July 25, 1895] 



NATURE 



1 1 



prepared as described above, the lead salt was obtained and 

 submitted to a process of fractional precipitation by adding 

 successive quantities of water to its solution in alcohol. By this 

 means crotonoleic acid was proved to be a mixture composed 

 for the most pirt of inactive oily acids, the lead salts of which 

 are precipitated first, whilst the true vesicating constituent (or 

 its lead salt) is principally contained in the last fractions, and 

 represents but a small pro])ortion of the original material. It 

 was observed that the conversion of the crotonoleic acid into a 

 lead salt did appreciably affect its vesicating power. 



The supposed active constituent of crolon oil, crotonoleic acid, 

 having thus been shown to be a mi.xture, the authors proceeded 

 to attempt to isolate the vesicating constituent from croton oil 

 direct. 



By saponifying that part of croton oil which is soluble in 

 strong alcohol with a mixture of lead oxide and water, and , 

 repeatedly fractionating an alcoholic solution of the lead salts 

 with water, the later fractions, which possessed the greatest 

 vesicating power, ultimately furnished, when submitted to a j 

 fseries of fractionations, a resinous substance having extraordinary 

 power as a vesicant. This substance could not be further 

 resolved by repeating the process of fractional precipitation of j 

 the alcoholic solution with water. The same substance was 

 isolated from the so called "crotonoleic acid," and the authors 

 propose to name it " croton-resin." To its presence the 

 vesicating property of croton oil is due. The composition of 

 croton-resin is expressed by the empirical formula CisHjgOj. 

 So far all attempts to crystallise it, or to obtain crystalline 

 derivatives from it, have been unsuccessful. It is a hard, pale 

 yellow, brittle resin, nearly insoluble in water, light petroleum, 

 and benzene, but readily dissolved by alcohol, ether, and 

 chloroform. When heated it gradually softens, and is quite 

 fluifl at 90° C. Croton-resin has neither basic nor acidic 

 properties: it may be boiled with a mixture of lead oxide and 

 water without being apprecial)ly affected. KbuUition with 

 aqueous potash or soda gradually decomposes it, destroying its 

 vesicating power. The products of this action are several acids, 

 some of which are members of the acetic series. By oxidation 

 of the resin with nitric acid a mixture of acids is obtained. 

 The constitution of croton-resin is therefore complicated, and its 

 molecular formula would appear to be at least (Ci^HigOj), or 

 CjdHjjOs. Since it is not saponified by a mixture of lead oxide 

 and water, and as no glycerol could be detected among the 

 products of its decomposition liy alkalis, it is not a glyceride, 

 and as it does not react with hydroxylamine or phenylhydrazine 

 or sodium bisulphite, it is probably neither a ketone nor an 

 •\ldehy<le. The evidence so far obtained jioints to the conclusion 

 that the constitution of the vesicating constituent of croton oil 

 may be that of a lactone or anhydride of complicated structure. 



" (Jn the Magnetic Rotation of the Plane of I'olari.sation of 

 Light in Litpiids. I'art I. Carbon Bisulphide and Water." By 

 I . VV. Rodger and W. Watson. 



The aim of this investigation is the determination in absolute 

 measure of the magnetic rotation of litpiids at different tempera- 

 lures, the effect of the chemical nature of the liquid on this 

 properly, and its correlation with other physical properties. 



The present communication contains a descri|ition of the 

 apparatus and method of experiment, and the results obtained 

 with the standard liquids, carbon bisulphide and water, fo;- 

 sodium light, in a magnetic field of constant intensity, and at 

 difk-renl temperatures between o' and the ordinary lioiling jioint. 



in the case of carbon bisidphitle three different samples were 

 used, and identical results were obtained with three separate 

 coils. In the following table are collected the mean values of 

 the liiiiling point (b. p.), density at o° (p„), and X'erdet's con- 

 slant at o" (7,,). Ver(let's constant may be defined as the rota- 

 tiiin in minutes of arc produced in a column of liquid when the 

 (hhiTence between the magnetic potentials at the ends of the 

 'I'himn is equal to one CCS. unit. 



It will be seen that the three different samples give practically 

 identical values for the three physical constants. 



The results obtained for the rotation of carbon bisulphide may 

 Ik- summed up in the follii«ing e()uation, where 7, is the value 

 of Xerdet's constant at the temperature /, 



7f = 0-04347 (1—0-001696/). 



NO. 1343, VOL. 52] 



The expression connecting rotation and temperature is there- 

 fore linear. 



