REVIEWS 167 



The work commences with an account of allotrophy and polymorphism, and 

 then the author proceeds to indicate the exact nature of the cooling curves of 

 different bodies. The various methods of obtaining cooling curves and plotting 

 the results are described. It is perhaps a pity that the ordinary autographic 

 methods of obtaining cooling curves were not more fully given ; however, the 

 compensation arrangement of Roberts-Austen for the determination of small 

 thermal changes in steel and other alloys is clearly indicated, and so is the simpler 

 form of the apparatus by Heyn. 



After a description of the methods employed for the determination of thermal 

 changes in bodies during heating and cooling, the nature of a physical mixture is 

 discussed, and the properties of aqueous solutions generally are dealt with. The 

 work of Guthrie, in connection with his experiments on the phenomena exhibited 

 by various solutions of ice and salt during solidification, is fully described. 

 Unfortunately, however, a mistake occurs in the freezing-point curve given in 

 Fig. 24, where the separations of excess ice and salt respectively, in the under- 

 and super-saturated solutions, are represented as horizontal straight lines, instead 

 of convex ones, thus indicating that the whole of the ice or salt separates from 

 the solution at a definite temperature. These separations, of course, really take 

 place throughout the whole range of cooling, from the initial solidification to the 

 eutectic line. 



The solubility curve of ferric chloride in water by Bakhuis Roozeboom is fully 

 described, and so are the various types of freezing. 



After dealing with aqueous solutions and fixed salts, the author proceeds to 

 show the analogies that exist between them and alloys, and he also incidentally 

 illustrates the application of the phase rule to the study of metallic solutions. He 

 divides the large number of alloys into groups according to the conditions deter- 

 mining their existence in the solid condition. Naturally binary and ternary alloys 

 alone are considered, as in only a comparatively few instances have alloys con- 

 taining more than three constituents been thoroughly investigated, since such 

 researches are necessarily extremely complicated. The binary alloys are classified 

 by the author in the following manner : 



(a) No chemical compounds of the two components exist. 



1. The two components form a continuous series of solid solutions. 



2. The two components form a mechanical mixture after solidification. 



3. The two components are partly soluble in each other ; the alloy after 



solidification consists of solid solutions or mechanical mixtures of solid 

 solutions. 



(b) The two components form one or several compounds with each other. 



1. The compounds are wholly or partly soluble in the components, or in 



one another. 



2. The compounds are completely insoluble, reciprocally, as well as in the 



components. 



The various types of binary alloys are illustrated by their equilibrium curves, 

 and especial mention is made of pairs of alloys used extensively on a commercial 

 scale. 



The section dealing with binary alloys is treated in an eminently practical 

 manner, and the essential properties of bearing metals, generally ternary alloys, 

 are described. It is pointed out that a bearing metal should consist of hard 

 grains, surrounded by a soft plastic ground mass, so that should the bearing 

 pressure become too great, the grains will be pressed into the plastic matrix, and 

 the form of the bush adapts itself to that of the journal. 



