Jtdy 2 2, 1880] 



NA TURE 



279 



apparatus — by heating platinous cliloride — the density at about 

 1,400° agrees with that calculated for fCU. Bromine produced 

 by heating platlnic bromide in the apparatus gave a density 

 equal to fBro at about 1,400°. Meyer and Crafts published 

 numbers in Complcs Sendiis, which gave for free bromine at 

 about 1,400°, a density between that calculated for Bro and that 

 for IBrj, viz., 4-43 (Br„ = 5-52, fBrj = 3"64). Meyer's vapour- 

 density method is somewhat adversely criticised in the last number 

 of the Berliner Berichte by Pettersson and Ekstrand, who g've 

 numbers which they regard as proving that the method does not 

 give good results at high temperatures when the substance under 

 examination is a solid. Solids, they say, condense on their sur- 

 faces considerable quantities of air, and when the solid is thrown 

 into the highly-heated apparatus this air is evolved, is measured 

 with the air representing the volume of the gasified substance, 

 and so vitiates the result. It is certainly worthy of note that 

 both Crafts and Meyer obtained a normal density for chlorine — 

 the only halogen element gaseous before being brought into the 

 apparatus — at the highest temperature at which they experi- 

 mented. Pettersson and Ekstrand regard Dumas' method as the 

 only altogether satisfactory one ; they describe a modification of 

 this process. It is to be remarked that the density of mercury 

 vapour — which chemists generally regard as consisting of atoms 

 — is shown by Meyer's results to be remarkably constant through 

 a large range of temperature. 



Alexr. NAUMANNhas arranged Meyer and Crafts' results on 

 the density of iodine vapour in a table (in the Berichte for June 

 14) showing the percentage dissociation of iodine molecules at 

 various temperatures ; the results are in keeping w ith the deduc- 

 tion made by Naumann from the kinetic theory of gases, viz., 

 that equal temperature-intervals correspond to a regularly in- 

 creasing amount of dissociation up to 50 per cent, but after this 

 to a decreasing amount of dissociation. Naumann regards this 

 agreement between the theoretically-deduced, and the actual 

 results as affording evidence in favour of the correctness of Meyer 

 and Crafts' measurements of high temperatures. This subject is 

 likely to receive a considerable amount of attention, as it has an 

 all-important bearing on the question of the elementary nature 

 of the so-called elements. Deville and Troost, in a recent 

 number of Compt. Rend., estimate the boiling-point of zinc as 

 940", which is 100° lower than the number generally accepted on 

 the evidence of older determinations by the same authors. 



Chemico-Phvsical investigation has lately led to some im- 

 portant results. Schneider, in a recent number of the Berliner 

 Berichte, hai shown that any solution of malic acid containing 

 more than 34'24 percent, of the acid rotates the pola:ised ray to 

 the right, whiLt a solution containing less than this amount is 

 Irevarotatory. Solutions of sodium malate are dextrorotatory 

 when of greater streni;th than 47 '43 per cent., but l.-evarotatory 

 when containing less than this quantity of the salt. 



Some little time since Briihl published — also in the Berichte — 

 an important paper on the connection between the refraction 

 equivalents and the chemical structure of carbon compounds ; 

 he showed that if the refraction equivalents are calculated for a 

 number of carbon compounds, by the help of Cauchy's formula, 

 for a ray of infinite wave-length, a distinct connection can be 

 seen to exist between the numbers thus obtained and the number 

 of "doubly -linked" carbon atoms in the compound. A further 

 communication by the same author appears in a recent number 

 of the same journal. The refraction equivalent of a carbon 

 compound is equal to the sum of the atomic refractions of its 

 constituent elements ; the value of the atomic refraction of 

 carbon varies according to the "linking" of the carbon atom — 

 for every pair of doubly-linked carbon atoms present in a 

 compound, the refraction equivalent of the compound is greater 

 by 2 than that' calculated by the use of the number expressing 

 the ordinar)' atomic refraction of carbon. The atomic refraction 

 of oxygen when doubly linked to carbon is 3'29, when in the 

 group OH, or when linked to two atoms, it is 271. The atomic 

 refraction of the halogen elements is constant. Briihl concludes 

 that the atomic refraction of a monovalent element is independent 

 of the atom-linking of its compounds, but that this statement does 

 not hold good for polyvalent elements. 



In connection w'ith this work of Briihl, the recent experiments 

 of Prof. Janovsky (VVien. AkaJ. An:., June 3) are of interest. 

