;26 



NATURE 



[(May 12, 1910 



a " light cut and a high speed will keep its sharp edge 

 better than a carbon-steel tool. The durability of all 

 steels, without exception, is very low at low speeds under 

 light cuts, and increases as the speed is raised, the dura- 

 bility being measured by the amount of metal cut away 

 before the tool becomes blunt. The engineer usually 

 requires the steel that will remove the greatest amount of 

 jiietal per hour without requiring too frequent sharpening, 

 and it is useful to express the " duty " of a tool steel by 

 the product of metal removed and corresponding cutting 

 speed, thus obtaining a quantity which is proportional to 

 the time rate of removing metal and to the durability of 

 the tool. 



To- account for the fact that an increase in the cutting 

 speed is accompanied by an increase in the durability of 

 the tool, it has been suggested that the evolution of heat, 

 and consequent rise in temperature of the cutting edge, 

 may be the influencing factor, and experiments are 

 described in the paper giving confirmation of this view. 

 In these experiments heat was applied artificially to the 

 tool while cutting by means of hot water, and tests were 

 made at different temperatures. A law has been deduced 

 from the results which may be stated thus : for constant 

 durability of the cutting tool the speed varies as the cube 

 root of the product of area of cut by thickness of shaving. 

 Experiments were also made on the effects of temper and 

 of the percentage of carbon on the durability of carbon 

 steel, and on the eflfect of the cooling process in the case 

 of high-speed steels. 



.Prof.' J. O. Arnold, in his paper on uniform nomen- 

 • clatiire of iron and steel, earnestly pleads with metallo- 

 graphists strongly to support. Prof, le Chatelicr in his 

 effort to abolish personal names . for the constituents of 

 steel. Mr. Sydney A. Grayson,, of Birmingham, gives the 

 iresiilts of some recent investigations on case-hardening, 

 from which it appears that it is necessary to classify case- 

 hardening compositions both by the carbon per cent, 

 obtained in the " case," and also by the graduation of the 

 carbon . diffusion, which is best shown graphically. This 

 classification is necessary on account of one composition 

 'being more suitable for certain kinds of work than another. 

 A high carbon " case," such as i-io per cent, carbon, would 

 be very efficient for the kind of work where the pressure 

 was fairly constant, such as a plain bearing, but it would 

 be very unsuitable and inefficient for parts which had to 

 resist repeated shocks, because of the strong tendencj' of 

 the high carbon- " case " to chip, or even to peel off. It 

 is advisable, where all kinds of case-hardening have to be 

 done, that two compositions be used, one of them to pro- 

 duce a high carbon wearing surface, and the other to 

 produce a medium carbon wearing surface. 



Mr. C. A. M. Smith, of East London College, adds to 

 his previous work on the elastic breakdown of certain 

 steels an investigation of the possibility of rion-axial load- 

 ing occurring in test-pieces held in the testing machine on 

 spherical seats, and shows that, in the- case of a 50-ton 

 machine in which the radius of the seats is \\ inches, the 

 eccentricity may amount to 0-15 inch, with a coefficient 

 of friction of o-i. The ratio of maximum to mean stress 

 would then be at least 2-2, and in one test where eccen- 

 tricity was known to exist, a ratio of 2-96 was found. 



A GEOLOGICAL SURVEY OF COLORADO.' 



nPHE State of Colorado is one of the most famous in 

 the history of American mining, but though its 

 Geological Survey was created in 1872, and has included 

 on its staff some distinguished men, it has done com- 

 paratively littfe, for it remained practically without funds 

 until 1908. The Survey has now been provided with an 

 annual subsidy and a staff, Mr. R. D. George being State 

 geologist with sixteen assistants. Its first annual report 

 has been issued, and shows that the Survey has been 

 organised on sound lines, for it contemplates cooperation 

 with the Federal Survey and private local geologists, and 

 the advancement of local education by presenting a collec- 

 tion to illustrate the mineral wealth of Colorado to every 

 high school in the State. 



The first volume consists of five valuable memoirs upon 

 the geology of Colorado, illustrr'ted by geological and topo- 



i CoIoraHo Geologic il Survey. First f^pn t 1908. By R. P. George. 

