IODIZED COLLODION FOR POSITIVES.
One very important object in connection with this part of the collodion process is to have chemicals of a good quality, and always employ those of a fixed standard.
Double iodide of potassium and silver (seepage 62) enough so that when the plate comes from the nitrate of silver bath, it will have an opaque cream color.
Remarks.—In the preparation of this sensitive collodion, it is necessary to be cautious and not add too much of the iodide of potassium and silver, for in that case the coating would flake off, and falling into the silvering solution, the operator would be obliged to filter it before he could silver his plate with safety as regards spotting it.
The method I employ is to add the plain collodion, bromide and iodide of potassium and silver, iodide of ammonium and hydro-bromic acid, and then cautiously add the double iodide of potassium and silver from five to ten drops at a time, trying the collodion from time to time by pouring a little on a narrow strip of glass, which I dip into the silvering solution, and let it remain for two minutes. If the coating assumes the proper color (a cream color), I shake the contents of the bottle, and then stand it aside to settle: it is better after it has stood for a week or two.
This collodion I have used after it has been made eight months, and produced fine and satisfactory results, and usethis nearly altogether in practice. Since the first edition of this work has been issued, I have sold over two thousand pounds of this preparation, and the demand is on the increase. I will append another preparation (No. 2) which I have successfully employed, and some operators prefer.
Bromo-Iodized Collodion for Positives.—No. 2.
Enough of the double iodide of potassium and silver to give the coating a cream color when it comes from the silvering solution. It will take from one to three drachms. Or this last may be omitted, and a few drops of a saturated solution of dry iodine in alcohol may be added. Either of these plans have been successful in my practice.
Remarks.—The iodide of potassium being insoluble in the collodion, it should be first dissolved in as little water as possible;i. e., take the quantity, 30 grains, put it into a one-ounce graduate, and with a glass rod stir it, adding water, drop by drop, only until all of the salt is dissolved. Then it may be poured into the collodion, and there will be a white powdery precipitate.
The bromide of ammonium will dissolve in the collodion, and can be put into it. When all of the accelerators are in, it should be well shaken, and then allowed to settle and become clear. When wanted, a sufficient quantity may be poured into a vial (seeFig. 34) for use, and the main or stock bottle should not be disturbed oftener than necessary. This last collodion is not as durable as the first, but is less trouble to prepare.
Bromo-Iodized Collodion for Negatives.
IODIZED COLLODION FOR NEGATIVES
This collodion should be allowed to stand and settle twenty-four hours before it is used: when wanted, it should be poured off into a collodion vial. The more free the collodion is from sediment and small particles of dust or undissolved cotton, the softer and more perfect will be the impression it makes.
In case the above proportions of iodide of potassium should not produce a cream-colored coating, when it comes from the nitrate of silver bath, more may be added: for example, if the coating is of a bluish tint, I would dissolve 6 grains of iodide of potassium in water, as before, and then try it: shake well, and test it by putting a little on a slip of glass, and dipping it into the silvering solution; if it coats to a cream-color, it is right.
It should be borne in mind, that after the addition of iodide of potassium here recommended, the collodion should be allowed to stand until settled, before undertaking to produce a picture, although the coating may be previously tested by means of a slip of glass.
Solution of Bromide and Iodide of Potassium and Silver.
Dissolve 130 grains of crystallized nitrate, of silver in 4 ounces of pure water, in a long 8-ounce vial. Then in a clean 1-ounce graduate, or some other convenient vesselcontaining half an ounce of water, dissolve 130 grains bromide of potassium. When this and the nitrate of silver are both dissolved, pour the solution of bromide of potassium into the vial containing the silver, and a thick yellow precipitate will fall. This is the bromide of potassium and silver. This should be washed by nearly filling the vial with water; shake it, and then let it settle, which it will readily do, and then pour on the water, leaving the yellow mass in the bottom of the vial; continue this operation of washing for at least ten changes of water; then, after draining off the water as close as possible, put into the vial four ounces of alcohol, shake it well and let it settle; then pour off as close as possible. By this means the water is nearly all taken out.
Pour into the vialthreeounces of alcohol; then in a small mortar finely pulverize one ounce of iodide of potassium, and the solution, which was before clear, will be more or less of a yellow color, and the bulk of the yellow precipitate will be diminished. I have sometimes completely re-dissolved the yellow precipitate, but this does not often occur, except there be more water present than is advisable. It is better to have an excess of bromide of potassium in the solution. This can be seen by its being white, and remaining undissolved in the bottom of the vial. This solution should be prepared in the evening, or in a dark room, and only the light of a lamp or candle employed.
Double Iodide of Potassium and Silver.
This solution is made in the same manner as in the foregoing article, substituting the iodide of potassium for the bromide—no bromide being used in this preparation.The yellow precipitate in this case will be re-dissolved and taken up in the solution: it may require more than one ounce of pulverized iodide of potassium to effect this, but it may be added in excess, so that the solution shall contain a quantity in powder.
Developing Solution.
DEVELOPING SOLUTION.
Put these into a quart bottle, and shake until the crystals are all dissolved, and this can be kept for a stock bottle, and when wanted for use pour into another bottle.
Shake this mixture well, and filter through a sponge, and it is ready for use. I file a mark in this bottle indicating five ounces, and another for 1 ounce: this will save time in mixing the solution.
Remarks.—In my recent tour of the United States, I found it difficult to obtain a good article of protosulphate of iron, and in its stead I used the common copperas, such as I could find almost in any store. I employ from one-fourth to one-half more than the quantity given above. If it looked a clear green, and free from a white or brownish powder, about one-fourth addition:i. e., four ounces, instead of three, as given above. If the solution in the stock bottle is not wanted for a week or more, a few crystals of the protosulphate of iron should be added, as it decomposes, and the strength is depreciated.
There is quite a difference in the strength of the acetic acid as sold by out country druggists, and the operator should be sure that he has No. 8, to which quality the above proportions are adapted. I never have employed the developing solution but once, but can see no objections to use it for a number of glass plates, but it should be filtered every time before using. The quantity of nitric acid may be increased, so long as a proper proportion is preserved with the strength of the bath. The effect of this addition of acid will be to brighten the impression; but if carried too far, the reduction (developing) will be irregular, and the harmony of the impression injured.
Fixing Solution.
