November 2, 1S93] 



NA TURE 



17 



suitable for use as a supplement to lectures and demonstrations. 

 The experiments described will impress the student with the 

 fact that "science is measurement," hence they are of the right 

 kind, for it is doubtful whether showy experiments are of any 

 educational value. Schools and university classes requiring a 

 good and accurate handbook of heat for the physical laboratory 

 would do well to adopt Mr. Hall's work. 



Messrs. Longmans and Co. have just published, for Dr. F. 

 Clemow, of the English Hospital, Cronstadt, " The Cholera 

 Epidemic of 1S92 in the Ru.siau Empire." Thfe author states 

 in his preface that to the English medical world Russia is almost 

 a closed book. The reason of this is tha% in consequence of the 

 <lifficulties of the Russian language, medical news from that 

 -country is rarely taken from the original source. Dr. Ciemow, 

 therefore, having a knowledge of Russian, set himself to give a 

 plain, unvarnished account of the epidemic of cholera which 

 iaU sunmer swept over the Russian Empire, and to bring to- 

 gether information bearing upon the subject directly from the 

 «nost authentic Russian sources. He seems to have spared no 

 pains to get the statistics as full and trustworthy as possible, and 

 was assured by the authorities that, notwithstanding the diffi- 

 cilties atteniing their efforts to obtain proper returns from 

 regions suc'.i as Central Asia an I Siberia, in no case \lid the 

 •error exceed 10 per cent. 



Carbide of silicon, SiC, the beautifully crystalline sapphire- 

 -ike substance whose preparation by M. Moissan with the aid 

 oi the electric furnace was described in our note of October 12, 

 j-'), 572, forms the subject of a communication to the current pub- 

 lication of the Zeitschrift fiir Anoi'ganische Cheinie, by Dr. 

 !\liihlhauser, of Chicago, whose preparation of the carbide of 

 boron formed the subject of our last week's chemical note. It 

 appears that Dr. Miihihiiuser had already completed a long and 

 very elaborate research upon the preparation of this interesting 

 compound upon a scale of considerable magnitude, for the ulti- 

 mate purpose of its manufacture, before the communication of 

 M. Moissan appeared. The mode by which it may be obtained 

 «n large quantities was perfected some time ago by Mr. Acheson, 

 and Dr. Miihihiiuser now gives details of the process, together 

 with considerable additions to our knowledge of its chemical 

 and physical nature. The process essentially consists in heating 

 a mixture of silica and carbon to the temperature of 3500^ by 

 means of the electric furnace, when carbon monoxide escapes 

 and silicon carbide is produced. 



SiOo-H3C = SiC + 2CO. 



Silicate of alumina may be employed instead of silica with 

 equally good results. The crystals obtained possess many of 

 the properties, particularly the hardness, of the diamond. Ac- 

 cording to the purity of the materials employed in their manu- 

 facture they are colourless, or coloured yellowish green, bluish 

 green, or pale blue. The name carborundum is suggested for 

 the substance. Upon the large scale the cheaper materials sand 

 and coke are employed, with the addition of common salt as a 

 flux. The latter acts mechanically, causing the unattacked 

 portion of the ingredients to bake together, thus facilitating the 

 separation of the crystals ; it also prevents loss of carbon 

 by surface oxidation. One hundred parts of the powdered coke 

 are mixed with one hundred parts of sand and twenty-five parts 

 of salt. The mixture is placed in an electric furnace built of 

 highly refractory fireclay. The electrodes are inserted through 

 apertures at the ends of the furnace, and are connected with a 

 •central bar of carbon, the high resistance, round which the 

 mixture is closely packed. The electrodes are in immediate 

 connection with a powerful current transformer, which is con- 

 nected in turn with an alternating current dynamo. The carbon 

 high resistance bar is raised by the current to an intense white 

 NJ. 1253. VOL. 49] 



heat, which is in turn communicated to the mixture. Gas is 

 rapidly evolved from the mass, and yellow and blue flames dart 

 out in all directions. As the heat increases the flame concen- 

 trates about one position until the fused salt rises to the surface, 

 when an energetic action occurs, the gases eventually forcing 

 their way through the liquid crut and heaping it up in the form 

 of a crater, from which a high flame shoots up surrounded at its 

 base by dense white clouds of vapour of salt, and eventually the 

 remainder of the salt wells forth from the crater like veritable 

 lava, carrying the dark impurities along with it. The interior 

 of the crater, where the reaction is proceeding, is now seen to 

 be white hot. The eruption soon commences to subside, the 

 flames cease to appear, the outer crust hardens, and the reaction 

 is complete. 



