3o8 



NA TURE 



{Feb. 19, 1874 



THE INDUCTION TUBE OF W.SIEMENS 



A TRANSLATION from a French periodical, La Na- 

 ture, of an article on " Tubes for silent electrical dis- 

 charges,"appearsinNATUREofJan.29(vol.ix.p. 244). After 

 referring to the action of the electric spark upon oxygen 

 gas, the author of the article continues : '' For the pur- 

 pose of more easily obtaining ozone, 1\I. Houzeau has 

 recently constructed an apparatus worked by a Ruhmkorff 

 coil, in which there are no longer sparks, but only dark 

 discharges— (;/J7«7'/(j— far more efficacious in the pro- 

 duction°of modified oxygen." Again, it is said, that M. 

 Houzeau "has recently devised an apparatus for the 

 preparation of ozone, which is spreading rapidly among 

 the laboratories, and which has already yielded very re- 

 markable results." A description of the apparatus is then 

 given ; further on, it is said, that " i\l. Houzeau is not the 

 only one who has made use of the tubes whose structure 

 he has made known, but that M. Boillot a writer, it 

 appears," well known to the readers of the ISlouitetir, " has 

 made some further propositions about them ; and lastly, 

 that M. A. Th^nard" (whose investigations constitute the 

 main subject of the article) " has brought to bear on the 

 construction of the tubes a further modification which 

 makes them still more efficacious." A description and 

 drawing of the apparatus of M. A. Thenard is given. 

 Those who are unacquainted with the facts of the case 

 will be surprised to learn that the invention thus publicly 

 announced, although, doubtless, in principle deserving of 

 the highest praise, was not made either by M. Houzeau, 

 ]\I. BotUot, or M. A. Tht^nard, but is simply a somewhat 

 clumsy form of the Induction-tube devised by W. Siemens, 

 which is described in his " Memoir on Electrostatic In- 

 duction," contained in Poggcndorff's Annaleii, for 1857 

 (vol. cii. p. 120). 



This Induction-tube is one of the iiiost remarkable, as 

 well as simple instruments, of chemical research which 

 has ever been devised ; enabling us, by the action of 

 electricity, to effect changes in the composition of gases 

 which may be compared with the chemical changes 

 effected in liquids by the agency of the voltaic battery. 

 A few words in explanation of the instrument may in- 

 terest the readers of Nature. 



The simplest form of induction-apparatus consists in 

 two thin glass plates, of which one side is coated with 

 tin-foil, and which are so arranged that the uncovered 

 surfaces are parallel to one another, and separated by a 

 uniform, narrow interval of about one or two milli- 

 metres filled, say, with air. If this apparatus be charged 

 with electricity by a sufficiently charged Lcyden jar, at the 

 moment of the charge the air between the plates becomes 

 luminous, and the same appearance is presented when 

 the apparatus is discharged. To produce this effect, 

 however, the apparatus must be charged beyond a certain 

 limit, determined, in each case, by the special arrangement 

 of the apparatus and the materials employed in its con- 

 struction. Now, if the two plates of tin-foil be respec- 

 tively connected with the terminals of a powerful Ruhm- 

 korff 's coil, the apparatus is successively charged with 

 electricity and discharged ; these operations being alter- 

 nately repeated in such rapid succession that the air, in 

 the interval between the plates, appears permanently 

 luminous. We have, moreover, evidence of the occurrence 

 in this interval of chemical changes determined by the 

 electric action, in the odour and characteristic properties 

 of ozone which may be recognised in a current of air or 

 oxygen compelled to pass between the plates. The con- 

 clusion drawn by Siemens from this experiment is, 

 that the electric polarisation of the particles of a 

 dielectric cannot be carried beyond a certain point ; 

 and that if it be attempted to accumulate electricity 

 in the apparatus beyond this point, the excess of this 

 tension or polarisation appears in the form of the 



dynamical phenomena occurring between the plates, 

 namely, light, heat, and chemical 



change. (Pos;gciidorff's Annalcii, 

 he. cit., p. 1 19). 



Now it is evident that in this 

 arrangement the two sheets of glass 

 may be replaced by two concentric 

 cylinders of glass, the interior of the 

 inner cylinder and the exterior of 

 the outer cyhnder being coated with 

 tin-foii, as in the case of the plates. 

 It is precisely this change which 

 is effected in the induction-tube of 

 Siemens, but with the additional 

 advantage that in the induction- 

 tube a regular flow of the gas to be 

 operated upon may be maintained, 

 that the experiment may be made 

 at any required temperature, and 

 the gaseous products of the experi- 

 ment collected for examination. 

 The construction of this induction- 

 tube will be readily understood 

 from the annexed drawing (taken 

 from Fogg. Ann. loc. cit.), where 

 the ring shows the horizontal sec- 

 tion of the tube. 



If the reader will be at the 

 trouble of comparing the descrip- 

 tion of the tube of M. Houzeau 

 and the drawing of the tube of M. 

 A. Thenard, with the description 

 and drawing of the induction-tube 

 of Siemens he will be satisfied of 

 the substantial identity, both in 

 principle and construction, of these 

 pretended novelties with that inven- 

 tion. At the same time if the 

 statement of these ridiculous pre- 

 tensions were limited to those made 

 in the article translated in NATURE, 

 vol. ix. p. 244, they would hardly 

 be worthy of notice, but this is not 

 quite the case. The induction-tube 

 of Siemens under the title of " the 

 tube of M. Houzeau," is being 

 rapidly acclimatised as a French 

 discovery. In the article on ozone 

 contained in a recent number of 

 the " Dictionnaire de Chimie," 

 which bears evidence of being the work of a highly 

 competent writer, where we might expect to find a compre- 

 hensive treatment of the subject, a similar lapse occurs. 

 We have there, too, a drawing of the tube of M. Houzeau, 

 which is described as " a happy modification of the tube of 

 M. Babo," but not a word is said about Siemens, the in- 

 ventor of the tube, whose name is simply dropped. Other 

 similar instances might be brought forward which have 

 afforded an opportunity of rectifying these mistakes, but 

 of which no advantage has been taken. I have therefore 

 ventured to make these remarks, not only I may say in 

 the interest of justice, but also, having myself made 

 many experiments with the induction-tube of Siemens, 

 I have learned, perhaps, more than others to appreciate 

 its value and feel myself under a special debt of gratitude 

 to the inventor. B. C. Brodie 



RECENT RESEARCHES ON TERMITES AND 

 HONEY-BEES 



THE accompanying letter, just received from Fritz 

 Miiller, in Southern Brazil, is so interesting that it 

 appears to me well worth publishing in Nature. His 

 discovery of the two sexually mature forms of Termites, 



S.i ACTUAL Size 



