CHEMICAL NEWS, August 25, 1876. Estimation of Colour in Water. 77 tion is made of the part absorption takes in this pheno | crease of absorption, but at 220° C. there is not so much menon, probably arising from their not having studied the light absorbed as there was at 16° C. From this we subject spectroscopically; and (2) that they speak of again infer that absorption of light at comparatively low metachromes as if generating light after the manner of temperatures is not dependent upon sensible heat or viincandescent bodies. That absorption plays an all- bratory motion. important part will be evident from what we have said in Section I., and that vibratory motion has little, if anything, to do with metachromatism we hope to make clear in the sequel. Our experiments demonstrate that metachromatism does not depend upon the surrounding medium, for bodies exhibit the change alike in nitrogen, air, carbonic anhydride, and hydrogen. It has been suggested that the phenomenon might in some way be due to volatilisation. A volatile body, however, exhibits the change under a liquid medium. Hence we conclude that it is due in some manner to the action of heat on the internal structure of the metachrome. Metachromatism is seen in solids, amorphous and crystalline,-in liquids, and in gases near their liquefying points (N2O4 and Br2*). These forms of matter have molecular structure in common; hence we attribute metachromatism to molecular alteration. What the nature of this alteration may be we think will be manifest after a close consideration of certain physical facts. Absorbed heat performs two kinds of work :i. Kinetic, sensible to the thermometer, and— ii. Potential. a. The overcoming of cohesion, molecular recession, or molar expansion, as, e.g., the conversion of ice into water, and water into steam. This kind of work is accompanied by a change of density. B. The overcoming of chemical attraction, atomic recession, or molecular expansion, which finally ends in decomposition, as, e. g., the resolution of PtC14 in PtCl2 and Cl2. I. It is a fact well known to mineralogists that many anhydrous silicates, after being subjected to a high temperature, have upon cooling permanently changed colours. This is shown in the following tablef in each example save that of olivine. It will be noted that where colour and density are both permanently altered, as in 3 and 4, the warm-coloured variety is less dense than the same mineral with a cold colour,-i.e., the densities are in the order of the metachromatic scale, a fact we anticipated in our study of this matter. This is also strikingly evident among allotropes, the notable exception being here, as elsewhere, that of phosphorus. Red amorphous phosphorus is denser than the yellow this very fact, however, will no doubt tend to throw light on some of its other anomalies. What we more especially call attention to here is, that bodies of identical chemical composition, without even a change of density in some cases (as in 2 and 5), may at the same temperature have different colours,—i.e., may absorb light in different degrees. From this we conclude that change of colour is not due to alteration of sensible heat. Perhaps we get a better illustration of the same fact in the behaviour of mercuric iodide. Examined spectroscopically at say 16° C., a band of red light is transmitted, extending from B to D. This narrows as the temperature rises; in other words, there is an increase of absorption up to about 140° C. The band of transmitted light now suddenly widens, and extends to a little beyond. As the temperature is on the rise there is still a gradual in II. Expansion by heat-i.e., decrease of density-is an all but universal law so far as we at present know. There are several exceptions, however, and many of these are among the silicates. Their anomalous behaviour is, as a rule, pointed out by the colour-change, as in the case of the zircon. This is not always the case, for there may be change of colour, as in the beryl, without alteration of density-i.e., without appreciable molecular approach or recession. On the other hand, we have in olivine an example of change of density, molecular recession, without a corresponding alteration of colour. More facts of the same nature might readily be adduced, from which we infer that molar expansion or contraction is not a necessary concomitant of metachromatism. We have, so far, excluded from our list of possible concomitants i. and ii. a: hence we are driven to the conclusion, backed by facts which space will not allow us at present to detail here, that the only necessary concomitant is ii. ẞ,-i. e., atomic approach or atomic recession; in other words, alteration of atomic potentiality. From the foregoing observations we learn(1). That metachromatism arises from increased absorption of light with elevation of temperature, the more refrangible increment increasing at a greater rate than the less refrangible. (2). That the only necessary concomitant is alteration of atomic potentiality; a change from the white towards the black end of the metachromatic scale signifying