Edited by ] James H. Gardiner, F.C.S. r Established (WITH WHICH IS INCORPORATED THE "CHEMICAL GAZETTE "). in the Year 1859. Published Weekly. Annual Subscription. free by post £1 Entered at the New York Post Office as Second Class Mail Matter. Transmissible through the Post-United Kingdom, at Newspaper rate; Canada and Newfoundland, at Magazine rate. CAPPER PASS & SON, Lim., The Governing Body invite applications for BEDMINSTER SMELTING WORKS BRISTOL, the above appointment. Commencing salary £220 to 250 (according to experience and qualifications), with regular increments. -Applications (not later than JULY 7) to THE SECRETARY, Birkbeck College, E.C. 4, from whom further particulars may be obtained. ESSEX EDUCATION COMMITTEE. EAST ANGLIAN INSTITUTE OF AGRICULTURE, CHELMSFORD. Wanted an ASSISTANT ANALYST AND LECTURER IN AGRICULTURAL CHEMISTRY. Applications must be made in accordance with the printed Applica- THE BRITISH COTTON INDU TRY APPOINTMENT OF DIRECTOR OF RESEARCH. The Ap lications must be received on or before JULY 21, 1919. British Cotton Industry Research Association, 108, Deansgate, Manchester. CHEMICAL APPARATUS Pure Chemicals for Research Work. JOHN J. CRIFFIN & SONS, LTD., KINGSWAY, LONDON, W.C STRONTIUM SULPHATE (Average sp. gr. 3.95). ssistant Assayer (aged 23 to 27) required at once. Experience in Assaying Gold and Silver essential. Permanency; good prospects. State age, experience, and salary re HE BRISTOL MINERAL and LA Dquired. Address, "A 23," CHEMICAL NEWS Office, 16, Newcastle THE COMPANY, LTD., are Owners of large deposits, and invite enquiries. Address, Carlton Chambers, Baldwin Street, Bristol, England. Telegraphic address" Beetroot," Bristol. Telephone No. 38, Bristol. MICA Telephone No. 2248J Avenue. Street, Farringdon Street, London, E.C.4. ssistant Metallurgical Chemist (21) requires Situation. Experience in both Ferrous and Non-ferrous Analyses, Case hardening, Heat Treatment. 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Youth (17), good knowledge of Chemistry, seeks Employment in Laboratory.-Address, A. H., 1, Phænix Lodge Mansions, Hammersmith, W. FOR SALE.-Copper WATER- or STEAM OVEN, of stout metal, 14x10x8 ins. inside, two moveable shelve, tubes in top and ends, inlet and drain pipes; in panelled teak case; suitable for constant temperature.-Address, C. W., CHEMICAL NEWS Office, 16, Newcastle Street, Farringdon Street, London, E.C.4 invited for the following LECTURESHIPS. In addition to the salary indicated, there is at the present time a War allowance of £78 per annum. 1. CHEMISTRY. Salary £300 to £450. 2. CHEMISTRY. Salary £250 to £380. The commencing salary will be dependent upon the experience of the applicant. Full particulars may be obtained on application to the SECRETARY, Municipal Technical School, Suffolk Street, Birmingham Allotropy of Ca bon NEWS THE ALLOTROPY OF CARBON. By MAURICE COPISAROW. THE application of the theory of allotropy (see CHEMICAL NEWS, cxviii., 265) propounded in general terms for all the elements, to a single characteristic case-the element carbon necessitates our dealing with the valency of the carbon atom and the complexity and varieties of the carbon molecules. In the light of the chemistry of carbon compounds the carbon atom can be regarded as potentially always tetravalent, as carbon monoxide, carbon compounds containing double or triple bonds, the triphenyl methyl series, and the poly-methylene group in no way undermines the conception of such potential tetravalency. 301 Dimroth and Kerkovius (Ann., 1913, cccxcix., 120) conclude from their study of the oxidation of carbon the carbon molecule to consist of pentagons as well as hexagons. Bragg (Proc. Roy. Soc., 1913, A, 610), studying the crystalline structure of diamond by means of the X-ray spectrometer, advanced a three-dimensional configuration for the structure of the diamond (see Fig. 2). (In connection with the X-ray spectrometric method of investigation of crystalline structures attention may be drawn to the work of Moseley-Phil. Mag., 1913, VI., xxvi., 1024; 1914, VI., xxvii., 703; Barlow-Proc. Roy. Soc., 1914, A, 623; and Ewald-Phys. Zeit., 1914, xv., 309). Hans Meyer (Monats., 1914, xxxv., 163), discussing the carbon "molecule," puts stress upon the difficulty, if not futility, of trying to define the chemical entity of the three forms of carbon. Debye and Scherrer (loc. cit.) conclude from the Lauegraphs of their modified X-ray spectrometric method of study, that diamond and graphite are the only two distinct forms of carbon, amorphous carbon being apparently simply finely divided graphite. They assign a tetragonal configuration to diamond and a trigonal to graphite. It is clear from the above that a method of investigation so by-general as to be applicable to all forms of carbon has not yet been proposed. The polyatomicity of a carbon molecule is proved 1. The existence of several forms of carbon, chemically and physically distinct from one another. 2. The high volatilisation-point of carbon. 5. Combustion of carbon (Rhead and Wheeler, Trans., 1910, xcvii., 2181; 1911, xcix., 1140; 1913, ciii., 461). 