August 13, 1896J 



NA TURE 



557 



be ihe most luminous of all salts umler the action of Rcintgen 

 rays, especially when in the form of the mineral known as 

 tungsten. He thinks it exhibits the phenomena even in a more 

 marked degree than platino-cyanide of barium. A solution of 

 tungstate of copper in tungstate of calcium, moreover, glows 

 with the same brightness as natural tungsten. A note on the 

 best form of tungstate of calcium for showing fluorescence has 

 also been published by Ur. Kerdinando (liazzi, of Perugia. By 

 a cerLiin process of heating in a coke furnace in the presence of 

 oxygen, the tungstate is reduced to a white saccharoid mass 

 which gives a much more brilliant glow than ordinary tungstate, 

 but the elTect can be further intensified by pulverising the mass 

 and repeating the process, the final product which Dr. Giazzi 

 calls the " bisaccharoid " form being, in his opinion, the best 

 substance for shortening Ihe exposure and intensifying the 

 brilliancy of photographs taken with Kontgen rays. 



Prof. Ciiuseppe Martinotti {Kivisla Scieiitifico-Indtistriak) 

 claims to have obtained shadow photographs of metal objects 

 by the use of difTerent kinds of light (including that of bisulphide 

 of carbon), the light from a sulphur flame being found the best. 

 Perhaps the radiations by which these results were obtained may 

 be identical with Le Bon's lumiire noire. This latter phenome- 

 non deserves to be more fully investigated by physicists than has 

 been done. 



At a recent meeting of the SocU'W Francaise de Physique, a 

 discussion took place on a new arrangement of vacuum tube 

 introduced by M. Colardeau, which gives, with short exposures, 

 great clearness of images. The ordinary " focus " tubes 

 are, according to M. Colardeau, open to several objections ; 

 amongst others, the thickness of the glass required to stand 

 the external pressure arrests the passage of a large proportion 

 of the rays ; the energy of the discharge is not sufficiently con- 

 centrated round the kathode, and the distance between the 

 kathode and anti-kathode is too great. The new form of tube 

 is a cylinder of not more than 6 or 7 mm. diameter, containing 

 a concave kathode of 4-5 mm. radius of curvature, which 

 nearly fills the width of the tube. The lamina inclined at 

 45°, forming the anti-kathode, is only 7-8 mm. distant from the 

 kathode, and just opposite the focus ; and the glass of the tube 

 is blown out into a hemispherical knob i/io mm. in thickness ; 

 the latter ofiers but little resistance to the passage of the rays 

 generated at the focus. With this disposition stereoscopic 

 radiographs were taken, which stand out in remarkable relief. 

 The tube has stood the lest of a discharge from a coil of very 

 large dimensions without the least injury. 



Finally, we would call attention to the excellent radiograph 

 of an entire newly-born child taken by Prof. A. Imbert and M. 

 n. Bertin-Sans, of the University of Montpellier, which is re- 

 produced in the Rti'ue Gc'iit'rale des Sciemes for June 30. In 

 sharpness of outline and general detail it far excels anything 

 previously attempted in this direction. 



METALLIC CARBIDES. 

 T TNTIL about three years ago, the only definite compounds of 

 carbon with metals whose existence had been proved with 

 certainty were the acetylides of some of the metals of the alkalis 

 and alkaline earths, and these were only known in an amorphous 

 and impure state. The construction of the electric furnace by 

 .M. Moissan in 1893, ■" which the heating power of the electric 

 arc was directly utilised, by extending the upper limit of work- 

 ing temperatures, added a powerful instrument of research to 

 the laboratory. Among the many new fields of work thus 

 opened up, the preparation of the difficultly reducible metals, 

 such as tungsten, molybdenum, manganese and chromium, was 

 attacked with much success by M. Moissan. These reductions 

 being neces.sarily effected in the presence of carbon, the form- 

 ation of definite metallic carbides of great stability soon became 

 apparent, the properties of which proved to be of such interest 

 that their preparation was sy.stematically attempted. Certain 

 metals, such as gold, bismuth, lead, and tin, do not form carbides 

 at the temperature of the electric furnace, neither do they dis- 

 solve any carbon. The metals of the platinum group dissolve 

 carbon with facility, but deposit the whole of it on cooling in 

 the form of graphite, the metals being unchanged. Copper, 

 silver and iron take up carbon in quantities that, although small, 

 are sufficient to cause marked changes in the physical properties 

 of the metals ; it is noteworthy that no definite crystalline com- 

 pound could be obtained with iron. On the other hand, fused 

 aluminium takes up carbon readily with formation of the crystal- 

 line carbide AljCs, and the oxides of many other metals furnish 

 NO. 1398, VOL. 54] 



.similar crystalline compounds when heated in the electric furnace 

 with an excess of carbon. The behaviour of these substances 

 with water furnishes the most convenient mode of classification. 