atomic recession, and a change from the black towards the white end atomic approach. (3). That where this change of potentiality goes far enough to affect chemical attraction sufficient to induce chemical action, then, for bodies obeying the law of colour sequence, a change of colour from the white towards the black end of the scale indicates combination, and the opposite order resolution into a lower compound. For much help received in this study of metachromatism our thanks are due to Dr. Frankland and Mr. Wm. Valentin. ON THE ESTIMATION OF COLOUR IN WATER. By CHARLES A. CAMERON. IN "Nesslerising" water it has been proposed to use solutions of caramel instead of standard solutions of ammonia for the purpose of comparison. I have, as well as other chemists, found that the standard solution of caramel, even when it contains much alcohol, becomes, after a time, turbid and useless, and also that it soon changes its hue. I do not think that the use of any coloured solution is so reliable as that of the standard solutions of ammonia; but to those who prefer the former I would recommend the use of coloured discs to be employed as follows:-Fill a Nessler tube with distilled water and place it over a disc so coloured that on looking down through the column of water it may, by the reflected light from the disc, have the colour of a solution of say o'005 gr. of ammonia per gallon of water mixed with the usual 5 per cent of Nessler's solution. A dozen discs would be sufficient; but in using them, Nessler's solution should be always of exactly the same composition. I would suggest that Mr. Sutton, who is so valuable an ally of the chemists who have not time or inclination to prepare their solutions, &c., might make a set of cylinders, discs, and solutions, in harmony with the above sugges tion. 78 Development of the Chemical Arts. ON SOME CHEMICAL RESEARCHES ON THE By SERGIUS KERN, St. Petersburg. It is well known that wrought-iron containing some tenths of per cent of copper is red-short; meanwhile in some of the best irons from Siberia was found from o'or copper and of soda. The entire furnace is surrounded with an air jacket and this again with a screen of masonry traversed by flues, which has the object of keeping back a part of the heat which would otherwise be lost by radiation. Another portion is supplied by the heat generated in the process by the combustion of the hydrochloric acid. The above-mentioned vertical drain-pipes serve to prevent the apparatus from being choked up with oxide or chloride of iron. It has been observed that when iron apparatus is employed for generating and conducting the hydrochloric acid gas this conveys along a certain quantity of ferric chloride, from which it cannot be freed before Here the iron is entering the decomposing furnace. ex-deposited either as chloride, or, if the formation of chlorine has already begun, i.e., as soon as watery vapour is mixed with the gases, as pulverulent oxide of iron upon the copper sulphate. This iron dust falls from the vertical drain-pipes through the grating into the space below, whence it is easily removed. It may here, however, be remarked that Deacon, according to private communications, has latterly omitted the partition walls from the decomposition furnace, by which he effects a more ready movement of the gaseous current without any disad-. vantage. In a Deacon's apparatus, which the author has seen at work in the establishment of Kunheim, at Berlin, the partition walls and the vertical drain-pipes had both been omitted without any detriment being observed in the course of several months' working. to o'03 per cent of copper. In some specimens of steel I found o2 per cent of copper; this steel was not brittle, and had been used with success for manufacturing steel axles. The presence of copper was found in several specimens of cast-iron coming from blast-furnaces of the South Oural mountains. These specimens, when amined and analysed, showed that the presence of copper in cast-iron may amount to a higher percentage than in steel or iron without altering the quality of the metal. Unfortunately it is not so with wrought-iron or steel. The specimen examined was much used for castings; it filled up the moulds beautifully, and had a very handsome appearance; fresh cut it had a dark grey colour. Under the microscope small grains of copper were easily remarked in the mass of the metal. This peculiar sample of cast-iron was carefully analysed, and the analysis gave the following average composition : After the mixture has passed through the decomposing furnace it consists of chlorine, water, nitrogen, superfluous oxygen, and unconsumed hydrochloric acid. The latter is condensed in an ordinary condensation apparatus, charged with dilute hydrochloric acid, or water, the temperature of the gases having been previously reduced by air-coolers. The gas is next freed from the accompanying water by passage through a tower filled with chloride of calcium, or, better, through a coke-tower, down which sulphuric acid flows. The gaseous mixture is then fit for absorption in the chloride