The stability of hydrophobic sols is determined by the free energy of interaction between the particles; this energy of interaction can be divided into the electrical repulsion and the van der Waals attraction. As the latter is practically constant for a given system, the major interest lies in the repulsive energy due to the superposition of two electrical double layers. The Reerink and Overbeek theory deals with the influence of the double layer thickness at a constant Stern potential on sol stability, a situation which occurs when indifferent inorganic electrolytes are added to sols. While, the theory by Ottewill, Rastogi and the present author explains the coagulation due to changes in the Stern potential caused by adsorption. A.n extended theory was also given which covers the general case of changing ionic strength and potential. The theoretical treatment thus obtained was in good agreement with the optical measurements of the coagulation kinetics of silver iodide sols by various coagulating agents. It was shown by experiments that the coagulation theory held also for the coalescence of two mercury droplets polarized at various potentials in electrolyte solutions. This indicates that the interaction between finely dispersed particles in hydrophobic sols is essen-tially the same as that acting between macroscopic mercury droplets.

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Each year, new plants of the chemical industry are being developed and automatic operations of the chemical processes are being attempted. In the application of automatic process control to chemical processes, one of the most frequent problem encountered is the lack of suitable automatic chemical composition measuring instruments. Measure-nients of physical properties are frequently used as indications of chemical compositions, but in many cases this proves to be unsatisfactory, because the physical properties are too dependent on other factors. Thus means are needed which are more exclusively dependent on the component to be measured. The major advantages of the electroana.lytical method descussed in this paper would be the simplicity of the elements in the instrumentation, the suitablity to the trace analysis, and the fact that the method are more exclusively dependent on the component to be measured. The methods of electro-chemical analysis for plant services could be divided into four classes; (1) Amperometry and Polarography, (2) Potentiometry, (3) Conductimetry (including High Frequency Method), and (4) Coulometry. The principles of these methods are outlined and the typical applications of the methods are reviewed with some emphasis on author's contributions in the field. The typical applications descussed in this paper are summerrized as follows.Amperometry and Polarography i) Continuous analysis of trace copper in process liquor of electrolytic nickel metal industry. ii) Continuous analysis of sodium hydrosulphite in the reduction process liquor of dye chemical industry. iii) Continuous analysis of uranium in the uranium refining plant. iv) Trace oxygen analysis in some inert gases.Potentiometry: i) Chlorination process control using the reduction-oxidation potential measurements. ii) Electrometric pH value determinations using the glass electrode. iii) Batch-wise process titrator.Gonductimetry (including High Frequency Method): i) Detailes of the conductimetric salt analyzer. ii) Four electrode method in conductimetry. iii) Continuous determination using dielectric constant measurements for petroleum refining processes.Coulometry: i) Moisture monitor by use of the direct coulometry. ii) Continuous coulometric titration for styrene and aniline determination.

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The potentiostatic methods (voltage-step method), galvanostatic methods, coulostatic methods (charge-pulse method), faradaic impedance methods, and faradaic rectification methods have been developed in these fifteen years for the study of fast electrode kinetics. Indirect methods such as photo-electric current by a flash light or a voltammetry using vigorous mechanical stirring possibly be used for this purpose.
These relaxation methods are based on measurement of the reaction rate under high rate of mass transfer, which is achieved by diffusion with steep concentration gradient or by vigorous stirring. So far as diffusion is the sole mode of mass transfer, the average flux of reducing species diffusing toward a plane electrode is given by 2C^o(D/πt)^I/2, where C⁰ is the bulk concentration of the reducing species, D its diffusion coefficient, and t the time elasped since the biginning of electrolysis. In a process with mixed control by mass and charge transfer, this conclusion is qualitatively valid, and diffusion is no longer rate-determining in a measurement at a sufficiently short time interval.
An overall electrode reaction is schematically given by a diagram as shown in Fig. 1. In relaxation methods, it is expected that chemical reactions, specific adsorption of the reactant or/and product, or the charge transfer process will be rate-determining, provided the the time of measurement is sufficiently short. It is noteworthy that the datum obtained at a time interval has to be analysed in relation to a corresponding rate-determining step. In pluse techniques mentioned above, measurement at a short time interval has restriction from charging of the double layer capacity, transient of the pulse from the net-work composing the cell circuit, and the rise-time of a pulse and detector used. The doublepulse galvanostatic method enables measurement at a very short time interval up to about few microsec. by using an ingeneous method of compensating double layer charging. A cathode ray oscilloscope usually used in these method is accompanied by meager precision and accuracy. The faradaic impedance method seems to be the most accurate one, while the upper limit of the frequency is about 20 kc which corresponds to the time interval of 5x10^-5 sec. The faradaic rectification method is promising at very high frequencies up to 50 or possibly to 100 me (10^-8 sec.), being unaffected by transients and double layer charging by using the double-pulse method or null method. The apparent cxchange current density evaluated by this method was 10 amp./cm² in the electrode process of Hg(I) in 1.1 M HClO₄, which corresponds to an apparent standard rate constant of ka^o =100 cm./sec. for an electrode process involving both soluble oxidant and reluctant of equal concentration of Ka^o = 5x10^-4 M (n=2, Do = D_R =10^-5 cm²/sec.) or to kaK =1000 cm./sec. for CK =510-5 M. The theory of the faradaic rectification has been developed by Barker1 and Matsuda- Delahay, and more extensively studied by Delahay-Senda-Weis. This review will cover rather an experimental point of view including the method of analysis and experimental techniques.

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[in Japanese]

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Oscillographic polarography is classiied into two types of Heyrovsky-Forejt's current control system and and lesmSevcik's potential control ryst.e n. These oscillographic polarographic methods have the merit of measuring the laradalc current under the steep concentration gradient of the depolarizer at the vicinity of the electrode surface, But the unfavorable overlapping of capacity current on faradaic current is pronounced as the potential or current scans more rapidly, and accordingly the selective and precise measurement of faradaic current become snore complicated. The authors employed Barker's square wave r: ethod coupled withh the modlised Randles-Sevcik's single wave polarograph, is presented inn detail, inch din, improvement on the elimanation of capacity current and the method of scanning of DC applied potential.

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