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NOvEM 554 THE PHOTOGRAPHIC NEWS. [November 21,1862. If we compare the albuminate with the chloride, we find that it is always in excess, excepting No. 10, Mr. Hardwich’s, where it is little more than half the quantity ; and that it ranges from this up to very nearly four times the amount, as in No. 12, Mr. T. R. Williams’s. It seems, therefore, to be the general opinion, that the albuminate should be in excess of the chloride—Mr. Hardwich, in his last edition of “ Photographic Chemistry,” having given the same formula as No. 8, Mr. G. W. Simpson’s. An inspection of the tables I have calculated, suggests several interesting questions, well worthy of discussion. Firstly, which of the three compounds of silver—the albu minate, the chloride, or the free nitrate—plays the most important part in positive printing upon albumenized paper? Table No. 2 seems to infer that the free nitrate does, so as it is largely in excess of the others; but I ask, whether such an enormous excess is really necessary ? It must be borne in mind, that the quantity there given is produced by sensitizing upon only a seventy-grain bath ; and if we use from “ one hundred to one hundred and thirty,” which we are recommended to do “ from expe rience,” we, of course, materially augment the excess there given; for we cannot make any addition to the quantity of albuminate or chloride by increasing the strength of the nitrate solution. Secondly.—What part does the free nitrate play?—is it a principal, acting in co-operation with the albuminate and chloride in the intricate process of the formation of the image ? or is it but an accessory, though, perhaps, a neces sary one, to its formation? We are told that the action of light upon chloride of silver decomposes it, by liberating the chlorine, and that silver, having a greater affinity for chlorine than it has for nitric acid, the nitrate of silver is in turn decomposed by the silver leaving the nitric acid to combine with the liberated chlorine; this decomposition and re-composition going on during the whole time of printing. According to this theory, which is generally, if not universally received, the nitrate of silver, as such, has nothing whatever to do with the formation of the image, but only furnishes a larger amount of chloride of silver for its production than the paper originally contained, so as to give it more vigour and intensity. This re-composition of chloride of silver during printing, must have its limits with respect to the quantity necesary to be supplied for the formation of a vigorous image ; and therefore, the free nitrate beyond what is requisite to furnish this amount, must be useless,—if it plays no other part than this. If it really has no other duty to perform, we have only to give at once, the required amount of chloride of silver, by increasing the quantity of salting chloride in the albumen, to enable us to do without any free nitrate what ever; but we know, that however large the quantity of chloride of silver, even in conjunction with the albuminate, it will not yield as good an image without the free nitrate, as it will do when it is present. Methinks, this may fairly be considered as affording presumptive proof, that the free nitrate of silver as such, does in some unknown way, tend to the formation of the image, in co-operation with the albu minate and chloride. Because chemical science is not sufficiently advanced for any one to be able to state horo the free nitrate acts, it surely is an unwarranted assumption to assert, that its mere presence is necessary to enable the chloride to give good results. But whether it acts only as a necessary accessory, or, as a prin cipal in co-partnership with the albuminate and chloride; what is the use of, or rather, the necessity for the greater portion of it; viz. that which is washed out after printing, and previous to toning? This tin-used free nitrate, if I may so term it, is, in many cases, fully four-fijths of what the paper took up from the sensitising bath, and nearly the whole amount of free nitrate which the sheet contained. Assuming, according to the Abbe Pujo’s statement, 135 to be the maximum number of minims of undiluted paper ordinarily takes dt, that only one-eighth chlorided albumen, that a sheet of ted to it, beautiful effect produced by low salting formulae. I know not how it has arisen, but a strange misconceptio" exists, respecting the amount of chloride of silver usual')' formed in a sheet of paper; I