Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9
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THE next ingredients employed in the manufacture of plain or normal collodion are alcohol and ether. Both these substances belong to a group of hydrocarbons whose basic compound radical, although hypothetical, is denominated ethyle, consisting of four equivalents of carbon combined with five of hydrogen, and represented in symbols by C4 H5 Ether is the oxide of this base, and alcohol the hydrated oxide; that is, chemically regarded, the only difference between ether and alcohol is, that the latter contains one equivalent of water, constitutionally combined, which is wanting in ether. The hypothetical compound base, ethyle, enters into combination with several of the alkaloids and acids, giving rise to distinct chemical combinations. This fact will lead us to seek a clue for various untoward and, as yet, unaccountable phenomena in the constitution of sensitized collodion, and its frequent want of permanency.
|Ethyle Symbol Ae,||C4 H5||Cyanide of ethyle||Ae Cy.|
|Oxide of ethyle, (ether,)||Ae O||Nitrate of the oxide of ethyle,||Ae O, NO5.|
|Hydrated oxide of ethyle,.(alcohol,)||Ae O, HO.||Nitrite of the oxide of ethyle||Ae O, NO3|
|Bromide of ethyle,||Ae Br.||Oxalate of the oxide of ethyle,||Ae, O C2 O3|
|Chloride of ethyle,||Ae Cl.||Hydride of ethyle,||Ae H.|
|Iodide of ethyle,||Ae I.||Zinc ethyle,||Ae Zn, etc.|
Some of the compounds of the ethyle series are crystallizable salts; but the most of them are volatile aromatic fluids, denominated ethers.
Although an equivalent of water is the only difference between alcohol and ether, yet no direct means have yet been discovered whereby an atom of water can be so combined with ether as to form alcohol, nor abstracted from alcohol constitutionally so as to leave ether. It is supposed, therefore, that the elements that enter into the formation of ether, and water and ether, owe their difference to a differ. Once in the grouping of the elementary atoms.
Ether, sometimes denominated, but very wrongly, sulphuric ether, is obtained by decomposing alcohol by means of sulphuric acid. One method consists in the distillation, of equal weights of rectified alcohol (spec. grav. .835 and sulphuric acid. As soon as ebullition commences, a colorless and highly volatile liquid passes over and is condensed into a receiver surrounded with ice or snow. This method is far from being a profitable one; for at a temperature below 260° Fahr. alcohol distils over; and, if' the heat be greater than: 310°, another of the numerous hydrocarbons, olefiant, gas, is generated, together with other gaseous and liquid bodies. By a second method the sulphuric acid is maintained at a temperature of about 300° Fahr., and a, stream of alcohol is made to enter the acid gradually. lit this way a large quantity of alcohol becomes converted into ether. There are two stages in the preparation of ether; by one an impure and crude ether is the result; by the latter the ether is rectified. The minutia; are as follows
Take of alcohol, four pints- sulphuric acid, one pint; potassa, six drachmas; distilled water, three fluid ounces. Add gradually fourteen fluid ounces of the acid to two pints of the alcohol in a tubulated retort, and drake frequently in order to produce an intimate mixture. Connect the retort, when placed on a sand-bath. with a proper condensing apparatus, furnished with. a long connecting-tube, so as to remove the vapors, if any should escape, as far as possible from the flame. Explosions are very apt to take place in the preparation of ether, unless great caution be taken. The temperature is now raised quickly until ebullition commences. As soon as half a pint of ether has distilled over, the remainder of the alcohol previously mixed with two fluid ounces of the acid is allowed to enter gradually through the tubulated aperture by means of a tube dipping beneath the mixture in the retort, and in quantity as near as can be equal to that which distills over. In this way continue the distillation until about three prints have passed over into the condenser.
The product thus obtained contains sulphurous acid, sulphuric acid, sulphovinic acid, and other impurities. By rectification most of these are removed as follows:
Add to the ethereal contents in the condenser the solution of the potassa in the distilled water, and shake them frequently during the twenty-four hours they are kept together in a stoppered bottle. After subsidence separate the supernatant ethereal solution by means of a syringe, and distill off two pints of this solution at a low rend gentle heat. The specific gravity at this stage will be about .750. By further rectification over newly burnt quicklime and chloride of calcium, ether may be obtained of a specific gravity of .720, or even lower. When perfectly pure its specific gravity is .713, and it boils at 95°. The sulphuric ether of commerce is not sufficiently concentrated for photographic purposes; and none can be relied upon excepting that which is obtained direct from establishments that prepare chemical ingredients for the photographer. When the specific gravity is .720, ether boils at 98°; this is the kind which is generally used in the preparation of collodion. When too long kept it undergoes decomposition, being converted partially into acetic void. It is a very important solvent of oils, resins, and alkaloids, and certain metalloids, as iodine, bromine, sulphur, and phosphorus. It does not dissolve potassa and soda, a very distinct characteristic from alcohol. It unites in all proportions with alcohol and with one tenth its volume of water. The impurities, as before, mentioned, are acids, alcohol, water, and oil of wine. The presence of acids are shown by litmus; alcohol combines with water when added in excess, and settles and forms the lower stratum; by decantation the upper stratum is removed, which now contains one tenth its weight of water; water is removed by distillation from fresh chloride of calcium; the acids by distillation from lime or potassa; the oil of wine is shown by the production of a milkiness when mixed with wager.