FIXING SOLUTION.
Remarks.—I put enough of the cyanide of potassium into the water to make the solution of such strength as to dissolve off the iodide of silver ("coating") in from twenty to sixty seconds. The operation is quite similar to that of hyposulphate of soda upon the coating of the Daguerreotype plate. A too concentrated solution is likely to injure the sharpness of the image.
Brightening and Finishing the Image.
HUMPHREY'S COLLODION GILDING.
The article I now employ for finishing off my Positives is in market, and known asHumphrey's Collodion Gilding. It is a new preparation, and exerts a powerful influence upon the image, having the same brightening effect as chloride of gold on the daguerreotype. There is no articlenow in market that equals this. I have until quite recently used a varnish for this purpose, but having something that is of far greater value, I have discarded it. It is one of the most valuable improvements since the application of the Collodion Film as a vehicle for producing photographic images. It is a new discovery, and is being rapidly brought into use by the first ambrotypers and photographers in America. It adds at least one-half to the beauty of an ambrotype, above any method heretofore in use. It isimperishable, giving a surface almost equal in hardness to the glass itself. It is easy of application; it gives a brilliant finish; it is not affected by a moist atmosphere; it is not affected by pure water; it is the best article ever used forfinishing ambrotypes; it will preserve glass negatives for all time; it will preserve thewhitesin the ambrotype; it gives a rich lustre to drapery; it will bear exposure to the hot sun; it preserves positives and negatives from injury by light. It is an article that, when once tried, the operator upon glass (positive, negative, or albumenized plates)will not do without.
The ingredients in the composition of this gilding are neitherpatentednorpublished, but it can be procured from any dealer in photographic chemicals.
Nitrate of Silver Bath.
NITRATE OF SILVER BATH.
I here give what I consider an improvement on the bath mentioned in the first edition of this work. I first published it inHumphrey's Journal, No. 23, Vol. VII.:
The nitrate of silver solution is an important mixture in the chemical department of the ambrotype process, andrequires the especial care of the operator in its preparation. I give the following as one of the most approved for general practice. It is well adapted to the production of positives, and its action is of great uniformity.
This proportion is to be observed for any quantity of solution. If I were to prepare a bath 40 ounces, I would proceed as follows:
Measure the water, and put into a two-quart bottle; then pour out 8 oz. of it in a pint bottle, and into this put the whole of the nitrate of silver (1800 gr.); shake it well until it is all dissolved. This forms a concentrated solution—into which put the following prepared iodide of silver:—
Dissolve in a 3 or 4 oz. bottle containing 1 oz. water, 10 gr. nitrate of silver; and in another bottle or graduate containing a little water, dissolve 10 grains of iodide of potassium; pour this into the 10 grain solution of nitrate of silver, and a yellow substance (iodide of silver) will precipitate; fill the bottle with water, and let it settle; then pour off the water, leaving the yellow mass behind; again pour on it clean water, shake it, and let it settle as before, and pour off again; repeat this for about six changes of water.
Then it (the iodide of silver) is to be put into the bottle containing the 8 oz. water and 1800 gr. of nitrate of silver; shake it well, and it will nearly or quite all dissolve; pour this into the two-quart bottle, and shake well; it will be of a yellowish white tint, and should be filtered through asbestos or sponge, when it will become clear. When clear, test the solution with blue litmus-paper; if it turns it red, it is sufficiently acid; if it does not change it, addoneortwodrops of nitric acid, chemically pure; then test it again; if it does not change it, addoneortwodrops more, or just enough to change the paper to the slightest red.
A solution prepared in this proportion will, like others, improve by age. An old bath is considered far more valuable than one newly prepared. These remarks may appear to old photographic operators as of no importance, but they must bear in mind that there are hundreds just adopting this new process of picture taking.
This solution will work more satisfactorily than the one I formerly used. It will work quicker in the camera, and isequallydurable.
Acknowledgment.—The following pages, under the head ofVocabulary of Photographic Chemicals, and treating upon the Chemicals used in Photography, are taken from the third edition of "Hardwich's Photographic Chemistry:"—
Vocabulary of Photographic Chemicals.
VOCABULARY OF PHOTOGRAPHIC CHEMICALS.
Acetic Acid.
Symbol, C{4}H{3}O{3} + HO. Atomic weight, 60.
Acetic acid is a product of theoxidationof alcohol.Spirituous liquids, when perfectly pure, are not affected by exposure to air; but if a portion of yeast, or nitrogenous organic matter of any kind, be added, it soon acts as aferment, and causes the spirit to unite with oxygen derived from the atmosphere, and to becomesourfrom formation of acetic acid or "vinegar."
Acetic acid is also produced on a large scale by heatingwoodin close vessels; a substance distils over which is acetic acid contaminated with empyreumatic and tarry matter; it is termed pyroligneous acid, and is much used in commerce.
The most concentrated acetic acid may be obtained by neutralizing common vinegar with carbonate of soda and crystallizing out the acetate of soda so formed; this acetate of soda is then distilled with sulphuric acid, which removes the soda and liberates acetic acid: the acetic acid being volatile, distils over, and may be condensed.
Properties of Acetic Acid.—The strongest acid contains only a single atom of water; it is sold under the name of "glacial acetic acid," so called from its property of solidifying at a moderately low temperature. At about 50° the crystals melt, and form a limpid liquid of pungent odor and a density nearly corresponding to that of water; the specific gravity of acetic acid, however, is no test of its real strength, which can only be estimated by analysis.
The commercial glacial acetic acid is often diluted with water, which may be suspected if it does not solidify during the cold winter months. Sulphurous and hydrochloric acids are also common impurities. They are injurious in photographic processes from their property of precipitating nitrate of silver. To detect them proceed as follows:—dissolve a small crystal of nitrate of silver in afew drops of water, and add to it about half a drachm of the glacial acid; the mixture should remain quite clear even when exposed to the light. Hydrochloric and sulphurous acids produce a white deposit of chloride or sulphite of silver; and ifaldehydeor volatile tarry matter be present in the acetic acid, the mixture with nitrate of silver, although clear at first, becomes discolored by the action of light.
Many photographers employ a cheaper form of acetic acid, sold by druggists as "Beaufoy's" acid;[A]it should be of the strength of the acetic acid fortiss. of the London Pharmacopœia, containing 30 per cent, real acid, and must be tested for sulphuric acid (see sulphuric acid), and also by mixing with nitrate of silver.
