PHOTOGRAPHIC CORRESPONDENCE.

Mr. Lyte on Collodion.—When I had the pleasure of meeting you in London, I promised that I would write to you from this place, and give you a detailed account of my method of making the collodion, of which I left a sample with you; but since then have been making a series of experiments, with a view, first, to simplifying my present formulæ, and next, to produce two collodions, one of great sensibility, the other of rather slower action, but producing better half-tones. I have also been considering the subject of

printing, and the best methods of producing those beautiful black tints which are so much prized; and I think that, although the processes formerly given all of them produce this effect with tolerable certainty, yet many operators, in common with myself, have met with the most provoking failures on this head, where they felt the most certain of good results.

I do not pretend to make a collodion which is different in its ingredients from that compounded by others. The only thing is that I am anxious to define the best proportions for making it, and to give a formula which even the most unpractised operator may work by. First, to produce the collodion I always use the soluble paper prepared according to the method indicated by Mr. Crookes, and to which I adverted in "N. & Q.," Vol. viii., p. 252. Take of colourless nitric acid of 1.50, and sulphuric acid of 1.60, equal quantities by measure, and mix them; then plunge into the mixture as much of the best Swedish filtering paper (Papier Joseph is also very good) as the liquid will cover; it must be placed in it a single piece at a time. Cover the basin, and let it remain a night, or at least some hours. Then pour off the liquid, and wash the paper till its washings cease to taste the least acid, or to redden litmus paper. Then dry it. Of this paper I take 180 grains to one pint of ether, and having placed them together, I add alcohol drop by drop, till the ether begins to dissolve the paper, which will be denoted by the paper becoming quite transparent. I have rather increased the quantity of paper to be added, as the after treatment rather thins the collodion. This, when shaken up and completely dissolved, forms the collodion. To sensitize I use two preparations, one prepared with potassium, the other with ammonium compounds; and, contrary to what many operators find the case, I find that the potassium gives the most rapid results. To prepare the potassium sensitizer, I take two bottles of, we will suppose, 6 oz. each; into one of these I put about half an ounce of iodide of potassium in fine powder, and into the other an equal quantity of bromide of potassium, also pounded; we will call these No. 1. and No. 2. I fill the bottle No. 1. with absolute alcohol, taking great care that there is no oxide of amyle in it, as that seriously interferes with the action of the collodion. After leaving the alcohol in No. 1. for two hours, or thereabouts, constantly shaking it, let it settle, and then quite clear decant it off into No. 2., where leave it again, with constant shaking, for two hours, and when settled decant the clear liquid into a third bottle for use. The oxide of amyle may be detected by taking a portion of the alcohol between the palms of the hands, and rubbing them together, till the alcohol evaporates, after which, should oxide of amyle be present, it will easily be detected by its smell, which is not unlike that exhaled by a diseased potato. Of the liquid prepared, take one part to add to every three parts of collodion. The next, or ammonium sensitizer, is made as follows. Take

Absolute alcohol 10 oz.
Iodide of ammon. 100 grs.
Bromide of ammon. 25 grs.

Mix, and when dissolved, take one part to three of collodion, as before. I feel certain that on a strict adherence to the correct proportion depends all the success of photography; and as we find in the kindred process of the daguerrotype, that if we add too much or too little of the bromine sensitizer, we make the plate less sensitive, so in this process. When making the first of these sensitizers, I always in each case let the solution attain a temperature of about 60º before decanting, so as to attain a perfectly equable compound on all occasions.

In the second, or ammonium sensitizer, the solution may be assisted by a moderate heat, and when again cooled, may advantageously be filtered to separate any sediment which may exist; but neither of these liquids should ever be exposed to great cold.

I dissolve in my bath of nitrate of silver as much freshly precipitated bromide of silver as it will take up. Next, as to the printing of positives to obtain black tints, the only condition necessary to produce this result is having an acid nitrate bath; whether the positive be printed on albumen paper, or common salted paper, the result will always be the same. I have tried various acids in the bath, viz. nitric, sulphuric, tartaric, and acetic, and prefer the latter, as being the most manageable, and having a high equivalent. The paper I now constantly use is common salted paper, prepared as follows. Take

Chloride of barium 180 grs.
Chloride of ammon. 100 grs.
Chloride of potassium 140 grs.
Water 10 oz.

Mix, and pour into a dish and lay the paper on the liquid, wetting only one side; when it has lain there for about five minutes if French paper has been used, if English paper till it ceases to curl and falls flat on the liquid, let it be hung up by a bent pin to dry. These salts are better than those generally recommended, as they do not form such deliquescent salts when decomposed as the chloride of sodium does, and for this reason I should have even avoided the chloride of ammonium, only that it so much assists the tints; however, in company with the other salts, the nitrate of ammon. formed does not much take up the atmospheric moisture, and I have never found it stain an even unvarnished negative. To sensitize this paper take

Nitrate of silver 500 grs.
Acetic acid, glacial 2 drs.
Water 5 oz.