In the case of water the results are best represented by 



7, = 0-0131 1 (I— ooi 305/— o-Oj 305/^). 



Here the rate of change of the rotation with temperature in- 

 creases as the temperature rises. 



In the case of water the quotient 7/p, where p is the density 

 is practically constant up to 20°, it then very slowly increases, 

 the rate of increase between 20' and 100" being practically 

 constant. 



For carbon bisulphide the quotient 7/p decreases at a constant 

 rate as the temperature rises, the rate of decrease being very 

 much greater than the rate of increase in the case of water. 



The measure of the molecular rotation which is usually 

 employed in chemical investigations is 



(M7/P) substance / (M7/P) water, 

 where M is the molecular weight. Although the authors post- 

 pone a detailed discussion of the validity of this expression, they 

 show that for carbon bisuljihide, at any rate, its value changes 

 with the temperature, and hence the conclusions obtained by its 

 use regarding questions of chemical constitution, especially of 

 tautomerism, are affected on this account. 



They also point out that the above expression involves the 

 properties ci water. The only justification for the use of water 

 in relative observations is the elimination of variations in the 

 strength of the magnetic field in which the observations are 

 made. If the temperature of observation is always the same, 

 this can readily be done. If, on the other hand, the temperature 

 varies, it is essential to know how the rotation of water alters 

 with the temperature. In the past this alteration was unknown, 

 and the arbitrary measure of the molecular rotation above 

 referred to has come into use. Since an expression for the tem- 

 perature variation has now been obtained it is to be hoped that 

 observers will employ a measure of the molecular rotation which 

 does not involve the properties of water. Indeed, other con- 

 siderations make such a measure all the more desirable. Up till 

 now the authors have made observations on eight liquids, 

 besides water and carbon bisulphide, and in all cases except that 

 of water the relation between rotation and temperature is linear, 

 and the quotient, rotation di\ided by density, diminishes as the 

 temperature rises. It is highly probable, therefore, that as 

 regards magnetic rotation, as in the case of so many other 

 ]3roperties, the behaviour of water is exceptional, and hence it is 

 particularly ill-suited for the use to which it has been put. 

 Again, on account of the snallness of the rotation in water, the 

 unavoidable inaccuracies in determining its rotation, and thus 

 estimating the strength of the magnetic field, produce a larger 

 percentage error in the results than if a liquid, such as benzene, 

 having a considerably higher rotation than water, were used for 

 this purpose. 



Chemical Society, June 20. — Mr. .\. Ci. \'crnon Harcourt, 

 President, in the chair. — The following papers were read : — On 

 the "isomaltose" of C. J. Limner, by H. T. Brown and G. H. 

 Morris. Lintner's isomaltose is shown to be merely impure 

 maltose, and the isomaltosazone derived from it is maltosazone ; 

 maltose is the only stdistance produced in the diastatic conversion 

 of starch which yieUls a crystallisable osazone. — Action of diastase 

 on starch : nature of Lintner's isomaltose, by A. R. Ling and 

 J. L. Baker. — The transformation of ammonium cyanate into 

 urea, by J. Walker and 1-". J. Hambly, The velocity of inter- 

 conversion of urea and ammonium thiocyanate under various 

 ctmditionsin aqueous solutions has been <iuantitativelystudied; the 

 numbers obtained can be interpreted bythe dissociation hypothesis. 

 — Note on the transformation of ammonium cyanate into urea, 

 by U. J. H. l-'enton.— Some derivatives of humulene, by A. C. 

 Chapman. A number of derivatives of humulene, the sesquiter- 

 pene contained in the essential oil of hops, are described. — Note 

 on thio-derivatives from sulphanilic acid, by Miss L. E. Walter. 

 The parasulphonate-xanthate, .SOsK.CulIj.S.CS.OEt, obtained 

 by the interaction of patassium xanthateand diazotised sulphanilic 

 acid, is readily converted into derivatives of the sulphydride, 

 .S().,K.C|iH4.SH, a number of w-hich are described together with 

 their oxidation produc;s. — Helium, a constituent of certain 

 minerals (part ii.), by W. Ramsay, J. N. Collie, and M 

 Travers. Fifteen out of about thirty minerals studied were found 

 to yield helium, the density of the several samples of gas 

 examined being alxiut 2*2 : the w-ave-length of sound in the gas 

 corresponds to i : \\, so that the atomic weight should be 4-4. 

 Helium has the solubility 0-007 'i water .at iS', and is hence the 



L 



