722 



NATURE 



[November 17, 192. 



Letters to the Editor. 



\The luiitor does not hold himself responsible for 

 opinion:: expressed by his correspondents. Neither 

 can he undertake to returny nor to correspond with 

 the uiriters of, rejected manuscripts intended for 

 this or any other part of Naturk. No notice is 

 taken of anonymous communications.^ 



The Polarisation of Double Bonds. 



In the Septeml)er number of the Philosophical 

 Maf^azine Sir Joseph Thomson has appUed the theory 

 of electrostatic induction to explain the mechanism 

 of polarisation of double bonds and of the orientation 

 of suhstituents in the benzene series. 



Electrostatic induction is what we have imagined 

 to be resjwnsible for the " general " electrical effect 

 of a substituent by producing a kind of drift of 

 electrons in the molecule as shown in the scheme 



C'--^©i-+©2-+©8-+©4-+® 



and we have attributed the superposed alternating 

 polar effect to other causes, and predominantly to the 

 laws of valency in their application to polarised com- 

 plexes. In such a system as that depicted above, Sir 

 Joseph Thomson suggests (p. 511) that as the result 

 of the existence of the electrostatic doublet between CI 

 and C,, electrons will crowd into C, from Cj, and into 

 C3 from C4, and thus an alternating condition will be 

 brought about in the chain. But for the same reason 

 that electrons pass from C.j into Cj, it would seem to us 

 that electrons should also pass from Cj into C.,, and the 

 effect would then be continuous although diminishing 

 in degree along the chain. The precise manner in 

 which the difficulty is overcome is not quite clear, but 

 we gather that Sir Joseph Thomson holds that 

 electrons may pass from one carbon atom to another, 

 if these are joined by a double bond, but not if they 

 are joined by a single bond, which view would require 

 the acceptance of the Kekule benzene formula in its 

 simplest form, and would be contrary to all the indi- 

 cations of modem researches on the conjugation of 

 ethylenic groups and on intra-annular tautomerism. 



A much more obvious, though not more serious, 

 objection to Sir Joseph Thomson's method of de- 

 duction of the alternate effect is that while it leads to 

 the right result in fifty per cent, of the cases, it leads to 

 the wTong result in the remaining fifty per cent. For 

 example, the direction of polarisation of the double 

 bond in vinyl chloride, the example which Sir Joseph 

 Thomson himself selects, is just the opposite of what 

 experiment indicates. Thus, he provides the carbon 

 atom which is attached to the chlorine with a greater 

 density of electrons than the other, as indicated by the 

 symbol CH^ CH • CI, where the lower dotted line 



represents, say *• electrons, and the other represents 

 2. - X electrons, the whole symbol thus indicating an 

 augmented electronic density on that side of the 

 double bond which is nearest the chlorine atom and a 

 decreased density on the other carbon atom. 



Now, it is easy to see that this process tends to 

 produce a positive charge on the CH, carbon and a 

 negative charge elsewhere, and consequently the 

 carbon atom of the CH., group should, if anything, 

 attract negative ions, and the product of the action 

 of hydrogen chloride on vinyl chloride ought to be 

 ethylene dichloride CH.,C1 - CH.^C1. But, as Sir 

 Joseph Thomson correctly states on p. 508, it is the 

 carbon atom to which halogen is attached in a sub- 

 stituted ethylene which attracts negative ions. Were 

 it proposed to escape this dilemma by assuming that 

 the atom with the diminished density of electrons is 

 the one which is ultimately found attached to the 



NO. 2820, VOL. I 12] 



positive ion or radicle of the reactant, then further 

 difficulties emerge and. for example, in the grtjup 



Cj «= Cj - C. "5 O, it would be necessary to postuUi' 

 passage of electrons in the direction indicated In- 

 arrow in order to reconcile Sir Joseph Thoni-vi 

 theory of the mechanism of induction with the expt-n- 

 mental fact that invariably Cj is the atom which is 

 found attached to the negative radi- '•• -- "m of the 

 reactant. Without going into detail )us that 



similar considerations apply to or;c..i y.i in the 



benzene series. 



Finally, the classification of atoms as " chemically 

 active " or " chemically inert," according as there is a 

 defect or excess of electrons respectively, is unsatis- 

 factory, since both types appear to be reactive under 

 the correct conditions. Charged centres in polarised 

 molecules are analogous to charged ions and it is 

 difficult to see why the comparison should not be 

 extended to their reactions. A. Lapu 



R. RoBi 



The University, Manchester. 



River Pollution. 



The Salmon and Freshwater Fisheries Act, I'y-' v 

 will come into operation on January i next, replaciiii^ 

 the many Acts, beginning with that of i86i, which 

 have been framed to regulate the fisheries of our 

 inland waters. The first of the series contained a 

 clause relating to the pollution of rivers, and this 

 clause has up to now been practically the only 

 statutory control we have had. It was reinforced by 

 the River Pollution Prevention Acts, and thus legisla- 

 tion was sufficient to prevent sewage being p>oured in an 

 untreated state into rivers, but not into estuaries, and 

 it proved ineffective in preventing poisonous effluents 

 from industrial concerns contaminating both. 



The new Act defines rather better the nature of the 

 pollution which will be regarded as an offence (Section 

 8), empowers fishery boards to institute proceedings 

 under the River Pollution Prevention Acts, 1876 to 

 1893 (Section 55), and provides (Section 73) for cases 

 being tried before the nearest court of summary 

 jurisdiction. 



The rivers in the meantime have been allowed \o 

 get into a serious state of deterioration, due to the 

 great developments of population and of industries. 

 Our legislation hitherto has prevented any undue 

 contamination by sewage of the non-estuarine parts 

 of the rivers. It was really strong enough to prevent 

 pollution by effluents from commercial works. But 

 the dominance and importance of the industries have 

 been usually overpowering, with the result that many 

 of our rivers and streams have been allowed to get 

 so severely polluted that they are almost, or altogether, 

 devoid of life. The estuaries, with the growth of 

 industries and of towns and cities, have been exposed 

 to pollution from trade effluents to a greater extent 

 than the river, and have had to carr>' a steadily 

 growing burden of sewage. The result, as is well 

 known, is that some estuaries are so badly polluted 

 as to prevent the passage of migratory fish, and 

 many others have got near the same state. With 

 the advent of the new Act we have inherited an 

 interesting and important problem, a problem which, 

 like previous legislation, is a product of the industrial 

 growth of the Victorian p>eriod. 



Alreadv some progress has been made by experi^i 

 ment and inquirv to state more distinctly the problemf 

 and the solution. The Ministry of Agriculttire andi 

 Fisheries has shown its sympathy and its appreciatioDj 

 of the condition of the freshwater fisheries by appoint-| 

 ing a Standing Committee on Rivers Pollution, and! 



