THE CHEMICAL NEWS. as this gives much tougher threads than foreign glass. IOI. THE difficulty which attended experiments with the By increasing the length of the needle, and also of the fibre used to suspend it, it was possible to employ fibres with a considerable amount of torsion, and still preserve the delicacy of the apparatus. Fine platinum wire was first tried; but this was soon abandoned in favour of glass fibres, which were found to answer so perfectly that I have since used nothing else. In requires some care. It should be drawn from flint glass, d In fitting up one of these apparatus threads were drawn out which were found to require, respectively :— 44 seconds, 30 28 102. Fig. 7 shows the form of apparatus which I have finally adopted, as combining the greatest delicacy with facility of obtaining accurate observations, and therefore of getting quantitative as well as qualitative results. It a is a torsion apparatus in which the beam moves in a horizontal plane, and may be called a horizontal torsion balance. ab is a piece of thin glass tubing, sealed off at the end b and ground perfectly flat at the end a. the centre a circular hole, c, is blown, and another one, c', at the end; the edges of these holes are ground quite fiat. a, c, and c' can therefore be sealed up by cementing flat transparent pieces of plate glass, quartz, or rock-salt, a, d, and d' on to them (83). To the centre of a b an upright tube, e f, is sealed, having an arm, g, blown on to it for the purpose of attaching the apparatus to the pump. hi is a glass index, drawn from circular or square (22) glass tube, and as light as possible consistent with the needful strength. A long piece of this tube is first drawn out before the blowpipe; and it is then calibrated with mercury until a piece is found having the same bore throughout: the necessary length is then cut from this portion. jk is a very fine glass fibre, cemented at j to a piece of glass rod, and terminating at k with a stirrup, cut from aluminium foil, in which the glass index, hi, rests. In front of the stirrup is a thin glass mirror, shown at k, silvered by Liebig's process, and either plane or concave as most convenient. At the ends of the glass index (h i) may be cemented any substance with which it is desired to experiment; for general observations I prefer to have these extremities of pith, as thin as possible, and exposing a surface of 10 millimetres square. The pith may be coated with lampblack or silver, or may retain its natural surface. 103. The preparation of the suspending thread of glass and for a half oscillation when the glass weight was hung on to The apparatus being fastened firmly to its stand, accurately levelled, and sealed on to the pump, a divided scale, a b (fig. 8), is placed four feet from the small mirror; and immediately beneath the scale is a narrow brass slit, c, illuminated by a lamp, d. In front is a lens, e, which | for some weeks, as the residual moisture in the pithw throws the image of the slit on to the mirror, where it is then have been absorbed by the sulphuric acid in the reflected back again on to the divided scale. Here the pump. angular movement of the bright line of light shows the (To be continued.) minutest attractive or repulsive force acting on the pith at the extremity of the movable index. In order to keep the luminous index accurately at zero, except when experiments are being tried, extreme precautions must be taken to keep all extraneous radiation from acting on the apparatus. A slightly conical paper tube, f, about 6 inches long, and as narrow as the angular movement of the ray of light will admit of, is cemented on to the glass window in front of the mirror; and a similar tube, g, is cemented on to the quartz window in front of the pith surface on which radiation is to act. The latter tube is furnished with card shutters, h, i, at each end, capable of easy movement up and down. The whole apparatus is then closely packed on all sides with a layer of cotton-wool, about 6 inches thick, and outside this is arranged a double row of Winchester quart bottles, j, j, filled with water and covered with brown paper, spaces being only left in front of the paper tubes. k and represent the positions of the candle 140 and 280 millims. distant from the pith. The whole arrangement has the appearance shown in fig. 8. 