PHOTOGRAPHIC NEWS. March 20, 1863, p.137
THERE is what I consider to be another fallacy which requires a passing notice, the belief in which has prevented any endeavour to ascertain whether it be not possible to obtain different --or better--tones than we do at present: I mean the belief that the base of the salting chloride has no effect in giving colour to the print; that the nitrates produced from these bases cannot have any effect, may be according to a pre-conceived theory, but it will be very evident that it is contrary to fact to any one who will watch the different hues produced by ammonium, sodium, and barium, provided they make use of their eyes. I ask, then, would it not be advisable to ascertain whether there be no nitrates, the addition of which will yield purple, black, or rich brown tones, according as the subject might require. Evidently the belief in this fallacy arises from what I also consider to be an erroneous idea as to the manner in which the double decomposition takes place when the dried chlorided albumen is sensitized by the nitrate of silver bath. According to an assumed theory, when the decomposition of the salting chloride takes place, the chlorine remains in the albumen, drawing to itself the silver from the bath; whilst the liberated nitric acid and oxygen, being left behind by the silver, draw to themselves, from the paper, the base of the salting chloride which the chlorine has liberated in consequence of its own greater affinity for silver. The chloride of silver being, therefore, formed in the albumen, and the nitrate of ammonia, soda, or baryta, as the case may be, being formed in the bath. Stating it shortly, it is assumed that the re-composition of the new chloride takes place in the paper, and the re-composition of the new nitrate in the bath.
When theories are at variance with facts methinks it is time that they were abandoned and others formed more in accordance with the results which practice exhibits; but instead of doing so, so tenacious of life is a fallacy, that we find persons who, although unable to deny the facts, are compelled to confess that they are at a loss to account for their existence, because they still persist in viewing them through the medium of a pre-conceived theory. Thus, in the celebrated controversy which took place about two years ago, respecting "the test[obliterated text] of used silver baths by the hydrometer silver meter[obliterated text] Dawson, the present lecturer on photography at Ki[obliterated text] -stated* that "theoretically the large amount of[obliterated text] arising from the double decomposition, must[obliterated text]late to such an extent as to render the hydrometer test useless;" and doubting the assertion " that such an accumulation did not practically take place, except to a very limited extent," he afterwards analyzed some old baths in order to satisfy his own mind on the point. Consequently, in a paper be subsequently read upon the subject, in allusion to one of these baths, he says**:--" I should certainly have expected to find a very much larger proportion of nitrates different from that of silver. The equivalent of nitrate of soda being 8497 (say 85), it follows that, for every two grains of nitrate of silver abstracted by decomposition, one grain of the former ought to be left in the bath. In the above case, certainly, and in some other baths I have tried, this accumulation of nitrate of soda or ammonia did not take place in any way commensurate with the quantity we ought to expect. Although these nitrates must inevitably be found, they are partly retained and taken away by the paper, in a way which I am at a loss to account for."
Again, persons have assumed that the nitrate of the base of the salting chloride does not affect the colour of the print, and though an intelligent use of their eyes cannot fail to tell them the contrary, they still adhere to this idea, and endeavour to find another cause for the colouration which they cannot gainsay. Thus, Mr. Hardwich, in the last edition of his Manual of Photographic Chemistry, page 479, in speaking of chloride of barium, says :--" It also slightly alters the colour of the photo-graphic-image when used in preparing positive paper, which may be due, in some measure, to a chemical combination of baryta with albumen." That it is the nitrate of baryta which produces the alteration of colour, is evidenced, I think, by the fact that it takes place in a much greater degree in plain salted paper, than it does in albumenized ; in plain salted paper the black colouring property of nitrate of baryta has not to contend against the red colouring of albumenate of silver, and no albumen being present, the peculiar colouration cannot here be produced by its combination with baryta. This theory of the nitrates of ammonia, soda, and baryta being formed in the bath, I believe to be based upon assumption, and to be contrary to fact. I maintain that the double decomposition and recomposition takes place on the surface of the paper ; the nitrate of silver solution leaves the vessel which contained it and adheres to the surface of the paper, permeating the film of dried chlorided albumen; I am therefore at a loss to conceive why theory should grant to the chloride of silver the privilege of being formed on the paper, where its constituents are present, but should deny the same privilege to the nitrate of ammonia, soda, and baryta, whose constituents are also present there. Whatever nitrates, otherwise than silver, are found in an old sensitizing bath for paper, I believe find their way there in consequence of a too long floating having dissolved them out of the albumenized surface of the paper where they had originally been formed.
