Colloids and the ultramicroscope : a manual of colloid chemistry and ultramicroscopy / tr. by Jerome Alexander.

  • Zsigmondy, Richard.
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: Colloids and the ultramicroscope : a manual of colloid chemistry and ultramicroscopy / tr. by Jerome Alexander. Source: Wellcome Collection.

Provider: This material has been provided by the Gerstein Science Information Centre at the University of Toronto, through the Medical Heritage Library. The original may be consulted at the Gerstein Science Information Centre, University of Toronto.

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    The definitions, however, are not based upon the proper- ties above referred to, but give homogeneity as the most important characteristic. Because of this state of affairs the moot question as to the nature of colloidal solutions hinges on the question of their homogeneity or heterogeneity. This very circumstance has lead to an important exten- sion of our knowledge. We must therefore next consider the concept homogeneity In his book: Heterogeneous Equilibrium, Bakhuis Roozeboom 1 states: We call a system homogeneous if all its mechanically separable parts show the same chemical constitution and the same chemical and physical properties. Gases or liquids which have been well mixed possess this homogeneity of constitution because of the smallness of molecules and the grossness of our means of observa- tion. We still are unable to observe directly particles the size of a crystalloid molecule. However, by means of the Faraday-Tyndall convergent beam of light, we are able in an indirect manner, with the aid of the Nichol prism, to demonstrate the existence of very small boundary planes, and therefore of particles of unusually small size. As Bredig 2 has already pointed out, Tyndall's method is the most sensitive for the recognition of the lack of optical homogeneity. By this method, as we shall see, we can detect smaller quantities of substances than by spectrum analysis; but just because of its enormous sensi- tiveness, the most extreme care must be taken in forming conclusions as to the nature of a solution, upon the basis of the results of an examination by it. 1 B. Roozeboom, Die heterogenen Gleichgewichte, Part I, p. 9, Braunschweig, 1901. 2 Bredig, Anorganische Fermente, Leipzig, 1901, p. 21.