 Pp. v + 243 ; »» plates. 4 mips. (He' ver. iqog ) 



NO. 2 II 5, VOL. 83] 



graphical maps. The stratigraphicat geology of the foot- 

 hills is described in a memoir by Mr. J. Henderson. Th( y 

 consist of a foundation of .Xrchean and .'\lgonkian roik^, 

 which are covered by a long succession of sediments, re- 

 presenting continuous deposition from. the. Carboniferous to 

 the Laramie, at the end of the Cretaceous. . This succession 

 consists of 10,000 feet of strata, partly marine and part'y 

 terrestrial, and apparently all conformable. The. beds were 

 laid down in the course ■ of a slow subsidence of the 

 country, so that the higher meinbers of the series overlap 

 one another on to the older rocks to the west. After the 

 Laramie there was a break, and the chief Cainozoic 

 deposits are of Miocene age. 



The other memoirs deal with economic geology. Each 

 is well arranged, and accompanied by a useful biblio- 

 graphv. Mr. R. D. George and Mr. R. D. Crawford con- 

 tribute an outline survey of the Hahns Peak mining field, 

 thirty miles from . the railway terminus at Steamboat 

 Springs. Hahns Peak itself is a porphyry laccolite, once 

 covered by Cretaceous rocks. The goldfield is one. of those 

 interesting cases in which no certain source has been dis- 

 covered of the gold in rich placer deposits. The lode 

 mines hitherto found yield silver-lead ores, and their work- 

 ing has not been remunerative. The popular local belief 

 as to the source of the gold is that it has come from, the 

 porphyrites, of which the junction with the sediments is 

 generally mineralised ; but it has also been attributed to 

 conglomerates at the base of the Dakota formation and 

 to pre-Cambrian metamorphic rocks. 



Mr. George contributes a valuable memoir on th 

 tungsten area of Boulder County, accompanied by noti- 

 on the intrusive rocks by Mr. R. D. Crawford. It includf - 

 a brief account of the tungsten deposits throughout th^^ 

 world, and of the technical uses of the metal. The Boulder 

 tungsten field consists of gneiss of sedimentary origin, 

 which is seamed by dylves of pegmatite, which the author 

 claims, in this instance, to be an intrusive rock and not. a 

 pneumatolytic product. There are also dykes of latite, a 

 rock intermediate between trachyte and andesite. Th>- 

 tungsten ores are mostly found in the granite ; the vein - 

 in gneiss are narrower and less profitable, as that rock 

 forms less open channels when disrupted. The veins ar* 

 verv irregular in .arrangement, but are generally steepl;- 

 inclined. The tungsten was introduced by four successive 

 depositions. There has apparently been considerable 

 difficulty in the concentration of the ore, owing to its 

 extreme friabilitv, and the author suggests the use of 

 magnetic methods, which have proved successful . in. Corn- 

 wall. This report is illustrated by a series of plates, of 

 which six are especially useful, as they show the various 

 tvnes of ores. 



The last report is by Mr. H. B. Patton, on the Montezuma 

 district of Summit Countrv. The rocks of this mining 

 field are the Archean schists and gneiss of the Front 

 Range, injected. by acid and diabase dykes. .The ores are 

 replacement veins comoosed of quartz containing. lead, zinc, 

 and a little cooper and some silver and. gold. . Unjike some 

 Colorado mining fields, descending water appears to have 

 had very slight effect upon the. ores, and there has been 

 little secondary sulphide concentration. The porphyritic 

 dvkes are of Cret.aceous date, and the ores were intro- 

 duced l.it"r than the formation of any rock in the district. 

 The distribution of the ores appears to be quite independent 

 alike of the dvkes, pegmatite veins, and cleavage. The 

 ore bodies lie along joint planes,' on which there may have 

 been some movement by strike faults. There is, however, 

 no direct evidence that the ores were connected with fault- 

 ing, for the cross-faults are barren, and the joint planes 

 mav have been mineralised simoly because they were planes 

 of weakness, which offered the ore-bearing solutions the 

 readiest channel to the surface. J. W. G. i 



UNIVERSITY AND EDUCATIONAL \ 



INTELLIGENCE. | 



BiRMiNGii.AM.— Mr. C L. Boulenger, of King's College,,^ 



Cambridge, has been appointed to the lectureship in(! 



zoology rendered vacant by the resignation of Mr. Leonard| 



Doncaster 



Dr. Leonard Parsons has been appointed assistani 

 lecturer in pathology and bacteriology to succeed Dr. 

 Leonard Mackcv. 



