August 23, 1894] 



NATURE 



411 



ing result has been obtained that these elements in solution 

 follow the law o( gaseous diffusion, the chlorine diffusing twice 

 as fast as the iodine. 



Prof. J. W. Briihl gave an account of his investigations on 

 tautomerism. By determining the molecular dispersion of com- 

 pounds, he has been able to obtain values which are indepen- 

 dent of temperature, and thus he has arrived at a sure means of 

 distinguishing between bodies containing the group HC — C = O, 

 or "keto" bodies, and those containing the group C = C(OII), 

 which he termed " enole " compounds. With simple ketones 

 and di-ketones no tautomerism or change from the keto to the 

 enole form was found to occur. Nor did it occur with the 

 alkyl derivatives of ketonic acids ; when, ho^vever, the alkyl 

 was replaced by an acid radical in these cases, tautomerism 

 occurred. The author had investigated derivatives of campho- 

 carboxylic and of malonic and succinic acids, and found the 

 above rule to hold good in these cases, although enolisation was 

 found to depend not only on the number of negative groups 

 present, but also on the position of these in the molecule, and on 

 the simultaneous presence of alkyl groups, which latter some- 

 times rendered the molecule more stable. .\n interesting com- 

 pound had been obtained, namely, mono-brom-formyl 

 camphor, which was a true ketone, and which was 

 the only compound known in which the keto form of 

 the formyl radical was present. In conclusion the assumption 

 of Lahr, that ketonic compounds possess a "labile" consti- 

 tution, was shown to be untenable, no continuous internal 

 atomic movement being probable. In the case of benzene 

 derivatives, on the other hand, such changes probably occur, and 

 are termed by the author " phasotropic." 



Prof E. Noelting read two papers entitled, respectively, "On 

 Dinitros Derivatives of the Aromatic Series," and "On 

 the Formation of Indazoles from Diazo-compounds." Both 

 papers dealt with compounds, which showed the dependence of 

 stability on molecular grouping. 



Dr. Caro described the method of obtaining a new rhodamine, 

 or pink colouring matter, by the interaction of chloral hydrate 

 and an alkyl derivative of metamidophenol. A salt of a leuco 

 base is formed, which latter on oxidation by ferric chloride 

 i^ave a blue colouring matter. It was shown by experiment that 

 on heating a solution of this blue compound in water it turned 

 to a fine pink, owing to an intra-molecular change. 



A p.iper followed, by Drs. G. G. Henderson and A. R. Ewing, 

 on " Tetrarsenites." The sodium salt, which was prepared by 

 adding arsenious oxide to acid sodium tartrate, was easily 

 soluble in water, and might be conveniently used for hypo- 

 dermic injections of arsenic. Other sails had been prepared, 

 and also a solution which probably contained the hypothetical 

 tartrarsenious acid from which they were derived. 



Dr. J. B. Cohen read a paper on "The Constitution of the Acid 

 Amides," in which he showed that these might be divided into 

 two classes — those which formed compounds with silver and 

 cryslallised in needles or prisms, and those which did not form 

 silver compounds and crystallised in plates. To account for 

 these differences he fell back on Ilantzsch's theory of the 

 stereo-isomerism of nitrogen compounds, and concluded that 

 the amides contain a hydroxyl group. 



A short discussion followed the paper, in which Prof. Dun- 

 stan quoted experiments which he had made on the action of 

 trichloride of phosphorus on acetamide, which did not bear out 

 Dr. Cohen's view of the constitution -of the latter body. 



Dr. Caro, however, did not consider Prof. Dunstan's experi- 

 ment conclusive. 



The report of the Committee on Isomeric Naphthalene 

 Derivatives was read. Work had been done on chlor-sulphonic 

 and brom sulphonic derivatives of naphthalene, and the results 

 tended to confirm the previous conclusions of the investigators. 



The report of the Committee on the -Vction of Light upon 

 Dyed Colours was re.ad by the secretary, Prof. Hummel. The 

 colours experimented with this year were chiefly yellows. Of 

 these by far the largest number, ranging from "moderately 

 fast" to "very fast," were to be found among the azo colours. 

 The azoxy colours give good fast tints upon silk and cotton. 

 The fastness of alizarin orange is probably greater than that 

 exhibited by most other colours of the alizarin group. Very 

 few fait yellows are derived from the natural colouring matters. 

