Ultra-violet rays as aid to digestion: Anon. (Elect. World, lxiii, 359)
- Book ID
- 104120087
- Publisher
- Elsevier Science
- Year
- 1914
- Tongue
- English
- Weight
- 66 KB
- Volume
- 178
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
Plasticity and Allied Properties of Clays and Kaolins. P.
ROHLAND. (Silikat-Zeits., ii, 3o.)--The author contends, in opposition to the views of Brown and Montgomery, that' all clays lose their plasticity when heated to a temperature at which the combined water begins to be evolved, 59 o° to 62o ° C. Above about 95 o° C., when the combined water has been driven off, the amount of heat absorbed by clays corresponds with the contraction, which increases progressively with the temperature, well-defined contraction taking place only in the cases of substances of marked colloidal nature. The plasticity, however, is dependent not on the combined water, but on the free water, which develops the colloidal properties latent in air-dry clays. The contraction on drying of clays is also a function of their colloidal nature, and therefore of their plasticity, this contraction not occurring with crystalloids. In many cases the colloids of clays are of organic nature, but some clays which Contain practically no organic matter owe their plasticity to the formation of the colloidal hydroxides of aluminum, silicon, or iron, when the clays come in contact with water. The well-known effects of caustic alkalies on the plasticity not only of clays but also of cements, trass, zeolites, and the like are due to the development of colloidal properties by hydroxyl ions, every substance of a plastic nature requiring a definite concentration of hydroxyl ions to produce the maximum proportion of colloidal constituents.