 According to Janovsky the linking of carbon atoms is of subor- 

 dinate influence in determining the refraction equivalents of 

 carbon compounds, for isomers with similar linking have un- 

 equal refractive indices. In homologous series a similar differ- 



ence of refractive indices corresponds to an equal difference o 

 groups only where the series belong to similarly saturated hydro- 

 carbons (abke in position). The refractive power of unsaturated 

 hydrocarbons is greater than that of saturated. Lastly, the 

 author shows that the determination of refraction-coefficients of 

 solid bodies from their solutions is unreliable, as the refractive 

 power depends on the state of aggregation. 



In the Aiinahs Chini. Phys. Long shows that a connection 

 exists between the velocities of diffusion and other physical 

 constants, and the composition of various salts ; thus the values 

 of the velocity of diffusion, molecular volumes, and electric 

 conductivity, are in the same order for the chlorides, bromides, 

 and iodides of the alkali metals. 



St.edel publishes in the Berichte the first part of an investi- 

 gation on the vapour-tensions of substituted halogen derivatives 

 of ethane ; his researches, which are not however yet completed, 

 seem to show that the increase of vapour-tension for i" (between 

 400 mm. and I,o5o mm.) is equal for a bromo-derivative and 

 that chloro-derivative which contains, in place of one bromine 

 atom, two chlorine atoms linked to one carbon atom : e.g. 

 CH3 - CHjBr and CH3 - CHClj : CH,C1 - CH.,Br and 

 CH3 - CCI3, &c. 



J. Varenne continues in Compt. rend, his researches on the 

 passivity of iron, which have been aheady noticed in Nature. 

 He finds that if a piece of iron be immersed in nitric acid of sp. 

 gr. I '325, oxides of nitrogen are evolved for a few moments ; the 

 escape of gas, however, suddenly ceases ; after a time it begins 

 again at one point of the metallic surface, spreads over the en- 

 tire surface, again ceases, once more recommences, and so on 

 intermittently. If an iron tube be very partially immersed in 

 strong nitric acid, and after passivity is established, the passive 

 part be placed in weaker acid for a time, it is found that by then 

 slowly immersing the tube further in the acid the whole becomes 

 passive, but that this passivity is very easily destroyed, e.g., by 

 shaking the tube. The passivity is less the more dilute the 

 weaker acid, the rougher the metallic surface, and the greater 

 the diameter of the iron tube. 



In the Berliner Berichte experiments are detailed by Reinitzer 

 and Goldschmidt, whereby these chemists have succeeded in 

 preparing the compound P4O, about the existence of which 

 there has been much difference of opinion. P^O is a reddish- 

 coloured amorphous substance produced by the action of phos- 

 phorus, or of zinc, on POCI3. 



Hoppe-Seyler publishes in ihft Zeitschri/t f. physiol. Chem. 

 a continuation of his work on chlorophyllan, a crystalUne sub- 

 stance closely resembling chlorophyll, obtained from green grass. 

 By treatment with alcoholic potash, chlorophyllan yields, 

 amongst other products, an acid characterised by giving a splendid 

 purple-coloured ethereal solution, which exhibits very marked 

 rose-red fluorescence. For this compound— CjuHj^Os— Hoppe- 

 Seyler proposes the name of dichromatic acid. The absorption 

 spectrum of the acid in ethereal solution is marked by two bands 

 between C and D, w hilst the spectrum of the fluorescent light 

 from the same solution exhibits two bright bands in exactly the 

 same positions. 



According to Adolf Mayer's experiments described in the 

 Berliner Berichte, oxygen has no direct influence on fermentation. 

 The addition of potassium-hydrogen tartrate to a strong syrup 

 containing yeast causes the yeast cells to grow rapidly, and 

 fermentation to proceed with e.ise. 



The meeting of the French Academy of Sciences, held on 

 July 5, presented some interesting incidents w hich are not likely to 

 "appear in the Comptes rendus. A very interesting discussion took 

 place between M. Wurtz and MM. Dumas and St. Claire Deville 

 on the occasion of the presentation of a memoir on the density 

 of vapour of iodiue by M. Troost. M. Dumas and M. St. Claire- 

 DeviUe asserted that it was impossible to accept the idea of a 

 dissociation of vaporised iodine at a high temperature, as no per- 

 manent alteration resulted from this alleged change in the compo-i- 

 tion of this substance. M. St. Claire Deville said he was;opposed 

 to all theories of molecules and atoms, as science had only to 

 deal with facts, and not with mere assumptions or speculations. 

 It might be supposed that the coefficient of expansion of 

 iodine increased rapidly with increase of temperature. M. Wurtz 

 ar'^rued that the diminution of the density was too consider- 

 able to be accounted for otherwise than by a dedoiMement of 

 molecules. All the speakers agreed that these phenomena, 

 which are very curious, should be carefully investigated with 



