October io, 1907] 



NA TURE 



589 



The Origin of Radium. 



In an earlier communication to Nature (September 26, 

 p. 544) I mentioned some experimental proof which had 

 been obtained of the existence in uranium minerals of a 

 new radio-active element differing from those which have 

 previously been identified. More conclusive evidence of the 

 individuality of this new substance has now been obtained 

 through the examination of the properties of its o radi- 

 ation. The a. rays which it emits are much more readily 

 absorbed by aluminium than the a rays from polonium, 

 with which it has been directly compared. Their apparent 

 range in air determined by the scintillation method is less 

 than 3 centimetres, and a more accurate determination is 

 somewhat difficult, since it has not yet been found possible 

 to obtain the new substance entirely free from thorium. 

 Certain operations are now being carried out with con- 

 siderable quantities of a uranium mineral containing no 

 thorium which it is hoped will result in the separation of a 

 highly active preparation of the new body free from other 

 radio-active substances. The short range of the a. particles 

 is, however, sufficiently characteristic to serve as a definite 

 means of identification. 



The new substancf also gives out a 3 radiation which 

 is much less penetrating and more easily absorbed than 

 that from uranium, the value found for the coefficient of 

 absorption being about i-8 for aluminium. 



Experiments which have been carried out with the view 

 of obtaining a quantitative separation of this new element 

 from small quantities of very pure uraninite have given 

 results which are in good agreement with one another, and 

 which indicate that the activity of the new element in 

 equilibrium with radium is about 0-8 of the activity of the 

 radium itself with which it is associated. This is about 

 the value to be expected if the new substance is inter- 

 mediate between uranium and radium when the ranges of 

 the a particles are taken into consideration. 



The name " ionium " is proposed for this new sub- 

 stance, a naine derived from the word " ion." This name 

 is thought to be appropriate because of the ionising action 

 possessed by this element in common with the other 

 elements which emit a radiations. 



Bertram B. Boltwood. 



Sloane L.aboratory, Yale University, New Haven, 

 Conn., September 27. 



Excretion from Plant Roots. 



This subject, discussed at intervals over the greater 

 part of a century, has been recently revived. Mr. Picker- 

 ing has suggested that the effect produced by one plant 

 on another is probably due to the indirect action of 

 bacteria. Dr. Russell attributes it to chemical changes 

 in the soil, whilst Schreiner and Reed in America 

 (Bulletin of the Torrey Botanical Club, June) and Mr. 

 Fletcher in India have described experiments tending to 

 show that some deleterious substance is excreted from the 

 root. The questions incidentally raised by these several 

 experimenters are not all identical, because, as Mr. 

 Pickering points out, his work has to do with initial 

 stages of growth, while that of others relates to sub- 

 sequent development. 



So far as excretion is concerned, it seems to be almost 

 excluded as a possible explanation, because it would 

 demand open orifices in the root which do not e.xist. 

 There is nevertheless another line of thought which may 

 have a more likely bearing on the subject. I refer to 

 ionised changes such as occur when hydrogen chloride 

 forms inside the red-blood corpuscle and sodium carbonate 

 on the outside, or when sodium hydrate forms in the 

 blood and hydrogen chloride in the stomach. Both these 

 changes are due to the selective power of the living cell 

 wall : and similarly it is probable that the cell wall of 

 the root exercises a like property, and that the substances 

 called plant foods do not pass into the root cell as such, 

 but suffer change. Thus it is explained why the liquid 

 outside the root becomes more basic, that on the inside 

 more acidic (Hall and Miller, Proc. Rov. Soc. 1005). 



May it not be eaually possible that, owing to such 

 changes, harmful substances may be formed in the soil 

 solution? J. Walter Le.^ther. 



.Agricultural Research Institute, Pusa, Bengal. 



NO. 1980, VOL. y6'] 



Pleochroic Halos. 



In the March number of the Philosophical Magazine I 

 gave reasons for believing that the pleochroic halos of 

 certain micas are referable to the radio-activity of the 

 enclosures which are invariably associated with the halos. 

 I cited in favour of this view the facts that all minerals 

 definitely recognisable as forming the centres of halos are 

 radio-active ; that the perfect sphericity of the halo in a 

 medium such as mica precluded any explanatjon involving 

 diffusion or segregation of colouring matter, and that 

 there was a very exact agreement between the known 

 effective penetrability of a rays in media of this density 

 and the maximum radius attained by the halo. I sub- 

 sequently found, by examination of specimens kindly lent 

 to me by Dr. Teall, that the san-.e reasoning was applic- 

 able to halos formed in cordierite. 



When first conceiving this idea, I started experiments 

 on cleavage flakes of biotite to ascertain if halos could be 

 induced by enclosing between the flakes specks of radium 

 bromide. For some two months I kept these preparations 

 under observation, but no change was apparent. They 

 were then put aside in view of experiments which necessi- 

 tated my abstention from any contact with radio-active 

 preparations. 



Within the last few days Dr. Teall has directed my 

 attention to the (independent) work of O. Mijgge, of 

 Konigsberg i. Pr., which appears in the July number of 

 Centralbl. fiir Mill., in which a coloration was success- 

 fully induced in cordierite by application of radium, a 

 coloration agreeing in properties with the halos in 

 cordierite. This sent me back to my slides, and I find 

 that a brown coloration has now developed around the 

 larger radium specks. These stains have all the appear- 

 ance of halos save that the radius is greater and the 

 boundary less defined, differences at once explicable on 

 the fact that the rays here travel in air before entering 

 the mineral, and hence possess a greater, and at the 

 same time a less sharply defined, range of effectiveness. 

 The coloration is faintly pleochroic, the direction of 

 greatest absorption agreeing with that of some naturally 

 occurring halos present in the flakes. 



There is, of course, nothing in these observations to 

 prove that the effects observed are obtained in the precise 

 manner in which radio-active enclosures appear 10 affect 

 mica. It may be that sufficiently intense $ radiation may 

 produce effects which in the mineral are almost certainly 

 referable to a rays. Still more protracted observations will 

 be required to differentiate between the rays. However 

 this mav be, the cumulative evidence seems to leave no 

 room for doubt that these extraordinary halos are indeed 

 due to radio-activity. In these halos we have, I believe, 

 the onlv instance so far observed in nature in which the 

 presence of radium can be determined by direct eye 

 observation of a radio-active effect. J. Joly. 



Geological Laboratory. Trinity College, Dublin, 

 September 30. 



Apus cancriformis in Great Britain. 



Since the publication of Baird's " Natural History of 

 the British Entomostraca " (1850), no record of the occur- 

 rence of Apus cancriformis in the British Isles has, so 

 far as I am aware, been published. Mr. Scourfield, in 

 his " Synopsis of the British Fresh-water Entomostraca " 

 (Journ. Quekett Micr. Club, [2], ix., 1904), remarks of 

 this species : — " it is doubtful whether this ought to be 

 included in any modern list of British Entomostraca." 



It is therefore of great interest to know that Apus 

 cancriformis, so long lost to observation, has actually re- 

 appeared in this country. It was found, during last 

 month, by my friend Mr. Frank Balfour Browne, in some 

 numbers in two small shallow pools on Preston Merse, 

 near Southwick, in Kircudbrightshire. These pools, he 

 believes, may be somewhat brackish, as they are probably 

 occasionally covered by the sea. The specimens which 

 he was good enough to send me were all females, mostly 

 of a good size, and bearing eggs. 



Robert Gurnev. 



Sutton Broad Laboratory, Catfield, Great Yarmouth. 

 October 6. 



