James H. Gardiner, F.C.S. ] [Established in the Year 1859. (WITH WHICH IS INCORPORATED THE "CHEMICAL GAZETTE "). 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 Council invites applications for the CHAIR OF ORGANIC CHEMISTRY. Salary commencing at £600 per annum. The Council also invites arplications for the Posts of two ASSISTANT LECTURERS AND DEMONSTRATORS. The salary in each case will commence at £200 per annum, and the appointments will be, in the first instance, for three years. At the end of this period the Assistant Lecturers will be eligible for promotion to Lectureships. Candidates are requested to send five copies of their applications and of not more than three testimonials, so as to reach the SECRETARY, Arms rong College, not later than JULY 19, 1919. July 11, 1919 The BRITISH SCIENCE GUILD The Latest Applications of Science to Industry! BRITISH SCIENTIFIC PRODUCTS EXHIBITION Patron: H.M. THE KING President: The Most Hon. THE MARQUESS OF CREWE, K.G Central Hall, Westminster, July 3-August 5 In a paper entitled "Glass making Before and During the War," Mr. Harry J. Powell, who for the past forty-five years has carried on glass manufacture at the Whitefriars Glass Works, gave an interesting résume of his experiences of glass-making. The perfection in glass work that has been reached by the firm, and the high position that they hold in the spheres of art, ornamental, and scientific glass ware, renders anything that Mr. Harry Powell has to say upon the subject of special interest and importance. The author opened with an account of the "toughened " glass of M. de la Bastie, a manufacture about which the Press of the day indulged in some very wild speculations. Mr. Powell at the time of the discovery of the process some forty-four years ago exhibited at the Society of Arts some specimen tumblers toughened by the inventor's method. Much interest was shown at the rough usage that they would stand without breaking; when, however, they did break it was more in the nature of an explosion than that of an ordinary fracture. Mr. Powell was sceptical of the practical value of the process from the first, and we know now that his doubts were justified. A very interesting history was given of the glass-making industry in London; there is a continuous record for over 300 years. In 1696 there were no less than 24 glasshouses in the London district; there were glass-works in Blackfriars in 1606. The Whitefriars glass-house is mentioned in the Tatler of August, 1710. Passing on to the period just before the war the author drew a very sombre picture of the state of English glass-making; speaking generally, there was little or no attempt to study glassmaking from the scientific standpoint, except in the isolated case of Messrs. Chance Bros., who "with difficulty kept alive the manufacture of optical glass." The scientific manufacture of glass was rapidly becoming a German monopoly. For all that, individual glass-makers in England were always on the alert to devisc new material to meet the various demands of industry. The Whitefriars Glass Works furnish a list that shows that in a quiet unobtrusive way they were doing an immense amount of laborious research. The following items are selected from the list of special glasses recently made :-Many kinds of "Crookes" glasses for spectacles, didymium glass for signal purposes, glass for Lord Berkeley's researches in electrolysis, glasses with special electrical properties, Dewar's flasks glass for thermometers, soda-glass for X-ray bulbs, and uranium glass. The needs of the war and the cutting off of supplies from Germany caused very considerable activity in the glass-making industry, and the labours of Prof. Sir Herbert Jackson and others has resulted in the issue by the Institute of Chemistry of formulæ for many pre-war German glasses. During the war immense quantities of soda-lime alumina glass was made at Whitefriars for mine-horns, some six hundred thousand of these having been constructed by the Hyposol Company, of Harrow Wealdstone. Mr. Powell was able to give a very gratifying list of the special glass manufactures undertaken by other glass makers during the war. The probable increased employment of automatic machinery in the manufacture of glass-ware and the effect it would have upon the industry was next discussed, and the paper concludes with some valuable remarks upon artistic hand-made productions, an art in which the firm of Powell and Sons excel, Mr. Powell enjoys the distinction of being an expert in elegant design and is also thoroughly acquainted with the technical branch of art glass work. Referring to a proposal that has been made that industrial designers should be trained at some central institution and sent out "to reform and enlighten the benighted glass manufacturers," he gave some very sound advice, suggesting that it would be wise for the would-be designer to first study in a glass house the nature of glass and how vessels are made; right design for glass is only possible when the properties and working methods are taken into consideration. In conclusion, referring to the future prospects of the British glass industry, attention was drawn to the recent attempt to obtain Government permission for unrestricted importation of glass-ware from abroad; if this is allowed there is little hope of the survival of the British glass industry. AZOBENZENE is reduced to benzidine by boiling with SnCl2 in HCI. After performing this reduction, in the course of a piece of work, it was noticed that on cooling short silky needles separated from the resulting solution. These needles were found to contain both tin and benzidine. After purification, analysis gave 22.7 per cent Sn, 410 per cent Cl, and 