ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
97 ' 
Internal Structure in Relation to Microstructure. — J. C. W. 
Humfrey [Trans. Faraday Soc., 1921, 17 , part 1). In a bar built up 
of two materials possessing different mechanical properties, uniform 
straining sets up stresses which produce asymmetry in the position of 
elastic limits. A remarkable photomicrograph showing the deformation 
of pearlite is given, illustrating the bending up of the lamellae. 
F. I. G. R. 
Internal Fracture in Steel Rails. — H. S. Rawdon [Trans. Faraday 
Soc., 1921, 17 , part 1). A magnetic method for locating internal 
defects is described, together with the microscopic appearance of 
internal cracks in rail steel. F. I. G. R. 
Internal Stress Irregularities. — J. N. Greenwood [Trans. 
Faraday Soc., 1921, 17 , part 1). The possible origins of internal 
stresses in pure metals and alloys are examined. They are (1) due to 
cold working ; (2) suppression of phase changes by rapid cooling. The 
case of tool steels receives special attention. F. I. G. R. 
ULTRAMICROSCOPY, COLLOIDS, Etc. 
Physics and Chemistry of Colloids. — The Svedberg [Trans. 
Faraday Soc., 16 , part 3, 1921). The author, one of the greatest 
exponents of colloidal physics, gives a brief but comprehensive account 
of the present state of knowledge on this subject, and insists that 
nearly every property of a colloid depends upon its structure, the most 
direct way of observing which is the ultramicroscope, and to some 
extent the ordinary microscope. By such means it is often possible to 
decide whether the phase in question is grainy, foamy or fibrous. The 
number and size of the particles can also be found in this way. It is 
to be remembered that the ultramicroscope gives practically no infor- 
mation about the form of the particles themselves. In the event of 
the particles being too small to be measured directly by the ultramicro- 
scope, it may be possible to measure their size by depositing gold upon 
them. The instrument may also be employed to observe the aggregation 
process in the case of secondary gels and sols. The author considers 
that there is a promising field for the development of colloids in 
industry. F. I. G. R. 
Reversal of Phases in Emulsions. — S. S. Bhatnagar (Trans. 
Faraday Soc., 16 , part 3, 1921). A microscopical method is described 
for determining the type of emulsion, by means of the “ colour- 
indicator ” process, in which use is made of some soluble oil dye. In 
the case of an oil-in-water emulsion the colour remains confined to the 
particles of oil which exist as globules, but in water-in-oil emulsions the 
colour covers the surface of the continuous phase. Certain difficulties 
in connexion with the method are discussed. F. I. G. R. 
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