Volltext Seite (XML)
THE PHOTOGRAPHIC NEWS. [Feb. 21, 1862. ON THE MANUFACTURE OF COLLODION. BY THOMAS SEBASTIAN DAVIS. To make the pyroxyline, take 84 ounces (avoirdupois) of ordinarily dried and pounded nitrate of potash and mix it in an earthenware jar with 104 fluid drachms of water. Pour upon this 4} fluid drachms of nitric acid, sp. gr. 1-42 and 81 fluid ounces of the strongest commercial sulphuric acid, sp. gr. about 1-845, and intimately mix the whole with a glass rod. As soon as the mixture is at the temperature of 150° to 145° Fah. introduce 100 grains of finely divided cotton, in small quanti ties at a time, taking speecial care that each quantity is saturated with the acids before the introduction of the next, and allow the whole to remain at rest, standing upon a non-con ducting surface, for about ten minutes. After the lapse of this interval, press the cotton with the glass rod against the bottom of the vessel, and pour off as closely as possible, the fluid mix ture. The pyroxyline should then be quickly washed in three or four changes of water, and subsequently in several addi tional ones, with the precaution of pressing as much of the moisture as possible from the cotton between each change ; by so doing, the cotton will be quickly and thoroughly freed from the slightest trace of acidity. As a precautionary measure, one or two of the latter washing waters may be rendered slightly alkaline by the addition of a few drops of ammonia : that used for the final cleansing should be neutral and distilled. The cotton may now be allowed partially to dry spontaneously, but the last traces of moisture should be driven off by the aid of a hot-water bath. As the quantity of water in the above formula constitutes the element of success, or otherwise, in the manu facture of the pyroxyline, it may be as well to refer to the ex treme ranges and the resulting effects. If we add 12 fluid drachms of water instead of the 10} recommended, the result would be that the greater portion of the cotton would be dis solved in the acids, and the remainder, if washed and dried, would be found to dissolve but sparingly in ether and alcohol, and yield a powdery, incoherent, and unsuitable film. If, upon the other hand, we were to reduce the quantity of water to 8 fluid ounces we should find that the cotton would be scarcely altered in its appearance when washed and dried, have but little solubility in an etherial mixture, and yield a film possess ing a “ crapy ” texture. It thus follows that all the more cha racteristic pyroxylines may be produced by a comparatively trifling alteration in the strength of the acids. When, how ever, the water is added to the extent given in the instructions, the detached particles of cotton will give a milkiness to the first washing waters, it will present, when wet, a semi-transpa rent appearance when held up to the light, and after subse quent desiccation will dissolve easily and scarcely without leaving a residue, either in glacial acetic acid or an etherial mixture of alcohol. From this pyroxyline the plain collodion is to be made as follows :— Ether, methylated, sp. gr. 720 to 730 4} fluid ounces Alcohol ... „ 837 ... 14 fluid drachms Pyroxyline ... 6} grains. The methylated ether referred to above can be commercially obtained of either the above strengths; the alcohol is the ordinary rectified spirit of 56-60 over proof of the distiller. The sensitizing solution to be added to the plain collodion is a question of importance second only to the manufacture of the pyroxyline. I deem it exceedingly desirable that care should be taken that the addition of the sensitizing solution to the plain collodion should not be attended with the slightest pre cipitation; rather that the slight milkiness which the plain collodion may retain even after long standing should imme diately disappear upon the addition. In order to ensure this effect, I recommend that a weaker alcohol should invariably be used in the manufacture of the plain collodion, than that which is employed as the solvent for the salts. I am aware that the greater facility with which the salts employed are dissolved by the weaker spirit has led to a practice at variance to the one advocated; but under such circumstances a precipitate gene rally occurs. The composition of the iodizing solution is to be as follows:— Iodide of potassium 6 grains Iodide of cadmium 18 grains Bromide of potassium 2 grains Chloride of ammonium ... 2 grains Alcohol, sp. gr. -805 ... .. 