826 



NATURE 



[December 8, 1923 



Letters to the Editor. 



\The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, nor to correspond with 

 the writers of rejected manuscripts intended for 

 this or anv other part of Nature. No notict is 

 taken of anonymous communications.] 



The Polarisation of Double Bonds. 



Profs. Lapworth and Kodinson in a letter 



under the above title in Nature of November ij, 



p. 722. raise some objections to a theorv which I 



pul)Ii.shed in the Philosophical Magazine in September. 



The first of these objections is to the difference which 



I make between the action of an external electric 



field on singly- and doubly-bonded atoms. It seems 



to me that such a difference must exist. For, suppose 



that there is a double bond between two carbon atoms 



C, =C,, the octets of electrons round C, and Cj have 



four electrons in common situated between C, and Cj. 



If an external electric field acts on the molecule, 



tending to make electrons move from left to right, 



some of the electrons held in common may be so 



far displaced from Cj and towards C, that they can 



no longer be regarded as shared with C^. If two 



of these are displaced far enough for this to happen, 



the octet round Cj will be intact and C, will be 



. saturated, while the octet round Cj will be reduced 



to a sextet, so that Cj will be unsaturated and 



chemically active ; there are still two electrons left 



between Ci and Cj to form a single bond binding 



C, and Cj together. If there were originally only 



a single bond between Cj - Cj, the octets round 



C-i and Cj have only two electrons in common ; 



if one of these moves so far towards Cj that it can 



no longer be regarded as completing the octet 



round C^, so as to make this atom unsaturated and 



active, there will only be one electron left between 



Cj and Cj to bind them together. We should expect 



that they would easily come apart and form oppositely 



charged ions. Thus in this case neither of the 



carbon atoms would become active chemically while 



in combination. 



Profs. Lapworth and Robinson object also that the 

 effect of electrostatic induction would only be manifest 

 at the beginning and end of a chain, that there 

 would be no poles in intermediate positions. It is, 

 however, only when the chain is entirely uniform 

 that the evidences of polarity would be restricted 

 to its ends. To take a very crude illustration : if 

 we have a number of cubes of soft iron and place 

 them face to face so as to form a uniform bar ABCDEF, 



then if this were placed in a magnetic field where 

 the force is parallel to the bar, the poles would be 

 at or near the ends. If, however, they were arranged 

 in diamond fashion, 



1> 



4 



there would be a series of consecutive poles at equal 

 mtervals along the chain. If they were arranged like 



there would again be consecutive poles, but the 

 mtervals would be different. With regard to the 

 objection that my theory- involves Kekul^'s structure 

 for the benzene ring, I used this structure in mv paper 

 because it was the simplest and most definite. But 



NO. 2823, VOL. 112] 



unless all the carbon atoms in the ring axe suppos- 1 

 to be the same* in all respects, almost any tbe<>: 

 would, 1 think, lead to analogous results. 



Again, Profs. lapworth and Robinson say th^ 

 according to the theory given in my paper, wli- 

 vinyl chloride is actecl upon by hydrochloric a' ' 

 the result should be C1H,C - CH,C1 and not, as I s. 

 H,C-CHC1.. I cannot agree with this at all I 

 effect of substituting CI for H is on tl>' 



?roduce an electric field which attracts u- 

 his, it is true, will extend to the (.ir! 

 vinyl chloride which is not chloriii;i • i i 

 it more likely to attract a chlorine at. :: ;• ., 

 before the chlorine wa.s introduc < 1 H ;; a . : 

 another CI atom is introducetj into tlu molccuic ti,. 

 carbon atom to which it goes is determined not h\ 

 the absolute value of the attraction in f>"i- i.;.rt ,.f ♦■ , 

 field but by the difference in the 

 CI atom will go to the part of the 

 attraction is greatest, and this will be the part < i 

 the field nearest to the chlorine atom which is li,' 

 origin of the attraction, so that the new chlorn.-- 

 atom will go to the carbon atom which is in th 

 part of the field ; that is, it will go to the 

 atom already chlorinated. J. J. Tho.m 



Trinity I^ge, Cambridge, 

 November 19. 



Experiments on Ciona and Alytes. 



In Nature of November 3, page 653, Mr. H. 

 Munro Fox announces that he aid not succe«l in 

 repeating my results in his Ciona experiments m 

 Roscoff : amputated siphons regainecf only their 

 normal length. Mr. Fox supposes that the extri 

 growth in length of the siphons in my experiment- 

 was produced by extravagant feeding, and not h\ 

 the regenerative activities of the animals. 



Before Mr. Fox publishes the full account of h: 

 work, which he promises, I beg him to note th- 

 following facts, namely : 



(i) The two principal cultures (operated an ! 

 control) of my Ciona were placed at the same tim- 

 and at the same stage of development, with tin 

 same provision of food, in two precisely similar 

 aquaria, which stood beside each other. The dimen 

 sions of these aquaria were 300 x 170 x 100 centi 

 metres. I did not undertake a quantitative estima 

 tion of the number of micro-organisms present ; but 

 the food available was, so far as I could see, rather 

 on the scanty than on the abundant side. 



All the specimens in the control culture possesses 1 

 short siphons, and therefore the influence of food 

 on the length of siphon is excluded. 



(2) I am not the first and only observer who has 

 noted the " super-regeneration " of the siphons after 

 they have been cut off several times. Mingazzini ' 

 asserts that siphons amputated three or four times 

 at intervals of a month became longer after each 

 regeneration Mingazzini was able in this way to pro- 

 duce artificially the local variety, " macrosiphonica," 

 found in the Gulf of Naples. ' I fully anticipated 

 that the decisive experiment on regeneration and 

 inheritance in Ciona would encounter violent 

 contradiction. On that account I took care lo 

 construct this critical experiment out of experiment- 

 which had already been made by other investigators. 

 That this was possible in the case of Ciona was one 

 of the reasons which led me to choose this sp)ecies 

 Indeed, I have had a predecessor (E. Schulz) also 

 on the question of the regeneration of the " Keim 

 plasma " out of somatic material, though his experi- 

 ments were made not on Ciona but on a; ' 



• " Sulla regenerazione nei Tunicata," Bolletino Soc. Nat. Nap 

 I., year 5, 1891. (An abstract of this paper appeared in th 

 Zoologisclur Jakresberickt for 1891 under the bead " Tunicata." 



