328 DK. WAI/I'KK I;<>>KNI1AIN AND MR. SYDNEY L. ARCHBUTT ON THE 



TAMMAN, since it indicates that the results of such heat measurements, even \vhrn 

 allowance is made for their unavoidable inaccuracies, must be considered with great 

 caution before they can be accepted. 



In the present case the difficulty was overcome by measuring the heat evolutions 

 on the series of cooling-curves already described in connection with the measurements 

 of the peaks along the eutectic line EF; these curves were taken from ingots so 

 treated that the reaction along the line CH had been allowed to reach completion, 

 ami on these curves the maximum should truly represent the quantity of the 

 compound present in the alloy. The data from these cooling-curves relating to the 

 reaction along the line IL, plotted in the usual manner, are shown in the third curve 

 in fig. 6; this curve shows a maximum near a concentration of 77 '2 per cent. zinc. 

 It will be seen that tins agrees nearly, but not quite accurately, with the end of the 

 eutectic line, as indicated on the upper curve of this figure, which falls at 78 '8 per 

 cent. zinc. The slope of one of the lines in the lowest curve of fig. G, however, is 

 somewhat flat, so that a small alteration of one or two of the observed points would 

 displace the maximum to an extent quite comparable with this discrepancy. The 

 authors, therefore, feel justified in saying that both the end of the eutectic line and 

 the maximum of the heat evolutions along the line IL are consistent with the 

 existence of a definite compound Al 2 Zn 3 . 



The determination of the position of the point H and of the curved portion of the 

 solidus from H to D, having been based entirely on microscopical evidence, will be 

 described in connection with that portion of the work, and we pass on to consider the 

 line of points shown on the diagram in fig. 4, mostly lying within the area CDHG. 

 It will be seen that these points lie on a perfectly smooth curve, starting from the 

 temperature 638 C., at which a minute heat evolution is observed in most varieties 

 of aluminium, including the comparatively pure variety used in preparing the present 

 series of alloys.* 



Samples of aluminium have, however, been obtained which do not show this heat 

 evolution, and this fact would suggest that the thermal change in question does not 

 occur in the purest varieties of aluminium, but that its occurrence is determined, and 

 ita intensity accentuated, by the presence of certain other elements. One of the 

 authors, in a recent research on the alloys of aluminium and manganese, found a series 

 of small heat evolutions starting from this temperature in nearly pure aluminium, and 

 continuing at the same temperature, but with increased intensity, with successive 

 tions of manganese until the concentration of the point Mn 3 Al is reached.! In 

 the present series of alloys the addition of zinc also appears to intensity the heat 



This point has frequently been observed in aluminium, and special attention was drawn to it by 

 1 - \v e Failure of the Light Engineering Alloys," ' Faraday Society,' 1910.) 



IIAIS and F. C. A. H. LANTSBERRY, "Ninth Report to the Alloys Research Committee of 

 5chanical Engineen-On the Properties of some Alloys of Copper, Aluminium, and 