[A]In this country the practitioner uses the article sold in market as "Acetic Acid, No. 8."—S. D. H.
[A]In this country the practitioner uses the article sold in market as "Acetic Acid, No. 8."—S. D. H.
Acetate of Silver.(SeeSilver, Acetate of.)
Albumen.
Albumen is an organic principle, found both in the animal and vegetable kingdom. Its properties are best studied in thewhite of egg, which is a very pure form of albumen.
Albumen is capable of existing in two states; in one of which it is soluble, in the other insoluble in water. The aqueous solution of the soluble variety gives a slightly alkaline reaction to test-paper; it is somewhat thick and glutinous, but becomes more fluid on the addition of a small quantity of an alkali, such as potash or ammonia.
Soluble albumen may be converted into the insoluble form in the following ways:—
1.By the application of heat.—A moderately strong solution of albumen becomes opalescent and coagulates on being heated to about 150°, but a temperature of 212° is required if the liquid is very dilute. A layer ofdriedalbumen cannot easily be coagulated by the mere application of heat.
2.By addition of strong acids.—Nitric acid coagulates albumen perfectly without the aid of heat. Acetic acid, however, acts differently, appearing to enter into combination with the albumen, and forming a compound soluble in warm water acidified by acetic acid.
3.By the action of metallic salts.—Many of the salts of the metals coagulate albumen very completely. Nitrate of silver does so; also the bichloride of mercury. Ammoniacal oxide of silver, however, does not coagulate albumen.
The white precipitate formed on mixing albumen with nitrate of silver is a chemical compound of the animal matter with protoxide of silver. This substance, which has been termed albuminate of silver, is soluble in ammonia and hyposulphite of soda; but after exposure to light, or heating in a current of hydrogen gas, it assumes a brick-red color, being probably reduced to the condition of a salt of thesuboxideof silver. It is then almost insoluble in ammonia, but enough dissolves to tinge the liquid wine-red. The author is of opinion that thered colorationof solution of nitrate of silver employed in sensitizing the albumenized photographic paper is produced by the same compound, although often referred to the presence of sulphuret of silver.
Albumen also combines with lime and baryta; and chloride of barium has been recommended in positive printing upon albumenized paper, probably from this cause.
Chemical composition of albumen.—Albumen belongs to thenitrogenousclass of organic substances. It also contains small quantities of sulphur and phosphorus.
Alcohol.
Symbol, C{4}H{6}O{2}. Atomic weight, 46.
Alcohol is obtained by the careful distillation of any spirituous or fermented liquor. If wine or beer be placed in a retort, and heat applied, the alcohol, being more volatile than water, rises first, and is condensed in an appropriate receiver; a portion of the vapor of water, however, passes over with the alcohol, and dilutes it to a certain extent, forming what is termed "spirits of wine." Much of this water may be removed by redistillation from carbonate of potash; but in order to render the alcohol thoroughlyanhydrous, it is necessary to employquick limewhich possesses a still greater attraction for water. An equal weight of this powdered lime is mixed with strong alcohol of ·823, and the two are distilled together.
Properties of Alcohol.—Pure anhydrous alcohol is a limpid liquid, of an agreeable odor and pungent taste; sp. gr. at 60°, ·794. It absorbs vapor of water, and becomes diluted by exposure to damp air; boils at 173° Fahr. It has never been frozen.
Alcohol distilled from carbonate of potash has a specific gravity of ·815 to ·823, and contains 90 to 93 per cent, of real spirit.
The specific gravity of ordinary rectified spirits of wine is usually about ·840, and it contains 80 to 83 per cent, of absolute alcohol.
Ammonia.
Symbol, NH{3} or NH{4}O. Atomic weight, 17.
The liquid known by this name is an aqueous solution of the volatile gas ammonia. Ammoniacal gas contains 1 atom of nitrogen combined with three of hydrogen: these two elementary bodies exhibit no affinity for each other, but they can be made to unite under certain circumstances, and the result is ammonia.
Properties of Ammonia.—Ammoniacal gas is soluble in water to a large extent; the solution possessing those properties which are termed alkaline. Ammonia, however, differs from the other alkalies in one important particular—it is volatile: hence the original color of turmeric paper affected by ammonia is restored on the application of heat. Solution of ammonia absorbs carbonic acid rapidly from the air, and is converted into carbonate of ammonia; it should therefore be preserved in stoppered bottles. Besides carbonate, commercial ammonia often contains chloride of ammonium, recognized by the white precipitate given by nitrate of silver after acidifying with pure nitric acid.
The strength of commercial ammonia varies greatly; that sold for pharmaceutica purposes, under the name of liquor ammoniæ, contains about 10 per cent, of real ammonia. The sp. gr. of aqueous ammonia diminishes with the proportion of ammonia present, the liquor ammoniæ being usually about ·936.
Chemical Properties.—Ammonia, although forming a large class of salts, appears at first sight to contrast strongly by composition with the alkalies proper, such as potash and soda. Mineral bases generally areprotoxides of metals, but ammonia consists simply of nitrogen and hydrogen united with oxygen. The following remarks may perhaps tend somewhat to elucidate the difficulty:—
Theory of Ammonium.—This theory supposes that a substance exists possessing the properties of a metal, but different from metallic bodies generally in being compound in structure: the formula assigned to it is NH{4}, 1 atom of nitrogen united with 4 of hydrogen. The hypothetical metal is termed "ammonium," and ammonia, associated with an atom of water, may be viewed as itsoxide; for NH{3} + HO plainly equals NH{4}O. Thus, as potash is the oxide ofpotassium, so ammonia is the oxide ofammonium.
The composition of thesaltsof ammonia is on this view assimilated to those of the alkalies proper. Thus, sulphate of ammonia is a sulphate of the oxide ofammonium; muriate or hydrochlorate of ammonia is a chloride of ammonium, etc.
Ammonio-Nitrate of Silver.(SeeSilver, Ammonio-Nitrate of.)
Aqua-Regia.(SeeNitro-Hydrochloric Acid.)
Baryta, Nitrate of.(SeeNitrate of Baryta.)
Bichloride of Mercury.(SeeMercury, Bichloride of.)
Bromine.
