptable to me, and probably to many others.
I excite my paper with equal proportions of saturated solution of gallic acid and aceto-nitrate of silver, one or two drops of each to the drachm of distilled water. I always plunge the bottle of gallic acid solution into hot water when first made, which enables it to take up more of the acid; on cooling, the excess crystallises at the bottom. This ensures an even strength of solution: it will keep any length of time, if a small piece of camphor be allowed to float in it.
J. W. Walrond.
Wellington.
[The resultant iodide from fifteen grains of nitrate of silver, precipitated by means of the iodide of potassium, will give the requisite quantity of iodide for every ounce of water; or about twenty-seven grains of the dried iodide will produce the same effect. It is however far preferable, and more economical, to convert all waste into chloride of silver, from which the pure metal may be again so readily obtained. Iodide of silver, collected in the manner described by our correspondent, is very likely to lead to disappointment.]
Albumenized Paper.—I have by careful observation found that the cause of the albumen settling and drying in waving lines and blotches on my paper, arose from some parts of the paper being more absorbent than others, the gelatinous-like nature of the albumen assisting to retard its ready ingress into the unequal parts, and, consequently, that those places becoming the first dried, prevented the albumen, still slowly dripping over the now more wetted parts, from running down equally and smoothly, thereby causing a check to its progress; and as at last these become also dry, thicker and irregular patches of albumen were deposited, forming the mischief in question.
The discovery of the cause suggested to me the propriety of either giving each sheet a prolonged floating of from ten to fifteen minutes on the salted albumen, or until every part had become fully and equally saturated; or, as a preliminary to the floating and hanging up by one corner on a line, of putting overnight between each sheet a damped piece of bibulous paper, and placing the whole between two smooth plates of stone, or other non-absorbent material.
Either method produces equally good results; but I now always use the latter, thereby avoiding the necessity of otherwise having several dishes of albumen at work at once.
Henry H. Hele.
Cyanide of Potassium (Vol. ix., p. 230.).—I have for a long time been in the habit of using a solution of the above-named substance for fixing collodion positives, because the reduced silver has a much whiter appearance when thus fixed, than when the hyposulphite of soda is used for the same purpose; but I cannot quite agree with Mr. Hockin that it is equally applicable to negatives, though in many cases it will do very well. I find the reduced metal is more pervious to light when fixed with the cyanide solution, particularly in weak negatives. Lastly, I find that a small quantity of the