.;2. 



NATURE 



[June 27, 19.18 



certain aotist^tic jMoperties, and also that metallic 

 silver immtrstKl in the water has an antiseptic action. 

 On this action the author has based the operation of 

 a drinkiiiK'-^vater sterilising station. By filling a glass 

 bottle to the Ijrim with water, immersing a silver wire 

 in the bottle so as to reach right down the neck, 

 allowing llie bottle to stand for fourteen days, and 

 then pouring out the water, the bottle is found to be 

 left in such a condition that if fresh water is poured 

 in ajid a silver wire again inserted, the water is 

 rendered germ-free for eight hours. Tests showed 

 that typhoid, cholera, and dysentery bacteria could be 

 destroyed in this way. 



In Science for Apiil 20 I'ruf. S. VV. Patr, writing 

 upon developments in the chemical industries of the 

 United States resulting from war conditions, refers 

 to the question of potassium supplies, and indicates 

 the progress which has been made towards rendering 

 the States independent of German sources. At present 

 there is much leeway to make up. Whilst more than 

 40,000 tons of potassium salts will be produced this 

 vear, the p)-e-war impoi'ts were nearly seven times 

 this quantity. Nevertheless, recent developments are 

 both interesting and encouraging. The brines of 

 Nebraska and California are just now by far the 

 largest source of available potassium compounds. 

 Next comes the kelp of the Pacific Coast, the utilisa- 

 tion of which is still in the developing stage, but 

 progressing rapidlv. More important still are the 

 alunite deposits iii Utah, which likewise are being 

 worked, as j-et, on a relatively limited scale. "We 

 are also," says Prof. Parr, "just beginning to get 

 glimpses of the possibilities of potassium salts from 

 cement furnaces, from the greensand of the Eastern 

 States, and from the felspars in various localities. 

 At the present rate the potash problem seems in a fair 

 way of solution." 



A \'XRY interesting lecture delivered before the 

 Chemical Society on February 21 by the Hon. R. J. 

 Strutt on "Active Nitrogen" is reported in the April 

 issue of tl>e Journal of the society. If a stream of 

 rarefied nitrogen passes through a tube in which a 

 vigorous jar discharge is maintained, and then into a 

 second vessel in which there is no discharge, it ex- 

 hibits a brilliant yellow light in the second vessel. 

 This " after-glow " persists in favourable circum- 

 stances for several minutes after the discharge has 

 been shut off. The fact that the luminosity can be 

 maintained only by the passage of the nitrogen from a 

 state of higher to one of lower potential energy would 

 alone suggest the presence of a special form of 

 nitrogen, but this became a certainty when it was 

 found that the gas reacts with gaseous hydrocarbons 

 forming hydrogen cyanide and with metallic vapours 

 giving nitrides. The existence of this "active" 

 nitrogen does not depend on indirect evidence or on 

 obscure spectroscopic phenomena; the hydrogen 

 cyanide can be isolated and identified in the ordinary 

 chemical way. W^hen nitrogen purified by prolonged 

 heating at 300° over sodium is employed the glow is 

 invisible through blue glass, but if oxygen or one of 

 its gaseous compounds (e.g^. carbonic oxide or dioxide) 

 is introduced into the glowing gas a hluish-violet 

 light is exhibited at tiie confluence of the two gases. 

 Active nitrogen does not react with hvdrogen or 

 oxygen, and tlie best conditions for its production are 

 a iow-pressawe and a Leyden jar discharge. Tiede and 

 Domcke were right in asserting that pure nitrogen 

 does not give the phenomenon, but wrong in stating 

 tliat oxygen is necessar\\ Other impurities, such as 

 carbonic oxide or dioxide, methane, ethylene, 

 hvdrogen sulphide, or mercurv vapour, will act equalh; 

 well. 



XO. 2539, VOL. lOl] 



In a paper publishfKl in tlie Monthly Weather Review 

 for December last Prof. R. DeGourcy Ward dis- 

 cusses the subject of " Meteorology and War Flying." 

 The paper is on the usual lines, and points out how 

 important some knowledge of meteorology is to the 

 airman, and how the various elements — pressure^ tem- 

 perature, etc. — influence flying. Perhaps the most 

 interesting part is that relating to clouds and thunder- 

 storms. Prof. Ward states that it is much safer not 

 to fly in a thunderstorm, and then goes on to give 

 instructions as to the best course to pursue when an 

 aviator finds himself hemmed in between enemy 

 country and an advancing stoim. 



The April part of the Proceedings of the Physical 

 Society of London contains two papeis on critical 

 angle refractometers of the Pulfrich type by Mr. J. 

 Guild, of the National Physical Laboratory, and by 

 Mr. F. Simeon, of Messrs. Hilger, respectively, which 

 serve as a good illustration of the way in which im- 

 provements in instruments can be effected by co- 

 operation between the makers and the users of the 

 instruments. The critical angle refractometer is the 

 most convenient instrument to use in tlie determina- 

 tion of the -refractive indices of glasses of diffo-ent 

 compositions, and it has been used at the National 

 Physical laboratory in the examination of more than 

 two thousand specimens. The experience of the in- 

 strument gained in the course of this work is em- 

 bodied in Mr. Guild's p>aper, and there seems little 

 doubt that in the near future an instrument wiH he 

 constructed which will give the absolute refractive' 

 index and the dispersion of a specimen of glass to 

 the fifth figure after the decimal place. 



An article on the nonius,, its origin, theory, and 

 use, by Senhor A. R. Machado, has been published 

 in the Revista de Quimica pura e aflicada (Oporto, 

 II. S^rie, Ano iii., 1918). Being a countryman of 

 Pedro Nunez, the author calls a vernier a nonius, and 

 proceeds to trace the history of this instrument from 

 the book " De crepusculis" by Nunez, published in 

 1542. In reality, there is no resemblance between 

 the contrivance of Nunez and that of Vernier, pub- 

 lished in 163 1. Nunez proposed inside the graduated 

 arc of a quadrant to draw concentric arcs and to 

 divide them respectively into 89, 88, 87 . - . 45 equal 

 parts, so that the alidade would always (more or less 

 accurately) touch a division-mark on one of the forty- 

 six circles. Though Ingenious, the proposal was^ any- 

 thing but a practical one on account of the difficulty 

 of dividing a quadrant into eighty-three or sixty-seven 

 parts. It was improved, though not made much more 

 practical, fifty years later by Curtius, whose Idea was 

 published by Clavius. There is nothing new in all 

 this; see, for example, Delambre's " Histoire de 

 I'astronomie moderne," i., p. 253, or Cantor's 

 "Geschlchte der Mathematlk," li., p. 580. But no 

 one put a small auxlliarv arc on the movable alidade 

 before Vernier. The author of the paper next 

 describes the various uses of the vernier, including 

 Mannheim's double one (vernier de vernier), proposed 

 in the Journal de Physique, 1873, to- meet the case 

 where none of the divisions of a vernl-er coincide 

 exactly with a division on the principal scale. 



Messrs. /. emd A. Churchill announce a translation, «, 

 by G. W. Robinson, of Dr. M. Gina's "Chemical W 

 Combination among Metals." In it the relation 

 between chemical composition and physical properties 

 Is discussed. The main portion of the book consists 

 of an account of all intermetalllc systems in which 

 compounds occur. Messrs. C. Griffin and Co., Ltd., 

 will shortly publish "Simple Experimental Hygiene, 

 Physlologv, and Infant Management for the l^se of 



