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