September io, 1891] 



NATURE 



455 



distinguishing between scalar and vector quantities in our di- 

 mensions. 



Prof. Gray disapproved of the term electromotive force, but 

 thought it was a term which could scarcely be eradicated now. 



Each speaker, in fact, discussed the subject from his own point 

 of view, with the result, as the President remarked, that the time 

 allotted had only served to open the discussion, but he hoped 

 that it would be continued in the technical journals during the 

 year, so that some definite conclusions might be arrived at in 

 1892. 



Wednesday morning was devoted to clearing off arrears. 



Prof. S. P. Thompson read two optical papers, one on the 

 measurement of lenses, and a second on a new polarizer. In 

 this instrument the polarization is effected by reflection from 

 black glass, but to avoid the angling of the beam a reflecting 

 prism is used in addition. This arrangement has the dis- 

 advantage that the axis of the beam undergoes a translational , 

 shift, so that rotation of the polarizer is out of the question. To 

 get over this difficulty two more reflectors are introduced, or 

 two quarter-wave plates may be used, one of which converts the 

 plane polarized light into circularly polarized light, while the 

 other reconverts it into light plane polarized in any azimuth. 



Dr. Webster then gave an account of some experiments on a 

 new method for determining v. The method is similar in some 

 respects to Ayrton and Perry's, and gave as a result in the pre- 

 liminary experiments 2*987 x 10^**. ' 



Prof. Riicker then gave an account of some experiments made 

 by Prof. Ayrton and himself, on the magnetic field near the 

 South London Electrical Railway, The experiments were 

 made in a house in Kennington Park Road with ordinary 

 galvanometers, and showed conclusively that the magnetic 

 disturbances on delicately suspended needles would be per- 

 ceptible at considerable distances. , 



Prof J. V. Jones, in describing some experiments on the i 

 periodic time of tuning-forks, maintained in vibration electrically, 

 stated that dry platinum-platinum contacts do not work satis- 

 factorily, whereas the results obtained with mercury contacts ' 

 are much better, at all events when changes of temperature are ■ 

 carefully guarded against. 



Mr. F, T. Trouton described some interesting experiments to ' 

 determine the rate of propagation of magnetization in iron, A j 

 large coil of iron wire, from 8 to 12 feet in diameter, was 

 supplied with one fixed coil wound on it, and throujjh which 

 the alternating current passed. A second exploring coil was 

 connected up with a telephone, and one experiment consisted ! 

 in endeavouring to find out the positions of nodes and inter- 

 nodes in the magnetized material from which it might have been 

 possible to have determined the lengthof the wave of magnetiza- 

 tion for a definite period of alternation. Nodes were observed in 

 the half of the ring remote from the magnetizing coil, but these i 

 were easily ascertained not to be the ones sought for, because \ 

 their position was not found to depend on the period of alterna- 

 tion. 



The President attributed the effects to mechanical vibrations 

 excited by magnetization. 



CHEMISTRY AT THE BRITISH 

 ASSOCIA TION. 



'X'HE proceedings of Section B at Cardiff were not felt to be 

 -*■ as interesting as on some previous occasions. Several well- 

 known chemists were not present, and no set discussions on 

 subjects of general chemical interest, which have been special 

 features at other times, took place. Still, in the course of the 

 meeting several papers of very considerable importance were 

 read, and provoked valuable comments. The President's Ad- 

 dress was listened to by an enthusiastic audience, and his remarks, 

 together with several of the papers contributed during the meet- 

 ing, should give a fresh impetus to the study of the metals. 



Prof Dunstan read the Report of the Committee on the 

 Formation of Haloid Salts. It has been found by Mr. Shen- 

 stone that chlorine, prepared by the action of hydrogen chloride 

 on manganese dioxide, attacks mercury readily, even when both j 

 substances are pure and dry, while that obtained by heating 

 platinous chloride only attacks mercury extremely slowly. In- 

 ' cidentally it has been discovered that pure platinous chloride is 

 a very difficult substance to prepare, an oxychloride being formed 



NO. II 41. VOL. 44] 



at the same time. The results so far obtained are to be regarded 

 as preliminary. 



