JuLYi;, 1919] 



NATURL 



391 



Chemiker- und Techniker-Zeitung, December i, 1918). 

 Deposits of unknown value underlie the extensive oil- 

 field of the Irak districts. Trial borings have shown 

 an oil-bearing tract of more than 1000 sq. km., ap- 

 parently capable of yielding a larger output of oil 

 than the Baku wells, and of better quality. The 

 northern limits of the oil zone lie in the province of 

 Kermanshah ; to the east it reaches to near Ispahan, 

 runs diagonally across Arabistan, continues along the 

 border hills of Dashti and Dashtistan behind Bushehr, 

 the most important of the Gulf ports, and ends in the 

 neighbourhood of Banda-Abbas, the terminus of the 

 great caravan-route, Meshed-Kirman. Borings made 

 in 1890 proved the exis'tence of rich oil deposits in the 

 Island of Kishem, off the coast. Since that date great 

 progress has been made in developing the industry. 

 Persian oil is said to be superior to the American ; 

 it contains a large percentage of benzene and kerosene. 



A WRITER in Zeitschrift fiir Instrumentenkunde 

 (November, 1918) describes a series of tests made on 

 a Benedick galvanometer of the differential type to 

 determine the cause of variations in its zero reading. 

 The instrument is of the d'Arsonval type, the moving 

 coil being suspended by a quartz fibre and the current 

 led in and out by four thin metal ligaments. Tests 

 show that the sensitiveness depends on the curvature 

 of the pole-faces, and an analysis of the results with 

 the aid of the equations of motion of the movement 

 shows that the change is due to an alteration in the 

 restoring force. As the suspension was unaltered 

 during the test, it follows that the effect is due to 

 ma^^etic action. This action is caused by the presence 

 of traces of iron in the copper winding. This assump- 

 tion is borne out by tests, which are described, show- 

 ing the change in sensitiveness due to varying the 

 position of the moving coil in the f.eld. There is an 

 after-effect causing a permanent motion of the zero 

 of the instrument in the direction of the last deflection. 



A PAPER by Messrs. F. B. Silsbee and R. K. Hona- 

 man, of the United States Bureau of Standards, 

 which appears in the Journal of the Washington 

 Academy for May 4, summarises the results of their 

 work during the last two years on the relative merits 

 of the various insulating materials used in sparking- 

 plugs. Cup-shaped vessels of the materials were 

 tested between 200''' and 900° C. in an electric furnace, 

 the resistivity being determined from the fall of poten- 

 tial between the molten solder inside and that outside 

 when a measured current passed fhrough the cup. 

 Measurements with direct currents were found to be 

 useless owing to the polarisation produced, but with 

 alternating currents of 60 cycles per second the re- 

 sults for the same specimen were always consistent. 

 At 500° C. the resistivities of a few typical materials in 

 megohms per cm. cube are : — Fused silica 340, best por- 

 celain 80, typical mica 70, aerc^lane plug porcelain 40, 

 motor-car plug porcelain o-8. A minute quantity of 

 impurity in the material appears to reduce the re- 

 sistivity considerably. The change of resistivity with 

 temperature is given by log,oR = c— bT, where R is 

 the resistivity, c is a constant between 10 and 12, 

 and b a constant between 00065 ^^^ 00085. 



In the science reports of the Tohoku Imperial Uni- 

 versity, vol. vii., No. 3, there is an account by 

 Murakami of an investigation of the structure of 

 ferro-carbon-chromium alloys. By utilising methods 

 of magnetic analysis and microscopic examination, 

 alloys containing less than 6 per cent, of carbon have 

 been systematically investigated, and a structural and 

 constitutional diagram of their normal states has been 

 obtained. The author confirms the existence of a 

 compound Cr^C, having a hexagonal crystalline form 

 as put forward by Moissan. The infljuence of this 

 NO. 2594, VOL. 103] 



carbide on the A, change in steels has been investi- 

 gated. Above this f>oint the carbide dissolves in 

 austenite, and, on heating to a high temperature, it 

 dissociates as follows : — 



2Cr,C = Cr,C, + 5Cr. 