of lime chambers. As a matter of course a drying apparatus is superfluous if a watery liquid is to be saturated with chlorine, as in the preparation of potassic chlorate. While analysing some iron samples for copper I often used, in case only traces of copper could be detected, the following method:-The specimen is dissolved in hydrochloric acid, and the copper and iron are precipitated by an excess of ammonia; the mixture is boiled and filtered; the blue liquor is evaporated nearly to dryness, and the resulting residue is dissolved in sulphuric acid. Into this solution a piece of magnesium ribbon is placed, which, in case of traces of copper, is quickly covered with a layer of this metal; that is easily observed under the ON SOME AMERICAN VANADIUM MINERALS. microscope. REPORT DEVELOPMENT OF THE CHEMICAL ARTS By Dr. A. W. HOFMANN. (Continued from p. 67.) Chlorine, Bromine, Iodine, and Fluorine. By Dr. E. MYLIUS, of Ludwigshafen. AFTER the mixture of hydrochloric acid and air has left the regulator, by its basis, it arrives in the decomposing nine chambers arranged in a horizontal plane, each of them provided with a grate or false bottom at its lower part. Upon this grating stand, in the first, and also in the second chamber, vertically arranged drain-pipes which have been plunged into a hot concentrated solution of 2 mols. copper sulphate and 3 mols. sodium sulphate, and then dried. The remaining chambers are filled with fragments of bricks or balls of clay (1.5 centimetres) which have been treated in the same manner with sulphates of furnace. This consists of a cast-iron box in which are "Berichte über die Entwickelung der Chemischen Industrie Während des Letzten Jahrzenends." (To be continued) By F. A. GENTH. I. Roscoelite. I AM indebted to Dr. James Blake of San Francisco, California, for a small quantity of the very interesting mineral, which he called "Roscoelite," in honour of Professor Roscoe, whose important investigations have put vanadium in its proper place among theelements. Roscoelite occurs in small seams, varying in thickness from 1-20th to 1-10th of an inch in a decomposed yellowish, brownish, or greenish rock. These seams are made up of small micaceous scales, sometimes of an inch in length, mostly smaller and frequently arranged in stellate or fan-shaped groups. They show an eminent basal cleavage; soft; the sp. gr. of the purest scales (showing less than 1 per cent of impurities) was found to be 2.938; another specimen of less purity gave 2.921; lustre pearly, inclining to submetallic; colour, dark clove-brown to greenish brown, sometimes dark brownish green. Before the blowpipe it fuses easily to a black glass, colouring the flame slightly pink. With salt of phosphorus gives a skeleton of silicic acid, a dark yellow bead in the oxidising flame, and and emeral green bead in the reducing flame. Only slightly acted upon by acids, even by boiling concentrated sulphuric acid; but readily decomposed by dilute sulphuric acid, when heated in a sealed tube at a temperature of about 180° C., leaving the silicic acid in the form of white pearly scales, and yielding CHEMICAL NEWS, Some American Vanadium Compounds. 79 a deep bluish green solution. With sodic carbonate | determination of the alkalies by J. L. Smith's method. it fuses to a white mass. The roscoelite which I received for investigation was so much mixed with other substances, such as gold, quartz, a felspathic mineral, a dark mineral, and very minute quantities of one of orange colour, that it was impossible to select for analysis material of perfect purity. For this reason I have delayed the publication of my results, which were obtained over one year ago, in the hope of being able to repeat my analyses with better and purer specimens; but I now give the results of my analyses because there is no prospect of getting any more of this mineral, as will be seen from a letter of Dr. Blake, dated San Francisco, April 5th, 1876, in which he says, that the mine in which it occurs cannot be worked any farther until a tunnel has been run, and that it is quite uncertain when this will be done. Although by no means perfect, my results approach the truth and give a fair idea of the composition of the mineral, even if the evident admixture of other minerals, varying in the different samples analysed, from about 1 to perhaps over 12 per cent, does not permit one to calculate the atomic ratio of the constituents and establish the constitution of this species. There is especially an uncertainty with reference to the quantities of silicic acid, alumina, and potassa which belong to the roscoelite, or which may have been introduced by admixtures of felspathic and other minerals, as will appear from the results given below, which show that the mineral, when decomposed with sulphuric or dilute hydrofluoric acid generally gives only about 6 per cent of potassa, while fusion with calcic carbonate and ammonic chloride yields from 8 to 9 per cent. Some of these uncertainties could have been removed, if a larger quantity of the mineral had been at my disposal. Particular attention