Mix, and lay the paper on this solution for not less than five minutes, and if English paper, double that time. The hyposulphite to be used may be a very strong solution of twenty to twenty-five per cent., and this mode of treatment will always be found to produce fine tints. After some time it will be found that the nitrate bath will lose its acidity, and a drachm of acetic acid may be again added, when the prints begin to take a red tone: this will again restore the blacks. Lastly, the bath may of itself get too weak, and then it will be best to place it on one side, and recover the silver by any of the usual methods, and make a new bath. One word about the addition of the bromide of

silver to the double iodide, as recommended by Dr. Diamond. I tried this, and feel most confident that it produces no difference; as soon as the bromide of silver comes in contact with the iodide of potassium, double decomposition ensues, and iodide of silver is formed. Indeed, farther, this very double decomposition, or a similar one, is the basis of a patent I have just taken for at the same time refining silver and manufacturing iodide of potassium; a process by which I much hope the enormous present price of iodide of potassium will be much lowered.

F. Maxwell Lyte.

Hôtel de l'Europe,
à Pau, Basses Pyrénées.

P.S.—Since writing the former part of this letter, I see in La Lumière a paper on the subject of printing positives, in part of which the addition of nitric acid is recommended to the bath; but as my experiments have been quite independent of theirs, and my process one of a different nature, I still send it to you. When I have an opportunity, I will send a couple of specimens of my workmanship. I had prepared some for the Exhibition, but could not get them off in time. I may add that the developing agent I use is the same in every way as that I have before indicated through the medium of your pages; but where formic acid cannot be got, the best developer is made as follows:

Pyrogallic acid 27 grs.
Acetic acid 6 drs.
Water 9 oz.

On Sensitive Collodion.—As I have lately received many requests from friends upon the subject of the most sensitive collodion, I am induced to send you a few words upon it.

Since my former communication, I believe a greater certainty of manufacture has been attained, whereby the operator may more safely rely upon uniformity of success.

I have not only tried every purchasable collodion, but my experiments have been innumerable, especially in respect to the ammoniated salts, and I may, I think, safely affirm that all preparations containing ammonia ought to be rejected. Often, certainly, great rapidity of action is obtained; but that collodion which acted so well on one day may, on the following, become comparatively useless, from the change which appears so frequently to take place in the ammoniacal compounds. That blackening and fogging, of which so much has been said, I much think is one of the results of ammonia; but not having, in my own manipulations, met with the difficulty, I have little personal experience upon the subject.

The more simple a collodion is the better; and the following, from its little varying and active qualities, I believe to be equal to any now in use.

A great deal has also been said upon the preparation of the simple collodion, and that some samples, however good apparently, never sensitize in a satisfactory manner. I have not experienced this difficulty myself, or any appreciable variation.

The collodion made from the Swedish filtering paper, or the papier Joseph, is preferable, from the much greater care with which it is used.

If slips of either of these papers be carefully and completely immersed for four hours in a mixture of an equal part (by weight) of strong nitric acid or nitrous acid (the aqua fortis of commerce) and strong sulphuric acid, then perfectly washed, so as to get entirely rid of the acids, the result will be an entirely soluble material. About 100 grains of dry paper to a pint (twenty ounces) of ether will form a collodion of the desired consistence for photographic purposes. If too thick, it may be reduced by pure ether or alcohol. However carefully this soluble paper or the gun cotton is prepared, it is liable to decompose even when kept with care. I would therefore advise it to be mixed with the ether soon after preparation, as the simple collodion keeps exceedingly well. Excellent simple collodion is to be procured now at the reasonable price of eight shillings the pint, which will to many be more satisfactory than trusting to their own operations.

To make the sensitizing Fluid.—Put into a clean stoppered bottle, holding more than the quantity required so as to allow of free shaking, six drachms of iodide of potassium and one drachm of bromide of potassium; wet them with one drachm of distilled water first, then pour into the bottle ten ounces of spirits of wine (not alcohol); shake frequently until dissolved. After some hours, if the solution has not taken place, add a few more drops of water, the salts being highly soluble in water, though sparingly so in rectified spirits; but care must be taken not to add too much, as it prevents the subsequent adhesion of the collodion film to the glass.

A drachm and a half to two drachms, according to the degree of intensity desired, added to the ounce of the above collodion, which should have remained a few days to settle before sensitizing, I find to act most satisfactorily; in fine weather it is instantaneous, being, after a good shake, fit for immediate use. If the sensitive collodion soon assumes a reddish colour, it is improved by the addition of one or two drops of a saturated solution of cyanide of potassium; but great care must be used, as this salt is very active.

Hugh W. Diamond.