The philosophy of positive printing upon albumenized paper is really such a comprehensive subject, that it would even be a vain attempt for any one with far greater abilities than I am possessed of, to endeavour to treat it satisfactorily in a paper which must necessarily be circumscribed in its length, in order to afford time for after discussion. I have, therefore, omitted even an allusion to those necessary accompaniments of printing--toning and fixing--and confined myself to the action of the preliminary sensitizing bath ; for, had I not done so, I must have encroached much more upon your time and attention, and I fear that you may think it has been trespassed upon too much already ; moreover, I deem that I have already furnished you with quite enough matter for an evening's discussion.
As a question naturally fixes attention to its own individual subject, allow me to state in that form, the various points which I consider particularly require elucidation, and upon which I invite your opinions,:--1st. What salting chloride for the albumen is the best to use, and why ? Also, is a combination preferable to a single one ? if so, what, and why ? and what proportion should the chloride bear to the albumen ? 2nd. How does the nitrate of the base of the salting chloride influence the colour of the print ? - 3rd. Supposing the albumenized surface of the paper be capable of being rendered insoluble previous to sensitizing, would that insolubility be an advantage ; or, would it not tend to diminish--or destroy--its capability of being sensitized by the nitrate of silver solution? 4th. Supposing we use a very strong sensitizing bath, is the vigour of the print dependent upon the length of time the albumenized paper is floated upon it ; and does its employment necessitate deeper printing than a weaker bath does? 5th. In sensitizing a sheet of albumenized paper, are two separate and distinct compounds of silver formed viz., the albuminate and chloride ; or, is a double compound formed ? 6th. Supposing two distinct and separate compounds of silver be formed by sensitizing, which of the three compounds of silver on the paper is the most important in the production of the image--the albuminate, the chloride, or the nitrate? What part does each play--and do they act conjointly or independently?
I do not mention the opinions I have advanced respecting dried albumen, and the manner in which the double decomposition and recomposition is effected when we sensitize a sheet of chlorided albumenized photographic paper, because they can be discussed incidentally with the points I have named.
In all philosophical discussions, but more especially when the subject is but little understood, mere assertion will never tend to enlighten us, however high an authority the person making it may be considered ; for we have had too many instances of men of science being led into grievous error and promulgating most extraordinary fallacies as facts; every gentleman, therefore, who gives his opinion upon any points that arise - in the discussion, will, I trust, state the reasons which induced him to form them, as he thereby gives the others an opportunity of showing whether they are fallacious or not. For the better elucidation of these points, I think I should be allowed the same privilege that counsel are, viz., that of cross-examination, which I will promise not to use rigorously. With this suggestion I now leave the subject in your hands to deal with in the manner you consider best.
ADDENDUM.
This, Mr. President and Gentlemen, is what I wrote for our last meeting, but its having been unavoidably postponed, a short addendum is now necessary. A paper has since been published in the journals, by MM. Davanne and Girard, "On the Action of Nitrate of Silver upon Albumen,"*** they state :-- "The combination of albumen with nitrate of silver varies according to the strength of the silver bath. Thus in treating five cubic centimetres of albumen with five grammes of nitrate of silver, we obtained very different precipitates, according as those five grammes of silver were dissolved, so as to form solutions of 15, 10, 5, 2~, or 1 per cent. With the solutions of 15 and 10 per cent., the albumen is strongly coagulated; it gives a heavy, abundant precipitate, which may be collected on the filter in the form of distinctly separate pellicles. With weak solutions of silver, the quantity of the precipitate is much less considerable. A notable quantity of albumen remains in the bath in a state of solution. The portion precipitated is soft, glutinous, and sticky."