5'4 per cent N. This shows that the substance has the composition NH2C6H4.C6H4NH2, H2SnC16, the values for which are 230 per cent Sn, 411 per cent Cl, and 5'4 per cent N. A series of stannichlorides of organic bases has recently been described by Druce, but be.zidine was not one of the bases used by him (CHEMICAL NEWS, cxviii., 1.). Benzidine stannichloride is readily soluble in warm water, but much less so in cold. It appears to be considerably hydrolysed when dissolved in water or dilute HCl, for a solution containing equivalents of benzidine hydrochloride and stannic chloride gives crystals on evaporation containing only a little tin, while with two SnCl4 molecules to one of base a deposit containing only about 10 per cent of tin is obtained. In the presence of a considerable excess of SnCl4, however, the body deposited has the above composition. The following was found to be a good method of obtaining this salt:-4'5 grms. of benzidine, 50 cc. of water, and 5 cc. of strong HCI are heated together till a clear solution is obtained, and then 26 grms. of SnCl4 (anhydrous), dissolved in a little water, is added. A deposition of crystals soon begins. When cold, the substance is filtered off and dried in a desiccator over potash. It consists of colourless needles, which are stable in dry air at ordinary temperatures but which evolves HCl and SnCl4 on heating to 100° C. Double Salt of Benzidine Hydrochloride and Mercuric Chloride. During the preliminary examination of the product of the reduction of azobenzene by acid stannous chloride, above described, HgCl2 was added to its solution to test for stannous chloride. Instead of the white amorphous precipitate of Hg2Cl2, a precipitation of white needles occurred. This precipitate was found to contain both benzidine and mercury but not tin. The percentage or mercury in the precipitate was found to vary somewhat with the conditions under which it was formed, but after recrystallisation from dilute HCl the following values were obtained:-38.1 per cent Hg, 26.9 per cent Cl, and 5'5 per cent N. These values indicate that the composition of the substance is NH2C6H4.C6H4NH2,2HCl, HgCl2. The calculated values for this composition are 38.0 per cent Hg, 26.9 per cent Cl, and 5.3 per cent N. The compound may by prepared by mixing hot solutions containing one equivalent each of mercuric chloride and benzidine hydrochloride. The body separates on cooling as long transparent blades. The compound is slightly soluble in cold dilute HCl and readily so in hot. Pure water turns it yellow, probably causing partial hydration. The yellow product is only slightly soluble in water, even on boiling. A very small quantity of HCl, however, causes it to dissolve readily. Chemical Laboratory, Paddington Technical Institute. IS THE ELECTRICAL CONDUCTIVITY By F. H. LORING. SILVER, whether taken at its fusion-point (liquid) or at ordinary temperatures, has a higher electrical con. ductivity than any other element under similar conditions. Mercury in a solid state has a much higher conductivity than when liquid. Generally speaking, all metallic elements would have an infinite conductivity at or close to the absolute zero temperature, whereas the semimetallic and non-metallic elements would become poorer conductors or even better insulators at low temperatures. These are, of course, well known facts. Conductivity is therefore profoundly modified by temperature, and the question arises-Can it be conditioned to a similar extent by any other cause? When comparing the conductivities of different substances, their physical states due to the temperature, &c., should be taken into account; and while it is not possible to make the comparisons when the states are on the average brought to the nearest point of coincidenceowing to lack of experimental data-there is generally sufficient information available to enable the different substances to be arranged in the order they would follow should the comparisons be made under such conditions. At ordinary temperatures bromine is a liquid, and being non-metallic it has a very high resistance; it is an insula'or, in fact, with a dielectric constant of 3, paraffin- | wax being about 2, while selenium is about 6. Ice at -2° C. has a dielectric constant approaching to 100, but probably conduction sets in at this temperature. At -200° C. the constant becomes 2.5, while pure water may be taken as about 80 at room temperatures. Non-metallic combinations afford a weaker class of conductors, as instanced by nitric acid when dissolved in water in the proportion by weight 31 per cent acid to 69 per cent of water. This is a maximum-conductivity solution which has a higher conductivity than other solutions containing salts of metals; in fact, it is the best liquid conductor known of the electrolytic class, the specific conductivity being 0 782 in ohms-1 cm.-1 at 18° C. If it be assumed that silver is made up of isotopes having atomic masses 107 and 111 in the respective proportions 7 to 2, which gives the mean atomic mass of 107.888, then there would be 22.2 per cent of the higher mass atoms calculated by taking the relative numbers 7 and 2, or 22.8 per cent by taking corresponding aggregates. In the same way, bromine, assumed to have isotopic atoms of masses 79 and 80 in respective proportions 1 to 13, would yield corresponding percentages 92.8 and 92-9, the mean atomic mass of this element being 79.928 on the assumption of these isotopes in the porportion indicated. Taking these two extremes it would appear that the higher the percentage of higher atomic mass isotopes the lower the electrical conductivity, since silver is the best conductor and bromine is an insulator. Therefore, electrical conductivity might be