6. The X-ray spectro-metric study of the modifications of carbon (Debye and Scherrer, Phys. Zeit., 1916, xvii., 277; 1917, xviii., 291; Olie and Byl, Proc. K. Akad. Wetens. Amsterdam., 1917, x!X., 920. Not only has the polyatomicity of carbon molecules been assumed, though more or less tacitly, but attempts have also been made to study the complexity of the mole cules and to establish the constitutional molecular formula of one or more of the forms of carbon. Kekulé (Zeit Angew. Chem., 1899, p. 950) regards a molecule of amorphous carbon as consisting of 12 atoms. Barlow and Pope (Trans., 1906, lxxxx.. 1742) suggested the possibility of a tetrahedron and triphenylene configura. tion for a carbon molecule (see Figs. 1. and 4a). Dewar (CHEMICAL NEWS, 1908, xcvii., 16) proposed a concentric ring formula, somewhat modified by Redgrove and Tomlinson (CHEMICAL NEWS, 1908, xcviii., 37). Dewar based his view on the moist oxidation of amorphous carbon to mellitic acid Whilst the method of moist oxidation can be applied more or less successfully to amorphous carbon and to some extent to graphite, the X-ray method is confined to diamond with a somewhat strained extension to graphite. Now, if we consider the problem from the point of view of linkages, i.e., of molecular structure in the light of the theory of allotropy, we secure a general method of investigation, embracing all forms of carbon, a method capable of extensive experimental verification on the basis of all the known chemical and physical properties. Investigating all possible representations of the structure of a carbon molecule we find that these possibilities resolve themselves into three fundamentally distinct classes or groups. I. A non-rigid molecular configuration, some valencies of which are free (See also Fig. 1). II. A rigid molecular configuration, some valencies of which are free (see Fig. 3). III. A rigid molecular configuration, all valencies of which are fixed (see Figs. 4a, 4b, and 2). Thus on theoretical grounds we expect to find in the case of carbon not more than three distinct allotropic forms, a conclusion in striking agreement with facts; i.e., the existence of three forms of carbon-amorphous carbon, graphite, and diamond. The several new modifications (graphitoid, &c.) of carbon suggested by Brodie, Berthelot, Luzi, and others have been proved to be either compounds or solutions and mixtures of carbon with some other elements. (See Porcher, CHEMICAL NEWs, 1881, xliv., 203. Bartoli and Papasogli, Gazz., 1882, xii., 113; 1883, xiii., 37; 1885, xv., 445. Moissan, Comptes Rendus, 1893, cxvi., 609; 1894, cxix., 976; 1895, cxx., 17; cxxi., 540; Ann. Chim. Phys., 1896, VII., viii., 289, 306, 466. Wiesner, Monats., 1892, xiii., 371. Weinschenk, Zeit. Kryst. Min., 1897, xxviii., 291. Hyde, Journ. Soc. Chem. Ind., 1904, xxiii,, 300. Trener, Jahresb. Geolog. Reichs. Wien., 1906, 405; Zeit. Kryst. Min., 1909, xlvi., 124; Charpy, Comptes, combustion of carbon per grm.-atom give the following Rendus, 1907, cxlv., 1173; 1909, cxlviii., 920. Le numbers (Berthelot and Petit, Ann. Chim., 1889, VI., Chatelier and Wologdine, Comptes Rendus, 1908, cxlvi., xvii., 89, 98):49). Debye and Scherrer's (loc. cit.) unification of amorphous carbon with graphite is untenable as it is in complete disagreement with all the chemical and physical properties of these two forms. No matter how finely divided the graphite may be (Acheson's or "colloidal " graphite) its behaviour towards moist oxidants, its products of oxidation, mode of combustion, and physical properties all greatly differ from those of amorphous carbon. Kohlschutter's (Zeit. Anorg. Chem., 1919, cv., 35, 121) effort to prove amorphous carbon and graphite to be physical forms of "black carbon," thus agreeing with Debye and Sherrer's (loc. cit.) conclusion, appears to be decidedly strained, ignoring as it does the more distinct chemical and physical differences of these two forms of carbon, the conditions of transition and the possibility of the "intermediary stages" being simply mixtures of graphite with amorphous carbon. H. Meyer (loc. cit.) and H. Meyer and Steiner (Monats., 1914, xxxv., 475), recording the dependence of the yield of mellitic acid from charcoal upon the latter's source and temperature of carbonisation, express some doubt as to the entity of the carbon "molecule" and the close connection of its constitution with the product of oxidation. But we must remember that deductions depend often more upon the character of interpretation of certain experiments than the experimental evidence itself. The yield of mellitic acid does vary with the source of the charcoal employed and the temperature, pressure, and duration of carbonisation, but the formation of the mellitic acid cannot be attributed to the presence of complex hydrocarbons, possibly retained by the charcoal carbonised at a comparatively low temperature, as a quantitative determination of the percentage of hydrogen, oxygen, and nitrogen invariably accompanying this kind of charcoal gives not more than I per cent of these gases, whilst the yield of mellitic acid reaches as high a value as 40 per cent. The dark residue (Bartoli