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340 THE PHOTOGRAPHIC NEWS. [July 18,1862. jurors, and the Secretaries of the English and French Societies. These, it appears, were taken with a 5} in. Voigtliinder portrait lens with a 2} in. aperture, and focus of 20 inches for a distance of seventeen feet from the lens. One of the groups now before us, that of Dr. Diamond and M. Laulerie, of which we spoke very highly last week, is about 12 by 10, and was produced with an exposure of seven seconds in a dull light. We have also received some ex cellent card portraits, one produced in less than a second, and others in one or two seconds. Mr. Claudet attributes much of this rapidity to the character of the developing solution, which he describes in a letter to Dr. Diamond, a copy of which he has kindly furnished us. We ought to remark here, that a typographical error has inadvertently crept into the formula, as given in our excellent contemporary, the Photographic Journal, which, in the letter, as below quoted, is corrected. After referring to the group, and the circum stances under which it was produced, Mr. Claudet says : — “ Acting on the principle of my father, that superiority in photography does not depend on the secret of some manipu lation, I did not hesitate to tell you that I had arrived at this extraordinary senstiveness by substituting formic acid in place of acetic acid in the developing-solution, and adding nitric acid to the nitrate of silver bath. I promised that I would give you a full description of my process, to enable you to publish it in the Photographic Journal for the interest of all. In fulfilment of my promise, I now give you that description. “ The formic acid I use is made by Messrs. Morson & Son, and in my developing-solution it replaces acetic acid. The nitrate of silver bath must be of the strength of 35 grs. to 1 oz. of distilled water. To 1 pint of this bath I add 3 drops of strong nitric acid. “ The developer consists of pyrogallic acid 20 grs , distilled water 7} oz., formic acid 1 oz., and 6 drs. of alcohol. “ The plate must be well drained after having been taken out of the nitrate bath; and this is a grand point for the success. “ By this process, in an ordinary fine light, with a 3-inch double lens by Voigtliinder, of 7} inches focal length for a distance of 25 feet, I take a portrait in the glass room in less than a second. “ I have found that Thomas’s collodion (one-half of his ordinary negative collodion and one-half of his cadmium collodion) is the best for my process, which has the following advantages:— “ 1st. The picture is brought on as quickly as with pro tosulphate of iron, being on a carte-de-visite plate, developed in one minute; and the half-tones are as delicate. “ 2nd. It does not require intensifying when the exposure has been for the right time. “ 3rd. If pictures can be taken instantaneously in the glass room at 25 feet, a process of such unusual rapidity must be invaluable for fixing the image of moving objects. This, for want of time only, I have not yet had the opportunity of attempting. “ I do not know by what process Messrs. Ferrier, Warnod, Wilson, England, and Breese, have been able to produce the beautiful instantaneous views which are admired at the International Exhibition; but I have no doubt that the accelerating action of formic acid, if not known by these successful operators, is capable in their hands of producing results still more extraordinary, Henry Claudet.” We may add that M. Ferrier, some time ago, attributed part of his success in instantaneous work to the use of formic acid. Messrs. Wilson, England, and Breese, all use an iron developer with acetic acid, and a bromo-iodized collodion. PHOTOGRAPHIC CHEMICALS: Their Manufacture, Adulterations, and Analysis. Potassium Salts (continued).—Chromate of Potash.—This and the bichromate are very important salts in photography. The chromate is prepared on the large scale from chrome salt, it bichromate, iron-ore (a mixture of sesquioxide of chromium and P"P toxide of iron), by ignition with nitre; the chromium oxydized to chromic acid, and after strong ignition for some time the mass is allowed to cool and exhausted with watet From this solution chromate of potash is prepared for com- mercial purposes by crystallization. If bichromate of potash be present in solution with this salt, the former may w converted into the normal salt by the addition of potash; it may be separated from nitre by crystallization, or by fusion, and the cautious addition of charcoal-powder till the violent detonation ceases; the mobile liquid then becomes pasty, and a small quantity of chromic oxide is separated: the mass is then exhausted with water, the solution filterdd and allowed to crystallize. The salt crystallizes in rigK prismatic crystals, which are of a brilliant lemon-yellow colour, changing to a red tint when heated. At a red heat it fuses, previous to which it decrepitates violently by emitting a green light; the crystals have an alkaline ne action, and a cooling, bitter metallic taste ; the salt is per manent in the air, and is not decomposed when heated per se. It is a powerful oxydizing agent, and causes the rapid combustion of charcoal, cotton, wool, and other organ 10 substances, when they have been dried after saturation with its solution. Chromate of potash dissolves in about tto parts of water, at the ordinary temperature, and is slightly more soluble at the boiling point. During its solution the temperature falls considerably. The colorific properties of this salt are very considerable, one part, by weight, imparting J distinct yellow colour to 40,000 parts of water. It is inso luble in alcohol, which also precipitates it from an aqueous solution. Commercial chromate of potash is seldom pure; to separate the impurities it must be freed by recrystallization from silica and alumina, then mixed with nitric acid, and nitrate of baryta dropped in as long as sulphate of baryta is precipitated. The chlorine is separated by adding chromate chloride of silver is test paper. When heated with oil of vitriol, pure oxy? 1 * is evolved; this method is sometimes used for prepari this gas. The salt dissolves in about ten parts of water * the ordinary temperature, and is much more soluble in boi. ing water. The solution is of a deep orange yellow colou. It is also remarkable for the intense colour which it is caP. ble of communicating to water. Possessing two equivalen! of chromic acid for one equivalent of alkali, this salt isstl a more powerful oxydizing agent than the chromate; wbel mixed with organic matter, it has a great tendency to Pan with some of its oxygen with reduction of the chromic ac“ to the state of sesquioxide of chromium. This change, hoe ever, only takes place under the stimulating action of sol radiation, and on this account bichromate of potash 0* become a very important addition to the photographic boratory. Bichromate of potash is liable to contain t same impurities as the neutral chromate, and may be P™ fied in the same way. , j Permanganate of Potash. — Through the exertions Messrs. Condy, this salt is now procurable in a statkaly almost perfect purity, and at a very cheap rate. It 18 fthe to be of considerable use to photographers, on account o it wonderfully rapid and perfect oxydizing action Whf the exercises on most kinds of organic matter. One o greatest annoyances in the preparation of photosttled solutions is the presence of organic matter in the ds of silver to the filtrate, as long as formed, after which the solution is filtered, evaporated to dryness, and the residue ignited in a platinum crucible; it is then dissolved in water, and the solution left to crys; tallize. When sulphuric hydrochloric, nitric, acetic, and many other acids are added to the aqueous solution of this gives up half its potash to them, being converted into natc, which separates after a slight concentration. Bichromate of potash forms large, bright red, rectangular tables and prisms; its powder is reddish yellow; wbel heated, it decrepitates, and then fuses considerably belo" redness, forming a transparent red liquid which crystallid on cooling. The salt is permanent in the air, and is acid! July , water. ' guarante graphic distilled L poses, us I machine and othe such wal knee a injuriou valued; The sab of mang parts of of water small qi powdere lamp, ti (a low i mass is quantity ’ide, ar rapidly Peroxid tallize 1 qntantit: tity of I tooling, shaped Weight desired bom de asbestot salt foi mafic i rough 1 to test oxygen water c in sixt wganii alcoho. paper, the aii also d atmos which "pecir organi hay 1 of pot TI Some distu entht Wees "I whic level tidal long qlles poin I wo and T lette kne first neen mas