This is an announcement that every one who knows anything at all about the subject, has been fully aware of long ago. If an egg be boiled what we deem soft, the white has very little consistence, but this consistence increases up to the point at which the yolk becomes, by boiling, what we designate hard; the albumen is then, what, for want of a better expression, I will call saturated with heat, and thus is perfectly coagulated; it is only therefore to this state that the term coagulated properly applies. The same, also, with respect to the combination of albumen with nitrate of silver. Albumenate of silver is, correctly speaking, only that combination of albumen which takes place when it is saturated with nitrate of silver, every combination below this is what may be considered as an imperfect albumenate. Common sense tells us that, as varying approximations to perfect coagulation are afforded by varying degrees of heat, so differing proportions of nitrate of silver must produce differing approximations to the perfect albumenate of silver.
I am ever willing to confess that I have formed an erroneous idea, when that idea is proved to he incorrect. I have, therefore, now to state that I have hitherto been in doubt whether, if the albumenized surface of a sheet of. photographic paper were rendered insoluble previous to sensitizing, this insolubility would not almost destroy its capability of being sensitized. This doubt is now dissipated, for Mr. Simpson has kindly furnished me with a piece of albumenized paper, the surface of which, Mr. Wood, of Edinburgh, has rendered insoluble by the aid of steam. This paper does not appear to have lost any of its capability of yielding either the albumenate or chloride of silver by sensitizing. A comparatively weak nitrate bath will, of course, produce good effects upon it, provided it be of sufficient strength to saturate the albumen in the ordinary time of floating, as a strong bath is only necessary when the albumen is soluble, because by hastening - the time when insolubility occurs, it prevents the solvent power of the water having full effect.
Ever since I have known anything of photography, I have been firmly convinced that the nitrates of the base of the salting chloride, affects the colour of the print; although this has: been strongly denied, the belief that such is the case has been daily gaining ground, and in Mr. Towler's "Lessons on Photography," No. 11, published in Humphrey's Journal, I now find my statement corroborated. In allusion to plain and albumenized paper, prepared for photographic printing, he says :-- "The chemical foundation in either, is an alkaline chloride, which by floating the paper on nitrate of silver, or ammonia nitrate of silver, becomes converted into chloride of silver, in a state of very fine division, mixed with the nitrate of the alkali employed. The latter salt modifies in a great measure the colour and intensity of the print produced. From this circumstance, we account for the different tones in different specimens of prepared paper. Some manufacturers use chloride of ammonium, others that of potassium, sodium, or lithium, in the salting of their paper ; each print, on this account, will have a different tone when it leaves the printing frame."