 The cultiv.ation of weld, which yields the only fast and, at the 

 same time, bright, natural yellows, is being gradually given up. 

 It is fortunate then that efficient substitutes can be obtained from 

 coal tar, which, contrary to popular opinion, is the source from 



NO. 1295, VOL. 50] 



which the greatest number of colours fast to light are derived 

 at the present time. 



Dr. W. Meyerhoffer read a paper on "Certain Phenomena 



of Equilibrium during the Evaporation of Salt Solution.s." For 

 a given mixture of salts in a saturated solution it was found 

 that there existed a certain transition temperature above which 

 double decomposition took place. Thus with a saturated solu- 

 tion containing ammonium chloride and sodium nitrate, sodium 

 chloride was formed above 6° C. , while below that temperature 

 no change took place. 



GEOLOGY AT THE BRITISH ASSOCIATION. 



/^F the forty-three papers presented to Section C this year, com- 

 ^^ paratively few are of lasting importance, geologists having 

 apparently saved up their best work for presentation at Zurich, or 

 else having exhausted themselves at the excellent and successful 

 session of the previous year. The President's address, contain- 

 ing an excellent epitome of the recent progress of mineralogy, 

 was rather fitted for quiet and thoughtful perusal than for readmg 

 to a mixed audience, but it will be looked back upon as one of 

 the most valuable of the contributions to the forthcoming 

 volume of Proceedings. It was followed up by only one paper 

 dealing with pure mineralogy, that of Mr. H. .\. Miers, on a 

 new method of measuring crystals. The two fundamental laws 

 of crystallography— namely, (l) the constancy of the angle in 

 crystals of the same substance, and (2) the law of simple 

 rational indices — seem to be violated by those crystals which 

 are liable to irregular variations in their angles, or those which 

 have the simple faces replaced by complicated "vicinal " planes. 

 Both these anomalies are exhibited by potash- and ammonia- 

 alum. Brilliant and apparently perfect octahedra of these salts 

 show large variations in the octahedron angle ; other crystals 

 show low vicinal planes in place of the octahedron faces. If 

 it be true, as is supposed, that the octahedron angle varies in 

 different crystals, it would be interesting to ascertain whether 

 progressive variations can be traced during the growth of a 

 single crystal, and whether some or all of the octahedron faces 

 change their direction in space if the crystal be held fixed 

 during growth. 



In order to solve this problem a new goniometer has been 

 constructed, in which the crystal is fixed at the lower end of a 

 vertical axis, so that it can be immersed in a liquid during 

 measurement. This device is in reality an inversion of the 

 ordinary goniometer with horizontal disc ; the liquid is con- 

 tained in a rectangular glass trough with parallel-plate sides; 

 one side is placed rigidly perpendicular to the fixed collimator, 

 and the other is perpendicular to the telescope, which is set at 

 90^ to the collimator. The trough is supported on a table 

 which can be raised and lowered, so that the crystal can be 

 placed at any required depth in the liquid. If the liquid used 

 be its own concentrated solution the crystal can be measured 

 during growth, and the changes of angle, if any, can be 

 observed at different stages. In order that it may be held 

 rigidly, the crystal is mounted, when small, in a platinum clip, 

 which it envelops as it grows larger. 



The results derived Irom the measurement of a large number 

 of alum crystals are as follows : — 



(1) The faces of the regular octahedron are never developed 

 upon alum growing from aqueous solution. 



(2) The reflecting planes (which are often very perfect) are 

 those of a very flat triangular pyramid (triakis octahedron) 

 which overlies each octahedron face. 



(3) The three faces of this triangular pyr.amid may be very 

 unequal in size. 



(4) The triakis octahedron which replaces one octahedron 

 may be different from that which replaces another octahedron 

 face upon the same crystal. 



(5) During the growth of the crystal the reflecting planes 

 change their mutual inclinations ; the triakis octahedron becomes 

 in general more acute, i.e. deviates further from the octahedron 

 which it replaces, as the crystal grows. 



(6) This change takes pLice not continuously, hv,\. per salliiin, 

 each reflecting plane becoming replaced by another which is 

 inclined at a small angle (generally about three minutes) to it. 



(7) During growth the faces are always those of triakis octa- 

 hedra ; if, owing to rise of temperature, re-solution begins to 

 take place, faces of icositetrahedra are developed. 



These observations prove that the growth of an alum crystal 