Symbol, Br. Atomic weight, 78.
This elementary substance is obtained from the uncrystallizableresiduum of sea-water, termedbittern. It exists in the water in very minute proportion, combined with magnesium in the form of a soluble bromide of magnesium.
Properties.—Bromine is a deep reddish-brown liquid of a disagreeable odor, and fuming strongly at common temperatures; sparingly soluble in water (1 part in 23, Lowig), but more abundantly so in alcohol, and especially in ether. It is very heavy, having a specific gravity of 3·0.
Bromine is closely analogous to chlorine and iodine in its chemical properties. It stands on the list intermediately between the two; its affinities being stronger than those of iodine, but weaker than chlorine. (SeeChlorine.)
It forms a large class of salts, of which the bromides of potassium, cadmium, and silver are the most familiar to photographers.
Bromide of Potassium.
Symbol, KBr. Atomic weight, 118.
Bromide of potassium is prepared by adding bromine to caustic potash, and heating the product, which is a mixture of bromide of potassium and bromate of potash, to redness, in order to drive off the oxygen from the latter salt. It crystallizes in anhydrous cubes, like the chloride, and iodide, of potassium; it is easily soluble in water, but more sparingly so in alcohol; it yields red fumes of bromine when acted upon by sulphuric acid.
Bromide of Silver.(SeeSilver, Bromide of.)
Carbonate of Soda.
Symbol, NaO CO{2} + 10 Aq.
This salt was formerly obtained from the ashes of seaweeds,but is now more economically manufactured on a large scale from common salt. The chloride of sodium is first converted into sulphate of soda, and afterwards the sulphate into carbonate of soda.
Properties.—The perfect crystals contain ten atoms of water, which are driven off by the application of heat, leaving a white powder—the anhydrous carbonate.Common washing sodais a neutral carbonate, contaminated to a certain extent with chloride of sodium and sulphate of soda. The carbonate used for effervescing draughts is either a bicarbonate with 1 atom of water, or a sesquicarbonate, containing about 40 per cent, of real alkali; it is therefore nearly double as strong as the washing carbonate, which contains about 22 per cent, of soda. Carbonate of soda is soluble in twice its weight of water at 60°, the solution being strongly alkaline.
Carbonate of Potash.(SeePotash, Carbonate of.)
Caseine.(SeeMilk.)
Charcoal, Animal.
Animal charcoal is obtained by heating animal substances, such as bones, dried blood, horns, etc., to redness, in close vessels, until all volatile empyreumatic matters have been driven off, and a residue of carbon remains. When prepared from bones it contains a large quantity of inorganic matter in the shape of carbonate and phosphate of lime, the former of which producesalkalinityin reacting upon nitrate of silver. Animal charcoal is freed from these earthy salts by repeated digestion in hydrochloric acid; but unless very carefully washed it is apt to retainan acid reaction, and so to liberate free nitric acid when added to solution of nitrate of silver.
Properties.—Animal charcoal, when pure, consists solely of carbon, and burns away in the air without leaving any residue: it is remarkable for its property of decolorizing solutions; the organic coloring substance being separated, but not actuallydestroyed, as it is bychlorineemployed as a bleaching agent. This power of absorbing coloring matter is not possessed in an equal degree by all varieties of charcoal, but is in great measure peculiar to those derived from the animal kingdom.
China Clay or Kaolin.
This is prepared, by careful levigation, from mouldering granite and other disintegrated felspathic rocks. It consists of thesilicate of alumina,—that is, of silicic acid orflint, which is an oxide of silicon, united with the base alumina (oxide of aluminum). Kaolin is perfectly insoluble in water and acids, and produces no decomposition in solution of nitrate of silver. It is employed by photographers to decolorize solutions of nitrate of silver which have become brown from the action of albumen or other organic matters.
Chlorine.
Symbol, Cl. Atomic weight, 36.
Chlorine is a chemical element found abundantly in nature, combined with metallic sodium in the form of chloride of sodium, or sea-salt.
Preparation.—By distilling common salt with sulphuric acid, sulphate of soda and hydrochloric acid are formed.Hydrochloric acid contains chlorine combined with hydrogen; by the action ofnascentoxygen (see oxygen), the hydrogen may be removed in the form of water, and the chlorine left alone.
Properties.—Chlorine is a greenish-yellow gas, of a pungent and suffocating odor; soluble to a considerable extent in water, the solution possessing the odor and color of the gas. It is nearly 2½ times as heavy as a corresponding bulk of atmospheric air.
Chemical Properties.—Chlorine belongs to a small natural group of elements which contains also bromine, iodine, and fluorine. They are characterized by having a strong affinity for hydrogen, and also for the metals, but are comparatively indifferent to oxygen. Many metallic substances actually undergocombustionwhen projected into an atmosphere of chlorine, the union between the two taking place with extreme violence. The characteristic bleaching properties of chlorine gas are explained in the same manner:—Hydrogen is removed from the organic substance, and in that way the structure is broken up and the color destroyed.
Chlorine is more powerful in its affinities than either bromine or iodine. The salts formed by these three elements are closely analogous in composition and often in properties. Those of the alkalies, alkaline earths, and many of the metals are soluble in water, but the silver salts are insoluble; the lead salts sparingly so.
The combinations of chlorine, bromine, iodine, and fluorine, with hydrogen, are acids, and neutralize alkalies in the usual manner, with formation of alkaline chloride and water.
The test by which the presence of chlorine is detected,either free or in combination with bases, isnitrate of silver; it gives a white curdy precipitate of chloride of silver, insoluble in nitric acid, but soluble in ammonia. The solution of nitrate of silver employed as the test must not contain iodide of silver, as this compound is precipitated by dilution.
Chloride of Ammonium.
Symbol, NH{4}Cl. Atomic weight, 54.
This salt, also known as muriate or hydrochlorate of ammonia, occurs in commerce in the form of colorless and translucent masses, which are procured bysublimation, the dry salt being volatile when strongly heated. It dissolves in an equal weight of boiling, or in three parts of cold water. It contains morechlorinein proportion to the weight used than chloride of sodium, the atomic weights of the two being as 54 to 60.
Chloride of Barium.
Symbol, BaCl+2HO. Atomic weight, 123.