Alcohol is the rectified spirit of wine of the specific gravity of 0.835, containing eighty-five parts of anhydrous alcohol and fifteen of water. When pure and anhydrous it, is the hydrated oxide of ethyle, (Ae O, HO.) It contains six equivalents of hydrogen, four of carbon, and two of oxygen (H6 C4 O2. All saccharine substances undergoing vinous fermentation give rise to the vapors of alcohol, which by distillation are obtained in a separate and more concentrated form. By the vinous fermentation sugar is converted wholly into alcohol and carbonic acid; and it is only from sugar, or substances which by chemical processes are converted into sugar, that the vinous exhalation can pre obtained. The ordinary alcohol of commerce is not sufficiently concentrated for the purposes of the photographer, because the water which it contains would precipitate a solution of pyroxyline, or produce an opaque solution. Like ether, therefore, it has to undergo a process of concentration. Whisky is the spirit from which the first alcohol is obtained, which contains water, a peculiar oil, and extractive matter. By distilling a hundred gallons of whisky, between fifty and sixty gallons of alcohol are received in the condenser of a specific; gravity of 0.835. By a second distillation, taking care to collect only the first portions and cautiously managing the heat, so as not to allow it to rise to the temperature of boiling water, alcohol may be obtained of a specific gravity of 0.825, which is the lightest spirit that can be received by ordinary distillation. At this stage it contains eleven per cent of water and some small portions of fusel oil.
The process by which most of the remaining water is separated from the alcohol is as follows"
Take one gallon of the alcohol of commerce; chloride of calcium, (freshly made,) one pound. Throw the chloride into the alcohol and, as soon as it is dissolved, distill off seven pints and five fluid ounces. Or, take of rectified spirit one pint, (imp. meas.;) lime, eighteen ounces. Break the lime into small fragments, mix with the alcohol in a retort properly connected, and expose the mixture to a gentle heat until the lime begins to slake; then withdraw the heat mail until slaking is finished. Now raise the beat gently and distill off seventeen fluid ounces. Alcohol thus obtained will have a density, when the operation is carefully managed, of 0.796.
Neither of the preceding fluid, taken separately, dissolves pyroxyline, a mixture of the two is required to perform this operation; the proportion in which they exist to this mixture, in order to attain to the maximum degree of photographic excellence, is a problem which has not yet beep absolutely solved. When there is a large excess of ether over the alcohol, the former menstruum will easily dissolve from one to one and a half per cent of the prepared cotton; and this proportion will scarcely exceed, under the most favorable conditions, from two to three per cent without producing a precipitate in the solution. On the contrary, if the, alcohol, in its purest state, exists in the, mixture in greater quantity than the ether, three per cent of pyroxyline is easily dissolved, producing a collodion of the proper consistency; the mixture, however, will dissolve from eight to ten per cent without producing any deposit in the collodion.
The property of ether in collodion is to communicate tenacity to the film, which, owing to the excess of this fluid, frequently peels off from the glass in one adherent sheet; beside this, ether is more liable to decomposition than alcohol, and is perhaps one of the causes of the want of permanency in collodion, although most probably pyroxyline is the principal cause. This want of stability, even in normal collodion, is increased by the quantity of air contained in the same vessels, giving rice to an ethereal effluvia which it did not possess before. This decomposition is much more rapid when the collodion is exposed to light.
Decomposition of Collodion.---The decomposition of normal) or plain collodion is a fact that can easily be verified; but experience shows also that the iodides and bromides when dissolved in pure alcohol and ether are not decomposed, or at any event in a very trifling degree, when properly protected to accurately closed bottles; the fluid does not change color materially, nor does it allow the presence either of free iodine or bromine; furthermore the solutions in question, when kept for any length of time, produce the same sensitive effects on plant collodion as if they were freshly made. The decomposition in collodion does not seem, therefore, to be superinduced by ether, alcohol, the iodides, or the bromides; for each, taken separately or in combination, when pure and properly protected, is not liable to any perceptible decomposition. But Van Monckhoven maintains, and all photographers are aware of the fact, that there is a very perceptible difference between freshly-made plain collodion and old plain collodion. The difference is this: if a plate be coated in newly-made plain collodion and then immersed in a solution of nitrate of silver and exposed before an object, and afterward submitted to the action of the developing fluid, no traces of the picture will appear; on the contrary, if the plain collodion be old, and a plate be treated with this as in the preceding case, the film will be whitened by the sensitizing solution, and twill be sensitive tip the action of light when exposed before an object, and will yield a picture. A second difference is this: the collodion, before thick and consistent, becomes thinner and exhales alt odor of nitric ether as it grows older.