105. I will not discuss at present the phenomena presented when the apparatus is full of air, or when the vacuum is imperfect, but will proceed to the effects observed when the exhaustion has been pushed to the highest attainable degree. However much the results may vary when the vacuum is imperfect, or when the apparatus is full of air, I always find them agree amongst themselves when the residual gas is reduced to the minimum possible; and I have also ascertained that it is of no consequence what this residual gas is. Thus I have started with the apparatus filled with various vapours and gases, such as air, carbonic acid, water, iodine, hydrogen, or ammonia; and at the highest rarefaction I find no difference in the results which can be traced to the residual vapour, assuming any to be present. A hydrogen vacuum seems neither more nor less favourable to the phenomena than does a water or an iodine If moisture be present to begin with, it is necessary to allow the vapour to be absorbed by the sulphuric acid of the pump, and to continue the exhaustion with repeated warming of the apparatus until the aqueous vapour is removed; then only do I get the best results. When pith surfaces are used at the extremities of the glass beam, they should be perfectly dry; and they are more sensitive if the apparatus has held a vacuum vacuum. NEW PROCESS FOR TITRATING ASTRINGENT SUBSTANCES. By M. FERDINAND JEAN. WHEN we pour drop by drop a solution of iodine into any decoction of an astringent matter, previously mixed with an alkaline carbonate, we remark that this solution is absorbed with a great energy. I have observed that the absorption of the iodine takes place, in these conditions, in the direct ratio of the quantity of astringent matter taken, and that I part by weight of tannic acid absorbs 4 parts of iodine before we can observe the presence of free iodine in the liquid. It is on this action of iodine on astringent matters that the process of titration is based which forms the subject of this note. The solution of iodine necessary for titrating tannin is obtained by dissolving in iodide of potassium 4 grms. of iodine, and adding to the solution distilled water in quantity suffici ent to make a volume of 1000 c.c. To ascertain the value of the solution of iodine, we introduce into a beaker Io c.c. of a solution of tannin at o'i grm. per cent; we mix it with 2 c.c. of an alkaline lye containing 25 per cent of crystallised carbonate of soda; then, by the aid of a graduated burette, we cause to fall into the alkaline liquid the solution of iodine until a drop of the mixture, taken with the glass stirrer and put on a leaf of starched paper, produces a light violet spot, which indicates the presence of free iodine and the end of the operation. The value thus obtained must be corrected, that is to say we must deduct from the number of cubic centimetres of the solution of iodine corresponding to o'or grm. of tannin, the volume of this solution, which it is necessary to employ as pure loss before obtaining a coloured reaction on starched paper. For this purpose we measure 10 c.c. of distilled water, which is mixed with 2 c.c. of the alkaline solution; then we pour drop by drop the solution of iodine until we obtain a spot on the starched paper. With a solution of iodine, containing 4 grms. iodine per litre, the correction is commonly from o'I c.c., but the greater or less purity of the carbonate of soda may perhaps affect this correction very slightly. For o'or grm. of tannic acid dissolved in 10 c.c. of water we must generally use 10'5 c.c. of the solution of iodine at 4 per thousand. Under the influence of iodine the alkaline solutions of tannin, even diluted, take a colouration so intense that it would not be possible to seize distinctly the colouration of iodide of starch if we added starch paste to the tanniferous liquid. This is why I have recourse to a leaf of white filter paper, which I cover by friction with a slight layer of powdered starch. The spots made on this paper with half a drop of liquor containing traces of free iodine are immediately absorbed and show the characteristic violet colouration, even when the liquid is deeply coloured. When the value of the solution of iodine is established with respect to a known weight of pure tannic acid, this test liquor may be employed to titrate the various astringent matters, if we adopt, as the authors of the processes for the determination of tannin hitherto published have done, tannic acid as the type of the active principle of astringent matters. But, if we wish to make very exact researches, it is necessary for each variety of astringent matter to be studied to ascertain the value of the solution of iodine by means of the pure astringent principle; for example, catechuic acid for catechu-moritannic acid for fustic; for the solution of iodine acts, without doubt, like other reagents in different proportion upon divers tannic acids. The tannic acid which I employ to establish the value of the solution of iodine is obtained by keeping