624 



NATURE 



[Oct. 25, 1888 



azonaphthol compounds, in which he drew attention to the 

 fact that the properties of these important colouring-matters 

 could only be satisfactorily explained by admitting that they 

 contained oxygen in the tetravalent condition. 



The vapour-densities of the chlorides of chromium have, for 

 the first time, been determined by Profs. Nilson and Pettersson, of 

 Stockholm. The interest attaching especially to the chromic 

 chloride, hitherto known as Cr 2 Cl 8 , in view of the recent re- 

 determinations of the densities of the'corresponding chlorides of 

 aluminium and iron, gives more than secondary importance to 

 the work of the Swedish chemists. Readers of Nature will 

 remember that these recent experiments by the indefatigable 

 workers just mentioned, and by Prof. Victor Meyer and his co- 

 workers at Gottingen, upon the composition of the molecules of 

 the chlorides of aluminium and iron, resulted in the conclusion 

 that the double formulae, Al 2 Cl (i and Fe.,Cl 6 , must be abandoned 

 in favour of the simpler formulae, A1C1 3 and FeCl 3 . This, of 

 course, meant that our old notions as to the tetrad nature of these 

 elements were incorrect, and that in reality they behave as triads. 

 Profs. Nilson and Pettersson now clinch the matter by showing 

 that chromium, which in many respects so much resembles 

 aluminium and iron, behaves in precisely the same way. Chromic 

 chloride was fortunately obtained in beautiful laminated crystals of 

 almost perfect purity. The minute traces of absorbed moisture were 

 readily eliminated by gently warming in a current of dry car- 

 bonic acid gas ; when this was accomplished the requisite quan- 

 tity was weighed out into a small platinum capsule in those 

 experiments which were conducted in the platinum density 

 apparatus, and in small pieces of ignited porous tubing when the 

 porcelain apparatus was employed. The chloride was found to 

 vaporize very slowly indeed at 1065 C, precluding the possi- 

 bility of taking densities below that temperature ; however, at 

 this comparatively low temperature, the density was 6 "135. 

 Now CrCl 3 corresponds to a density of 5*478, while Cr 2 Cl 6 

 must of necessity require a number twice as great, and hence 

 cannot exist in the gaseous state. On increasing the temperature 

 to 1190°, the value of 5 '5 17 was obtained, which remained prac- 

 tically constant up to nearly 1300 . Over 1300 the molecules 

 of CrCl 3 commence to break up into those of CrCl 2 and free 

 chlorine. This is a most decisive result, and one which cannot 

 possibly lead to any other conclusion than the adoption of the 

 formula CrCl 3 . It is only fair to mention that Messrs. Friedel 

 and Crafts on carrying out vapour-density determinations of 

 aluminium chloride by Dumas's method for 250° above its boil- 

 ing-point (183°), have very recently [obtained results which 

 appear to indicate that this chloride may condense to the double 

 molecule A1 2 C1 B at these comparatively low temperatures. How- 

 ever this may be, there can be no doubt in the cases of iron and 

 chromium that the triad formula is the only one compatible 

 with experiment, and we shall be very glad to see the doubt in 

 case of aluminium completely cleared up by further experiments. 

 The determinations in the case of the lower chloride of chromium, 

 CrCI 2 , have been made under great experimental difficulties. This 

 substance is the most difficultly volatilized of any yet submitted 

 to vapour- density determinations. It required the most intense 

 heat of the hottest procurable furnace, and even then was only 

 very slowly converted into vapour. It was obtained perfectly 

 pure by reduction of the chromic chloride utilized for the former 

 experiments, by gently heating in a stream of hydrogen. At the 

 lowest observable temperature, I300 u -I400° C, the density was 

 found to be 7 "8, considerably lower than the number required by 

 Cr 2 Cl 4 . On further increasing the heat to 1600°, the density 

 gradually diminished to 6 "2, showing that at some still higher 

 temperature one would finally attain the value 4*25 corre- 

 sponding to CrCl 2 . Hence chromous chloride again resembles 

 ferrous chloride, the only difference being that the former is much 

 more difficult to vaporize. 



