lium as a white curdy quickly-subsiding precipitate, which requires 50 parts of boiling water and 200 parts of cold water for its solution, and is less soluble in water containing chlorhydric acid.-Iodid of potassium (next to sulphid of ammonium the most sensitive reagent) gives a pale yellow precipitate of iodid of thallium, which appears to be slightly soluble either in water or excess of the reagent.-Bichlorid of platinum throws down a pale orange precipitate of platinchlorid of thallium which is slightly soluble in water and is decomposed on ignition, evolving chlorine with loss of thallium and leaves a crystalline alloy of platinum and thallium.-Metallic zinc separates all the thallium in the metallic state, from neutral solutions often in the form of brilliant radiated needle-shaped crystals, from acid solutions as a heavy black powder. Thallium is in many cases most easily and certainly detected by spectral analysis. The spectrum is characterized by a single bright green line coincident with Bad. This line is however usually perceptible for but a moment, owing to the volatility of the thallium compound, and hence its intensity and duration do not safely indicate the richness in thallium of pyrites, flue-dust, &c. Of crude sulphur a piece as large as a pea is nearly burned away on a platinum loop and the residue is examined in the spectroscope; or better, the sulphur is mostly dissolved by means of sulphid of carbon, and what remains is tested spectrally. In pyrites, flue-dust, and lead-chamber sediment, it may be usually detected at once by the spectroscope. The sublimate procured by strongly heating finely pulverized native sulphids in a closed tube, often gives the reaction when none can be obtained directly from the sulphids themselves. ANALYTICAL CHEMISTRY. S. W. J. 10. Estimation of Sulphuric Acid in sålts of the alkalies.-It is well known that precipitated sulphate of baryta may retain alkaline salts in quantities of 1.5 to 2 per cent, which cannot be removed by the most careful washing. STOLBA (Dingler's Polyt. Jour., April, 1863) obtains the sulphate of baryta pure by digesting it (after washing until the washwaters no longer react of baryta) with 40-50 c. c. of a cold saturated solution of neutral acetate of copper and some acetic acid, at nearly a boiling heat, for 10-15 minutes. (The commercial crystallized acetate of copper is purified from sulphuric acid and at the same time saturated with sulphate of baryta, by adding to its boiling solution a slight excess of chlorid of barium and acetic acid and filtering from the precipitate.) During the digestion, enough acetic acid must be present to prevent the formation of basic salt on boiling. Should basic salt form, which may be readily perceived at the bottom of the vessel, more acetic acid must be added, and the digestion must be renewed for 10-15 minutes. During the process, the vessel containing the precipitate should be constantly agitated. The alkaline salts retained by the sulphate of baryta undergo double decomposition with acetate of copper, and the resulting products all admit of entire separation from the precipitate by means of hot water. The precipitate is washed until no reaction for copper is manifest on mixing the washings with ferrocyanid of potassium. This method the author also found satisfactory for the estimation of sulphuric acid in presence of a large excess of nitrate of baryta and chlorid of barium. S. W. J. PHOTOGRAPHY. 11. Dry Process; by MM. TEISSERE et JACQUEMET, of Marseilles.— Any collodion which gives good results by the wet process may be used in this, provided that it contains at least one per cent of iodids and per cent of bromids. The following formula is recommended: The plate is covered as usual, and sensitized in a bath containing Distilled water, Nitrate of silver, Glacial acetic acid, 100 cub. c. m. 8 grams. 2 cub. c. m. The plate is then transferred to a bath of distilled and filtered water, where it should remain until the plate ceases to appear oily. It is then passed successively through three other baths of filtered water. In the first two, filtered spring water may be used, but the last should be filled with distilled water. The plate is next washed in a solution of tannin, containing 100 cub. c. m. 3 grams. dissolved in the In preparing this solution the tannin should be first pure water, and filtered before the alcohol is added. Before applying the preservative, two portions of the solution should be measured out and placed in separate glasses. That from the first glass should be poured over the plate several times, until the coating has been thoroughly soaked. The excess is then drained off and the plate washed over with the solution in the second glass, which