read of thirty grains. Thi quantity must be produced from what may be deemed a" exceptional formula); as the sheet of paper must contain Hi grains of chloride of ammonium, or their equivalent; a taking 135 minims to be what it takes up of the albumenize mixture, there must be forty grains to each ounce of albumen to be 8206 as I have calculated it, this compara tively large amount requires only a, fractional part of a grain of nitrate of silver to convert the whole into albuminate of silver. These 16 J grains of dry albumen will never require more than a fractional part of a grain of nitrate of silver, to con vert them into the albuminate, unless the atomic weight of pure albumen be estimated much lower than ice shoubl be warranted in assuming that of such a complex organic Wf pound to be. I have had the curiosity to calculate this; and find, that for 16g grains of dried albumen to require one grain of nitrate of silver to convert it into the albumi nate, the atomic weight of pure albumen must be 2868'75. Thus, whatever may be the atomic weight, the greater or lesser portion of albumen in the albumenizing mixture, creates no necessity for a stronger or weaker sensitising bath ; it is the quantity of salting chloride which it con tains that must regulate its strength ; I do not think suffi cient attention is paid to this fact. The greater the amount of salting chloride in the albu- men, the more sensitive the paper becomes; but the quantity of chloride of silver which is absolutely necessary to produce good effects, is extremely small,—as evidenced by the results produced by using Marion’s and T. R. Williams’s low salting formulae. Upon referring to Table No. 1,* we shall fin 1 ' the proportion of dried albumen to the salting chloride, is, in Marion’s 9 to 1, the fraction being too small to be worth consideration ; in T. R. Williams’ it is 10, to 1. That tire albuminate and chloride of silver will not bear the same proportion, I have shown in my first communication, proving the fallacy of the Abbe Pujo’s assertion that they will do so ;f nevertheless, in these low salting formula, the albu minate is much in excess of the chloride ; in Marion’s it i nearly 34 times the quantity, and in T. R. Williams’s vet) nearly 4 times. up ; and also, according to Stockhard, unau p— of the albumen is left upon evaporation; 16Z grains of dry albumen is the greatest quantity which a sheet of paper will be surfaced with. If we consider the atomic weight of pure to produce such an amount. I believe, photographers, as a body, are not much co" versant with chemistry, and thus are led to believe a thi to be a fact, because the knowledge of chemistry is b. sufficiently advanced for those who are chemists to explain how the contrary can be the truth. Thus, it has been col. fidently asserted, and as confidently believed, that the ha* of the salting chloride has no influence whatever on the colour of the picture. That this is another of “ the fallacies of the scientific,” any one may convince himself, who wil take the trouble to observe attentively the different colou produced by the action of light upon papers salted wit barium and ammonium ; I do not mention sodium, as have never printed on paper so salted. Much twaddle, unde the guise of science, has been published in the journals T specting the use of chloride of barium, and I have even beet - Judging by the quantity of each compound of silver f sent in the sheet of paper, the albuminate ranks ned1. importance to the free nitrate, and last of all, the Chloric,' and yet it is to this latter compound that the chief honour'’ given for the production of the picture. That the chloride is not of the paramount importance which has been attribu. may fairly be questioned, when we consider the effect produced by low salting formula,. * age 523. t 1’age 494. * No. 13, told that : paper; he ray or otl ground; Those v io because 28 my OWI possible el rhen addi was empl only answ fleet; bu lelief. In Mr. I Ine grain Won of c ducing t Is equival Sain of cl "l5th of Md be ] *1 sodium te colour, tty powei ^chloride floride of he nitrati itrates. The chi bat of am ‘tagine h< Rtise what ium add, M yet nc Arion’s 1 ability t Ammoniun ^fancied 'A of bar it h n in eq The the. A image, 4 the r chloi jtefi upot Placed in Positive pr " many c: "then, w "g the cii M on a loride of Mth the "trefore, ] Ned tha V8ensitiz Tality twi ’meh for In takin "y that s Rrticular "t lead to idded to ■ । 1 the wor< >nd the S yet cl Cn his er [ Allow m . think wo “tious tab
