544 



NA TURE 



[October 21, 1922 



be designated as polar and non-polar. The polar 

 character of the valency in the majority of salts is 

 definite ; there is experimental evidence for the 

 transference of electrons in these substances. The 

 non-polar forces are particularly in evidence in the 

 linkings of organic compounds, and it is extremely 

 unlikely that transference takes place to an appreci- 

 able extent here. Without entering into a discussion 

 of the nature of the non-polar forces, which may be 

 electromagnetic, there are two explanations which 

 may be given of the undoubted positive and negative 

 relationships of groups in organic compounds. In 

 the first place, there may be a partial transference of 

 an electron between the group and the residue of 

 the molecule, or alternately there may be a varying 

 concentration of polar molecules in the typically 

 non-polar substance. 



I venture to put forward a plea for the considera- 

 tion of this second possibility. An equilibrium may 

 be imagined to exist between the polar and non-polar 

 substances which will be affected by the temperature, 

 solvent in which it is dissolved, etc. Thus, in an 

 organic substance AX the equation, 



AX^AX^AX 



may represent this kind of equilibrium, and the 

 more electronegative the group X the more will 

 this reaction proceed to the right. In those substances 

 where the stability of the non-polar arrangement is 



- + 

 very great, the occurrence of both forms, AX and 

 + - 



AX, will be possible, and in the presence of a suitable 

 solvent these may give rise to the respective ions. 

 This view is in agreement with the occurrence of a 

 group in some compounds with an electropositive, 

 and in others with an electronegative tendency. 

 The ease of replacement of the group X by another 

 group will be determined by the concentrations of 

 the polar body, the polar state being the active form 

 of the substance. These concentrations may be so 

 small as to escape the ordinary methods of measure- 

 ment, and yet be sufficiently great to explain the 

 velocity of the chemical action. 



W. E. Garner. 

 University College, Gower Street, W.C.i, 

 October 4. 



The X-ray Structure of Potassium Cyanide. 



Writing in a contemporary (J.A.C.S., Feb. 1922), 

 Richard M. Bozorth gives details of X-ray investiga- 

 tions into the crystalline structure of KCN, and 

 corroborates the view expressed in a letter to this 

 journal (Nature, Aug. 11, 1921, vol. 107, p. 745) 

 that the underlying structure is the face-centred cube. 

 He gives 6-55 A as the length of its edge, which agrees 

 very \\ ell with the 6-54 A furnished by my measure- 

 ments. He goes further in that he assigns definite 

 positions to the carbon and nitrogen atoms and 

 questions the opinion, expressed by Langmuir, that 

 these constituent atoms of the CN radicle have a 

 common outer electron shell. 



Bozorth's conclusions are, to a certain extent, 

 based on the assumption that the relative intensities 

 of the spectra would fall off in a normal manner if 

 the structure were quite like that of NaCl, that is, if 

 the carbon and nitrogen atoms formed a single cluster 

 of electrons which occupied the same position in the 

 KCN structure as the chlorine atom does in NaCl. 

 He publishes no numbers representing the observed 

 intensities, but gives 100 : 10 : 3 as the relative values 

 of the [100], [200], and [300] reflections that would 

 be required to satisfy the requirements of his par- 

 ticular structure. My own measurements gave 16-17 



NO. 2764, VOL. I io] 



as the relative value to be assigned to the [200] 

 reflection, and the corresponding figure for NaCl is 

 20. Now the fact that KCN has a lower fusing- 

 point than NaCl suggests that even at ordinary 

 temperatures the heat vibrations are of unusual 

 amplitude, and this in itself affords a ready explana- 

 tion of the fact that the intensities of the spectra die 

 away more rapidly than is normally the case. The 

 probable electron distribution in a composite CN 

 radicle is another important factor which would 

 cause the normal sequence to fall off rapidly. 



Bozorth gives 1-15 A as the distance between 

 the centres of the carbon and nitrogen atoms, and 

 3-0 A as the distance between either of these and 

 the potassium atom. He treats the carbon and 

 nitrogen atoms as though they were of the same size, 

 but he does not state whether or not the inter- 

 nuclei distance is to be taken also as the effective 

 diameter. In one case his figures would give 4-85 A 

 as the diameter of the potassium atom compared 

 with 4-15 A, which represents, probably to within 

 0-03 A, its value in the other ionised salts in which 

 it occurs (W. L. Bragg, Phil. Mag., Aug. 1920). 

 If, on the other hand, 4-15 A be accepted as its 

 diameter in KCN — and measurements on NaCN 

 justify this procedure — then Bozorth's figures would 

 give 1-85 A as the effective diameters of both carbon 

 and nitrogen ; W. L. Bragg's values are 1-54 A and 

 1-30 A respectively. 



Fortunately, there is outside evidence which bears 

 directly on this question. From viscositv measure- 

 ments A. O. Rankine has found (Proc. Roy. Soc, 

 July 1921) that the C 2 N 2 molecule behaves in collision 

 like two overlapping hard spheres, each having the 

 size of a bromine atom. The diameter of the bromine 

 atom is 2-38 A, and that of a Langmuir CN radicle, 

 as provided by X-ray measurements, is 2-39 A. 



P. A. Cooper. 



Research Dept., Royal Arsenal, Woolwich, 

 September 20. 



Sex Change in Mollusca. 



With reference to Dr. R. Sparck's statement 

 (Nature, October 7, p. 4S0) that the male stage in 

 the oyster is due to the coldness of the temperature, 

 it should be pointed out that in various hermaphrodite 

 mollusca, such as Helix and Arion, the reason for the 

 passage of the indifferent epithelial cell, either to 

 oogonium or spermatogonium, is at present unknown. 

 Older authors considered that those cells near yolk, 

 or near a superior nutrimental radius became eggs, and 

 that those less exposed to steady streams of nourish- 

 ment became spermatocytes. 



More recent work has shown that the matter is very 

 deep-seated, and such a conclusion as the above 

 cannot be taken as representing the real state of affairs. 

 I have found that oocytes appear in regions of the 

 ovotestis which are scantily provided with yolk, and 

 that sperm cells appear in regions rich in nutriment. 



Whether temperature has anything to do with this 

 has not yet been ascertained, but experiments are now 

 in progress, which should settle the question. 



In the case of Saccocirrus it has been shown that 



spermatocytes caught up and enclosed in yolk cells 



]i,i\ 1- 1 hi Lr metabolism so altered that thev assume the 



appearance of oocytes, together with nucleolar ex- 



t haracteristic of the typical oocyte. 



But in Helix two epithelial cells side by side often 

 metamorphose, one into an oogonium, another into a 

 spermatogonium, and one seems obliged to believe 

 that factors other than temperature or abundance of 

 nutriment are concerned. J. Bronte Gatexby. 



Trinity College, Dublin University, 

 October 7. 



