126 



NA TURE 



[June 6, 1907 



LETTERS TO THE EDITOR. 

 [The Editor does twt hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond -with the writers of, rejected 

 manuscripts intended for this or any other part of Nature 

 No notice is taken of anonymous communications.] 



The Origin of Radium. 



In a previous letter to Nature (January 17) I gave an 

 account of some experiments which I had made upon the 

 growth of radium in preparations of actinium. The results 

 obtained were in substantial agreement with the earlier 

 observations of Boltwood in this Journal (November 15, 

 1906), but it was pointed out that there was no definite 

 evidence that actinium itself was the true parent of radium. 

 The experimental results could be equally well explained 

 by supposing that the parent substance of radium was 

 ordinarily separated from radio-active ores with the 

 actinium, but had no direct radio-active connection with 

 the latter. 



Observations have been continued upon the growth of 

 radium in the actinium solution prepared in the manner 

 indicated in my first letter. The rate of growth was found 

 to be uniform over a period of 120 days, and to agree 

 •closely with the rate of growth observed in the solid pre- 

 paration of actinium which had been set aside for a period 

 of two and a half years. .Xnother sample of actinium was 

 then taken and successively precipitated with ammonium 

 sulphide in order to remove the radium from the solution. 

 In this way a solution of actinium was obtained initially 

 almost entirely free from radium. By examination of the 

 o-ray activity, it was found that the actinium after this 

 ■chemical treatment contained an excess of radio-actinium. 

 This was shown by the rise of the activity to twice its 

 initial value in about twenty days, and then a gradual 

 ■decay to a steady value. 'Special care was taken to 

 measure accurately the ratn of growth of radium in the 

 solution at short intervals in order to see whether it de- 

 pended in any way upon the variation of the activity. 

 No such connection was observed, for the radium was 

 produced at a constant rate over the whole period of 

 examination, viz. in days. 



For equal quantities of actinium, the rate of growth 

 of radium observed in this solution was 1.5 times greater 

 than the normal. Ihis indicated that onlv a portion of 

 the actinium had been precipitated, while the radium-pro- 

 ducing substance had been precipitated with the actinium 

 m excess of the normal amount. This conclusion was con- 

 firmed by an examination of the filtrates, which were found 

 to contain more than half the actinium. After suitable 

 chemical treatment, a small precipitate of actinium was 

 again obtained which was about one hundred times as 

 active, weight for weight, as the original preparation. This 

 actinium precipitate was dissolved in hydrochloric acid, 

 and observations of the amount of radium' in it were made 

 at regular intervals. No appreciable growth of radium 'di'as 

 observed over a period of eighty days. If there were anv 

 growth at all, it was certainly less than one two-hundredth 

 part of that normally to be expected. In order to make 

 certain that the absence of apparent growth of radium in 

 this solution could not be ascribed to the precipitation of 

 the radium in some non-emanating form, the solution was 

 again chemically treated. The actinium was precipitated 

 with ammonia and re-dissolved in hvdrothloric acid. 

 Again no growth was observed over the period of ex- 

 amination, viz. twenty days. The solution in its present 

 state contains a just measurable quantity of radium, viz. 

 about 2x10-'- gram. 



From these observations I think we may safely conclude 

 that, in the ordinary commercial preparations of actinium, 

 there exists a new substance which is slowlv transformed 

 into radium. This immediate parent of radium is 

 chemically quite distinct from actinium and radium and 

 their known products, and is capable of complete separ- 

 ation from them. 



It is not possible at present to decide definitely whether 

 this parent substance is a final product of the transform- 

 ation of actinium or not. It is not improbable that it mav 

 prove to be the long-looked-for intermediate product of slovv 

 transformation between uranium X and radium, but with 

 VO. 1962, VOL. 76] 



no direct radio-active connection with actinium. If this 

 be the case, the position of actinium in the radio-active 

 series still remains unsettled. 



It is intended to continue observations on the growth 

 of radium in the solutions described above. Experiments 

 are also in progress to isolate this new substance in order 

 to examine its chemical and radio-active properties. 



Manchester, May 30- E- Rutherford. 



The Structure of the Ether. 



I WELCOME the interesting and helpful letter from Dr. 

 O. W. Richardson, of Princeton, in Nature of May 23, 

 in which he adduces arguments against an ether flow 

 along magnetic lines of force, and in favour of a flow in 

 the direction of the Poynting vector EH. The result 

 comes out much the same, but it is probably a better way 

 of regarding the matter. Prof. Hicks also has given a 

 simple geometrical proof that a magnetic field cannot 

 consist solely of ether flow ; and I am referring to this 

 in a note, already printed, in the Phil. Mag. for June. 



We shall doubtless hear in due course from the mathe- 

 matical physicists to whom the first idea of a magnetic 

 ether flow is due, whether they are satisfied with the 

 modification of their original conception now introduced. 

 Meanwhile, I doubt if integration of momentum, without 

 regard to direction, can be sound. Oliver Lodge. 



Birmingham, May 28. 



Root Action and Bacteria. 



The remarkable and all but fatal effect of growing grass 

 over the roots of freshly planted apple trees has been 

 studied at the \\'oburn Experimental Fruit Farm since 

 i8()4, and formed the subject-matter of the third report 

 of that station (1903). No satisfactory explanation of the 

 action was obtained. Experiment showed that it could 

 not be attributed io the abstraction of food or moisture 

 from the soil by the grass, nor to the influence of the grass 

 on the soil temperature or on the gaseous contents of the 

 soil, and subsequent experiments have excluded the form- 

 ation of acid or alkali from the possible causes. The con- 

 clusion drawn was that the action was probably that of 

 a poison produced either directly by the grass or indirectly 

 through the agency of bacteria. Since the publication of 

 this report, further work has been done on the subject, 

 and the view that bacterial agency is concerned has be- 

 come much strengthened. The action is not confined to 

 ajiy particular grasses, nor to apple trees, but different 

 grasses and different kinds of trees act and suffer, re- 

 spectively, to different extents. The difference in the 

 results, however, produced by different soils are much more 

 conspicuous, especially in cases where trees are not grassed 

 over until a few years after they have been planted. 

 Though the deleterious action of grass may generally be 

 noticed throughout the country, many notable exceptions 

 have been met with, and these cannot be explained by 

 any of the patent characteristics of the soils in question. 

 \'arious pot experiments have been made which emphasise 

 these observations. Trees grown in earth in pots are 

 affected by grass in just the same way as they generally 

 are in the field, the grass reducing the growth and vigour 

 of the tree by at least 50 per cent. ; but if the trees are 

 grown in sand instead of earth (suitable nourishment being 

 supplied), the grass has very little effect on them, reducing 

 their vigour by about 5 per cent, to 10 per cent. only. 



Following up this and other observations, twenty-six 

 similar trees were planted in pots last February under 

 various conditions ; seventeen of them were in soil or sand 

 which had not been heated, and nine of them in soil which 

 had been sterilised, or partially sterilised, by heating to 

 about 200° C. and to 82*^ C. respectively, the water lost 

 •n the process being made good. Of the seventeen in 

 unsterilised material, al! started into growth uniformly at 

 the same time, whereas of the nine in sterilised soil two 

 •itarted about two days later, six did not start until at 

 least fourteen days later, and one has not started yet. 



The heating of the eartii, especially to the low tempera- 

 ture of 82°, cannot have appreciably affected its chemical 

 composition, and. indeid, the starting of a tree into growth 

 is independent of iiaui ishnient supplied to it, as is shown 



