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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Bandzählung
- No. 1404, July 31, 1885
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The photographic news
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Band 29.1885
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- Register Index III
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THE PHOTOGRAPHIC NEWS. [July 31, 1885. here, it also increases the tendency to blister ; but this can be avoided by the use of ammonia in hypo, and also in the salt bath after the hypo; also by not taking them out of the salt bath, but letting the water into the salt bath gradually. Paper (silvered on this solution) one day old becomes very difficult to tone unless a very large amount of alkali is used in the toning bath, the action of the alkali being to soften the now insoluble albumen, and allow its being toned. I add the formula that has worked well on the brilliant albumen papers in the market:— Nitrate of silver .. ... ... ... 437} grains Water ... ... ... ... ... 12 ounces Nitric acid 3 drops Chrome alum 5 grains After silvering twelve sheets upon this solution, add the same amount of silver solution, composed as given. By experience it has been found that one ounce of silver will silver one dozen sheets of paper. By doing this, constant good prints are obtained, and poor ones when this is neglected. Chrome alum added to an alkaline silver solution will be precipitated. Its good effects are to be had only from an acid silver solution —Philadelphi'i Photograjihcr, Pa. o STRENGTH OF THE HYPO BATH FOR GELATINE NEGATIVES. BY W. E. DEBENHAM.* The question of the strength of the hypo bath for negatives is one which has from time to time been referred to, generally, I think, in connection with a statement that a strong bath will not fix a plate so rapidly as will a more dilute solution ; but, so far as I am aware, there has not been published anything like a complete and systematic set of experiments, and statements are still made of a most conflicting character. Certainly, at the last meeting of this Society, some plates were fixed in the presence of the members, and one thing which had been on all hands antici pated was realised, namely, that a dry gelatiuo-bromide of silver plate would take longer to fix in a bath saturated with hypo- sul phite of soda, than in one which was only half that strength. This was only what was to be expected, as the salt at thatjdegree of concentration does not at all readily yield up its water of solution to the gelatine. Indeed, as some other considerations will show, it actually is capable of withdrawing some of the water- from a softened gelatine film, and thereby renders it less amenable to the solvent action of the soda salt. However, as we do not dry our films before placing them in the hypo, this experiment, however interesting in itself, does not bear much upon the question at issue. Another experiment that was made, was the placing of two halves of a wetted plate (thus more nearly realising the actual conditions of our work) in dishes, one of which contained a saturated solution of hypo, and the other a solution of half that strength. Here there was a curious conflict of experiences, for being carried out four times, in two cases the Saturated solution worked the more rapidly, and slower in the other two. The slight differences in favour of the one on the other solution, it was proposed to ex plain by the fact that the plates which fixed more rapidly in the stronger solution had been soaked in water for a longer time previous to being placed in the hypo. If this really hid had any infl ience it should have been the other way, since it is only reasonable to suppose that as a dry plate fixed slower than in a saturated solution, and one which had been swelled in water for three minutes fixed quickly, a plate soaking half an hour should, if there was really any difference, be softer still, and fix yet more rapidly. There was, however, another condition imported into this trial which may explain the apparent contradictions. The plates that had been long soaking were placed in hypo dishes that were kept in agitation during the whole time of fixation. This would end to remove the water from the film, and replace it by satu- t ated solution of hypo, temporarily hardening the film by ab- rstraction of its water. In this way, the varying results of the experiments thus made may be explained without violence. In the enquiry as to whether a strong or weak hypo bath fixes the more rapidly, the question first arises : What strength would be considered respectively as strong or weak ? A very common recommendation has been to make the bath with five parts of water to one of the salt; and if this be considered a • before the London and Provincial Photographic Association. medium strength, two of water to one of hypo may be taken as strong, and ten of water to one of hypo as weak. A saturated solution of hypo is of course more than merely strong; it is very strong, as strong as possible, and it is probable that it is not generally known how strong it really is. Hyposulphite of soda is one of those substances which dissolve in proportions at different temperatures. For the purposes of these experiments, I made a saturated solution on a day recently when the temperature was, for a July day, moderate, the maxi mum for the day being 73° Fahrenheit. I found 1 part by weight (1,000 grains) of water take up just 2 parts (2,000 grains) of hypo. The next, morning, however, although the lowest temperature during the night had been 57°, I found that 240 grains, or nearly one-eighth, had gone down in crystals. The hulk of solution was a little more than two volumes (2150), so that a measured ounce of saturated solution at 73° would contain nearly an ounce by weight of hypo itself. It will thus be seen what a very strong solution of this salt is a saturated one, and even when diluted with an equal quantity of water, it is still what would generally be considered as strong. I may remark that although what would pass as saturated solution is nearly enough exact for the purpose of the photo grapher, when an exact experiment is in question it is necessary to be particular, and the solution which is near the top of a bottle, with crystals lying at the bottom, will not readily become saturated, nor remain in that condition if subjected to varying temperatures. In order to try the effect of solutions of varying strength, I made up five solutions as follows:—No. 1, saturated ; No. 2, equal parts crystals of hypo and of water; No. 3, 2 parts of water to 1 of hypo ; Nos. 4 and 5, respectively 5 and 10 parts of water to 1 of hypo. Plates, one made with bromide only, and the other containing 3 per cent, of iodide, were then soaked for three minutes in water, and placed in the solutions, with the result which I have arranged in a tabular form. 1.—Saturated solu tion of hypo 2.—Equal weights of hypo and water 3.—Hypo... Water ... 1 part ... 2 parts 4.—Hypo... ... 1 part Water ... 5 parts 5.—Hypo... ... 1 part Water ... 10 parts Pure bromide plate fixed ia Bromide with 3 per cent, iodide plate fixed in 20 seconds 20 seconds 20 „ 20 „ 30 » 50 ,, 40 „ 3 minutes 90 „ 8 „ The fixing was conducted in black dishes, so that it might be clearly seen when the result was obtained.' Nevertheless, it is difficult to tell to a second exactly when the last of the bromide is gone, and the time given for the two strongest baths must only be taken to mean that the plates were apparently fixed by the time stated (twenty seconds), and does not denote that some of them might not be fixed in a little shorter time. The third bath, one of hypo to two of water, which is still a strong one, shows but little falling off in speed of action upon a pure bromide plate, but when, as in most commercial, and perhaps privately made emulsions, some iodide is contained, the fixing is notably slower. The most striking difference is shown when using a weak 10 per cent, or moderate 20 per cent, bath for plates, containing even the small percentage of iodide mentioned. Here the 1 to 5 bath required three minutes, and the 1 to 10 bath eight minutes for complete visible fixation, whilst the bro mide plates required only forty and ninety seconds respectively. The experiments were repeated several times with very similar results. Where a difference appeared, an average has been given. A curious appearance presented itself upon the plates fixed in the saturated solution. After fixation, and when light was freely admitted, a very slight milkiness was observable, which dis appeared upon washing. Of course it might be suggested that this milkiness was due to an undissolved silver compound, but upon replacing the plate—after having become clear during washiog—in the saturated solution, a similar milkiness again made its appearance, and was therefore doubtless due to the effect of the saturated solution in depriving the gelatine of a portion of the water which it had imbibed. The total result of these experiments is altogether in favour of strong solutions of hypo for speedy fixation. Even in the case of the saturated solution, although there was no increase of rapidity
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