CONSTITUTION OF THE ALLOYS OF ALUMINIUM AND ZINC. 



327 



taking a series of cooling-curves of alloys cooled slowly from fusion under careful 

 standard conditions, the heat evolutions being measured in the manner described in 

 connection with the eutectic line EF. These determinations give the points repre- 

 sented in the second curve of fig. 6, and it will be seen that these points indicate the 



t * 



Timt /tltrmti 



Tii 



u 



Fig. 7. 



existence of a well-defined maximum lying exactly under the point C. This un- 

 expected result can, however, be explained in a simple manner when it is remembered 

 that the compound whose reaction is being measured crystallizes freely from the 

 liquid along the line BC of the liquidus, while to the right of the point C this 

 compound is the result of a slow reaction between a solid and a liquid. In these 

 circumstances it is not surprising to find that in a series of alloys cooled at a standard 

 rate the quantity of this compound would increase steadily as we pass from the 

 concentration of the point B to that of point C, but that immediately on passing 

 beyond C the quantity of the compound would decrease. The maximum obtained 

 from such a series is therefore a misleading one, and does not represent the composition 

 of any phase. The authors believe that this is an observation of some importance in 

 the application of the methods of investigation styled " Thermal Analysis " by 