was paid to the correct determination of the vanadium and the form in which it exists in the roscoelite. The separation of vanadium is attended with great difficulties, and I have not found any of the methods of separation to give fully reliable results. This is in part owing to the incomplete precipitation of the vanadic acid, and in part to the impossibility of washing the precipitates completely without loss of vanadium. It was therefore always determined by the only method which I found to give fully reliable results-by titration with potassic permanganate. After the separation from the other elements, the vanadic acid was reduced by hydrosulphuric acid into V204, which, after the excess of hydrosulphuric acid had been expelled by continued boiling, was re-oxidised into V205 by the permanganate. I have satisfied myself by numerous experiments that no matter whether only a very minute quantity of sulphuric acid is present, or a very large excess, the V204 is completely oxidised into V2O5 by this process. For the determination of the state of oxidation of the vanadium in the roscoelite, a quantity of the mineral was dissolved in dilute sulphuric acid in a sealed tube at a temperature of about 180° C., and was titered after cooling; the liquid was then reduced by hydrosulphuric acid, and after boiling off the excess of the latter it was again titered. From the quantity of oxygen required for oxidation in both cases it was found that vanadium in the mineral is present as V6011=2V203, V205. The determinations of the other elements were made by the usual methods. The finely-powdered mineral was dried (unless otherwise stated) for two days over sulphuric acid, and the different samples gave the following results : (a.) Purest Scales. The analysis was made by dissolving one portion in sulphuric acid and determining in this the quantity and state of oxidation of the vanadium, the silicic acid, and insoluble impurities. The latter were left behind in dissolving the silicic acid in sodic carbonate and gave 0.85 per cent; a second portion was decomposed by sodic carbonate and nitrate, and a third for the The V6O11 given below is the mean of the two determina- Insol. silicates, a. quartz, gold, &c.} [0·85] Al2O3 FeO CaO b. 47.69 47.82 43°46 48.60 e. Ca. 8.91 [5.60] 46.81 15'78 1'58 2'00 2'43 1'74 I'95 2.31 trace 0.60 5'96 8.89 20.16 .. MgO 4'96 5'13 5°32 5'95 6'34 3.87 100 22 10100 100'87 100'00 100'00 II. Psittacinite, a New Hydrous Vanadate of Lead and Copper. In a paper on "American Tellurium and Bismuth Minerals," read before the American Philosophical Society at the meeting of August 21, 1874 (Proc. Am. Phil. Soc., xiv., 223-231), I mention, on the authority of Mr. P.. Knabe, a siskin green pulverulent mineral from the "Iron Rod Mine," Silver Star District, Montana, as a new "Tellurate of lead and copper." I had at that time no opportunity to examine into the merits of this mineral, having mislaid the small sample which he had sent me. On receiving a copy of my paper Mr. Knabe furnished me with several specimens, which gave me a sufficient quantity of fair material for an analysis. A qualitative examination proved it to be a hydrous vanadate of lead and copper and not a tellurate. When I communicated this result to Mr. Knabe he gave me an interesting account of how he fell into his error. At the Uncle Sam's Lode, in Highland District, occurs with the tetradymite a siskin green mineral, which has not yet been analysed, but which appears to be a tellurate. It looks exactly like the pulverulent variety of the psittacinite from the Iron Rod Mine. When Mr. Knabe dissolved the latter in hydrochloric acid, the evolution of chlorine indicated the presence of a higher oxide; the solution precipitated with an excess of ammonic sulphide gave sulphides of lead and copper and a filtrate, which, on addition of an acid, gave a black pre cipitate-vanadic sulphide-which he mistook for tellur-, is produced. ous sulphide. Psittacinite occurs in very thin cryptocrystalline coatings, sometimes showing a small mammillary or botryoidal structure, also peruverlent; colour, siskin green, sometimes with a grayish tint, to olive green. Before the blowpipe it fuses easily to a black shining mass. With fluxes gives the reactions of vanadium, lead and copper. Soluble in dilute nitric acid, the solution yielding on evaporation a deep red mass. As it was impossible to get any of the mineral in a pure state, I had to use coatings with quartz attached to them, sometimes contaminated with a little limonite; but these admixtures could not influence the analysis farther than very slightly with reference to the amount of water which it contains. e. 42.38 15'77 {CHEMICAL NEWS, August 25, 1876. When first obtained this substance was supposed to be the radicle sulphocyanogen, but it was always found on analysis to contain a small and somewhat variable amount of hydrogen, which excess of chlorine will not remove; hence it is termed pseudo-sulphocyanogen. The action of chlorine, for instance, is not completely represented by the equation 2NH4SCy+Cl2 = 2NH4C1+2SCY; some secondary