Volltext Seite (XML)
October 17,1862.] THE PHOTOGRAPHIC NEWS. 503 water the better, as otherwise a film of insoluble carbonate or chloride, adhered to the surface, and caused irregular toning. Mr. Wall has found that keeping the toning solution before nse, was the best remedy for mealiness. After some further conversation on the subject, Mr. LEAKE briefly replied to various objections. He thought that notwithstanding all that had been said, a microscope ex amination of the surfaces would prove the superiority of plate glass. As to toning, he believed the best results were obtained by using a bath made some time, but if it were necessary, to use it as soon as mixed, a large excess of acetate of soda would give similar results to age. As to the use of carbonate of soda in the toning bath, he believed it to be the worst thing which could be used. After some further conversation, Mr. Wall, referring to the process of printing on resinized paper, thought that societies might with propriety, at times, step out of their routine, to thank individuals for liberally giving to the public valuable processes, through other channels than their own meetings. He therefore begged to propose a vote of thanks to Mr. Cooper, for the account of his process pub lished in the Photographic News. The vote of thanks was passed by acclamation. Mr. Simpson exhibited a panoramic picture taken by Mr. Sutton on one of his dry plates, with just the same exposure as ho would have given to wet collodion. The picture gave general satisfaction. Mr. Simpson also showed a varity of charming card pictures, by Window, Robinson, and Southwell. Mr. Carbutt, of Chicago, showed an album with many very fine card pictures, which were much admired. Messrs. Schnadhorst, J. Chaplin, and W. Chaplin, were elected members of the society. The proceedings then terminated. • Corxespondence. IODIDES AND BROMIDES IN COLLODION * * Continued from p. 479. Dear Sir,—Since writing to you a few days ago, I have Wore closely examined the “ Proceedings of the South London Photographic Society,” published in the Photo- GRAPIIIC News of the 10th May, 1802. I shall remark, categorically, on Mr. Blanchard’s experi ments, the results of which were then laid before the meeting. Without intending anything in the way of offence, I must Tecord my opinion that the publication of the results, backed by Mr. Blanchard’s reputation, have caused, doubtless, much heart-breaking and vexatious disappointments to all those who have taken them as conclusive. And conclusive they must have been considered, especially when you and Mr. Fry endorsed those results. In the first experiment of Mr. Blanchard, the necessary equality of conditions in the iodizing and bromo-iodizing Solutions, insisted on in my preceding letter, has not been observed. In the one case the salting solution is 3} grains; And in the other 5 grains, a little less than double. Now I ask Mr.’B., in all fairness, how the result could be otherwise than in favour of the 5} grain collodion, even if there had been no bromide in the latter? And if, as I understand him, 2 distinct samples' of collodion were used, how could the results of the one be reasonably arrayed against the other? In the second experiment the error is repeated—no less ‘bat 6} grains in one case, and only 3} in the other—but no mention either is made whether only one collodion or two Were used. Irrespective of the great difference in results, his matter alone would cause—an iodide of potassium is ’elected against a sensitive bromo-iodizer! Now if Mr. lanchard had taken the iodides of potassium and cadmium equal proportions for his iodizers in the one case, against A bromo-iodizers o f ammonium and cadmium (by way of Pproach to equality of conditions), he would have found the dourts very difficult of decision one way or the other. Nor an he say how much cadmium was in the 41 grains of emonium and cadmium of his bromo-iodizers, for the more mumium the more sensitive the collodion. In short, by a still further consideration of the matter, the amount of bro mide is so large, that the proposed iodizer of half potassium and half cadmium would have proved superior to his bromo- iodizer. In experiments 3 and 4, if, instead of taking potassium only for one half the plate, he had added 14 grains iodide of cadmium to it, and arrayed its results against those of the bromo-iodized half plate, he would have found them run parallel to each other, for there would have been intimate equality in the two solutions. And indeed my own experience would point even to a superiority of the iodized collodion over the bromo-iodized one, simply on account of the excess of bromide. Experiment 5 proves simply the correctness of Mr. Sutton’s experiments, that bromide alone is insensitive to light, or rather causes insensitiveness. But if Mr. B. had been aware of the principle of excitation propounded by me in my previous letter, he would have been fairer to poor bromide. He would have not used bromide of cadmium alone, but a mixture of the bromides of ammonium and cadmium, and the resulting produce would not have been quite so feeble as it turned out. Although the result of experiment 6 was not produced at the meeting, Mr. B. has given sufficient particulars regard ing it. Like the preceding ones, I must, at the risk of a charge of rudeness, pronounce it utterly unfair. No approach to equality of conditions in the iodizing and bromo-iodizing solutions are observed. If, instead of simply 34 grains of potassium in the one case, he had added 1, grains of iodide of cadmium to the same, and then developed with pyro, he would have found the result superior to the bromo-iodized half plate: for the proportion of bromide used is too large to array against the said simply iodised collodion, although the latter were under pyro development. Still less would it have stood against the same iodized collodion, if iron development had been used with the latter, as in the iodizers of the pre ceding five experiments. And now, as regards the whole of these experiments con jointly, the marvel is, how the coating and developing of these plates was satisfactorily done. There must have been a hitch somewhere. The coating first—how were the two col lodions applied? if simultaneously, how was the excess poured off, and a proper uniform coating given ? and under any circumstances the two collodions, whether of one sample or not, being differently iodized,and having therefore different setting properties, how was this part of the process regu lated, so as to ensure the necessary amount of setting to each half of the plate ? if lowered into the bath by one of the long ends downwards to allow of this, how was the excitation regulated? And in the case of the last experiment, how were the iron and pyro developers prevented from running into each other, and the necessary amount of development given each half of the plate. It occurs to me that the experiments in question should have been performed with one sample of collodion, variously iodized and bromo-iodized, as required, and with the necessary equality of conditions for a fair trial, with separate plates with one bath and one strength of developers. Trusting that you will find a corner for this letter also —I remain, dear sir, yours truly, Augustus Webb. Meerut, N. IF. P. India, 2^th July, 1862. Potograppic glotes anir (Queries, Resinized Paper. Dear Sir.—By correcting an error, in the 23rd lino you will oblige. As I have never found the benzoin become yellow, but always black, it should be bleach or whiten by exposure to the light and air. I am proceeding very satisfatorily with this process. I have also much improved the formula, or I may say remodelled it, as the salting solution is not in the substance of the paper, but entirely on the surface. The finished print much resembles ivory. I shall forward results and particulars at my earliest opportunity.—I am, sir, yours obediently 21 Jude street. H. R. Nichols,