Barium is a metallic element, very closely allied to calcium, the elementary basis oflime. The chloride of barium is commonly employed as a test for sulphuric acid, with which it forms an insoluble precipitate of sulphate of baryta. It is also said to affect the color of the photographic image when used in preparing positive paper; which may possibly be due to a chemical combination of baryta with albumen: but it must be remembered that this chloride, from its high atomic weight, containslesschlorine than the alkaline chlorides.
Properties of Chloride of Barium.—Chloride of bariumoccurs in the form of white crystals, soluble in about two parts of water, at common temperature. These crystals contain two atoms of water of crystallization, which are expelled at 212°, leaving the anhydrous chloride.
Chloride of Gold.(SeeGold, Chloride of.)
Chloride of Sodium.
Symbol, NaCl. Atomic weight, 60.
Common salt exists abundantly in nature, both in the form of solid rock-salt and dissolved in the waters of the ocean.
Properties of the pure Salt.—Fusible without decomposition at low redness, but sublimes at higher temperatures; the melted salt concretes into a hard white mass on cooling. Nearly insoluble in absolute alcohol, but dissolves in minute quantity in rectified spirit. Soluble in three parts of water, both hot and cold. Crystallizes in cubes, which are anhydrous.
Impurities of Common Salt.—Table salt often contains large quantities of the chlorides of magnesium and calcium, which, being deliquescent, produce a dampness by absorption of atmospheric moisture: sulphate of soda is also commonly present. The salt may be purified by repeated recrystallization, but it is more simple to prepare the pure compounddirectly, by neutralizing hydrochloric acid with carbonate of soda.
Chloride of Silver.(SeeSilver, Chloride of.)
Citric Acid.
This acid is found abundantly in lemon-juice and inlime-juice. It occurs in commerce in the form of large crystals, which are soluble in less than their own weight of water at 60°.
Commercial citric acid is sometimes mixed with tartaric acid. The adulteration may be discovered by making a concentrated solution of the acid and addingacetate of potash; crystals of bitartrate of potash will separate if tartaric acid be present.
Citric acid is tribasic. It forms with silver a white insoluble salt, containing 3 atoms of oxide of silver to 1 atom of citric acid. If the citrate of silver be heated in a current of hydrogen gas, a part of the acid is liberated and the salt is reduced to a citrate ofsuboxideof silver; which is of a red color. The action of white light in reddening citrate of silver is shown by the author to be of a similar nature.
Cyanide of Potassium.
Symbol, K, C{2}N, or KCy. Atomic weight, 66.
This salt is a compound of cyanogen gas with the metal potassium. Cyanogen is not an elementary body, like chlorine or iodine, but consists of carbon and nitrogen united in a peculiar manner. Although a compound substance, it reacts in the manner of an element, and is therefore (likeammonium, previously described) an exception to the usual laws of chemistry. Many other bodies of a similar character are known.
Ether.
Symbol, C{4}H{5}O. Atomic weight, 37.
Ether is obtained by distilling a mixture of sulphuricacid and alcohol. If the formula of alcohol (C{4}H{6}O{2}) be compared with that of ether, it will be seen to differ from it in the possession of an additional atom of hydrogen and of oxygen: in the reaction, the sulphuric acid removes these elements in the form of water, and by so doing converts one atom of alcohol into an atom of ether. The termsulphuricapplied to the commercial ether has reference only to the manner of its formation.
Properties of Ether.—It is neither acid nor alkaline to test-paper. Specific gravity, at 60°, about ·720. Boils at 98° Fahrenheit. The vapor is exceedingly dense, and may be seen passing off from the liquid and falling to the ground: hence the danger of pouring ether from one bottle to another if a flame be near at hand.
Ether does not mix with water in all proportions; if the two are shaken together, after a short time the former rises and floats upon the surface. In this way a mixture of ether and alcohol may be purified to some extent, as in the common process ofwashingether. The water employed however always retains a certain portion of ether (about a tenth part of its bulk), and acquires a strong ethereal odor; washed ether also contains water in small quantity.
Bromine and iodine are both soluble in ether, and gradually react upon and decompose it.
The strong alkalies, such as potash and soda, also decompose ether slightly after a time, but not immediately. Exposed to air and light, ether is oxidized and acquires a peculiar odor.
Ether dissolves fatty and resinous substances readily, but inorganic salts are mostly insoluble in this fluid. Hence it is that iodide of potassium and other substancesdissolved in alcohol are precipitated to a certain extent by the addition of ether.
Fluoride of Potassium.
Symbol, KF. Atomic weight, 59.
Preparation.—Fluoride of potassium is formed by saturating hydrofluoric acid with potash, and evaporating to dryness in a platinum vessel.Hydrofluoric acidcontains fluorine combined with hydrogen; it is a powerfully acid and corrosive liquid, formed by decomposing flour spar, which is afluoride of calcium, with strong sulphuric acid; the action which takes place being precisely analogous to that involved in the preparation of hydrochloric acid.
Properties.—A deliquescent salt, occurring in small and imperfect crystals. Very soluble in water: the solution acting upon glass in the same manner as hydrofluoric acid.
Formic Acid.
Symbol, C{2}HO{3}. Atomic weight, 37.
This substance was originally discovered in thered ant(Formica rufa), but it is prepared on a large scale by distillingstarchwith binoxide of manganese and sulphuric acid.
Properties.—The strength of commercial formic acid is uncertain, but it is always more or less dilute. The strongest acid, as obtained by distilling formiate of soda with sulphuric acid, is a fuming liquid with a pungent odor, and containing only one atom of water: it inflames the skin in the same manner as the sting of the ant.
Formic acid reduces the oxides of gold, silver, and mercury,to the metallic state, and is itself oxidized into carbonic acid. The alkaline formiates also possess the same properties.
Gelatine.
Symbol, C{13}H{10}O{5}N{2}. Atomic weight, 156.
This is an organic substance somewhat analogous to albumen, but differing from it in properties. It is obtained by subjecting bones, hoofs, horns, calves' feet, etc., to the action of boiling water. The jelly formed on cooling is termed size, or when dried or cut into slices,glue. Gelatine, as it is sold in the shops, is a pure form of glue.Isinglassis gelatine prepared, chiefly in Russia, from the air-bladders of certain species of sturgeon.
