NEW BOOKS Colloids B y H . R. Kruyt. Translated by H . S. ann Klooster. 23 X 16 cm; p p . xi -i 261. New York: John K i l e y and Sons, 1917. Price: 83.60. I n the general introduction the chapters are entitled: preliminary consideration of colloidal systems; boundary phenomena; capillary electrical phenomena. Part I1 deals with suspensoids and the headings of chapters are: stability of suspension; charge and stability; constitution of the double layer; kinetics of flocculation; optical properties of suspensoids; properties of suspensoids from the kinetic point of view; formation of suspensoid sols; historical outline of the development of the theory of suspensoids. Emulsoids are taken up in Part I11 with chapters entitled: general properties of emulsoids; stability of emulsoids; protein sols, osmotic phenomena; gels. There is a final chapter on special sols which constitutes Part IT. I n spite of the fact that dyeing-a typical adsorption process-may take a very long time a t room temperatures and some minutes even a t the boiling-point, Iiruyt states definitely, p. 34, that adsorption equilibria are reached quite rapidly. “Robert Marc has found that the adsorption of starch by powdered crystals is go per cent complete within a few seconds. In general, adsorption equilibria of this kind are established in a few minutes. Whenever we meet with an adsorption reaction that does not reach a final value within this period of time, we can be reasonably sure that it is not a simple one. For instance, in the adsorption of oxalic acid by charcoal, the condition reached after ten minutes apparently does not represent complete equilibrium since the concentration of the liquid continues to decrease, although very slowly, for several hours. Further investigations have shown that the adsorbed oxalic acid reacts with dissolved oxygen, and that this process is catalytically accelerated in the adsorption layer. This combination of adsorption and chemical reaction occurs frequently. Pure adsorption processes are characterized by a rapid attainment of the final state of equilibrium.” “The phenomena observed when a sol is flocculated by means of an electrolyte such as .11CI3 agree well with the changes in boundary potential. When increasing amounts of A1CI3 are added to a negatively charged sol of mastic, we notice that small concentrations cause flocculation, somewhat higher concentrations produce another stable sol of opposite sign, i.e., positively charged, while still higher concentrations bring about another flocculation. . . . We have, therefore, fist a non-floccillation zone, next a primary flocculation zone, then another non-flocculation zone in which the sol has the opposite sign and, finally, a secondary flocculation zone. “This phenomenon is designated as an irregular series. I t will always occur when the potential-lowering effect of the cation is far in excess of the potential-raising effect of the anion, This lowering effect may be due either to a high valence of the ion or to a high degree of adsorbability. Polyvalent cations give, therefore, irregular series when they are combined with monovalent anions. But monovalent organic cations act in the same way. For instance, strychnine nitrate, as well as new fuchsin, yields an irregular series with AS& sol, and AgX03 with the sol of HgS, because in each case the cation is strongly adsorbed,” P. 85. “In recent times, chemical arguments have been advanced which seem to indicat,e that the cellulose molecule is not exceedingly large. I t has been erroneously assumed in organic chemistry that n, in the formula (CaHioOs),, is large; in reality, this quantity is completely unknown since we lack the means of determining the molecular &e of a non-volatile and insoluble (Le,, non-molecularly dispersible) substance. From the researches of Bergmann and those of Pringsheim, one gains the impression that there is a possibility of obtaining cellulose temporarily-although only under unstable conditions-as a monomolecularly dispersed substance, in which case n = I according to the ebullioscopic method. These chemical investigations are thus a confirmation of the concept. developed here, Viz., that sols are polymolecularly dispersed particles. Other experiments of Bergmann prove that the development of the organic chemistry of proteins is proceedine in the pame direct,ion,” p. 176.
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“ 4 n important difference between suspensoids and emulsoids lies, as we have seen, in the fact that the latter, when deprived of their electric charge, do not flocculate. This is exactly the point which has led to a separation of the statics of emulsoids from that of suspensoids. “In order to explain this difference, we must look elsewhere for a suitable hypothesis which can be tested experimentally. Evidently, emulsoids have a second stability factor which prevents the flocculation of the unchanged particles. Remembering that the condition of non-flocculation signifies a probability of adhesion not largely deviating from aero, we realise that thissecond factor, which keeps the colloiding particles from permanently uniting, must be of a different nature. Since the characteristic difference between suspensoids and emulsoids is due to the hydration of the particles, we immediately assume that it is the film of water which furnishes a second protective factor. I n other words, emulsoid particles may be protected against flocculation both by their electric charge and by their hydration. When we have at our disposal a means of eliminating hydration, we can readily verify this assumption, p. 180. “We have already seen that the addition of minute quantities of an electrolyte to a starch or an agar-agar sol removes the charge but not the stability. On adding alcohol to such a discharged sol, one observes an immediate flocculation. This proves, therefore, that we are dealing, in every caae, with two stability factors but that it is immaterial in which order they are removed. The removal of one can be accomplished wiithout evident effect, but the removal df both inevitably causes flocculation,” p. 181. “It has been shon-n that the power of salting out depends on both the nature of the cation and that of the anion. The different cations can be arranged in a series of decreasing precipitat,ing power, from left to right, when used in equal molecular concentration. A similar series exists for anions. These series are called lyotropic series. Cation series: LiSa--I
