278 



NATURE 



[October 27, 192 1 



established scientifically to information at present 

 only obtainable in newspaper reports. Emphasis 

 need not be laid on the obvious advantages of a 

 jihn sound-record over an ordinary mechanically 

 produced g-ramophone record. Combinations of 

 picture films and ordinary gramophones have 

 been frequently tried without success sufficient to 

 ensure their survival in practice. The difficulty, 

 of course, mainly arises from the impossibility of 

 preserving synchronism between a gramophone 

 record and a film the length of which is gradually 

 but inevitably shortened by the repairing of fre- 

 quent breakages. \\'ith the sound-record also 

 upon a film, the appropriate adjustment can 

 always be made, especially in the ideal case where 

 a single film bears both picture- and sound-records, 

 side by side, under which conditions it becomes 

 automatic. The arrangement of two separate 

 films, run both in recording and reproducing on 

 the same shaft, has, according to the Times 

 report, been adopted by Mr. Bergland ; Mr. 

 Grindell Matthews, on the other hand, announces 

 that he has been able, in spite of the small space 

 available, to secure the advantages of a single 

 film, a newspaper reproduction of which is given. 

 In neither case are the reported details complete 

 enough to indicate the actual mechanism em- 

 ployed. One point of somewhat curious interest 



seems, however, to be fairly definitely established. 

 An examination of the printed reproduction of 

 Mr. Grindell Matthews 's film shows that the sound- 

 record is of what may be called the ordinary type 

 — i.e. it consists of the trace of transverse move- 

 ments of a spot of light on a moving film, so 

 familiar in oscillograph and other wave-motion 

 records. A talk which the author was fortunate 

 enough to have recently with Prof. Arrhenius, 

 who was present at the first demonstration 

 of the new Swedish talking pictures, made it clear 

 that Mr. Bergland also relies on this same plan. 

 It is not easy to see how such transverse records 

 lend themselves to effective sound-reproduction. 

 On the face of it, they would appear to be 

 distinctly inferior for this purpose to the 

 records described and illustrated in this 

 article, and details of the manner in which 

 the selenium is actuated will be awaited with 

 interest. 



We have yet to learn also by what mechanism 

 synchronisation has been effected. For, although 

 the principle involved is very simple, and the 

 general method of procedure is quite obvious, 

 there have no doubt arisen in practice details 

 which present serious difficulties. We may hope 

 to hear before long what these are and how they 

 have been surmounted. 



The Oppau Explosion. 



THE directors of the Badische Anilin- und Soda- 

 fabrik state in the Zeitschrift fiir Ange- 

 luandte Chemic for October 4 that the explosion 

 at the nitrogen fixation works at Oppau on Sep- 

 tember 21 took place in a store containing about 

 4^00 tons of ammonium sulphate nitrate. They 

 explain that, before the war, only sulphate of am- 

 monia was made at Oppau ; ammonium nitrate 

 was manufactured during the war, and since then, 

 mixtures of ammonium nitrate and potassium 

 chloride, and more recently ammonium nitrate 

 and sulphate for use as fertilisers. They defi- 

 nitely state that no ammonium nitrate was present 

 in the works at Oppau at the time of the explo- 

 sion, and go on to say that while the explosive 

 nature of ammonium nitrate is well known, this 

 feature can be completely eliminated by mixing it 

 with potassium or sodium chlorides ; the double 

 salt, 2NH4N03-(NH4)2S04, had also been shown 

 to be non-explosive when pure as well as when it 

 is produced on the viorks scale. They proceed to 

 quote evidence as to the non-explosive character 

 of this salt from the fact that it gives no distension 

 in the Trauzl block test, when exploded by means 

 of a detonator containing 2 grams of mercury 

 fulminate, and in substantiation of its innocuous 

 character they adduce the fact that in factories 

 producing it no accident has occurred for a number 

 of years, when explosives have been applied to 

 it for the purpose of breaking up blocks of the 

 mixed salts which have set hard. They deny that 

 NO. 2713, VOL. 108] 



Oppau was completely destroyed, and say that 

 the portion of the factory devoted to the produc- 

 tion of ammonia from the air and of ammonium 

 sulphate is comparatively uninjured, so that the 

 manufacture could be started again, and they end 

 with an assurance that the production of ammonia 

 by high pressure as carried out by the Badische 

 Anilin- und Sodafabrik has nothing whatever to do 

 with the explosion. 



It may be remarked in connection with this 

 statement that no reference is made to experimen- 

 tal work on the explosive character of their pro- 

 duct on a larger scale than by attempting to fire 

 it by a No. 8 detonator in a Trauzl block. It is 

 known, however, to explosive technologists that 

 ammoniurn nitrate responds only feebly to such a 

 detonator, but that it can be brought up to detona- 

 tion by a suitably chosen initial impulse. 



The Times of October 12 gives an account of 

 some very remarkable evidence brought out at a 

 sitting of the German Parliamentary Committee 

 appointed by the Reichstag to inquire into the 

 explosion. It appears from the evidence that the 

 process was being worked intensively and without 

 adequate chemical control, and it is stated that in 

 the preparation of the ammonium sulphate nitrate 

 the ammonium nitrate was not always dissolved, 

 but passed on to the store as such. Evidence was 

 also given as to the fact that blasting was resorted 

 to for the purpose of breaking up the hardened 

 mass, and in a further report, published in the 



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