262 



NA TURE 



[July 13, 1893 



series of readings for the determination of the throw with 55 cm. 

 water with reference to 40 ctn. will serve. The series is taken 

 quite at random from the others. 



40 cm. 55 cm. 



46 II-4 



4 9 

 5-0 

 4-2 



4 3 

 39 

 40 



4-3 

 46 



4 '4 

 4-5 

 4-6 



ir 4 

 ir'o 

 irg 

 11-5 



II '2 



11-6 

 II -4 



io'4 



II -2 



io'4 



lO'O 



The readings are grouped separately, but it will be under- 

 stood that they were taken in piirs alternately. 



The complete results are given in the curve (Fig. 2). It is 

 seen that for such a poor conductor as distilled water the inter- 

 ference completely masks the absorption effects. The intensity 

 of the transmitted ray does not sleadliy decrease; on the con- 

 trary, far more may be transmitted through a thick than through 

 a thin layer of the absorbent medium. The transmission follows 

 the same general law as for light with a thin plate ; we are, in 

 fact, dealing with a "thin" plate — a plate whose thickness is 

 comparable with the wave-length. The intensity of the trans- 

 mitted ray is a minimum for a plate \K thick, a maximum for \K 

 thick, a minimum again for \k, and so on. 



The points on the curve round the maximum at \\ are some- 

 what irregular, and the two maxima do not absolutely agree. 



Excluding the Russian physicist as a negligible majority, it 

 will ht seen that my value of k is somewhat low. The cause 

 may lie in the fact that not the whole of the field surrounding 

 the wires lies in the water. 



The uncertainty due to this stray field might be easily 

 avoided in one way, namely, by making one wire into a 

 tube surrounding ihe other, and using this tube also as the 

 jar for the electrolyte. This was, in fact, the arrangement 

 originally intended to be adopted. Several disadvantaees 

 attended it, however, and led to its final rejection in favour of the 

 simple wires and glass jar. First, such a condenser reflects 

 under all circumstances a considerable portion of the incident 

 energy.' Secondly, the vaiiation of the position of the top 

 surface of the electrolyte relatively to the top of the jar would 

 intiodiice fresh interference phenomena. This appeared directly 

 from the work of Mr. Barton to which I have already had 

 occasion to refer. Lastly, the large surface of metal in contact 

 with the Hquid would render distilled water rapidly impure. 



This investigation was carried out in the Physical Institute of 

 the Uiiiver-ity of Bjnn. I desire particularly to express my 

 thanks to Prof. Hertz for his most useful advice and suggestions. 



Chemical Society, June i. — Dr. Armstrong, President, in 

 the chair. The following papers were read: — On azi-com- 

 pounds of the ortho-series, by R. Meldola, E. M. Hawkins, 

 and F. B. Burls. The constitution of the orthazo-compourds is 

 still unsolved owing to the contradictory results obtained by 

 different investigators using different method?. The azo-3' 

 naphthoic have been represented by the formulDe X . NH . N : 

 CioHg : O and X . N^ . CjoH^ . OH. The principal evidence 

 in favour of the former hydrazone formula was furnished by 

 Goldschmidt and Brubacher ; it is, however, rendered invalid 



Taking the mean, we may say the wave-lengths in air and water 

 are respectively :— 



A» = 900. A„ = io8 cm. 



This gives us for the coefficient of refraction and the dielectric 

 constant — 



« = 8-33. K = 69-5. 



The following are the values of K found by previous investi- 

 gators, all that are known to me : — 



Method usecl. 



Alternated cnrre 



Ruhmkorff coil 



nts \ 



Authority. 



Heerwagen ' 

 Rosa'' ... . 

 Rosa ^ ... 



79-56 

 7570 

 70 'OO 



Cohn and Arons * 

 Tereschin^ 



Hertz oscillations .. 



Cohn" ... . 

 EUinger ' 

 Itschegtiaeflf^ 



76 00 

 83-80 



7350 

 81 -oo 



17s 



1 IVied. Ann., vol xlvlii, p. 35, 1893. 5 rtid., vol. xx -vi. p. 792. 1889. 



- f'''!' Mftg., vol. xxxi. p 200, 1891. li Ibid., vjl. xlv. p. p. 370, 1892. 



» Ibid., vol. xxxiv. p. 3^4. 1892. i" Ibid., vol. xlvi. p. 513, 1892. 



< Wied. Ann., yX xxxiii. p. 13, 188S. 8 phil. Mag., vol. xxxiv. p. 3S8, 1 



NO 



1237 



VOL. 48] 



by the authors' experiments. On reduciny an acetyl derivative 

 of the form X . N^ . Ci„H6 . OCoHjO or X . N(CjH30) . N : 

 CjoHg : O with zinc dust and acetic acid, four products result, 

 viz. :^X . NH . CoHjO, C,„Hi,(NH . C^HjO) . OH/3, X . NHj 

 and CjdHg . NH2 . OH6. — The production of a fluorescein from 

 camphoric anhydride, by J. N. Collie. On heating camphoric 

 anhydride with resorcinol and a small quantity of zinc chloride 

 at 180°, a fluorescein is obtained having the c:imposition 

 C22H22O5 ; it is a reddish powder with a greenish lustre and 

 shows a beautiful green fluorescence in dilute aqueous solutions. 

 — Researches on the terpenes, HI. The action of phosphorous 

 pentachloride on camphene, by J. E. Marsh and J. A. Gardner. 

 Camphene and phosphorus pentachloride interact at ordinary 

 temperatures, yielding a compound of the composition 

 CjoHjsPClj ; on treatment with water a product is obtained 

 from which two crystalline isomeric camphenephosphonic ,acid=, 

 C10H15PO3H2. have been isolated. On heating camphene with 

 phosphorus pentachloride, a crystalline substance, CjdHj^PCIj 

 is obtained ; on treating this with sodium carbonate, a salt of 

 the composition C]0Hj4ClPO2NaH results, whilst on oxidation 

 it yields chlorocamphenephosphonic acid, CjoHijCIPOaHo.— 

 The composition of a specimen of jute fibre produced in England, 

 by A. Pears, junr. — Note on the combination of dry gases, by 

 W. Ramsay. In connection with the results recently obtained 

 by Baker, the author states that in 1886 he recorded the fact 

 that dry hydrogen chloride does not combine with dry ammmia, 

 even in presence of solid ammonium chloride. — Ortho-, para-, 

 and peri-disulphonic derivatives of naphthalene, by H. E. Arm- 



^ J. Ritter voii Geitler, Doctor-Dissertation, Bonn, Jan., 1S93. 



