Syo 



NATURE 



[December 15. 1923 



i,i ;, .... ;... .. 



rotn|Mirative dctcrn 



T'- ' '*■; which i, ;.,,. 



( ill- .iliph.itir all ohi ., 



i.itt (1 I'.iiiviilfnt 

 iiiMi-.uur .,\.\\.>., sU' Ji a-. i)iii.i.s.su;m ciilnride, do not. The 

 rrsiilt>i <«l>tain«-«l hv K«'nrirk have Ix-cn much extended 

 by an ■:,() (Hit with thr ^ainc t\)if of 



nppai.i ■ iiorwalilson in in>.- lali'iraturx-. 



The gcmnii jiMill iH these ex|Krni! • i d 



in the followini: terms : 

 Consider tin .\ .tem : 



v\ 



olution of 

 iic. = <-) 

 A 



Air 



Aqueous sol 11 lion of 



KCl (COIK . () 



B 



'I'lic positive potential of A will lie ((pial to that of T>. 

 It \w now add to the solution i; a .>inall fiuantil\- ol a 

 substance S (generally a non electrolyte or weak 

 tlertrolyte) which has a stion- tnulency to concentrate 

 at till' air H interface, it is found that thr [)ositivc 

 j)ot(iiti.il ol A rises markedly aho\c ih.u ol 1!. iln- 

 \alue ol the (|uaiitit\. positive potential of A minus 

 that of H. \ar\inu with the concentration of S in the 

 way that is charai tcri^iir of adsorption phenomena. 

 What is the interpnlation ol this phenomenon ? 



Quincke has shown thai a bubble of air in water 

 placed in an electrical j)otential gradient travels towards 

 the anode — i.e. the bubljle fiehaves as it it wm 

 negatively charged. From this it would follow that 

 the P.D. at the air-water interface is such that the 

 negative half lies t( twards the air side. As an electrolyte 

 such as potassium chloride is negatively adsorbed at 

 an air li(iuid surface, it is probable that a P.D. of the 

 chatat icr indicated by Quincke's experiment exists 

 at the A-air interface. If we accc])i this conclusion, 

 it follows that the effect of S is markedly to reduce 

 this P.D. (or to reverse it). Xow the P.D. at the air- 

 water interface is prohaltK due to the existence of a 

 doublr layer containin- ludrowl ions on the outside 

 and hydrogen ions on the inside, or to oriented water 

 molecules regarded as electrical bi-poles. If S is a non- 



of t/as liuliblf 



run., p.ir.i 

 of water. II 

 These results 

 those nbtainr 

 th«M. 

 ful . ■ 



a substance which possesses lit 

 • an understand whv its << 



r could result in ' 



last few years H. A. McTai^' 



experiments on the electnc < .ii.iimoi. 



^ in aqueous solutions and other liquii 



' aliphalie a( ids and al<oht)Is in aqueo 



■ the surface I'.l)., anfl that this efic 



1 uith their influence on the su- 



lie also finds that acids redi; 



•led a.s a corroijoi 

 -McTaggart ha^; fo'; 

 1 ri- and tetravalent cati 

 t only reducing but e 



power- 



11- tlic- 



P.D. (/.'. tlie bubble becomes positive! 



experiments also show that polyvahi.^ .. _ , 



such as the ferrocyanide ion, a< t in the opposite direc- 

 tion to the poly\alent cations — i.e. they increase the 

 nc-ati\c ( hari;e on the bubble or dimini.sh a previously 

 existing positi\i- one. 



The subjects which I ha\-e lieen di.icu- -lu 



intere^tinLi bearini,' on tli<- formation and stubUity of 

 loaius and iioths. It air be violently churned up with 

 Water, only comparati\ cK large bubbles are produced, 

 and these quickly rise to the surface and burst. If 

 now a \txy small quantity of a substance which con- 

 centrates at the air-water interface be added an iilmo>t 

 milk-white " air emulsion " of small bu' 

 duced, which rise to the surface and produ' i ,...,.;.. . . 

 ihirabje froth. It i> clear that the diminutioji in inter- 

 facial tension facilitates the sul)division or dispers.d 

 of the air. The existence of the surface layer will al-^ » 

 confer a certain amount of stability on the resultant 

 froth, since it will -i\e ri>e to forces which resist the 

 thinning of a bubble w.dl. .\ny sudden increase in 

 the surface will produce a momentiir\" diminution in 

 the concentration or '" thickness " of the surface layer, 

 and hence a rise in surface tension, which will persist 

 until the normal thickness or coiKcntration i~ readjusted 

 by diffusion of molecules from the i'i-'<^ • ilume — a 

 process which in \erv dihitc ,-olv.t!- '"upy a 



perceptible time. 



(To he contintted.) 



Obit 



Dr. .Vi.f.xaxder Gleichen. 

 '^yHE sudden and unexpected death of Dr. Alexander 

 ■■- Gleichen on October 2i is reported from Berlin. 

 Bom at Niederschonwcide on September 23, 1862, 

 Dr. Gleichen coinnienced hi.s hi.:her education at the 

 Neu-Ruppiner Academy, and later studied mathematics 

 and natural philosophy at the University of Berlin. 

 After passing his final examination at the University 

 of Kiel, he became an assistant and then a head teacher 

 at the Kaiser-VVilhelm Academy. At the same time 

 he acted as " Privatdozent " at the Technical High 

 School of Charlottenburg, where he lectured upon 

 geometrical optics, a subject with which his name will 

 always be associated. He also lectured upon mathe- 

 matics at the Helene Lange College for Women. 



Dr. Gleichen's academic career terminated in 1904, 

 when he was called to the German Patent Office, with 



NO. 2824. VOL. 1 12] 



u a ry. 



which he was connected until the end of 1 " ;le 



thus occui)itd. he was able to produce tin ur 



Optik. aiui later to act as editor of the scicntilic and 

 technical sections of the ojitical and mechanical central 

 journal. From 1910 until his death Dr. (ileichen was 

 engaged in the scientitic work of the C. P. Goerz 

 o])tical establishment, where the opportunity was 



attorded him "' ou-ilx in - li;< vn,>, i:d l-n,,\vlcd./e of 



ophthalmic \\ r- 



increasing deiiKiMu:- >>i ^..v -,k. w, u .:i..,.- 

 Beyond Germany. Dr. Cileichen is best 

 writer of optical text-books of particular \ai le to me 

 student whose object it may be later to apply his 

 knowledge to the practice of the art. This combination 

 of theor>' and practice is most marked in his " Schule 

 der Optik," published in 1914. and in his " Theorie der 

 modemen optischen Instrumente " of 191 1. The latter 