Properties of Gelatine.—Gelatine softens and swells up in cold water, but does notdissolveuntil heated: the hot solution, on cooling, forms a tremulous jelly. One ounce f cold water will retain about three grains of isinglass without gelatinizing; but much depends upon the temperature, a few degrees greatly affecting the result.
Gelatine forms no compound with oxide of silver analogous to the albuminate of silver; which fact explains the difference in the photographic properties of albumen and gelatine.
Glycerine.
Fatty bodies are resolved by treatment with an alkali into an acid—which combines with the alkali, forming asoap,—and glycerine, remaining in solution.
Pure glycerine, as obtained by Price's patent process of distillation, is a viscid liquid of sp. gr. about 1·23; miscible in all proportions with water and alcohol. It is peculiarly a neutral substance, exhibiting no tendency to combinewith acids or bases. It has little or no action upon nitrate of silver in the dark, and reduces it very slowly even when exposed to light.
Gold, Chloride of.
Symbol, AuCl{3}. Atomic weight, 303.
This salt is formed by dissolving pure metallic gold in nitro-hydrochloric acid, and evaporating at a gentle heat. The solution affords deliquescent crystals of a deep orange color.
Chloride of gold, in a state fit for photographic use may easily be obtained by the following process:—Place a half-sovereign in any convenient vessel, and pour on it half a drachm of nitric acid mixed with two and a half drachms of hydrochloric acid and three drachms of water; digest by a gentle heat, but do notboilthe acid, or much of the chlorine will be driven off in the form of gas. At the expiration of a few hours add fresh aqua-regia in quantity the same as at first, which will probably complete the solution, but if not, repeat the process a third time.
Lastly, neutralize the liquid by adding carbonate of soda until all effervescence ceases, and a green precipitate forms; this iscarbonate of copper, which must be allowed several hours to separate thoroughly. The solution then contains chloride of gold in a neutral state, and free from copper and silver, with which the metallic gold is alloyed in the standard coin of the realm.
The weight of a half-sovereign is about 61 grains, of which 56 grains are pure gold. This is equivalent to 86 grains of chloride of gold, which will therefore be the quantity contained in the solution.
The following process for preparing chloride of gold is more perfect than the last:—dissolve the gold coin in aqua-regia as before; then boil with excess of hydrochloric acid to destroy the nitric acid, dilute largely with distilled water, and add a filtered aqueous solution of common sulphate of iron (6 parts in 1 part of gold); collect the precipitated gold, which is now free from copper; re-dissolve in aqua-regia, and evaporate to dryness on a water bath.
Avoid using ammonia to neutralize chloride of gold, as it would be liable to occasion a deposit of "fulminating gold," the properties of which are described immediately following.
Properties of Chloride of Gold.—As sold in commerce it usually contains excess of hydrochloric acid, and is then of a bright yellow color; but when neutral and somewhat concentrated it is dark red (Leo ruberof the alchemists). It gives no precipitate with carbonate of soda, unless heat be applied; the free hydrochloric acid present forms, with the alkali, chloride of sodium, which unites with the chloride of gold, and produces a double salt, chloride of gold and sodium, soluble in water.
Chloride of gold is decomposed with precipitation of metallic gold by charcoal, sulphurous acid, and many of the vegetable acids; also by protosulphate and protonitrate of iron. It tinges the cuticle of an indelible purple tint. It is soluble in alcohol and in ether.
Gold, Fulminating.
This is a yellowish-brown substance, precipitated on adding ammonia to a strong solution of chloride of gold.
It may be dried carefully at 212°, butexplodes violentlyon being heated suddenly about to 290°. Friction also causes it to explode when dry; but the moist powder may be rubbed or handled without danger. It is decomposed by sulphuretted hydrogen.
Fulminating gold is probably an aurate of ammonia, containing 2 atoms of ammonia to 1 atom of peroxide of gold.
Gold, Hyposulphite of.
Symbol, AuO S{2}O{2}. Atomic Weight, 253.
Hyposulphite of gold is produced by the reaction of chloride of gold upon hyposulphite of soda.
The salt sold in commerce as sel d'or is a double hyposulphite of gold and soda, containing one atom of the former salt to three of the latter, with four atoms of water of crystallization. It is formed by adding one part of chloride of gold, in solution, to three parts of hyposulphite of soda, and precipitating the resulting salt by alcohol; the chloride of gold must be added to the hyposulphite of soda, and not the soda salt to the gold.
Properties.—Hyposulphite of gold is unstable and cannot exist in an isolated state, quickly passing into sulphur, sulphuric acid, and metallic gold. When combined with excess of hyposulphite of soda in the form of sel d'or, it is more permanent.
Sel d'or occurs crystallized in fine needles, which are very soluble in water. The commercial article is often impure, containing little else than hyposulphite of soda, with a trace of gold. It may be analyzed by adding a few drops of strong nitric acid (free from chlorine) dilutingwith water, and afterwards collecting and igniting the yellow powder, which is metallic gold.
Grape Sugar.
Symbol, C{24}H{28}O{28}. Atomic weight, 366.
This modification of sugar, often termedgranular sugar, orglucose, exists abundantly in the juice of grapes, and in many other varieties of fruit. It forms the saccharine concretion found in honey, raisins, dried figs, etc. It may be produced artificially by the action of fermenting principles, and of dilute mineral acids, upon starch.
Properties.—Grape sugar crystallizes slowly and with difficulty from a concentrated aqueous solution, in small hemispherical nodules, which are hard, and feel gritty between the teeth. It is much less sweet to the taste than cane sugar, and not so soluble in Water (1 part dissolves in 1½ of cold water). Grape sugar tends to absorb oxygen, and hence it possesses the property of decomposing the salts of the noble metals, and reducing them by degrees to the metallic state, even without the aid of lights The action however in the case ofnitrate of silveris slow, unless the temperature be somewhat elevated.Canesugar does not possess these properties to an equal extent, and hence it is readily distinguished from the other variety.
Honey.
This substance contains two distinct kinds of sugar, grape sugar, and an uncrystallizable substance analogous to, or identical with, the treacle found associated with common sugar in the cane juice. The agreeable taste of honey probably depends upon the latter, but its reducingpower on metallic oxides is due to the former. Pure grape sugar can readily be obtained from inspissated honey, by treating it with alcohol, which dissolves out the syrup, but leaves the crystalline portion.