the tannin of Pelouze at 80° in the water-bath. At this temperature a portion of tannin, about 42 per cent, melts, agglomerates into a greyish spongy mass, which contains the impurities of the tannin with the resins; the pulverulent part constitutes pure tannin and 105 c.c. of the solution of iodine at 4 per thousand correspond to o'or grm. of this tannin, whilst only 93 of the solution of iodine are required to saturate o'or grm. of the gummy matter. The titration of tannin by means of the solution of iodine being very rapid and very exact, I determined to apply it to the assay of natural astringent matters. For this purpose I had to ascertain whether the matters which accompany the tannin in vegetable extracts are without action on the solution of iodine. For this purpose I exhausted with 100 c.c. of distilled water 1515 grms. of oak bark, which, assayed according to Honer's process, contained 6.5 per cent of matter fixable by hide, and I performed in to c.c. of this decoction, containing consequently o'or grm. of tannin matters, the titration with a solution of iodine of which 105 c.c. corresponded to o'or grm. of pure tannic acid. If the extractive matters which accompany the tannin had acted on the solution of iodine I should have had to employ more than 105 c.c. of this solution; but in three assays I obtained the coloured reaction on starched paper. After having poured 9.8 c.c. of the solutions of iodine, I found then 5'92 c.c. per cent of tannin instead of 65 c.c., the value found in using Hammer's process. The discrepancy of o'58, which the two processes give, must be attributed to the colouring matters which have been fixed by the hide along with the tannin in the assay by Hammer's process. In a second experiment I treated the same decoction of oak bark with an excess of powdered hide, and having separated by filtration the hide charged with tannin, I obtained, with 10 c.c. of the filtered decoctions, the reaction upon the starched paper after having employed 17 c.c. of the solution of iodine; whilst before the action of the hide it would be necessary to employ 98 c.c. But these 17 c.c. of solution of iodine, corresponded to 1'02 per cent of gallic acid, the average quantity of this acid, which has been remarked in French barks. Finally a decoction of oak bark was precipitated by acetate of copper. The tannate and the gallate of copper were separated by filtration, the filtered liquid was neutralised by carbonate of soda, then filtered anew to separate carbonate of copper. Io c.c. of the clear solution, after an addition of 2 c.c. of a lye of carbonate of soda, only required o'r c.c. of the solution of iodine to produce a coloured reaction upon starch. This result shows very clearly that the extractive matters do not act on the solution of iodine, since we have only employed of this solution the volume which would have been necessary if we had operated upon distilled water, and nevertheless the liquor separated from the gallate and the tannate of copper contained all the extractive matters, save a small quantity of brown_acids which the acetate of copper had precipitated. Having shown that in the decoction of oak bark it is only tannic and gallic acids that absorb the solution of iodine, the process of titration that I propose may be employed with all safety for the assay of tanniferous matters. I have found that crystallised gallic acid decomposes the solution of iodine exactly in the same ratio as tannic acid. If then we wish to determine separately the gallic and tannic acid, we must determine at first the volume of the solution of iodine corresponding to the two acids jointly; then, after having separated the tannic acid by powdered hide, titrate the gallic acid remaining in solution. On deducting from the volume of the solution of iodine corresponding to the two acids that which belongs to gallic acid alone, we obtain the quantity of tannic acid.-Bulletin de la Société Chimique de Paris. ESTIMATION OF POTASSIUM AS ACID TARTRATE.