Under the title, "Coagulation of Albumen," I find in the leading article of the British, for Feb. 10th, some statements of the editor's, which require a passing notice. Alluding to MM. Devanne and Girard, he says:--" They go into another phase of the question, which has disturbed the equanimity of our antagonist, Mr. George Price--we mean that of the amount of albuminate of silver, in comparison with the chloride, produced upon a piece of positive photographic paper, on being sensitized on the nitrate of silver bath." Now, there is not a single word of truth in any part of this assertion; the whole of it is- such pure fiction, as not to have even the shadow of a fact for its foundation. I am no antagonist of Mr. Shadbolt in any way whatever, not having as yet entered into any controversy with him and moreover, my antagonism is against fallacies, and not against persons. I was the first person who drew attention to the erroneous ideas prevalent respecting the coagulation of dried albumen; and I believe also, that I am the only one who has calculated. from an atomic weight, the amount of albuminate of silver on a sheet of albumenized photographic paper; and how my equanimity can possibly have been disturbed by. so doing, I am at a loss to imagine, I only know that it has not been so in reality, for nothing I have ever written respecting the impossibility of coagulating dried albumen, has yet been disproved, although I have publicly challenged any one to do so. Mr. Shadbolt takes an exceedingly lofty flight in the realms of fiction, when he states the subject of M.M. Davanne and Girard's investigations to be "the amount of albuminate of silver in comparison with the chloride, produced upon a piece of positive albumenized paper on being sensitized on the nitrate of silver bath ;" the plain matter of fact being that their paper has no reference whatever to the amount of albuminate of silver in comparison with the chloride; they investigate simply "the action of nitrate of silver upon albumen," without any reference to either the alkaline chloride on the paper before sensitizing, or the chloride of silver produced by its being sensitized; and they state merely that varying strengths of the nitrate of silver solution produces varying degrees of coagulation of the albumen, and therefore varying compounds of albumen and nitrate of silver; a previously well-known fact. Because I calculated according to a particular atomic weight, it is a strange perversion of logic to assume, as Mr. Shadbolt does, when he says that its combination in other proportions is "an idea apparently ignored by Mr. Price." It happens, however, that for more than twenty years I have been well aware of the different character of the precipitates which varying strengths of solutions of metallic salts produce when mixed with albumen.
Mr. Shadbolt also says :--he alludes to the subject "for the purpose of discussing the accuracy or otherwise of certain propositions advocated and maintained by the editor of a contemporary and one of his correspondents, in opposition to certain others held by ourselves and one of our contributors." As what I have written appeared in the NEWS long before the British [obliterated text] any notice of the subject, I cannot have stated opinions [obliterated text] opposition" to certain others held by its editor and one of contributors; moreover, Mr. Shadbolt is the only person who has written in the British on the subject, and then it was only in reply to a letter of mine, when, amidst much misrepresentation and personal abuse of myself, he denied that this contributor entertained the opinion had attributed to him in that letter. What I wrote respecting the non-possibility of coagulating dried albumen was corroborated by Mr. Simpson before this; and it must be borne in mind that I commenced writing about albumen two years ago, although it is only lately that I have succeeded in arousing attention.
Mr. Shadbolt also says :--" It has been contended by one or both of our opponents that albumen, in contact with nitrate of silver and some other metallic salts, does not undergo coagulation, but merely combination with the metallic base." I am sorry to say that there is also not a word of truth in this statement; neither Mr. Simpson nor myself have ever said or written anything of the kind; and as Mr. Shadbolt has not ventured to gainsay aught that I have advanced, and has not published his opinions upon the subject of albumen, we cannot be his "opponents." He proceeds to say :--." We, on the contrary, maintained that there was no evidence to show that coagulation did not come about contemporaneously with combination, and cited several authorities in support of this view." This statement of what-he himself wrote in his own former leader, is also pure fiction; Mr. Shadbolt maintained nothing whatever of the kind he now says he did, nor did he cite any authorities to the purport he states; in what he did say on the subject he merely attempted to show that coagulation and insolubility were considered as synonymous terms, and to prove it he cited an authority who said -nothing upon the subject.
I have reluctantly felt compelled, in justice to myself, to take this notice of Mr. Shadbolt, and much regret to find that such gross misstatements and fictions can emanate from the editor of a scientific journal which claims to hold high rank amongst its contemporaries. With an apology for the extra length of time my addendum has claimed your attention, I now leave the proposed questions in your hands, to discuss in whole or part, or not at all, as you think best.
*PHOTOGRAPHIC NEWS, vol. v. n[obliterated text]
**PHOTOGRAPHIC NEWS, vol. v. p.116, and BRITISH JOURNAL OF PHOTOGRAPHY, vol. viii, p.103
***PHOTOGRAPHIC NEWS, vol. vii. Page 53.