-TITUT1ON OF THE ALLOYS OF ALUMINIUM AM> /.INC. 



325 



eutectic line at this concentration is really due to the formation of a definite 

 aluminium-due compound whose existence is confirmed by other evidence. 



at ilo'C 



' ~ .*'. t . 



Fig. 6. 



We have now to consider the nature of the heat evolutions along the lines CH and 

 IL of fig. 4. 



The fact which has already been stated that in slowly cooled alloys eutectic is 

 found to the right of the point F, while this eutectic disappears when full equilibrium 

 has been obtained, points to the conclusion that there is in these alloys a gradual 

 reaction at some temperature above that of the eutectic line, and that this reaction, 

 when allowed to complete itself, results in the total absorption of the liquid phase 

 which would otherwise have solidified along the dotted line FP. The existence of a 

 scries of heat evolutions along the horizontal line CH at once suggests that such a 

 reaction is represented by these heat evolutions, and this view is confirmed when it is 

 rememlxM-ed that in curves of more rapid cooling these heat evolutions are much less 

 marked, an observation which indicates the occurrence of a gradual reaction. We 

 have, further, the discontinuity in the liquidus curve at the point C, which also 

 suggests that we are here dealing with a compound which is produced by a reaction 

 of the solid which had begun to crystallize along the branch of the liquidus CD, with 

 the liquid phase which is present when the temperature of the line CH is reached. 

 It is well known that such a reaction taking place between a solid and its mother 

 liquor results in the formation of sheaths of the new compound, and that these 