Prof. Vivian B. Lewes read a paper on the spontaneous 

 ignition of coal. His experiments lead him to reject the expla- 

 nation of Berzelius, which attributes spontaneous ignition to the 

 oxidation of pyrites contained in the coal. The heat given off 

 by the combustion of the pyrites present in the most dangerous 

 kind of coal, even if localized, would not be sufficient to raise 

 the temperature of the adjacent coal to the ignition point. The 

 cause of spontaneous ignition of coal is to be found, rather, in 

 its power, especially when finely divided, of absorbing oxygen, 

 which causes the slow combustion of some of the hydrocarbon 

 constituents even at the ordinary temperature. The action may 

 increase under favourable conditions until ignition of the coal 

 results. The risk is greatest with large masses of coal, and with 

 the ordinary air supply on board ships. The oxidation increases 

 rapidly with the initial temperature of the coal, so that c )al 

 fires are found to occur most often on ships frequenting tropical 

 climates. It may be roughly estimated that the absorbing power 

 of a coal for oxygen is proportional to its power of taking up 

 moisture. 



In the discussion which followed, Prof Bedson mentioned 

 his experiments on the heating of coal-dust at various tempera- 

 tures up to 140° C, He had noticed that in some cases com- 

 bustible gases were given off by the coal, 



A feature of special interest was the exhibition by Ludwig 

 Mond of specimens of nickel-carbon-oxide and metallic nickel 

 obtained therefrom. In the paper read in conjunction with 

 this exhibit an account was given of the discovery and proper- 

 ties of the above compound. The physical properties have 

 been described in the Journal fur physikalische Chemie. 

 Chemically, nickel carbonyl is most inactive, numerous experi- 

 ments made to introduce the carbonyl group into organic 

 substances by its means having been uniformly unsuccessful. 

 Experiments were described having for their object the direct 

 extraction of nickel from its ores by means of carbon monoxide. 

 It was found that, as long as the nickel is combined with arsenic 

 or sulphur, the process is entirely successful on a laboratory 

 scale. Such ore, or matte, or speiss, is calcined, reduced by 

 water gas at 450°, cooled down to a suitable temperature, and 

 treated with carbon monoxide in a suitable apparatus. On ex- 

 posing a heated surface to the gas containing nickel-carbon- 

 oxide, it is possible to produce, direct from such gas, articles of 

 solid nickel, or goods plated with nickel, resembling in every 

 way those obtained by galvanic deposition of metals, and repro- 

 ducing with the same exactitude and fineness any design upon 

 such articles. This result can also be obtained by immersing 

 heated articles in a solution of nickel-carbon-oxide in such 

 solvents as benzole, petroleum, tar oils, &c., or by applying such 

 solution to the heated articles with a brush or otherwise. 



A specimen of iron-carbon-oxide was exhibited, which Messrs. 

 Mond and Langer have obtained as an amber-coloured liquid, 

 which, on standing, deposits tabular crystals of a darker colour, 

 and solidifies entirely below - 21" C. to a mass of needle- 

 shaped crystals. It boils at 102° C, but leaves a small quantity 

 of green-coloured oil behind. Several analyses and vapour- 

 density determinations have been made, but it is not yet certain 

 whether a pure substance has been obtained or a mixture of 

 several iron carbonyls. The authors hope shortly to publish a 

 full account of this interesting substance, which differs consider- 

 ably in its chemical behaviour from nickel-carbon-oxide. 



Mr. Crook es described his experiments on the electrical 

 evaporation of metals and alloys. If a brush of gold is placed 

 in a vacuum tube and connected with the negative pole of an 

 induction coil at ordinary temperature, and if a piece of glass be 

 placed underneath the gold in the tube, on passing the current 

 a metallic mirror appears on the glass, increasing in thickness to 

 a leaf, which can be peeled off, and which is perfectly homo- 

 geneous. Films of silver and platinum can also be obtained. 

 It is found that different metals thus treated evaporate at different 

 rates, one or two, such as aluminium and magnesium, being 

 apparently non-volatile. It is thus possible, in the case of the 

 aluminium-gold alloy discovered by Prof. Roberts-Austen, to 

 separate a large portion of the gold from the aluminium by 

 electrical evaporation. 



T. Turner gave an account of experiments which he had made 

 to discover the cause of the red blotches which often appear on 

 the surface of brass sheets on rolling, and which are a great 

 source of annoyance to Birmingham manufacturers. They are 