*, By P. CASAMAJOR. IN most cases which present themselves to the chemist, in which potassium is to be estimated, it is accompanied by sodium, and the course usually pursued is to estimate the potassium directly as platino-potassic chloride. The precipitate obtained has the advantage that its weight is very great when compared to the weight of potassium in combination. There are difficulties, however, connected with the process, and there are cases in which it is not applicable without elaborate preparation; but platinic chloride, although expensive, is an excellent reagent, and, its use. in experienced hands, very good results are obtained by Indirect processes are also in use, one of which consists in combining potassium and sodium with either chlorine or sulphuric acid, and in estimating the total quantity of salts by one operation and the quantity of either chlorine or sulphuric acid by another operation. From these two quantities the potassium and sodium can this process. be calculated. Very good results are also obtained by There is also a very curious indirect process due to lieve that it is not generally known, and because it preGay-Lussac, to which I call your attention because I besents a singular example of the expedients to which chemists have resorted to estimate potassium in presence of sodium. This process, which was in use some years ago in French saltpetre works, and may still be in use, is based on the following facts:-When 50 grms. of pure chloride of potassium are dissolved in 200 c.c. of water, the temperature of the liquid falls 114° C. If we take 50 grms. of chloride of sodium the fall of temperature will be only 19° C. Gay-Lussac has directed that the glass vessel in which the solution takes place should weigh 185 grms.-a point of some importance, as the vessel must acquire the temperature of the liquid it contains. To test a mixture of potassium and sodium salts they are brought, in the first place, to the state of chlorides and dried, and 50 grms. of the mixture are taken and dissolved in 200 c.c. of water. A decrease of temperature is noted, and the proportions of potassium and sodium chlorides are obtained from a table in which these proportions are placed, opposite numbers indicating the decrease of temperature. If this table is not at hand, the quantity of potassium chloride in 100 parts of the mixture may be found by calling the percentage of chloride of potassium x, and the decrease of temperature, in degrees C., d. 100-x will be the percentage of sodium chloride, and we shall have Then * Read before the American Chemical Society, September 7, 1876. My purpose this evening is to describe a process for the estimation of potassium as acid tartrate, a process which has the advantage of being direct, and which gives results much more rapidly than can be obtained by any other means, while for accuracy they compare favourably even with those obtained by platinic chloride. The occasion which led me to estimate potassium as acid tartrate was a series of experiments on the process of Messrs. Duncan and Newlands for separating potassium from the low products of sugar-houses by the addition of sulphate of alumina, and the consequent production of potassium alum. To avoid an excess of sulphate of alumina, which would be a waste, it became necessary to ascertain the quantity of potassium in each batch of products. For this determination platinic chloride is not very well adapted, as the first requisite was celerity rather than accuracy. The use of platinic chloride requires, in the first place, a thorough destruction of the organic matter by heat. The ashes, obtained as sulphates, are treated, in the next place, by an excess of barytic chloride, which gives a solution containing the chlorides corresponding to the sulphates in the ashes, and an excess of barytic chloride. From this solution, properly reduced in volume, potassium may be precipitated by platinic chloride. Instead of this series of preparatory operations, to be followed by those required by the nature of the double chloride, it occurred to me, at first, to treat a small quantity of the low saccharine product by an excess of sulphate of alumina, and, from the quantity of alum obtained, to calculate that of sulphate of alumina required for the quantity of low products to be treated on a large scale. This idea afterwards led to that of substituting tartaric acid for sulphate of alumina, and, on trying tartaric acid, the results were so uniform and satisfactory that I was induced to apply it to the determination of potassium in compounds of all kinds. Cream of tartar presents, over every other compound of potassium, the incomparable advantage that, while its solubility is very feeble, the estimation of it, by a titrated alkaline solution, is an operation that only takes a few minutes. To determine the quantity of cream of tartar that we may have to analyse it can be placed in a beaker glass with a sufficiency of water, which it is advantageous to heat, to increase the solubility of the acid tartrate. A few drops of litmus solution will impart a red colour, which will persist as long as any cream of tartar remains in the solution. If now we add a solution of potassa, drop by drop, to the contents of the beaker glass, the acid tartrate will be converted to the basic, and, while the change is going on, the unconverted cream of tartar will