556 W. L. Bowen — The Binary System. 



of obtaining information as to temperatures at which phases 

 appear and disappear, and at the same time a knowledge of the 

 nature of the phases themselves. 



A small charge of any mixture, wrapped in platinum foil, is 

 held at a definite temperature for a period of time which is 

 deemed sufficient to insure equilibrium for that temperature 

 and composition, and is then quenched by allowing it to fall 

 into a dish of mercury at room temperature. 



The chilling is so abrupt that any phase present at the fur- 

 nace temperature is ' fixed ' and ready to be studied under the 

 microscope. By running a series of quenchings progress is 

 made towards a knowledge of the phases present at equilibrium 

 for each composition, at all temperatures — in short, towards 

 the data necessary for an equilibrium diagram. 



By the quenching method many changes of phase may be 

 detected and studied which either take place too slowly or 

 involve too little energy change to give an appreciable break 

 on a heating curve. With many transformations, moreover, 

 especially in the more viscous substances, superheating is likely 

 to occur when the heating is rapid, as in running a heating 

 curve, so that the actual break observed may come at a temper- 

 ature higher than that at which the transformation concerned 

 would take place if equilibrium prevailed. In quenching work 

 it is the endeavor to make the time sufficiently long that all 

 transformations which can take place at the temperature of the 

 furnace may be complete. 



In this work the thermoelement junction in the quenching 

 furnace was distant from the charge 1/2 cm. or more. The 

 small temperature difference between the charge and the fur- 

 nace element was determined at frequent intervals over the 

 temperature range desired by hanging a standard element in 

 the position of the charge and reading both. The differences 

 found were applied as corrections to the readings of the fur- 

 nace element in the course of the work. 



The furnace temperature was kept constant by noting it fre- 

 quently and making the necessary changes in the resistance of 

 the circuit. For the more careful work the current from a 

 storage battery was used. 



Several scores of quenchings were made. Of these, only the 

 more significant will be tabulated (Table II), more especially 

 those which determine the limit of stability for the various 

 phases. 



