1903.] The Properties of the Aluminium- Tin Alloys. 



281 



cast alloys were annealed together for 20 hours at a temperature never 

 varying more than a few degrees from 400 C. Filings were then 

 taken from the specimens, and 0*5 gramme in each case was treated 

 with water. The specimens were placed alongside one another in a 

 water bath kept at 80 90 C. Some of the experiments were con- 

 tinued for six weeks, but as the evolution of gas in the latter stages is 

 very slight, the later ones were stopped at the end of four weeks, and 

 any small residual evolution neglected. 

 The results obtained are shown below : 



Theoretically 1/100 gramme atom of aluminium evolves 334*5 c.c. of 

 hydrogen at N.T.P. (Diagram 2.) 



Examination of polished plates of the alloys after corrosion with 

 water shows that the action begins round the edge of the areas of 

 aluminium-rich constituent. Our experiments indeed go to show that 

 the decomposition of water is entirely ascribable to this part of the 

 alloy. We got, it is true, a slight evolution of hydrogen when small 

 pieces of the more fusible, tin-rich constituent expressed from the 

 alloys on heating were placed in water, but, as we shall show later, 

 the composition of this exuded metal is not the same as the eutectic. 



The photograph marked " 1 " illustrates the result of this water action 

 continued for 124 hours at room temperature, on a polished plate 

 containing 65 per cent, aluminium. The aluminium-rich areas have 

 been worn down and corroded, leaving the tin-rich network in relief. 



Microscopic Structure. 



The microscopic structure of these alloys is illustrated by the accom- 

 panying photographs. The ingots were prepared as already described, 