may be collected and used for the first treatment of a second plate. Lastly, the plate is washed under a tap supplied with pure water to remove the excess of tannin, and air dried. The time of exposure for views is stated as from 1 to 14 minutes with a quarter plate Jamin view-lens of 10 c. m. focus, under best conditions. Before developing, the edges of the plate should be varnished with a fine camel's hair brush. Having soaked the plate for a few minutes in pure water, it is next dipped in the silver bath used for sensitizing and drained. It is then dipped into a shallow flat glass dish containing a sufficient quantity of the following developer: Distilled water, Glacial acetic acid, 200 cub. c. m. By rocking the dish the liquid is kept continually rolling over the surface, and the development is carefully watched by the light transmitted through the glass. If the exposure has been well timed the image will appear slowly, but with all the details sharply defined and the lights wholly unstained. It is then only necessary to add to the developer, a few drops at a time, of a weak solution of nitrate silver until the blacks are sufficiently intense * 28.34 cubic centimeters = 1 liquid ounce. 1 gram 154 grains. for a good negative. If the exposure has been too much prolonged the image will appear rapidly and will have a tendency to fog. A good result can nevertheless be frequently obtained even then by adding pure acetic acid to the developer and thus retarding the process. Towards the end, if necessary, a little of the silver solution may be added to give the required intensity. If the exposure has been too short the image will be proportionally slow in coming out, and the details will not readily appear. The development can then be hastened, and a satisfactory negative generally obtained, by adding to the developer a few drops of a saturated solution of pyrogallic acid, followed by one or two drops of a weak solution of silver. If this is not sufficient, increase the amount of both until the details appear, and then intensify by adding acetic acid and solution of silver if necessary. If during the process the developer becomes clonded it should be at once poured off and replaced by a fresh quantity of the original developer. When the image is sufficiently intense, the plate is carefully washed and fixed in a solution of hyposulphite of soda, in the ordinary way. After again washing, a weak solution of gum arabic is spread over the plate which is then dried and varnished. It will be seen that the above process is essentially the same as that of Maj. C. Russell, described by Prof. Emerson in this Journal, vol. xxxiv, p. 134. It contains, however, some details as to formulas and manipulation which are new and of practical value. Our experience has been that although the washing of the sensitized plate should be begun in a bath of distilled water, it may be finished under a tap as well as by the more complex process here recommended. Moreover, we find an advantage in soaking the plate in a bath of hot water before developing, as recommended by Dr. Draper, and we employ by preference the developer of Major Russell to any we have yet seen. Our formula for the developer is: For solution No. 1, pyrogallic acid 4 grams, alcohol of 90 pr. ct. 25 cub. c. m. For solution No. 2, nitrate of silver 1.2 grams, citric acid 3 to 4 grams, according to circumstances, distilled water 25 cub. c. m. We begin by adding to 25 cub. c. m. of pure water 16 drops of No. 1 and 8 drops of No. 2. With this we flow the plate and keep the developer rolling over the surface until the details appear, and then add to the developer a few drops at a time of No. 2, until the required intensity is obtained, returning the developer to the measuring-glass before each addition. If the plate has been over exposed we retard the process by adding acetic acid. If under exposed, we hasten the development by increasing the amount of pyrogallic acid and subsequently of nitrate of silver, when the details are well out. A few experiments gives the operator perfect control over the process. If the developer becomes turbid during the process, it should be at once poured off the plate, washed, and the process renewed with a fresh portion of the developer, increasing the amount of citric acid, which tends to prevent this change. To persons who have not steady hands, the use of a shallow glass dish in developing as recommended above will be found of great advantage, especially when the process is prolonged. Another modification of the dry process proposed by Mr. Fassitt, one of our own photographers, is worthy of attention. It is based upon the use of an infusion of malt instead of tannin as the preserving agent. The infusion is