continue to colour the litmus red. When the last particle of acid tartrate has been converted to the basic, an addition of the smallest particle of potassa solution will turn the litmus blue. We may now note that the quantity of potassa added to convert the acid tartrate into the basic is exactly the same as the quantity already in combination as acid tartrate. We may note, moreover, that the equivalent of cream of tartar is exactly four times greater than the equivalent of potassa, so that if we have added I grm. of potassa to turn the litmus blue, we must have had 4 grms. of acid tartrate, holding in combination I grm. of potassa. After every addition of potassa the contents of the beaker should be thoroughly stirred, to dissolve the portions of acid tartrate which are undissolved, but which gradually become soluble as potassa is added. Before the change to the basic condition is complete the crystals of bitartrate disappear, and the red solution becomes perfectly clear. This is an indication that the end is near. That acid tartrate of potassium is so well adapted to Having had occasion to use this table repeatedly, I have verified these numbers and found them correct. Chancel has also given us another column, representing the number of grammes of cream of tartar which 100 c.c. of water, containing 10 per cent alcohol, will dissolve at the same temperature. These numbers are nearly 57 per cent of those corresponding to pure water. To discover the minimum of alcohol which will render a mixture with water incapable of dissolving cream of tartar, a great many experiments were made, and it was found that the mixture containing 60 per cent of alcohol fulfils this condition. By bringing all the liquids containing acid tartrate of potassium to the condition of containing at least 60 per cent of alcohol in volume, I have been able to obtain the whole potassium in the shape of insoluble cream of tartar. Alcohol of this strength is not, however, to be used from the first, as it may in some cases interfere with the solution of the compounds to be analysed, and sometimes our potassium may be precipitated in other forms than cream of tartar. It should only be used at the last stage, immediately before throwing the precipitate on a filter, so that the acid tartrate in solution may be thrown down. It should also be used to wash the precipitate on the filter, to free it from tartaric and acetic acid, as we shall see hereafter. To enable me to explain the method of procedure in estimating potassium as acid tartrate, let me take the simplest case which can present itself, which is the analy sis of a solution of pure potassa in water. Suppose we have a deci-normal solution of potassa, containing 47 m.grms. of potassa for every c.c. of solution. If we drop to c.c. in a beaker glass we may convert the whole of it into acid tartrate if we add a sufficient quantity of tartaric acid. As to what constitutes a sufficiency, we may note that there ought to be enough to precipitate all the potassium to be tested, the minimum being four times as much acid as there is potassium in the compound. We may, however, use a quantity of tartaric acid six times greater than the quantity of potassium to be precipitated. Beyond this, in the presence of alcohol, the precipitate is apt to contain an excess of acid. I am unable to say in what shape this excess of acid exists; but if we use a marked excess of tartaric acid, as much as ten or twelve times more than the potassium to be precipitated, the test by a titrated solution of potassium will give an excess of 2 or 3 per cent. If we have any means of getting approximately at the quantity of potassium in a substance to be tested, we should use six times as much tartaric acid as the supposed quantity of potassium. If, on making the test, we should find that we have gone too wide of the mark, the quantity obtained in a first test will allow us to determine, to a certainty, the quantity to be used in a subsequent analysis. As every test takes less than an hour, both tests together will take up less time than a single analysis by any other process. (To be continued). REPORT ON THE DEVELOPMENT OF THE CHEMICAL ARTS (Continued from p. 221.) Chlorine, Bromine, Iodine, and Fluorine. As an interesting fact we may call to mind that at the Paris Exhibition in 1867 large quantities of the silicofluorides of sodium and barium, of soda-ash, and caustic soda were displayed by Tessié du Motay as products obtained by the application of fluoride of silicon and hydrofluo-silicic acid on the large scale. The hydrofluosilicic acid was obtained by smelting silicic acid, fluorspar, and charcoal in a blast-furnace, and receiving in water the fluoride