 During cooling the reverse change takes place only 

 slowly, and this influences the position of the trans- 

 formation point. On one hand, if the rate of cool- 

 ing is sufficiently slow, the change occurs at about 

 700° C. ; while on the other, if it is quick, the trans- 

 formation point is very conspicuously lowered, and in 

 extreme cases completely suppressed. A specimen 

 having a normal transformation point shows a 

 pearlitic or troostitic structure, one having a lowered 

 transformation point a martensitic structure, and 

 when the transformation is suppressed an austenitic 

 structure. The self-hardening of a chromium steel is 

 related to the lowering, or, in extreme cases, the sup- 

 pression, of the A, transformation, and hardness is 

 caused by the solid solution of the carbide Cr,C, in 

 iron and chromium. The author has come to the 

 conclusion that there are three ternary compounds, 

 namely, a, /3, and y double carbides. The micro- 

 graphic and magnetic characteristics of these com- 

 pounds have been investigated by him. 



The results of some interesting tests on locomotive 

 piston-valve leakage are given in Engineering for 

 July 4. The tests were conducted by the test depart- 

 ment of the Pennsylvania Railroad at Altoona, and 

 have extended over several years ; a specially arranged 

 testing plant was employed. The results were erratic, 

 and the following abstract of some of the results takes 

 account only of all that appeared normal. With a 

 standard two-ring valve, 12 in. in diameter, in plain 

 bushing, the leakage at each end of the valve ranges 

 between 171 lb. and 183 lb. per hour with saturated 

 steam; between 194 lb. and 210 lb. with steam at 

 100° superheat; between 181 lb. and 197 lb. with 

 steam at 200° superheat; and between 122 lb. and 

 132 lb. with steam at 300° superheat. For the bush- 

 ing with ports a leakage between 302 lb. and 326 lb. 

 per hour occurred with saturated steam; between 

 425 lb. and 448 lb. per hour for 100° superheat; and 

 between 383 lb. and 414 lb. per hour for 200° super- 

 heat. The length of valve-travel, when it ranged 

 between 2 in. and 6 in., was found to have but little 

 effect upon leakage. The speed of the valve (strokes 

 per minute) had no appreciable effect upon leakage. 

 As much as 15 h.p. was required to drive the valve 

 in tests at 300 revs, per minute. 



Messrs. George Allen and Unwin, Ltd., have in pre- 

 paration "Defective Housing and the Growth of 

 Children," by Dr. J. L. Dick. Three lectures recently 

 delivered before the University of Cambridge are an- 

 nounced for publication by the Cambridge University 

 Press. They are " Science and War " (the Rede lec- 

 ture), by Lord Moulton ; " Italian Studies : Their Place 

 in Modern Education," by Prof. T. Okey; and the 

 Leslie Stephen lecture on Pope, by Dr. J. W. 

 Mackail. The same publishers also oromise a revised 

 edition of Dr. A. Marker's "Petrology for Students." 

 Messrs. Longmans and Co. announce for publica- 

 tion in the autumn a new book, limited to 105 copies, 

 by A. Thorbum, entitled "A Naturalist's Sketch- 

 Book," containing 60 plates, 24 in colour and 36 in 

 collotype. It will form a companion volume to the 

 same author's "British Birds." Among other books 

 in the press for appearance by Messrs. Longmans we 

 notice " An Introduction to General Phvsiologv," 

 Prof. W. M. Bayliss; "The Principles of Child 

 Phvsiology, Pure and .Applied," Dr. W. M. Feldman ; 

 "The Physiology of Muscular Exercise," Prof. F. A. 

 Bainbridg'e; "Cement," B. Blount; "Applied Aero- 