Hydrochloric; Acid.
Symbol, HCl. Atomic weight, 37.
Hydrochloric acid is a volatile gas, Which may be liberated from the salts termed chlorides by the action of sulphuric acid. The acid, by its superior affinities, removes the base; thus,—
NaCl + HO SO{3} = NaO SO{3} + HCl.
Properties.—Abundantly soluble in water, forming the liquid hydrochloric or muriatic acid of commerce. The most concentrated solution of hydrochloric acid has a sp. gr. 1·2, and contains about 40 per cent, of gas; that commonly sold is somewhat weaker, sp; gr. 1·14 = 28 per cent. real acid.
Pure hydrochloric acid is colorless, and fumes in the air. The yellow color of the commercial acid depends upon the presence of traces of perchloride of iron or organic matter; commercial muriatic acid also often contains a portion of free chlorine and of sulphuric acid.
Hydriodic Acid.
Symbol, HI. Atomic weight, 127.
This is a gaseous compound of hydrogen and iodine, corresponding in composition to the hydrochloric acid. It cannot, however, from its instability, be obtained in the same manner, since, on distilling an iodide with sulphuricacid, the hydriodic acid first formed is subsequently decomposed into iodine and hydrogen. An aqueous solution of hydriodic acid is easily prepared by adding iodine to water containing sulphuretted hydrogen gas; a decomposition takes place, and sulphur is set free; thus: HS + I = HI + S.
Properties.—Hydriodic acid is very soluble in water, yielding a strongly acid liquid. The solution, colorless at first, soon becomes brown from decomposition, and liberation of free iodine. It may be restored to its original condition by adding solution of sulphuretted hydrogen.
Hydrosulphuric Acid.
Symbol, HS. Atomic weighty 17.
This substance, also known as sulphuretted hydrogen, is a gaseous compound of sulphur and hydrogen, analogous in composition to hydrochloric and hydriodic acids. It is usually prepared by the action of dilute sulphuric acid upon sulphuret of iron, the decomposition being similar to that involved in the preparation of the hydrogen acids generally:—
FeS + HO SO{3} = FeO SO{3} + HS.
Properties.—Cold water absorbs three times its bulk of hydrosulphuric acid, and acquires the peculiar putrid odor and poisonous qualities of the gas. The solution is faintly acid to test-paper, and becomes opalescent on keeping, from gradual separation of sulphur. It is decomposed by nitric acid, and also by chlorine and iodine. It precipitates silver from its solutions, in the form of black sulphuret of silver; also copper, mercury, lead, etc.; but iron and other metals of that class are not affected, if theliquid contains free acid. Hydrosulphuric acid is constantly employed in the chemical laboratory for these and other purposes.
Hydrosulphate of Ammonia.
Symbol, NH{4}S HS. Atomic weight, 51.
The liquid known by this name, and formed by passing sulphuretted hydrogen gas into ammonia, is a double sulphuret of hydrogen and ammonium. In the preparation, the passage of the gas is to be continued until the solution gives no precipitate with sulphate of magnesia and smells strongly of hydrosulphuric acid.
Properties,—Colorless at first, but afterwards changes to yellow, from liberation and subsequent solution of sulphur. Becomes milky on the addition of any acid. Precipitates, in the form of sulphuret, all the metals which are affected by sulphuretted hydrogen; and, in addition, those of the class to which iron, zinc, and manganese, belong.
Hydrosulphate of ammonia is employed in photography to darken the negative image, and also in the preparation of iodide of ammonium; the separation of silver from hyposulphite solutions, etc.
Hyposulphite of Soda.
Symbol, NaO S{2}H{2} + 5 HO. Atomic weight, 125.
The hyposulphite of soda commonly employed by photographers is a neutral combination of hyposulphurous acid and the alkali soda. It is selected as being moreeconomical in preparation than any other hyposulphite adapted for fixing.
Hyposulphite of soda occurs in the form of large translucent groups of crystals, which include five atoms of water. These crystals are soluble in water almost to any extent, the solution being attended with the production of cold; they have a nauseous and bitter taste.
Hyposulphite of Gold.(SeeGold, Hyposulphite of.)
Hyposulphite of Silver.(SeeSilver, Hyposulphite of.)
Iceland Moss.
Cetraria Islandica.—A species of lichen found in Iceland and the mountainous parts of Europe; when boiled in water, it first swells up, and then yields a substance which gelatinizes on cooling.
It contains lichen starch; a bitter principle soluble in alcohol, termed "cetrarine;" and common starch; traces of gallic acid and bitartrate of potash are also present.
Iodine.
Symbol, I. Atomic weight, 126.
Iodine is chiefly prepared at Glasgow, fromkelp, which is the fused ash obtained by burning seaweeds. The waters of the ocean contain minute quantities of the iodides of sodium and magnesium, which are separated and stored up by the growing tissues of the marine plant.
In the preparation, the mother-liquor of kelp is evaporated to dryness and distilled with sulphuric acid; the hydriodic acid first liberated is decomposed by the hightemperature, and fumes of iodine condense in the form of opaque crystals.
Properties.—Iodine has a bluish-black color and metallic lustre; it stains the skin yellow, and has a pungent smell, like diluted chlorine. It is extremely volatile when moist, boils at 350°, and produces dense violet-colored fumes, which condense in brilliant plates. Specific gravity 4·946. Iodine is very sparingly soluble in water, 1 part requiring 7000 parts for perfect solution: even this minute quantity however tinges the liquid of a brown color. Alcohol and ether dissolve it more abundantly, forming dark-brown solutions. Iodine also dissolves freely in solutions of the alkaline iodides, such as the iodide of potassium, of sodium, and of ammonium.
Chemical Properties.—Iodine belongs to the chlorine group of elements, characterized by forming acids with hydrogen, and combining extensively with the metals (see chlorine). They are however comparatively indifferent to oxygen, and also to each other. The iodides of the alkalies and alkaline earths are soluble in water; also those of iron, zinc, cadmium, etc. The iodides of lead, silver, and mercury are nearly or quite insoluble.
Iodine possesses the property of forming a compound of a deep blue color with starch. In using this as a test, it is necessary first to liberate the iodine (if in combination), by means of chlorine, or nitric acid saturated with peroxide of nitrogen. The presence of alcohol or ether interferes to a certain extent with the result.