of silicon contained in the flue gases,t a process founded on the observations of Bredberg (1829) and Berthier (1835), and elaborated in its details by F. Bothe. Recently Christy and Bobrownicki|| have taken out a patent in England for obtaining ammonia from ammoniacal waters by means of hydrofluo-silicic acid. They precipitate the ammonia from such water by means of hydrofluo-silicic acid, and decompose the precipitate by means of quicklime without the application of heat. Whether this attempt to employ a siliceous compound in extensive chemical operations will meet with a better fate than its predecessors time alone must decide. It is the first mention of fluorine in chemical technological literature for the last five or six years. The applications of fluorides seem in fact to be dominated by some hostile influence. Even the use of hydrofluoric acid for etching on glass, which appeared secure from rivalry, will probably experience considerable limitation in consequence of an American invention. B. C. Tilghmann§ uses for etching on glass and other brittle materials a jet of sand violently projected against the surface of the object by means of a current of air or of steam. (The details of this process are, of course, strictly mechanical.) Against such a rival fluoric acid cannot possibly maintain its ground for etching, especially where large surfaces are concerned. It will be restricted to the production of fine delicate designs, such as the graduation of measuring instruments. The Sulphur Industry of Sicily. Extracted from the Report of the Mining Engineer, LORENZO PARODI, ¶ by Dr. ANGELO BARBAGLIA, Professor of Chemistry at the Instituto Tecnico of Rome. Sulphur is a widely diffused element which occurs under the most various forms both in the free and the combined state. In a free condition it forms rich deposits, which may be divided into two classes; such as are found on the surface of the earth in the neighbourhood of extinct volcanoes (solfatare) forming earthy strata from 6 to 10 metres in thickness saturated with sulphur, and underground beds (solfare) in which the sulphur is so intimately * "Berichte über die Entwickelung der Chemischen Industrie Während des Letzten Jahrzehends." + Details concerning attempts at the industrial utilisation of hydrofuo-silicic acid will be found in the article on the compounds of silica. Bothe, Wagner Jahresber., 1868, 265. Ber. Chem. Gesell., 1873, 1322. SB. C. Tilghmann. The sand-blast for cutting hard bodies. Sull estrazione dello solfo in Sicilia e sugli usi industriali del medesimo. Relazione dell ingegnére Lorenzo Parodi al Ministro d'agricultura, industria e commercia. Firenze, 1873. The SEVERAL analytical processes have been used by me for the estimation of carbon, hydrogen, ash, and sulphur in various coals, and most of them were found to be very accurate, but rather troublesome in execution. following process was used with great success and may be strongly recommended for laboratories of iron works, &c. By this process the work is easily and quickly executed, giving at the same time very accurate results. 1. Estimation of Hygroscopic Water. 3 grms. of the substance in a finely divided state are dried in a porcelain crucible placed in a beaker with a small quantity of sand on the bottom of it. The beaker is covered with a watch-glass, and the whole is placed on a sand-bath and heated for about three hours to a temknown by the dryness of the watch-glass. The substance The end of the operation is easily perature of 110°. when dried is weighed, and the percentage of loss is next calculated. 2. Estimation of Carbon and Hydrogen. The best process was found to be Liebig's :-The ignition of 1 grm. of coal or peat with lead chromate (PbCrO4) in a tube of hard glass, 0.25 metre long. The resulting carbonic acid, water, and sulphuric acid are passed through a potash apparatus containing caustic potash (1 part of KHO dissolved in 2 parts of H2O), and two U-tubes, the first containing ignited calcium chloride, the second a solution of lead nitrate. The increase in weight of the potash apparatus and of the first U-tube will show the quantity of carbonic acid and water obtained. Knowing that carbonic acid contains 27.2 per cent of carbon, and water III per cent of hydrogen, the percentage of carbon and hydrogen may be easily calculated, 3. Calculation of the Calorific Power. As one part of carbon in burning yields 8080 calorific units, and I part of hydrogen in burning 34,460 calorific units, the calorific power of the coal may be quickly found. Example.-Coal from Donetz Mountains, near the village Grouchevka, South of Russia : Carbon Hygroscopic water : Per cent. 58.0 ΙΙΟ ΙΟ 23'0 6'0 99'0 |