122 



NATURE 



[March 21, 191 1 



with ammonium vhlorido or of barium nitrite with 

 ammonium sulphate, is gently heated in a vacuum. It 

 has now been shown by Messrs. Neogi and .Adhicary, of 

 the Rajshahi College, Bengal (Journ. Chem. Soc., 

 February), that the salt may be obtained in fairly large 

 quantities by evaporating and subliming in a vacuum a 

 very roncentrated solution of ammonium chloride mixed 

 with sodium or potassium nitrite. The evaporation is 

 carried out in an exhausted distilling flask connected with 

 a condenser and heated by moans of a paraflfm bath at 

 50°-6o° C, the Geryk purfip being worked constantly when 

 the critical moment is reached at which solidification 

 begins. The temperature is then raised gradually to 80°, 

 when the solid nitrite begins to sublime, and forms a thick 

 crust in the upper part of the flask. The salt, which was 

 analysed by a variety of methods, is extremely hygroscopic, 

 but may be kept undecomposed in an ordinary desiccator 

 or in sealed tubes ; in a vacuum desiccator the salt is de- 

 composed by the action of the acid on its vapour. 

 Ammonium nitrite is volatile with steam, and does not 

 explode when reheated ; vapour-density determinations at 

 100° showed that the '-alt had d.roniposed completely into 

 nitrogen and steam. 



As interesting contribution to the chemistry of the 

 indigo-group is described in the S'xtzxmgsherichie of the 

 Vienna Academy by Prof. M. Kohn, who has acted upon 

 isatin with the Grignard reagent in various forms and 

 obtained a series of aryl-derivatives of dioxindol, 

 /COs /CROH 



The action is remarkable in that only one of the carbonyl 

 groups is attacked, a result that is perhaps due to the 

 fact that isatin is more correctly represented by the 



formula 



/CO. 

 CeH/ >C.OH. 



In this connection, it is noteworthy that a similar limita- 

 tion is found in the case of phthalimide, a closely related 

 substance, which may also be formulated in two ways as 

 XO. /.C-=NH 



C„H/ >NH or C6H4< >0 

 ^CO^ 



^CO' 



An article on air-resistance to plane surfaces is con- 

 tributed to Engineering for March 10 by Mr. A. W. Johns. 

 The pressure on plates placed normal to the direction of 

 relative motion has alone been considered. Values of K 

 in the formula P = KAV', where P is the pressure, A is 

 the area, and V is the speed, have been tabulated in the 

 article from the results obtain«ki by many experimenters. 

 Square, rectangular, and circular plates are included. Mr. 

 Johns compares the various results, and arrives at the 

 following conclusions : — (i) The value of the coefficient K 

 for the same plate decreases as the speed increases. 

 (2) For rectangular plates, the' value of K for the same 

 speed and area increases as the ratio between the lengths 

 of the side^ increases, and this increase is generally in 

 accordance with Hagen's formula, viz. 



P = AV*(o-oo3 + 0000049), 

 where q is the ratio of the sides of the plate. (3) For 

 similarly shaped plates the values of K are the same at 

 " corresponding speeds " ; that is, the " law of similitude " 

 -can be applied to the motion of plates through the air. 

 This law asserts that for exactly similar bodies the 

 •dimensions of which have a ratio L, exactly similar 

 ^phenomena attend the motions if the speeds have a ratio 

 t/h. For example, Dines' result for a 12-inch square 



NO. 2160, VOL. 86] 



plate at 40 miles per hour is K = 0-0029. ^^ ^ 60-inch 

 square plate the " corresponding speed " would b< 

 40v'JJ = 90 miles per hour, at which speed K would hav.- 

 the same value, viz^ 0-0039. Stanton's result for a 60-inch 

 square plate is K 350-0032 for speeds between o and 25 

 miles per hour. 



Bulletin No. 44 of the University of Illinois givf • 

 account of an investigation of built-up columns under load, 

 carried out by Messrs. A. N. Talbot and H. F. Moore li- 

 the University of Illinois Engineering Experiment Station 

 In the laboratory tests, the amount and distribution of th' 

 stress over the cross-section and throughout the length <>■ 

 the channels or other component parts of steel and wrought - 

 iron built-up columns were investigated. The stresses in tb' 

 lattice bars were also determined. Deformation of th. 

 channel members was measured by means of Ames test 

 gauges mounted on suitable frames. These instrument- 

 magnify change of length by means of clockwork operating 

 a hand rotating over a dial. They read directly to o-ooi 

 inch, and by estimation to o-oooi inch. The deformation of 

 the lattice bars of one of the columns was measured by 

 Ewing's well-known extensometer. The stress distribution 

 both with axial and with eccentric loading was examined. 

 Similar tests were conducted on the columns of a railroad 

 bridge under the load of a locomotive and cars. It was 

 found that considerable local fle.xural action exists in the 

 channel or angle members of columns. Marked changes 

 in the stress distribution were found at cross-sections short 

 distances apart. Stresses 40 to 50 per cent, in excess of 

 the average stress were measured. The distribution of 

 stress among the various lattice bars was very irregular. 

 The results show the futility of attempting to determine 

 the stresses in the lacing of a centrally loaded column from 

 theoretical considerations. No relation was found between 

 the stresses observed and the stresses computed by any of 

 the usual column formulas. Copies of this bulletin may 

 be obtained gratis upon application to W. T. M. Goss, 

 University of Illinois, Urbana, Illinois. 



The Aeronautical Society of Great Britain will publish 

 immediately, as No. 6 of the Aeronautical Classics, " The 

 Flight of Birds," by G. A. Borelli, which first appeared 

 in 1680. This study of bird-fiight has been translated 

 from the original Latin for the first time into English by 

 the editors, Mr. T. O'B. Hubbard and Mr. J. H. Lede- 

 boer, and includes a biographical notice and reproduction 

 of the original diagrams and illustrations. The six 

 " Classics," including Cayley, Wenham, Walker, Lana, 

 Pilcher and Stringfellow, and Borelli, can be obtained 

 separately in paper covers at is. net, or in one bound 

 volume, with a specially designed cover, at 7s. 6d. net. 



Messrs. Witherby and Co. have in the press an illus- 

 trated volume entitled " Photography for Bird-lovers," by 

 Mr. Bentley Beetham. The book will be a practical guide 

 to the pursuit of bird-photography in all its branches. 



OUR ASTRONOMICAL COLUMN. 

 The Sydney Observatory. — From an extract from the 

 Sydney Morning Herald, reprinted in the March number 

 of The Observatory (No. 433, pp. 117-S). we regret to 

 learn that the State Government does not intend to act on 

 the recommendation made by the Public Service Board, 

 two years ago, that the Sydney Observatory should be 

 removed to a more suitable site and properly reorganised. 

 This observatory was founded half a century ago on a 

 site which was then suitable, but which is now enwrapped 

 by the dust and smoke of a great city, and its possibilities 

 otherwise vitiated by the thick haze overhanging Darling 

 Harbour. The instruments are obsolete, and Mr. Ray- 

 mond, the officer in charge, has to perform his various 



