776 



NA TURE 



[November 24. 1923 



upon the n ' rccognwed that 



the practic the realisation 



of such a stiicmc would be great. The Council, 

 however, eventually passed a resolution recording its 

 opinion that an increased knowlf ' ' the ocean 

 systems was not merely of scient > st but of 



practirn' ■••• ■ 't the exj<...i..vi.w(i hik! the 



loreca^ i affecting life btith m ilic 



sea anu w.. ........ .....i .such an investigation must 



necessarily be extended over many years, but that it 

 could usefully be initiated by a preliminary recon- 

 naissance on the lines suggested in the memorandum. 

 The Council therefore recommended the proposals 



to the fav. iteration of the govcrnmem 



and scieir us of all countries. In \' 



resolution tiH- ^ oimk n was careful to point out th. 

 such an unricrtnking as this went far beyond t! 

 limits both of its resources and of its ma- ' — 

 must be regarded as a distinct and world 

 prise. It affirmed, however, its readiness, r,... 

 proposal meet with adequate support, to umi 

 the general direction of the work Tt was geu -;.. 

 felt that there was no ot! ng organisati' 



equally competent. 



The next meeting of the Council will be held, 

 usual, in Copenhagen. 



Electrometric Methods in Analytical Cheniistrv.' 



'|'llll\'l\' years ago electronu'tiic iiutliods of 

 * .iii,tl\sis wiTf too complix foi technical pur- 

 posi^, hut till importance ot ii\(lrogen ion con- 

 cfntration " rc-directed attention to them, with result- 

 iiijj; simplification. 



W lull a piece of silver is dipped in a solution, a 

 soliitiiiii pressure is exerted, silver ions being driven 

 into st)hition until equilibrium is established between 

 the osmotic pressure of the ions in the solution and 

 the solution pressure of the silver. Hydrogen behaves 

 similarly, as does chlorine. It thus becomes possible 

 to find a suitable electrode for any reaction giving 

 a change in valency. 



In the reduction of potassium permanganate the 

 electrolytic potential («) is given by the formula : 



0-058 [Mn'^ 



'-'•+"m ^°^ [HPLMnO.']- 



If the log expression is kept constant there results 

 a normal electrode. In practice such an electrode 

 must be combined with one which changes its 

 potential during the course of the titration. It is 

 possible to titrate silver with halides, sulphides, 

 cyanides, and thiocyanates, and vice versa. An 

 interesting feature is the possibility of the simul- 

 taneous titration of halides in admi-vture, there being 

 successive falls of potential as each is reacted upon 

 by the silver solution. In the presence of protective 

 colloids there is of course no apparent precipitation. 

 It is interesting to note that this does not interfere 

 with the titration. 



Protective colloids stop crystal growth and con- 

 sequently increase somewhat the solubility of the 

 precipitate. This solubility is usually so low that 

 an increase of even loo per cent, does not lead to 

 appreciable errors. It thus becomes possible to 

 estimate directly small amounts of metal in, say, blood 

 serum. Certain organic substances, such as silver 

 salvarsan, contain silver in such a form that it is not 

 acted upon by chlorides. Use is made of sulphides, 

 the diameters of the ions of which are such that 

 monovalent cations of the dimensions of silver ions 

 are unable to resist their influence. Ionic dimensions 

 play an important part in determining the insolubility 

 of certain precipitates. 



Titrating zinc in acid solution with potassium 

 ferrocyanide, curves not of the usual bi-logarithmic 

 type are obtained. The abnormality is due to small 

 amounts of ferric iron. On filtering through alu- 

 minium powder, reduction to ferrous iron takes place 

 and normal curves are obtained. 



For nickel and cobalt in admixture electrometric 



> Synopsis of a paper presented to the Manchester Sections of the Society 

 of Chemical Industry, Society of Dyers and Colourists, Institute of Chemistry, 

 and the Manchester Literary and Philosophical Society, on November 2, by 

 Prof. W. D. Treadwell of the Technical H^hschool, Zilrich. 



NO. 2821, VOL. 112] 



uir.ttuiii with pot, .iiiide is the b<:«!f. The 



complex ions ''Ni(C.\ , .iiii Co(OH)(CN)j . 

 The curves obtained \ uld no evidence of 

 tion of intermediate complexes. 



For oxidation and reduction tr i platinised 



electrode is most satisfactory', iitanium may ! 

 estimated very accurately in the presence of iron aft 

 filtration through a cadmium powder filter in 

 atmosphere of carbon dioxide and subsequent titrati- 

 with potassium dichromate. If a blank electrode i 

 employed it is liable to become passive at the en 1 

 of the titration, producing a sudden drop of potent: 

 instead of a rise. 



With regard to dye-stuffs there is little to add 

 the excellent methods of Knecht, but where electr 

 metric methods are used, frequent use is made > : 

 cadmium filters for reduction. Titrating primary 

 amines in acid solution with sodium nitrite a sudden 

 rise in potential is obtained with the first drop in 

 excess of the latter. 



For the estimation of free halogens an e.xampie 

 was given of the estimation of o-i per cent, of bromine 

 in sodium chlorate by distillation with hydrochlor; 

 acid followed by titration with arsenious acid. 



An especially resistant electrode for the estimatio:! 

 of insoluble oxides is obtained by passing an allo\ 

 of 90 per cent, gold with 10 per cent. copi>er throui: 

 a bunsen flame, when it becomes covered with a th 

 layer of a copper oxide. 



In conductivity titrations the conductivitv usuallv 

 changes sharply enough to indicate the end-poin? 

 but where weak acids are concerned care must ! 

 exercised. Use is made of a Wheatstone brid^ 

 and an alternating current. The millivolt:;;- : 

 may still be used by the introduction of a rot.itin- 

 switch, the poles in the solution being changed s: . 

 to eight times a second. The current then l^com 

 virtually a continuous one. The method is the be- 

 one for alkaloids and also for water in organic liquid- 

 An example of the latter is the estimation of water 

 in so-called absolute alcohol. A salt is added which 

 completely ionises in aqueous solution, e.g. jxjtassium 

 perchlorate. The alcohol is rapidly stirred and the 

 conductivity measured. The solubility of the salt 

 is a linear function of the water present, and from an 

 examination of the curves obtained its content may 

 be deduced. Conductn iry methods are excellent for 

 determining and comparing the hardness of waters. 



The last fe^\- years has seen the replacement of 

 electro-deposition methods by titration methods, and 

 very accurate results may now be obtained even 

 with the simplest equipment. The behaviour of 

 titration electrodes requires further study, and from 

 the work now being carried out on surface adsorption 

 and surface actions in general, much progress mav be 

 expected in the future. L. G. R. 



