CONSTITUTION OF THE ALLOYS OF ALUMINIUM AND ZINC. 



317 



in the molten aluminium ; in the case of alloys near the zinc end of the series a 

 previously prepared alloy of equal parts of aluminium and zinc was usually melted 

 first and further zinc subsequently added. All the ingots upon which the results 

 stated in the paper are based have been chemically analysed, and the results obtained 

 are shown in Table I., p. 316. In the majority of cases it will be seen that the 

 analytically determined composition agrees very closely with that aimed at } in a few 

 cases where discrepancies of over 1 per cent, are found this is due to repeated melting 

 of the ingots in question. 



During their preparation and subsequent treatment the alloys were carefully 

 protected from contamination with foreign materials. The extent to which this was 

 attained is illustrated in Table II., where the analyses of two alloys are given 

 together with their composition (as regards impurities) as calculated from the 

 materials used. 



TABLE II. 



In most of the experiments the melting-furnace was heated by gas, but in other 

 experiments a small electric resistance-furnace was employed. 



Oxidation of the metals was minimised by keeping the temperatures of the melting- 

 furnaces as low as possible consistent with the complete fusion of the alloys ; it was 

 not found practicable to protect the surface of the alloys by a flux, or other covering, 

 without risking contamination from substances liable to be reduced by the molten 

 aluminium. 



The thermal study of the alloys was carried out by means of a series of cooling- 

 curves taken by the " inverse-rate " method with the delicate potentiometer installed 

 for that purpose at the Laboratory. The ingots used for obtaining these cooling- 

 curves weighed 300 gr. and were cooled in a furnace which was placed in a closed 

 water-jacketed steel vessel, the thermo-couple being introduced into the alloys 

 through suitable apertures in the top of the water-jacket. The cooling alloys were 

 thus entirely protected from draughts or other extraneous disturbances. 



In a first series of cooling-curves the rate of cooling was such that when the alloys 



