January 19, 1905] 



NATURE 



281 



small horizontal paddle wheel almost exactly like a 

 Crookes's radiometer. If the sound waves converge to one 

 side of the wheel it will spin rapidly in the corresponding 

 direction. 



From the Volta Bureau of Washington we have received 

 two reprints, one dealing with the so-called " visible 

 speech " alphabet introduced into England by Dr. 

 Alexander Melville Bell in 1865-7, 3"^^ 'he other being an 

 essay, by Dr. William Thornton, on teaching the deaf 

 and dumb to speak, published in 1793. The reprints are 

 illustrated by portraits of Drs. Bell and Thornton, and 

 a biographical notice also accompanies Dr. Thornton's 

 paper. 



We have received the report for 1903-4 of the Scientific 

 Society of St. Paul (Brazil), and have been able to 

 gather from it that the society was founded in June, 

 1903, the city already having a historical and geographical, 

 a medical and an agricultural society. It numbered in 

 April last fifty-si.x effective, four contributing, one corre- 

 sponding member, and two " socios ouvintes," a total of 

 sixty-three members, of whom twenty-eight were found- 

 ation members. The membership list now, however, shows 

 thirteen corresponding members. There have been held 

 two preliminary, one inaugural, fourteen ordinary, and 

 four " economic " meetings, and from the account of these 

 meetings the papers seem to have been interesting and 

 varied. \ desirable improvement would be the publication 

 of the reports in one of the international languages. 



The question as to whether the trioxide of nitrogen, 

 NjOj, is capable of existence has frequently been dis- 

 cussed, but until recently has remained unanswered owing 

 to the lack of experimental data. When the brown gas 

 produced by the action of starch or of arsenious anhydride 

 on nitric acid is passed through a freezing mixture, it 

 condenses to a blue liquid, which does not solidify at 

 — 90°. But the determination of its vapour-density shows 

 that the gas is completely dissociated, and Ramsay and 

 Cundall showed in 1885 that no contraction takes place 

 when the monoxide and dioxide are mixed. The blue 

 solution might therefore be regarded merely as a solution 

 of NO in NjOj. The actual existence of the trioxide has 

 recently been demonstrated by Wittorff (Zeif. anorg. 

 Chem., vii., 209), who has investigated the freezing point 

 of mixtures of different composition. A liquid having the 

 empirical composition N,Oj solidifies to a blue crystalline 

 solid, which melts at -103° C, and is undoubtedly the 

 pure trioxide. As the proportion of N„0, is increased 

 the freezing point at first falls to a eutectic temperature 

 at -112° C, and then rises to the freezing point of the 

 peroxide. In this way, by accurate work at low tempera- 

 tures, it has been possible to solve one of the long-debated 

 problems of inorganic chemistry. 



It has long been suspected that in solution the di- 

 chromates might perhaps be dissociated into neutral 

 chromates and free chromic acid, thus, 



K,Cr,0,:;::;K,CrO^-l-Cr03. 

 Purely chemical methods have given but little inform- 

 ation as to the nature of the dissolved salt. As the result 

 of an ingenious application of physicochemical methods, 

 the problem has recently been solved by Abegg and Cox, 

 and these authors have been able actually to determine the 

 proportion of free chromic acid in dichromate solutions of 

 different concentrations. The method, which is described 

 in the Zeitschrift fiir physikalische Chemie (vol. xlviii. p. 

 725), depends on saturating a solution of a dichromate with 

 neutral and basic mercuric chromates, HgCrO,, and 

 NO. 1838, VOL. 71] 



HgCrO^.HgO. In presence of these two salts the con- 

 centration of free chromic acid in the solution is main- 

 tained constant at 0706 mol. per litre at 50° and 0'456 

 mol. at 25°, and any excess of chromic acid must be 

 combined either as chromate or as dichromate. It is calcu- 

 lated that in the case of potassium dichromate complete 

 dissociation occurs at a dilution of 1000 litres, whilst at 

 100 litres 99 per cent, of the salt is dissociated, at 10 litres 

 91 per cent., and at a dilution of i litre 62 per cent. Even 

 in the strongest solutions, therefore, the greater part of 

 the dichromate is dissociated into chromic acid and normal 

 chromate. 



.Messrs. Whittaker and Co. will shortly publish a new 

 book entitled " The Insulation of Electric Machines," by 

 Mr. H. W. Turner and Mr. H. M. Hobart. 



Messrs. George Bell and Sons have published parts i. 

 and ii. of "Elementary Algebra," by Messrs. W. M. 

 Baker and A. A. Bourne, in one volume at 4s. 6d. The 

 book may be had with or without answers. 



The twenty-fourth volume of the Geographical Journal 

 has now been published. It contains the monthly numbers 

 from July to December, 1904. As usual, the volume is 

 richly illustrated by means of blocks and a profusion of 

 well executed maps. The volume should be added to the 

 library of every geographer and teacher of geography. 



Messrs. Newton and Co.'s new supplementary list of 

 lantern slides includes several sets which should prove 

 very valuable to science teachers and lecturers. Among 

 these instructive slides we notice photographs by Mr. 

 W. M. Martin illustrating the embryology of a chicken ; 

 British birds and nests photographed by Mr. R. B. Lodge ; 

 photographs of insects and other small forms of animal 

 life ; photomicrographs of rock sections ; and photographs 

 of diseases of the bone, by Dr. C. T. Holland. 



A revised and enlarged edition of Dr. Arthur Keith's 

 " Human Embryology and Morphology " has been pub- 

 lished by Mr. Edward Arnold. This edition differs from 

 the last in several particulars. The chapters dealing with 

 the early development of the human embryo and the form- 

 ation of the placenta and membranes have been re-written. 

 Much of the chapter dealing with the urogenital system 

 has been amended, and numerous additions have been 

 made in other sections of the book. 



OUR ASTRONOMICAL COLUMN. 



Observations of Comets 1904 d and 1904 e. — The 

 results of several observations of comets 1904 d and 

 1904 e, respectively, are published in a supplement to the 

 Astronomische Nachrichten, No. 3987. 



The latter object was observed at Bamberg by Prof. 

 Hartwig on January i and 2, and was seen as a circular 

 patch about 2' in diameter, having a nucleus which was 

 not symmetrical. The magnitude of this comet has been 

 variously estimated. In the above observation Prof. Hart- 

 wig recorded it as no, but Prof. Nijland, observing at 

 Utrecht on January i, estimated it as 9-5, whilst Prof. 

 Ambronn, observing at Gottingen on January 2, found it 

 to be 10. The brightness at the time of discovery, as 

 given by M. Borrelly, was equal to the tenth magnitude. 



The following is an extract from the daily ephemeris of 

 comet 1904 d published by Herr M. Ebell : — 

 i2h. {M.T. Berlin). 



1905 



Jan. 20 

 ,, 24 

 „ 28 



Feb. I . 

 .. 5 



a (true) 



S (true) 



log ' 



Brightness at time of discovery = i. 