1 fluid ounce. * Concluded from p. 79. I give the preference upon chemical and photograph 1 ® reasons, to the combination of iodide of potassium and iodide of cadmium over the combinations of other iodizing salts, and tM stability and solubility of the latter combines conveniently witl the instability and sparing solubility of the former. The alkaline iodide is, moreover, eminently qualified to give a great and ex cessive vigour of intensity, whereas, the metallic salt by itself imparts an image of the opposite character. A combination d the two in the above proportions yields probably the best image that can be realized by the use of iodides alone. The prefer ence may be given to the potassium iodide over the ammonium, inasmuch as the former is less liable to decomposition, and th® consequent liberation of free iodine, than the latter. Th® iodide of sodium is almost identical in its action and properties with iodide of potassium; but as the latter can be obtained with greater facility in a state of purity, convenience suggests its employment. The effect of adding chlorides and bromides to the combination of the above salts is to lessen the exagge rated contrasts which are likely to attend the use of a plain iodized collodion, to give greater immunity from stains and fogging, and what is of considerable moment, permit a longer exposure, wher necessary, for the delineation of objects situated in shade, will out the prevention of the vigorous rendering of the higher light The beneficial effects of the chloride of ammonium will be bid trifling as far as regards the use of the collodion for the wet pro cess. It will give however greater sensibility, increased bright ness of negative, and general correctness of tone to plates, from which the whole of the free nitrate of silver has been washed away for the purpose of applying a preservative. With respect to the introduction of the potassium bromide in preference to the bromide of ammonium, it may be remarked that although it be less freely soluble in alcohol, yet for negative picture®, in combination with mixed alkaline and metallic iodides, it is sufficiently so to produce the desired effect. By its use we pre vent the possibility of double decomposition, which under cer tain circumstances may otherwise take place. The salts, as de scribed, should bo dissolved without heat in about three-fourth® of the alcohol, and after having been frequently shaken therein for two or three days, and carefully filtered, the remainder® the spirit maybe then added. The iodizing solution is to/! mixed with the plain collodion in the proportion of one volu/ of the latter to three of the former, and it will be found ti the resulting compound will meet every possible requirement 0 the artistic photographer, with the exception of very rapid sef sibility. In furtherance of the object of obtaining increased sensibility, I have tried many published and original experi ments, but without meeting with any marked success, unac companied with some serious inconvenience. The generality of these experiments have been directed to the introduction of such salts into the sensitizing solution as form by double decom position with nitrate of silver, insoluble compounds more or less effected by actinic power. The salts which can be successfully introduced for the purpose are obviously limited to those which I are partially soluble in a mixture of alcohol and ether, and afford I insoluble compounds when the electro-negative element enters into combination with the metallic base. In accordance witl 1 the above conditions I have selected for my experiments th® acetates, malates, citrates, succinates, benzoates, arseniates, ar senites, cinchonates, &c. The only instances in which I hat’ obtained any indications of increased sensibility have been % ; those in which the salts introduced have possessed an alkali® reaction. Amongst these I may especially mention the arsenil® of potassium. As silver salts of a character so formed are prot® to reduction under the influence of the ordinary developin agents, their employment is to a greater or less extent attend®® with a general fogging of picture. In following out some expe riments in connection with sensibility, I introduced the ter chloride of gold into the sensitizing solution in the place of tbe less soluble chloride of ammonium. The exaltation of sensi bility caused by this addition was both marked and decided, but the known facility of reduction to which this salt is subject, apart from the influence of light, under the action of pyrogallis and protosulphate of iron solutions, defeated the possibility of its successful application. So great is the aptitude of this sall to reduction, that the introduction of a single plate covered wit) a film containing a mere trace thereof is sufficient to render" • large quantity of the nitrate of silver bath solution inapplicabl for further photographic purposes. It was therefore with son 10 surprise that I subsequently found that Mr. Barnes, in his eX. I cellent and able manual upon the use of collodion upon a H’’? I substratum of albumen as a dry plate process, had not only tried. 'in excess) in excess)