reaction taking place by which hydrogen is introduced. From some experiments made some time ago to obtain this substance in a pure state or of a definite composition it would appear that the hydrogen is not the only element which varies in its amount in differently prepared specimens. Slight variations in the temperature and strength of the solution of sulphocyanate employed producing comparatively considerable differences in the composition of the product. When ammonio-sulphocyanate is acted upon by chlorine 7:25 in excess for some days the filtrate from the yellow pre15'57 cipitate still gives the sulphocyanide reaction with ferric salts, and no chloride of nitrogen has been produced, even when the action of chlorine was continued on the same solution for more than a week. (NH4Cl+Cl2 will yield the nitrogen chloride in half an hour.) 4'00 NH4SČy solution absorbs chlorine rapidly with rise of temperature. When the containing vessel is kept cool (10° to 15° C.) and the chlorine not used in excess a light yellow precipitate is produced, which, after washing with hot water, in which it is slightly soluble, appears to undergo a decomposition. It gave, on analysis, the following figures: 1'00 : 0'97 : 2.16 2.19 I'00 : O'93 : 2°31 : ΙΟΙ : 2.25 : 1'00 : 1'00 : 2:27 : 2.12 The average of the five analyses gives the ratio of 1.00 : 0.98: 2:25 : 2.15 9'00: 9'00 : 20'00 : 18.00 corresponding to— Psittacinite occurs, sometimes associated with gold, and small quantities of cerussite, chalcopyrite, and limonite upon quartz, at several of the mines in Silver Star District, Montana, especially in the Iron Rod Mine and New Career Mine, and its occurrence in these mines is looked upon as a favourable indication, for, when it is met with, the vein becomes immediately, or soon after, University of Pennsylvania, Philadelphia, PSEUDO-SULPHOCYANOGEN (CNSH). It is well known that when sulphocyanides, more especially the alkaline salts, are treated with chlorine, bromine, or iodine, a yellow body almost entirely insoluble in water With these figures the formula CNHS agrees sufficiently well, but the tripled formula, C3N3S3H3, seems to agree better with its decomposition by heat product, mellone. The tripled formula is perhaps better written thus :— N-N H-SS-H H A considerable amount of hydrocyanic acid is given off from the substance when suspended in the solution which has been submitted to the action of chlorine. But after washing and drying at 100° C. no HCy is given off when suspended in water or in dilute acids. The pseudo-sulphocyanogen may possibly be utilised as shades of yellow and is exceedingly permanent, requiring a water or oil colour. It may be obtained of several a high temperature for its decomposition, and is not altered by the action of light either in a dry or moist condition. It is also unaffected (as far as the experiments have continued) when ground up moist with plumbic, bismuth, and argentic nitrates, and argentic sulphate. Mixed wet with solid argentic nitrite and exposed to sunlight a blackening occurs, but only due to intermixed reduced silver. Further experiments on the action of salts on this substance aided by sunlight are in progress, and the results, notice. with your permission, will form the subject of a future W. R. H. Royal College of Chemistry. CHEMICAL NEWS, August 25, 1876. Platinum Combustion Tubes. ON SOME OF THE CHANGES IN THE PHYSICAL PROPERTIES OF STEEL, PRODUCED BY TEMPERING. By A. S. KIMBALL, Prof. of Physics in the Worcester Institute of Industrial Science. A FEW interesting, and, to a certain extent, novel results, have recently been developed in our laboratory, which I venture to present in their present incomplete form, since the pressure of other duties will postpone, for a few months, further investigations in this direction. Up to the present time the larger number of our experiments have been made upon the behaviour of tempered bars under a transverse stress, although a few qualitative trials have been made upon changes in electric conductivity and coefficients of expansion. I. The modulus of elasticity decreases as the hardness of the steel increases; in other words, the harder the bar the greater the deflection produced by a given weight. Many manuals of practical mechanics give a higher modulus for tempered than for untempered steel. Reuleaux, in "Der Constructeur" (p. 4), states that it may be increased 50 per cent by hardening. Coulomb and Tredgold state that hardening has no influence whatever, while Styffe finds that the modulus is diminished. For our first experiment, five pieces of good tool-steel, each 13" long, were cut from a half-inch square bar. These were carefully annealed, squared, and polished. No. I was laid aside, and the others were hardened in cold water in the usual manner; No 2 was "drawn" on a hot plate to a dark blue; No. 3 to a purple; No. 4 to a straw-colour; No, 5 was left hard. The modulus of elasticity was then determined by measuring the deflection produced by a weight applied at the middle of the bar. The probable error of the experiments did not exceed onefifth