Such being the case, it seems evident that the pyroxyline is the cause of the decomposition, or that the pyroxyline contains sometimes extraneous matter that produces this decomposition; and when the change has once set in, the newly formed bodies may react upon the iodides or bromides when introduced, and tend to produce a variety of decompositions according to the facility or difficulty with which they undergo change.
But the next question is: What are the differences between freshly-made iodized collodion and an iodized collodion that has been kept long ? They are as follows
Firstly. New collodion is more sensitive to light than old collodion.
Secondly. Although more sensitive, it produces images which are much less intense than those produced by old collodion, that is, the shadows are not so deep or black. The images are mere surface-pictures when developed with the sulphate of the protoxide of iron.
Thirdly. If the plates be washed after sensitizing, (in the dry process,) when freshly-made collodion is used, no image will appear; on the contrary, with old collodion the washing does not prevent the picture from appearing.
Fourthly. The shadows of the picture developed by the protosulphate of iron are entirely soluble in nitric acid when a freshly-made collodion is used; and are not entirely soluble with an old collodion.
Fifthly. New collodion is colorless, or nearly so; whereas old collodion sometimes is as deeply red as a strong solution of burnt sugar.
Sixthly. New collodion has the odor only of alcohol and ether; but old collodion has a peculiar ethereal smell resembling that of nitric ether and aldehyde.
We are indebted to Van Monckhoven for the summation of these differences in juxtaposition, and many photographers will recognize the truth of them.
The third question to be asked is then the following: What substance in solution will communicate to recently prepared iodized collodion the properties of old collodion ? Hardwich says that grape-sugar, glycyrrhizine, and nitroglucose will render fresh collodion much more intense, but that they diminish its sensitiveness. Such is also the action of the substance, be it what it may, contained in altered collodion, it renders collodion more intense but less sensitive.
Furthermore Hardwich remarks, that, if these substances be employed to increase the intensity of the shadows in the
image, they ought to be added cautiously because they deteriorate from the keeping properties. But nitro-glucose is said to be an impurity in pyroxyline; it is analogous in several respects to pyroxyline; and it is prepared with sulphuric acid, nitric acid, and sugar; but lignine or cellulose yields sugar when treated with sulphuric or nitric acid; hence in the preparation of pyroxyline grape-sugar is formed at the same time, and by the further action of the acids, nitro-glucose is produced. That there exists a duplex compound in collodion may be shown by adding water to it; a precipitate will be formed, of which one part is fibrous and the other gelatinous.
But the identity between the unknown substance and nitro-glucose is apparently shown by the identity of properties. If nitro-glucose be dissolved in alcohol, it forms a colorless solution with an odor of alcohol, which has no effect at this stage on collodion, nor on an alcoholic solution of nitrate of silver; but, after the expiration of a few days, it assumes a rose-colored tinge and the odor peculiar to old collodion; furthermore, at this second stage, it now communicates to fresh collodion all the properties of old collodion, and forms a precipitate in nitrate of silver in alcohol. Van Monckhoven in addition has convinced himself that the precipitate formed in old collodion by an alcoholic solution of nitrate of silver is six times as bulky as that which would be the result from the iodide of silver, and that its properties were the same as those in the precipitate formed by mixing the rose-colored nitro-glucose with alcoholic nitrate of silver.
Preparation of Glycyrrhizine.--This substance is obtained by boiling liquorice-root in water for some time, and adding sulphuric acid to the concentrated syrup. A white precipitate is formed, containing glycyrrhizine, albumen and sulphuric acid. The albumen is removed by washing the precipitate, first in acid-water, then in water, and afterward by solution in alcohol. Carbonate of potash is then added to decompose the alcoholic solution, and to precipitate the sulphuric acid. By evaporating the liquid, glycyrrhizine remains as a yellow, transparent mass.
Preparation of Nitro-glucose.--Add one ounce of powdered sugar to a mixture of two fluid ounces of sulphuric acid, one of nitric acid. Stir the mixture for a few minutes with a glass rod; a tenacious mass may thus be collected from the fluid, and washed in warm water by kneading it until every trace of acid is removed.
Collodion iodized with the ammonium salt is the least stable; whilst a cadmium collodion is the most permanent. Collodion in which the alcohol is in larger abundance than the ether is more stable, and at the same time more fluid; it adheres well to the glass, forms no rides in flowing, and is in fact quite structureless.
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