 The carbides of molybdenum, MooC, of tungsten, W^C, of 

 titanium, TiC, of zirconium, ZrC and ZrCj, and of chromium, 

 Cr^C and Cr.,C.j, do not decompose water at the ordinary tem- 

 perature. Of those reacting with water, the carbides of lithium, 

 LLjCj, calcium, CaC„, strontium, SrC.,, and barium, BaCj, 

 furnish pure acetylene ; of aluminium, AI4C3, and of beryllium, 

 Be.jC, pure methane ; of manganese, Mn^C, a mixture of equal 

 volumes of hydrogen and methane ; whilst .the metals of the 

 cerite group give crystalline carbides of the type RC, (CeCj, 

 LaC._,, VCo, and ThC*), all of which react with cold water, 

 forming a complicated gas mixture containing hydrogen, 

 acetylene, ethylene, and methane. But the most complex 

 reaction is that furnished by uranium carbide, UnCs, with water. 

 In this case, in addition to a gaseous mixture containing 

 methane, ethvlene, and hydrogen, liquid and solid hydrocarbons 

 are produced in abundance, more than 100 grams of liquid 

 hydrocarbons being obtained in one experiment from four kilo- 

 grams of carbide. Cerium and lanthanum carbides have also 

 furnished small quantities of solid and liquid hydrocarbons. 



With the exception of chromium and zirconium, which form 

 CrjC, and Cr3C2, ZrCo, and ZrC respectively, only one carbide 

 of each metal appears to exist, the formula of which is usually- 

 simple, and not always in accordance with what would be ex- 

 pected from the position of the metal in the periodic system. 

 Thus, whilst the carbides of calcium, strontium, and barium 

 have the formuh'e CaCo, SrCo, and BaC2, and yield pure acety- 

 lene upon treatment with water, beryllium forms Be^C, from 

 which pure methane is obtainable (Lebeau). As already men- 

 tioned, aluminium forms .A.IJC3 giving pnfc methane, whilst the 

 higher members of the same group, yttrium and lanthanum, give 

 VCj and LaCj, yield, with water, complicated mixtures of acety- 

 lene, hydrogen, ethylene and methane, together with some 

 liquid hydrocarbons. Cerium and zirconium, again, which are 

 closely allied in the periodic system, form carbides having 

 totally different properties, CeC, giving acetylene and methane 

 with water, ZrC and ZrCa being unattacked under the same 

 conditions. 



These discoveries have already been applied technically in two- 

 directions — in the commercial production of acetylene from 

 calcium carbide for enriching coal gas or for burning alone, and 

 in the production of the carbides of silicon, CSi (discovered by 

 Acheson), and of titanium CTi, both of which are extremely 

 hard, the latter even cutting diamond. In organic chemistry, 

 also, they aft'ord a direct synthesis of many hydrocarbons, and 

 offer a means of preparing pure methane and acetylene in large 

 quantities. But perhaps their greatest interest lies in their 

 bearing on certain geological problems. Starting with the fact 

 that cast iron on solution in dilute acids gives a mixture of 

 hydrocarbons, Bjasson and Mendelejeff twenty years ago sug- 

 gested, independently, that the deposits of petroleum may be due 

 to the infiltration of water into molten masses of metallic car- 

 bides, and this view was supported by an observation made 

 about the same time by Silvestri, that some lavas of Etna con- 

 tained petroleum. 



In discussing this question in the light of his own observations, 

 described before the Royal Society on June iS, M. Moissan pro- 

 tests against too hasty generahsation in this matter, as petroleums 

 of different origins may exist, there being clear evidence in some 

 cases that bituminous schists have been formed by the decomposi- 

 tion of organic matters. On the other hand, there is the continuous 

 evolution of methane at Bulgonak and in Pennsylvania, which 

 might well be formed by the action of water upon aluminium 

 carbide ; the presence of free hydrogen in the submerged 

 volcanic vents at Santorin (Fouque), and the occurrence of 

 petroleum and carbonaceous products towards the end of a 

 volcanic eruption, the violence of which would be fully accounted 

 for by the supposition of the entry of w.ater upon metallic 

 carbides at a high temperature. There is also the possibility of 

 explaining the occurrence of petroleums of different composition, 

 for whereas a deposit of the carbides of the alkaline earths 

 would yield acetylene, which at the extremely high temperature 

 necessarily produced and in presence of free hydrogen might be 

 expected to yield hydrocarbons of the Russian type, the carbides 

 of aluminium and uranium, at perhaps a lower temperature, 

 might account for petroleums of the American type. The whole 

 work is extremely suggestive to vulcanologists, and will doubtless 

 result in further investigation on the geological side. 



G. N. H. 