Iodide of Ammonium.
Symbol, NH{4}I. Atomic weight, 144.
This salt may be prepared by adding carbonate of ammoniato iodide of iron, but more easily by the following process:—A strong solution of hydrosulphate of ammonia is first made, by passing sulphuretted hydrogen gas into liquor ammoniæ To this liquid iodine is added until the whole of the sulphuret of ammonium has been converted into iodide. When this point is reached, the solution at once colors brown from solution of free iodine. On the first addition of the iodine, an escape of sulphuretted hydrogen gas and a dense deposit of sulphur take place. After the decomposition of the hydrosulphate of ammonia is complete, a portion of hydriodic acid—formed by the mutual reaction of sulphuretted hydrogen and iodine—attacks any carbonate of ammonia which may be present, and causes an effervescence. The effervescence being over, the liquid is still acid to test-paper, from excess of hydriodic acid; it is to be cautiously neutralized with ammonia, and evaporated by the heat of a water-bath to the crystallizing point.
The crystals should be thoroughly dried over a dish of sulphuric acid, and then sealed in small tubes containing each about half a drachm of the salt; by this means it will be preserved colorless.
Iodide of ammonium is very soluble in alcohol, but it is not advisable to keep it in solution, from the rapidity with which it decomposes and becomes brown.
The most common impurity of commercial iodide of ammonium is sulphate of ammonia; it is detected by its sparing insolubility in alcohol.
Iodide of Cadmium.
Symbol, CdI. Atomic weight, 182.
This salt is formed by heating filings of metallic cadmiumwith iodine, or by mixing the two together with addition of water. It is useful in iodizing collodion intended for keeping, since it does not become brown from liberation of free iodine with the same rapidity as the alkaline iodides.
Iodide of cadmium is very soluble both in alcohol and water; the solution yielding on evaporation large six-sided tables of a pearly lustre, which are permanent in the air. The crystalline form of this salt is a sufficient criterion of its purity.
Iodide of Iron.
Symbol, FeI. Atomic weight, 154.
Iodide of iron, in a fit state for photographic use, is easily obtained by dissolving a drachm of iodine in an ounce ofproof spirit—that is, a mixture of equal bulks of spirits of wine and water—and adding an excess of iron filings. After a few hours, a green solution is obtained without the aid of heat. The presence of metallic iron in excess prevents the liberation of iodine and deposit of peroxide of iron which would otherwise speedily occur. It is very soluble in water and alcohol, but the solution rapidly absorbs oxygen and deposits peroxide of iron; hence the importance of preserving it in contact with metallic iron, with which the separated iodine may recombine. By very careful evaporation, hydrated crystals of protoiodide may be obtained, but the composition of the solid salt usually sold under that name cannot be depended on.
Theperiodideof iron, corresponding to the perchloride, has not been examined, and it is doubtful if any such compound exists.
Iodide of Potassium.
Symbol, KI. Atomic weight, 166.
This salt is usually formed by dissolving iodine in solution of potash until it begins to acquire a brown color; a mixture of iodide of potassium andiodate of potash(KO IO{5}) is thus formed; but by evaporation and heating to redness, the latter salt parts with its oxygen, and is converted into iodide of potassium.
Properties.—It forms cubic and prismatic crystals, which should be hard, andvery slightly or not at all deliquescent. Soluble in less than an equal weight of water at 60°; it is also soluble in alcohol, but not in ether. The proportion of iodide of potassium contained in a saturated alcoholic solution, varies with the strength of the spirit,—with common spirits of wine, sp. gr. ·836, it would be about 8 grains to the drachm; with alcohol rectified from carbonate of potash, sp. gr. ·823, 4 or 5 grains: with absolute alcohol, 1 to 2 grains. The solution of iodide of potassium is instantly colored brown by free chlorine; also very rapidly by peroxide of nitrogen; ordinary acids, however, act less quickly, hydriodic acid being first formed, and subsequently decomposing spontaneously.
Iodide of potassium, as sold in the shops, is often contaminated with various impurities. The first and most remarkable iscarbonate of potash. When a sample of iodide of potassium contains much carbonate of potash, it forms small and imperfect crystals, which are strongly alkaline to test-paper, and become moist on exposure to the air, from the deliquescent nature of the alkaline carbonate.Sulphate of potashis also a common impurity; it may be detected by chloride of barium.
Chloride of potassiumis another impurity; it is detected as follows:—Precipitate the salt by an equal weight of nitrate of silver, and treat the yellow mass with solution of ammonia; if any chloride of silver is present, it dissolves in the ammonia, and after nitration is re-precipitated in white curds by the addition of an excess of pure nitric acid. If the nitric acid employed is not pure, but contains traces of free chlorine, the iodide of silver must be well washed with distilled water before treating it with ammonia, or the excess of free nitrate of silver dissolving in the ammonia would, on neutralizing, produce chloride of silver, and so cause an error.
Iodide of potashis a fourth impurity often found in iodide of potassium: to detect it, add a drop of dilute sulphuric acid, or a crystal of citric acid, to the solution of the iodide; when, if much iodate be present, the liquid will become yellow from liberation of free iodine. The rationale of this reaction is as follows:—The sulphuric acid unites with the base of the salt, and liberates hydriodic acid (HI),a colorless compound; but if iodic acid (IO{5}) be also present, it decomposes the hydriodic acid first formed, oxidizing the hydrogen into water (HO), and setting free the iodine. The immediate production of a yellow color on adding a weak acid to aqueous solution of iodide of potassium is, therefore, a proof of the presence of an iodate. As iodate of potash is thought to render collodion insensitive (?), this point should be attended to.
Iodide of potassium may be rendered very pure by recrystallizing from spirit, or by dissolving in strong alcohol of sp. gr. ·823, in which sulphate, carbonate, and iodate of potash are insoluble. The proportion of iodideof potassium contained in saturated alcoholic solutions varies with the strength of the spirit.
Solution of chloride of barium is commonly used to detect impurities in iodide of potassium; it forms a white precipitate if carbonate, iodate, or sulphate be present. In the two former cases the precipitate dissolves on the addition ofpuredilute nitric acid, but in the latter it is insoluble. The commercial iodide, however, is rarely so pure as to remain quite clear on the addition of chloride of barium, amere opalescence, therefore, may be disregarded.