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38 THE PHOTOGRAPHIC NEWS. [January 25, 1867. done; and when she is done with it, all the skill obtained in it will cease to be available for any other purpose. So far as this reason has weight, we are afraid it will remain in continual operation. Nevertheless, we believe that there is extended scope in photography for the employment of women, and that many duties in connection with the practical branches of the art might be performed by them, especially in large establishments, where the alleged neces sary supervision to avoid carelessness might be maintained. Some few gentlemen we know engaged in photography have been as successful in the experiment as others have been unsuccessful. Mr. F. R. Window informed us some time ago that his experience in employing young girls as printers was successful and satisfactory. The subject is an interest ing one, and we can only glance at it now; but we shall be glad to hear the experience of others of our readers. SILVER IN THE WHITES OF ALBUMENIZED PRINTS. Our readers are aware of the connection of Mr. Spiller’s name with the earliest detailed experiments ascertain ing the presence of silver in the whites of albumenized prints, and of his continued labours in devising means for its removal. They are also aware that, some months ago, in a letter in our columns, he pointed out that a communication we reproduced from the pages of an esteemed American contemporary, by Mr. Carey Lea, on the same subject, did less than justice to him in detailing similar experiments, without mentioning those of Mr. Spiller published years ago. Misconceiving the spirit of this letter, Mr. Lea regarded it as offensive, and a short correspondence, dis playing some little feeling, ensued. The last letter of this correspondence, one from Mr. Lea, appeared in a recent number, and we appended a note suggesting that the case was one simply arising out of mutual misunderstanding. As it was purely a personal matter, and arose out of corre spondence confined to our own columns, it surely might have been allowed to rest. But a contemporary, sniffing the battle from afar, regards it as “a free fight,” and, reproducing Mr. Lea’s letter we published a fortnight ago, devotes two columns to an article it heads “ Vindicatory.” Assuredly Mr. Lea’s character would be in bad case if it needed such vindication. He possesses, fortunately, a name which is honoured for the valuable practical work with which he is associated, and which will not be affected in any way by a passing discussion on a personal matter, any more than will that of Mr. Spiller, a name not less honoured for the practical scientific labours of its owner. We will not do Mr. Spiller so much injustice as to suppose that he needs any defence from the offensive censure and still more offensive patronage of the writer in question. We refer to the matter because he is deliberately charged with misquoting Mr. Lea’s article. Mr. Spiller, it is stated, " alters” one expression into another. Now this is simply untrue, and it is based upon another statement which is untrue. It is first asserted by this writer that we reproduced from his pages a certain article, which was, in reality, reprinted from the Philadelphia Phoixt- grapher, and distinctly accredited to that journal; and he charges Mr. Spiller with “ altering ” a passage on no other ground than that the article he quoted correctly from our American contemporary was different from that which appeared in the British pages! It is, perhaps, scarcely worth while to notice such mis representations : certainly not worth while to comment on them. It is only because a specific charge of “ altering ” a quasi-opponent’s sentences is brought against an esteemed contributor to these columns that we take any trouble to refute the calumny. Had the unnecessary interference been confined to an expression of the writer’s opinions on the subject with which he meddled, we should not have felt it necessary to notice them, however offensively expressed. ON THE PREPARATION OF PURE SILVER. BY WILLIAM CROOKES, F.R.S. Professor Stas has lately published a very important memoir on this subject, and as this is a matter which lies at the root of almost all photographic operations, a brief account of the process adopted by this greatest living master of rigorous analysis cannot fail to interest our readers. The method furnishes the metal with more ease and rapidity than any other known way, and it has the special advan tage of giving it in a state of rare purity. It must ulti mately supersede all other laboratory processes where pure silver is required. It is based upon the complete reduction which ammoniacal solutions of silver compounds undergo when added to ammoniacal cuprous sulphite, or to a mix ture of sulphite of ammonia and any ammoniacal salt of copper. At the ordinary temperature this reduction takes place slowly, with deposition of black, blue, or grey silver, according to the dilution of the liquids. Above a tempera ture of 60° C. the reduction is almost instantaneous, and the silver is precipitated in a state of division correspond ing to the dilution of the liquid, its colour varying from grey to pure white. The details of the process are as follows :—Silver coin is dissolved in dilute and boiling nitric acid ; the solution of nitrates of silver and copper is evaporated to dryness, and the saline mass fused. This fusion is necessary to destroy the nitrate of platinum which is often formed in dissolving silver coin.* After cooling, the nitrates are dissolved in an excess of ammoniacal water. The ammoniacal solution is allowed to rest for forty-eight hours. The limpid liquid is filtered through a double filter of paper, and then diluted with distilled water until it contains no more than two per cent, of its weight of silver. Neutral sulphite of ammonia is prepared by the direct saturation of ammonia with sulphurous acid gas. In order to ascertain the exact quantity of sulphite of ammonia required for the complete precipitation of the silver from the ammoniacal solution of silver and copper, a definite volume of sulphite of ammonia is heated to the boiling point, and the volume of the metallic solution decolourised by the sulphite was ascertained. Experiments have in fact proved that as soon as the hot solution of sulphite of ammonia is not coloured blue by the ammoniacal solution of cupric oxide, there remains no trace of silver dissolved in the liquid ; because in this case all the copper exists in the cuprous state, the presence of which is incompatible with that of any compound of silver dissolved in ammonia. The quantity of sulphite of ammonia necessary for the preparation of the liquid having been determined, it is added to the argentiferous solution, and, after being well mixed, it is left to itself for forty-eight hours in a closed glass flask, to prevent the contact of the air. At the end of this time about a third of the silver is reduced at the ordinary temperature, and precipitated in the form of a shower of crys tallized silver of a greyish white colour, and very brilliant. The decanted blue liquid is now placed in a water bath in quantities of ten litres at a time, and raised to a temperature of 60° to 70 s C. The time required to cause the elevation of temperature is quite sufficient for the complete reduction of the silver to the metallic state, and for the reduction of the cupric sulphite to the state of cuprous sulphite,! es P°' cially if care be taken to have a sufficient excess of sulphite of ammonia present. The silver being removed from the solution, the cold liquid is decanted, and the silver precipitated from the cold and warm solutions is washed separately with ammoniacal water. The washings are performed by decantation, and are continued as long as the washing water is perceptibly * The author has found by several trials that silver coin frequently contains iron, nickel, and traces of cobalt, platinum, and gold. . . f If the coin originally contained neither nickel nor cobalt, the ligina now becomes colourless. If, however, nickel is present, it has a slisht green tint; and it takes, on the other hand, a reddish tinge if there is coholt in solution.