338 DR. WALTER ROSENHAIN AND MR. SYDNEY L. ARCHBUTT ON THE 



cent, of zinc) in figs. 28 and 29. The former figure shows the structure of this alloy 



quenched from a temperature above the line GH, and the presence of liquid at the 



liniment of quenching is quite evident from the presence of a finely-granulated 



matrix in the section of the quenched specimen; on the other hand, in fig. 29, the 



structure is that of the same alloy quenched from a temperature just below the line 



<;il. ami here, although perfect homogeneity has not been attained, the absence of 



liquid is quite evident, although some cracks and cavities are found, but these are 



present in all quenched specimens of this somewhat brittle alloy. The results of 



further quenching experiments are indicated on the diagram by dots surrounded by 



small circles in those cases where liquid was found and by squares in those cases 



where the alloy proved to have been completely solid. A much larger number of 



quenching experiments were made than those shown on the diagram, but only those 



have been plotted which lie close to the limiting temperature, since the others are of 



no direct importance in determining the solidus, and merely served as guides for the 



choice of fresh quenching temperatures. 



For the determination of the solidus curve from H to D over twenty quenching 

 experiments were made, but only fourteen are plotted. The solidus curve has been 

 drawn in such a manner as to pass between the nearest circles and squares (indicating 

 liquid and solid respectively), some account being taken of the amount of liquid 

 which was indicated by the observations on the various specimens. 



In order to illustrate the appearance of " liquid " in the quenched specimens, photo- 

 micrographs representing the results of two quenching experiments are shown in 

 figs. 35 and 36. Fig. 35 (x!50) refers to alloy No. 50 (49'8 per cent, of zinc) 

 quenched from a temperature of 467 C. The presence of liquid is indicated iu this 

 case by the broadening of the crystal boundaries and the presence of minute fusion 

 spots in the crystals themselves. Fig. 36 ( x 150) shows a similar alloy quenched at a 

 temperature just above the solidus. Here the indications of liquid are confined to 

 small traces in the crystal boundaries, and there are no fusion spots. 



General Conclusions. 



The general conclusions arrived at as a result of the pyrometric and microscopic 

 investigations of the aluminium-zinc alloys, which have been described above, may 



now be summarized. They are represented graphically in the equilibrium diagram 

 of fig. 4. 



The addition of aluminium to zinc first depresses the freezing-point until a eutectic 



"mn is reached at a concentration of 95 per cent, of zinc and a temperature of 



Further addition of aluminium raises the freezing-point until a concentration 



5 per cent, of zinc is reached where there is a small but distinct break in the 



sing-point curve. From this point the freezing-point curve rises smoothly until 