and "mellogen Papasogli, loc. cit.; Dickson and Easterfield, Proc. Chem. Soc.. 1898, 163). remaining after the first oxidation, gives on exhaustive oxidation again mellitic acid and also some oxalic acid. To attribute the varying yield of mellitic acid to the existence of several modifications of amorphous carbon, as some investigators are inclined to do, is quite unwarranted as such an explanation of the somewhat varying quality and properties of charcoal would necessitate the assumption of a whole series of modifications of amorphous carbon, corresponding to every source of charcoal and practically to every 20-50° of temperature of carbonisation. The causes of the dissimilar behaviour of various samples of charcoal are probably much simpler and nearer at hand. Such causes may be : 1. A high temperature of carbonisation, which, reducing the porosity of the resulting amorphous carbon or charcoal, increases in consequence its resistance to oxidation. 2. A high temperature of carbonisation facilitates the conversion of amorphous carbon into graphite, so that we may deal with charcoal containing a bigh percentage of finely divided graphite (Arsem, Trans. Am. Electrochem. Soc., 1911, xx., 105). 3. A high percentage of mineral matter contaminating charcoal may affect its properties in more than one way. Thus we find that there are three distinct allotropes of carbon corresponding to the three, theoretically possible, fundamentally different configurations. The following considerations may serve as a pioneer attempt to assign to each modification its constitutional formula. The calorimetric measurements of the heat of complete Amorphous carbon Cals. 97650 These figures indicate the sum total of the energy liberated during the formation and degradation of the possible complexes (Rhead and Wheeler, loc. cit.) plus that of the oxidation of the carbon monoxide to carbon dioxide. (It must be noted that the calorimetric measurements of the heat of combustion of the modifications of carbon differ considerably with every experimenter. Compare data of Favre and Silberman, Ann. Chim., 1852, III., xxxv., 357; Berthelot and Petit, loc. cit.,; Mixter, Am. Journ. Sci., 1905, IV., xix., 440; and Roth and Wallasch, Ber., 1913, xlvi., 896). Taking equal weights of amorphous carbon, graphite, and diamond, and subjecting them to complete combustion, we find that the amount of heat evolved is different for each form of carbon, although the number of atoms taken and the number of CO2 molecules formed is identical. Looking for the cause of this dissimilarity of thermic values we are driven to attribute it to the different stability of the molecules in the three cases, which must depend upon the mode of linkage of the units constituting the molecule as well as the complexity of the molecule itself. Returning to our classification of theoretically possible configurations we expect that the least stability will be exhibited by molecules whose units have the power of free rotation, or, in other words, which have free valencies; the maximum stability will be found in the molecule all the constituent units of which are in a state of rigidity and all valencies fixed; the intermediate case being a molecule having some valencies free, but a rigid structure. Now, considering the fact that the greater the stability the smaller will be the evolution of heat on complete combustion (compare the case of phosphorus), and correlating this with the calorimetric measurements quoted above, we find that Amorphous carbon is represented by Class I., where none of the atoms are rigid. Graphite, Class II., the atoms are rigid but some valencies free. Diamond, Class III., all atoms are rigid and all valencies fixed. These deductions find strong support in the character of the products of the moist oxidation of carbon. The molecule of amorphous carbon with none of its units rigidly fixed, as might be expected, is the least resisting to oxidants and yields mellitic acid. Graphite with its partially fixed units gives rise to graphitic oxide or acid, of diamond are practically unaffected under the same conan acid more complex than mellitic. The rigidly fixed units ditions of oxidation. (V. Meyer - Ber., 1871, iv., 801; Ann., 1875, clxxx, 175. Schulze-Ber., 1871, iv., 802, 806. Standenmaier-Ber., 1898, xxxi., 1481; 1899, xxxii., 1394, 2824. Dickson and Easterfield--loc. cit. Meyer and Steiner-loc. cit.). It would appear to be very probable, on the basis of the theory of the constitution of the three types of carbon advanced above, that the values of any selected physical property should show a regular gradation from amorphous carbon to the diamond, the value for graphite lying between the values for the two other forms. If we find that such a gradation appears when a number of physical properties are taken, we can say that this behaviour is consistent with the hypothesis on which the present discussion is based, and it may therefore in this sense be regarded as affording evidence confirming the hypothesis. Below are collected the values for a number of physical constants, which have been determined for all three forms |