June lo, 1922] 



NATURE 



749 



To sum up the whole position, a teacher of biology 

 must be prepared to make his subject his life's work. 

 It is lamentable, however, that even in some of the 

 greatest of our public schools there is little room 

 for the progressive student. The chief form of 

 recognition or promotion consists of extra duty, and 

 it is just this extra duty that puts an end to the 

 "dea of study. If a man is to teach biology properly 

 e cannot hope to satisfy the demands of the head- 

 aster who looks for a colleague who will take an 

 tive part in the games of the school and a com- 

 jnission in the Corps, etc., and yet unless a man does 

 do these things his chances of success in the scholastic 

 world are poor. Of course things are improving 

 and the high standard of work demanded by uni- 

 versity scholarships is making the position of the 

 e teacher a more important one. 

 I do not think, however, that F. K. is quite just 

 hen he advocates a vigorous protest against the 

 inions of examiners. The universities are naturally 

 xious to get hold of the best boys available, and 

 ey are surel}^ the best men to select their material, 

 e know that all examinations are more or less 

 nsatisfactory, but they are the only possible method. 

 The chief fault lies in the lack of co-ordination 

 tween the university and the public school, and 

 s is not altogether the fault of the university. 



A. G. Lowndes. 



a-Farticles as Detonators. 



When an a-particle passes through matter it may 

 be considered that the matter in the proximity of the 

 path of the swiftly moving particle is momentarily 

 raised to a high temperature. Looked at in this light 

 the action of an a-particle may be likened to that of a 

 detonator and it may be possible to detonate a 

 sufficiently unstable substance by the action of these 

 particles. This has been found to be the case with 

 the familiar explosive compound, nitrogen iodide. 



The experiment forms a rather striking lecture 

 demonstration. Nitrogen iodide is prepared in the 

 usual way by the mixture of finely ground iodine and 

 strong ammonia and allowed to dry overnight in the 

 open air. On bringing a fairly strong radioactive 

 source (say the active deposit of radium) within 3 or 4 

 cms. of the compound the iodide explodes. It may 

 readily be shown by the use of screens of suitable 

 thickness placed over the source that the result is 

 due to a and not to ^ or other rays. 



Detonation is not caused by the first o-particle 

 which happens to strike the substance, but seems to 

 be a probabiUty effect. With a button of nitrogen 

 iodide of about o- 1 cm.** area a source of radium-C 

 equivalent in 7-ray activity to about 3 mg. of radium 

 placed I cm. away causes the button to explode in 

 about 20 seconds, i.e. when between 10' and 10* 

 a-particles have struck it. Increasing the size of the 

 button or the strength of the source decreases the time 

 necessary. Quantitative measurements are not very 

 accurate, as it is difficult to ensure identical conditions 

 of experiment. Doubtless other unstable compounds 

 might be found which would also be exploded in this 

 manner. G. H. Henderson. 



Cavendish Laboratory,' Cambridge, May 23. 



Active Hydrogen and Nitrogen. 



Two brief comments are suggested by the interest- 

 ing work of Dr. F. H. Newman on the activation of 

 hydrogen and nitrogen described in the Philosophical 



NO. 2745, VOL. 109] 



Magazine for March. The failure of the reaction pro- 

 duct of the active nitrogen with sulphur, phosphorus, 

 and iodine to give a test for nitrides is not evidence 

 of the absence of a chemical reaction between those 

 elements and nitrogen, for all three are more electro- 

 negative than nitrogen and the compounds formed 

 would be sulphides, phosphides, and iodides, re- 

 spectively. That this is in fact the case is shown 

 in some experiments of mine with Dr. A. C. Grubb, 

 which are now in process of publication, in which 

 tests for sulphides and phosphides were actually 

 obtained after exposing the corresponding elements 

 to a stream of active nitrogen formed in the 

 corona discharge. Our experiments did not include 

 iodine. 



Further, the evolution of gas when the bulb, in 

 which these same three elements had been exposed 

 to active hydrogen, was heated from -40° C. to 

 100° C. is not evidence of the failure of these elements 

 to react with the active hydrogen, for the compounds 

 formed would be hydrogen sulphide, phosphine, and 

 hydrogen iodide, all of which arfe gaseous at the 

 latter temperature though liquefied at the former, 

 and would thus be evolved in the gaseous form when 

 heated to increase the pressure as noted. Here 

 again my experiments with Dr. R. S. Landauer 

 and with Dr. William Duane, already published, 

 show that phosphine and hydrogen sulphide are 

 actually formed, the latter being confirmed by the 

 dynamic method of Dr. Newman. 



Gerald L. Wendt. 



Chicago, Illinois, U.S.A. 



In reply to the comments made by Prof. Wendt, 

 although no traces of the nitrides of sulphur, phos- 

 phorus, and iodine were found in. the experiments 

 on the activation of nitrogen, this was not unexpected, 

 as it was considered highly improbable that any 

 chemical compounds formed would respond to the 

 nitride test. As the absorbed gas was not rehberated 

 on heating, it appeared that chemical combination 

 had taken place, the compounds so produced being 

 very stable. Several other elements actually formed 

 nitrides with the active nitrogen. These two facts 

 suggested that chemical compounds were produced. 

 The experiments of Prof. Wendt, now in the course 

 of publication, seem to confirm this view. 



As regards the action of active hydrogen on these 

 three elements, it was found that at temperatures 

 above 0° C, absorption of the gas occurred, although 

 at a decreased rate. At these temperatures, if the 

 chemical products formed are hydrogen sulphide, 

 phosphine, and hydrogen iodide, they must be 

 present in the gaseous state. There are other factors 

 to be considered in order to account for the dis- 

 appearance of the hydrogen, for the production of 

 these gases will not explain the decrease in pressure. 

 They are probably " trapped " within the solid 

 present in the tube, and only reliberated on heating. 

 Some of the gas which was evolved on the application 

 of heat was re-absorbed when an electric discharge 

 was passed through it, or when exposed to a -ray 

 radiation. This re-absorbed gas was hydrogen, 

 which may have been produced by the dissociation 

 of the chemical compound formed originally, or it 

 may have disappeared originally by occlusion within 

 the solid. Although chemical action does account 

 for the disappearance of some of the hydrogen, 

 other processes, such as occlusion, have to be taken 

 into account. 



F, H. Newman. 



University College, Exeter. 