of 1 per cent. The experiment was varied in many ways; several qualities of steel and bars of different dimensions were employed with uniform results. In some grades of steel a difference of more than 10 per cent has been found between the modulus of the hardened and that of the annealed bar. II. The increase of deflection in a given time is greater the harder the steel. It is well known that the deflection of a bar left under stress will increase for a long time. I am not aware, however, that comparative tests of the rate of increase in steel of different tempers have previously been made. III. The immediate set increases with the hardness of the steel. In the experiments each bar was of course loaded with the same weight, which was allowed to act for the same number of minutes. IV. A bar recovers from a temporary set with greater rapidity the harder it is. The remarkable fluctuations in the line of the bar observed by Prof. Norton (Amer. Journ. of Science and Arts, April, 1876) became more marked and had a wider range as the hardness of the bar increased. In none of the experiments referred to was a permanent set produced, though in some cases forty-eight hours had elapsed before the bar recovered its original line. In a few experiments an attempt was made to determine the approximate hardness of the bars by grinding. The results obtained, however, could not be considered very reliable. A more satisfactory method was found in the determination of the temperatures employed in hardening and drawing, by the specific heat of platinum, or by the use of the pyrometer. I am indebted to Mr. F. C. Blake for the accuracy with which the experiments referred to in this note have been conducted.—Âmerican Journal of Science and Arts, CORRESPONDENCE. 81 ON THE PRESENCE OF ARSENIC IN THE VAPOURS OF BONE-MANURE. To the Editor of the Chemical News. SIR,-In the CHEMICAL NEWS (vol. xxxiv., p. 68) you criticise a book bearing the above title. In the course of your remarks you say:-"Miasms or organic poisons could scarcely meet with a more efficient corrective than chloride of arsenic, fluorine, and other of the volatile compounds said to be given off. On the other hand, sulphuretted hydrogen and sulphide of ammonium are admirably calculated to purge the atmosphere of arsenical fumes." I wish, as this opportunity presents itself, to lay before contradict the suggestion that sulphuretted hydrogen you a fact repeatedly observed, which seems calculated to would form a purge for an atmosphere contaminated with arsenical fumes. The same fact would throw some doubt on the other suggestion, viz., that trichloride of arsenic is a corrective for miasms and other organic poisons. While making some experiments on the purification of hydrochloric acid from arsenic, the late Mr. Henry Deacon suggested to mix the arsenical hydrochloric acid in the gaseous state with gaseous sulphuretted hydrogen. Accordingly, some gaseous hydrogen chloride was mixed with arsentrichloride and sulphuretted hydrogen, in one case in as dry a condition as the use of concentrated sulphuric acid will permit, in another case saturated with aqueous vapour. In the one case, when the gaseous mixture was dry, no trace of sulphide of arsenic had deposited on the side of the glass vessel containing the mixture; in the other case, in which some liquid hydrochloric acid was introduced into the vessel, so that its sides were wet, a little chloride of arsenic had been decomposed and deposited as sulphide. In both instances, however, large quantities of sulphide of arsenic were formed when the gaseous mixture was driven through a wash-bottle containing water. The experiments were repeated constantly with the same result. The conclusion is that gaseous arsentrichloride does not react upon gaseous sulphuretted hydrogen. You will readily admit that sulphuretted hydrogen will arsenical fumes, and you will doubt with me, seeing that form no purge for an atmosphere contaminated with chloride of arsenic will not act in the gaseous state upon sulphuretted hydrogen, whether arsentrichloride will, under those conditions, correct the noxious miasms or DR. FERD. HURTER. Laboratory of Messrs. Gaskell, Deacon, and Co., Widnes, August 19, 1876. organic poisons.—I am, &c,, PLATINUM COMBUSTION TUBES. To the Editor of the Chemical News: SIR,-Your correspondent, writing on the subject of pla tinum combustion tubes in the CHEMICAL NEWS (vol. xxxiv., p. 67), says :-"With a platinum tube filled with cupric oxide in the manner above described it would be possible to perform a succession of analyses; thus greatly economising time. This arrangement of apparatus is based on purely theoretical considerations. I have had no opportunities of practically testing the value of platinum combustion tubes." I am happy to be able to supply the practical experience which C. J. H. W. lacks. In a paper on the "Determination of Carbon in Steel," published in the Journal of the Chemical Society, for October, 1870, I state that a platinum tube was employed, and that "I was thus saved from the annoyance caused by the fusing or cracking of |