The product of this remarkable reaction is an ellipsoidal 

 hardened mass, surrounding the carbon high resistance, and is 

 found upon making a section to consist of six distinct byers. 

 The first, close against the carbon bar, is a zone of graphite, 

 which occurs in the form of hollowed hexagonal plates, pseudo- 

 morphs of silicon carbide, from which they are produced by 

 dissociation at the extremely high temperature in the neigh- 

 bourhood of the bar, silicon escaping as vapour. The second 

 and by far the largest zone consists of the crystals of silicon 

 carbide. They are largely found in elongated aggregates, 

 radiating in all directions from the axis of the ellipsoid ; the 

 individuals forming the aggregates are bluish or yellowish-^reen, 

 and of all sizes up to crystals a centimetre in diameter. Numerous 

 isolated and highly perfect crystals of considerable size and great 

 beauty are likewise found between the aggregates. Surrounding 

 this zone of crystals is a narrow zone of amorphous carbide of 

 silicon, outside which is found a layer of nodules of minerals 

 produced from the impurities during the reaction ; the fifth layer 

 consists of the remains of uncombined mixture, and the sixth 

 the crust of common salt. The crystals obtained by employing 

 silicate of alumina are usually colourless or pale blue, and have 

 been employed by M. Nikola Tesla in his new lamp for the 

 transformation of electrical waves into waves of light. The 

 powdered crystals explode violently when heated with potassium 

 and lead chromates, but burn quietly with chromate of lead 

 alone, forming dioxides of carbon and silicon. The powder 

 exhibits a vivid greenish-yellow luminosity when heated in a 

 platinum crucible. It is only very slightly attacked by the 

 oxygen of the air under these circumstances, only o'5 per cent, 

 uniting in an hour. The fine powder, moreover, remains sus- 

 pended in water for months without subsiding, although the 

 specific gravity of the carbide at 15^ is 3 '22. 



The additions to the Zoological Society's Gardens during 

 the past week include a Macaque Monkey {Macaciis cynomcl- 

 giis, i ) from India, presented by Mr. Robert Gallon ; a Chest- 

 nut-eared Finch {Ainadim castonotiis) from Australia, a De 

 Filippi's Meadow Starling {Sturuel/a defilippi) from South 

 America, presented by Mrs. Kemp- Welch ; two Laughing 

 \\\r\^'a^zx%{Dacelo giganica) from Australia, presented by the 

 Executors of the late Mr. Fred Burgess ; a Punctured Sala- 

 mander {Amblysioina punctaturn) from North America, pre- 

 sented by Mr. J. H. Thomson, C.M.Z. S. ; four Common 

 Toads {Bufo vulgaris) from Jersey, presented by Mr. J. 

 Stanton ; two White-handed Gibbons [Hylovales lar. 6 S), a. 



Bulbul {Hypsipc'tes ) from the Malay Peninsula, a 



Red and Yellow Macaw {Ara cliloroptera) from South America, 

 five Green Lizards {Lacerta viridis), three Black-spotted Toads 

 {Bufo mclanosiictus), four Schlaginlweit's Frogs {Rans cyatio- 

 p'llyctis) from Ceylon, two Slow-worms {Angitis fragilis), three 

 Fire-bellied Toads {Boinbinator igiuus) European, deposited ; 

 a Bir-tailed Godwit [Liinosa lapponica), two Dunlins {Tringa 

 alpiiia) British, purchased. 