conditioned by the proportion of isotopes present. From the accompanying table it will be seen that the rule holds good for the elements having isotopes of such values and in such relative proportions as to make up the present accepted atomic masses. While the suppositions involved are self-supporting a note of caution is necessary, since the probability of arriving at a true representation of | facts is not necessarily strengthened by the concidence of two or more hypotheses being in mutual agreement. With a small balance of probability in favour of a given hypothesis, one may attempt to work out the consequences with a view of finding some related property which will throw light upon the subject under investigation. From the rule in question, the conductivity should be very low when the lower or higher atomic mass isotopes are absent, as would appear to be the case with regard to H, He, C, O, N, and F, all atoms of such elements being whole numbers and those of each element alike in mass. It is generally believed that the isotopes of radio-active change are electrically equal if they are of the same atomic number, and consequently occupy the same group-place in the periodic table. The atomic number is supposed to represent the magnitude of the nuclear positive charge. Why, then, should the mass variation in any way modify the conductivity? Or, as radium, probably a conducting element (being a pronounced metal), changes into an inert gas by the loss of one helium atom for each radium atom disintegrating, the inert element should itself be a conductor in the liquid or solid states, since the isotopic proportion should be the same in both elements, assuming dual species as suggested in the case of silver for example. Whether the condensed emanation which as a solid glows like a tiny arc lamp (o use Ramsay's description of its behaviour when frozen with liquid air) is a proper conductor or not is unknown. In the solid state the emanation is not transparent; but, on the other hand, it has no metallic properties so far as is known. According to E. Bouty (Comptes Rendus, cl., 149) the dielectric cohesion of neon is less than that of helium, and it is therefore the lowest so far known. Discharges pass through neon so readily that the small potential difference produced by passing it from one vessel to another is sufficient to make it glow, and in pumping operations it exhibits a fire-like appearance. This is perhaps worthy of note, because neon appears to have isotopes according to J. J. Thomson's positive-ray experiments, but confirmation of this atomic duality is considered necessary. From the values given in the table it would seem that whether the conductivity increases or decreases with temperature it might depend upon the isotopic proportion; so that from antimony, which has over 50 per cent large-mass isotopes, to bromine the resistance temperature coefficient should be negative, but the physical state of the element introduces complications. The behaviour of alloys in not exhibiting the change of resistance with temperature as expected might be explained by the solid solutions of different metals having atomic masses which would give the differential effect, the respective metals acting as if they were isotopes from the electrical point of view. Lead from different sources and having presumably different proportionate numbers of isotopes should have slightly varying electrical conductivities according to these views. The difference in mass (i) between the isotopes of a given element (a difference of, for example, 1, 2, or 4), the percentage (p) of higher mass isotopes as given in the table, and the decimal fraction of the mean mass (ƒ) are of necessity related as shown by the equation The only known means of direct separation and mass measurement of atoms is the positive-ray method of Sir J. J. Thomson; but unfortunately rays are only obtainable from the gaseous or volatile elements, and those atoms nearly alike in mass would not be distinguishable photographically. Mercury is slightly volatile at low temperatures, but the lines on the plate are not sharp enough to distinguish between mass values of 199 and 203, especially if by any chance the assumed heavier atoms carry the even charges (see CHEMICAL NEWS, 1914, cx., 25). Improvements, however, in the positive-ray method may be expected. For a discussion on the possibility of separating isotopes, see F. A. Lindeman and F. W. Aston in the Philosophical Magazine for May, 1919, 523. In this paper it is sug gested that theoretically different isotopic atoms are separable, but practically the difficulties are exceedingly great, the various methods considered being1. Fractional distillation. 2. Diffusion or effusion. 3. Gravitation. 4. Centrifugal separation. 5. Electrical method of positive rays. E. F. Northrup, Vincentini, and others. C. Hering in Met. and Chem. Eng., Jan., 1915, p. 23, gives temperature curves of resistivities compiled from available data. (NOTE.-The resistance of practically all dielectrics decreases with rise of temperature, and the dielectric capacity bears no simple relation to dielectric resistance). The electrical method yields only microscopic quantities, and thus far it has a limited application, as, for example, no lead isotopes, or indeed lead atoms at all, can be projected and photographed. The centrifugal method is regarded as the most promising. I have carried out experiments on pulverised materials by subjecting them to the impelling influence of an indented cylinder revolving at a high speed (diam. 18", speed approaching 3000 r.p.m.), thereby obtaining a whirl of the material in an annular space (6" radial depth) round the cylinder (the dimensions are somewhat |