An exceedingly useful and handy resume" of results in the 

 " modern geometry of the triangle" is published in the just 

 issued Proceedings of the Association Francaise pour l'Avance- 

 ment des Sciences, Congres de Toulouse, 1887. It is entitled 

 "Premier Inventaire de la Geometrie du Triangle," by M. E. 

 Vigarie. A second " Inventaire," which the author proposes to 

 draw up, will be occupied with the extensions to certain (as 

 Harmonic) quadrilaterals and polygons, and to space figures. 



We have received Part 3 of "A Catalogue of the Moths 

 of India," compiled by E. C. Cotes, First Assistant to the 

 Superintendent, Indian Museum, and Colonel C. Swinhoe. Of 

 the first two parts, dealing respectively with Sphinges and 

 Bombyces, we have already given some account (Nature, 

 vol. xxxvii. p. 386). The present part deals with Noctues, 

 Pseudo-Deltoides, and Deltoides. 



The Trustees of the Australian Museum, Sydney, have issued 

 Part I. of a catalogue of the fishes in the collection of the 

 Museum. It relates to recent palaeichthyan fishes, and has 

 been compiled by Mr. J. Douglas Ogilby. 



A remarkable book on "The Butterflies of the Eastern 

 United States and Canada, with especial reference to New 

 England," by S. H. Scudder, of Cambridge, Mass., U.S.A., is 

 about to be published in monthly parts. It will be completed 

 in twelve parts, the first of which will appear in November. 

 The preparation of this elaborate work was first announced by 

 the author in 1869. Since that time he has had it always in 

 hand, and during the last eight years he has devoted to it 

 undivided attention. According to the prospectus which has 

 been issued, Mr. Scudder has not only availed himself of the 

 personal aid of a host of willing friends and correspondents, 

 who have confided to him their voluminous field notes and 

 numerous specimens, but he has carefully gleaned every fact of 

 value from the natural history journals and other publications, 

 and supplemented all by his thirty-five years' experience in the 

 field. It is claimed that no systematic work on butterflies has 

 ever appeared in any language comparable with it in the com- 

 plete elaboration of a single limited fauna, in attention to every 

 stage of life, in thorough and excellent illustration of every 

 period of the butterfly's existence, and in careful detail of all 

 structural features. The book will contain seventeen plates of 

 butterflies, six of eggs, eleven of caterpillars, two of the nests of 

 caterpillars, three of chrysalides, two of parasites, thirty-three of 

 ^ructural details in all stages of life, nineteen maps and groups 

 of maps to illustrate the geographical distribution of the butter- 

 flies, and three portraits of early naturalists of America — in all, 

 about two thousand figures on ninety-six plates, of which forty 

 or more will be coloured. The printing of the plates was begun 

 three years ago, and is now nearly finished. 



A third edition of Mr. R. Milne Murray's " Chemical Notes 

 and Equations'' (Maclachlan and Stewart, Edinburgh) has 

 been issued. The book is intended for the use of students. In 

 this edition a section on the electrolysis of salts has been 

 introduced, and some additions have been made to the 

 descriptive part of the work. 



The latest number (No. 3, vol. iii.) of the Journal of the 

 Bombay Natural History Society contains, amongst other 

 papers : unscientific notes on the tiger, by J. D. Inverarity ; 

 butterflies and ants, by Lionel de Niceville ; on the Lepidoptera 

 of Karachi and its neighbourhood (part 2), by Colonel Swinhoe ; 

 notes on some bees and wasps from Burmah, by Captain C. T. 

 Bingham ; notes on the origin of the belief in the bis-cobra, by 

 G. A. Da Gama. Mr. Da Gama says that the term bis-cobra 

 is not of Oriental origin, but is a contraction of the Portuguese 

 bicho-de- cobra. The early Portuguese settlers in India named 

 the animals they met with from their most prominent features. 



