CONSTITUTION OF TIIK ALLOYS OF ALUMINIUM AND XI NT. 



321 



of a third group of reactions. It will be seen that a series of small heat evolutions 

 can be traced throughout the succeeding alloys up to and including pure aluminium, 

 forming a generically connected series with the point shown in this curve, but 

 presenting tin- curious feature that they occur at successively higher temperatures as 

 the concentration approaches pure aluminium. 



( 'urve No. 45 ( I*', I per cent, zinc) shows the same four points which have just been 

 described in Curve 55, but the peaks at 443 C. and 257 C. are now much smaller. 

 In ( 'urve No. 35 (33'2 per cent, zinc) only the two upper points persist, all the lower 

 points having disappeared ; the same remarks apply to Curve No. 05. 



In further reference to the points occurring in Curves 55 to 05 it should be pointed 

 out that the apparently feeble character of this heat evolution arises in part from the 

 fact that it occurs so soon after the commencement of freezing of the alloys ; that 

 portion of the cooling-curve upon which this peak is shown slopes backward very 

 steeply, and a very considerable evolution of heat is therefore required to arrest and 

 even to reverse this steep slope. This circumstance somewhat militates against 

 accuracy in the determination of these peaks, the actual peaks shown on the curves 

 being in some cases not very much larger than experimental perturbations which now 

 and then occur. In order, however, to show definite evidence of the existence and 

 constant occurrence of these heat evolutions, three cooling-curves of the same ingot 

 are reproduced in fig. 3 ; a comparison of these three curves will clearly demonstrate 



St 



SSI 



'.f 



'C 



Fig. 3. 



tin- constant occurrence of this heat evolution in spite of the apparent smallness of 

 the peak on eacli individual curve. 



The group of cooling-curves, as shown in figs. 1 and 2, cannot readily be translated 

 into an equilibrium diagram, even with the aid of the additional intermediate curves 

 which were obtained by the authors, and a larger amount of experimental evidence 



VOL. 00X1. A. 2 T 