prepared in the following way: Seven parts of crushed or ground malt are digested with 24 parts of warm water, the mixtures being well stirred for 10 or 15 minutes at a temperature of 70° C. It is then slowly cooled and, having been strained through a cloth, is carefully filtered. The same collodion and silver bath are used as in the wet process. When the plate is sensitized it is placed in a flat dish of distilled water, which is waved over the surface until the plate ceases to appear oily. It is then drained for a moment and the malt solution turned on and off, as directed above for the tannin, when the plate is again drained and dried. The exposure is about the same as with the tannin process. Before developing, the plate is soaked in water and well washed under a tap. It is then dipped for a minute in the silver bath, drained, and developed with the usual iron developer. The formula recommended is as follows: 120 to 170 grains. 5 drachms (liquid). Crystallized green vitriol, 10 ounces. If sufficient intensity is not obtained at first, to a fresh portion of the same developer may be added a few drops of the following solution, and the process repeated: The results are said to be superior to those of the tannin process, especially for transparencies on glass. M. Julliet, a French photographer of Mons, gives the following receipts for the dry collodion process, which are said to give remarkably fine negatives, excellently well adapted for enlarging by the solar camera, and the beauty of the enlarged prints made by him he attributes entirely to the delicacy of the negative: Should be kept for a month to a month and a half, until the color, at Before developing, the plate is moistened with a small amount of distilled water without washing and then flooded with a solution containing which is allowed to rest on the plate for a minute and then drained off, when the developer is applied. Two solutions are prepared. The developer consists of 5 grams of No. 1, mixed with 15 grams of No. 2, and is rolled on the plate in the usual way until it becomes turbid. It should then be poured off, and the plate washed and fixed in the usual way. If, however, the details are not all brought out by the first developing, the process should be repeated with a fresh portion of the same solution. We hope that the details here given may serve to make the dry process more popular with our amateur photographers. For out-of-door work, when the time of exposure is not an important point, it is so much more convenient than the wet process that it will be greatly preferred if once fairly tried. Care in regard to the purity of the materials and the condition of the baths will ensure success by the one process as certainly as by the other. III. METALLURGY. J. P. C., JR. 1. On the Occurrence of Titanium in Pig Iron, and some Remarks on the Use of Titaniferous Minerals in the Manufacture of Iron and Steel; by EDWARD RILEY, F.C.S.'-The presence of small cubical red crystals, with a metallic lustre, has long been observed in the hearths of old blast furnaces-they may be said, in fact, to be universally present to a greater or less extent-occurring most largely in the hearths of furnaces where clay iron-stone, or siliceous iron ores (such as the red hematite and Forest of Dean ores) are used. The crystals are always more abundant when the furnaces are used for making the best grey iron, the most perfect crystals that have come under the author's observation being some from the Low Moor ironworks; while the largest quantity were from the iron works in the Forest of Dean, and the Pontypool iron works, some of which crystals were massed together, and had the appearance of copper. The iron from the above works has a great commercial reputation for its quality, and, as a rule, the better the quality of iron made in a blast-furnace the more titanium is found in the hearths. In the examination of a large number of the hearths of the Welsh blast-furnaces, where common iron for rails and bars is chiefly made-in one works eighteen were inspected during their removal-the crystals were observed disseminated through the mass, but were only very small in size and minute in quantity. The red crystals were first supposed by Wollaston to be titanium; but Wöbler has subsequently shown them to be a mixture of a nitrid and cyanid of titanium, containing 18 per cent of nitrogen and 4 per cent of carbon. The composition of the crystals, however, varies-as some will be found to be readily converted into titanic acid on boiling with strong nitric acid, while others are quite unattacked by this reagent. Read before the British Association at Newcastle, and extracted from the London Chemical News, Nos. 206 and 207, Nov. 7 and 14, 1863. |
