ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
439 
bearing points, finished in black lacquer. Fitted with a strongly made 
push-bar switch and lamp socket, six feet of twin flexible wire, and wall- 
plug or lamp bayonet fitting. Opalite electric bulb, made of special 
mixture of glass, which presents a fine opal surface, having no structure 
or granular matter to interfere with the detail of the object under 
observation. This bulb is eminently suitable for critical illumination, 
and is supplied to suit any voltage. The lamp is made by Ogilvy and 
Co., 18 Bloomsbury Square, London. 
GEOLOGY, Etc. 
Ordovician Lavas of N. Pembrokeshire. — G. M. Part ( Qeol . 
Mag., July, 1922). Six drawings of micro-sections accompany the 
paper. Most of the specimens are porphyritic with abundant small 
phenocrysts of felspar. The rest consist of plagioclase of low refractive 
index. 
Microscopic Determination of Non-opaque Minerals. — E. S. 
Larsen {U\S. Geol. Survey Bull., 679, 1921). Data for refractive 
indices by immersion are given for some 950 species. 
ULTRAMICROSCOPY, COLLOIDS, Etc. 
Colloids, or the Material of Life.— S. C. Bradford {Science 
Progress , No. 65, July, 1922). In addition to an historical account, the 
author discusses the application of the ultramicroscope and the im- 
portance to industry of catalytic reactions. 
Diffusion in Deformed Gels.— E. Hatschek {Science Progress , 
No. 65, July, 1922). These gels remain isotropic for diffusion under 
stress. Experimental procedure is discussed. 
The Kinetics of Coagulation.— J. N. Mukherjee and B. C. 
Papaconstantinou {Phil. Mag., 44, No. 260, August, 1922). The 
rate of coagulation is discussed, more particularly with a view to 
reconciling theory with ultramicroscopic determinations. 
Size of Colloid Particles and Adsorption of Electrolytes. — 
H. D. Murray {Phil. Mag., 44, No. 260, August, 1922). A cardioid 
eondenser fitted to an ordinary microscope was used instead of an 
ultramicroscope. Small particles require a higher minimal concentra- 
tion of electrolyte than large particles. 
Distribution of Particles in Colloidal Suspensions.— A. W. 
Porter and J. J. Hedges {Phil. Mag., 44, No. 261, Sept., 1922). 
Countings were taken at various depths. The ultramicroscope was 
used horizontally, illuminated by a vertical beam. Three distinct layers 
are recognized in suspensions : (1) A surface layer of thickness com- 
parable with the range of inter-molecular forces. (2) A layer less than 
0 • 1 mm. thick, to which the gas laws can be applied. (3) A layer 
some 2 mm. thick which gradually merges into the main body of the 
suspension. 
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