1904.] Properties of the Alloys of Silver and Cadmium. 229 



1 mm. in diameter. Near the outside of the specimens these crystals 

 occupy the whole area, but towards the centre the hard white alloy 

 is segregated, forming a cement between the red crystals (see fig. 7). 

 It seems clear that these two constituents are separated at temperatures 

 above 420, and that the white constituent fuses at that temperature. 

 The white constituent is readily attacked by nitric acid, and may be 

 the compound AgCds. 



The 40-per-cent. alloy, when slowly cooled, is homogeneous and 

 consists of small crystals, about O3 mm. in diameter, which become 

 more regular hexagons when re-heated for 24 hours at 350 and chilled, 

 and also when heated at 570 and chilled, but do not increase in size. 

 The alloy remains homogeneous under these conditions, and evidently 

 consists of the compound Ag 2 Cd 3 . 



The portion of the series between the 40- and the 25-per-cent. alloys 

 consists of hard slightly pinkish crystallites of Ag 2 Cd 3 , set in a matrix 

 which approximately corresponds in composition to AgCd 3 . The 

 alloys can be etched with nitric acid, and the unattacked crystallites, 

 at first forming almost the whole of the mass, become somewhat rare 

 in the 30-per-cent. alloy, and disappear altogether before the 25-per- 

 cent, alloy is reached. 



Specimens containing less than 25 per cent, of silver are much more 

 rapidly attacked by nitric acid than those richer in silver, and when 

 corrosion takes place it is a magma of cadmium with very little silver 

 that is attacked and darkened, leaving the harder white crystallites of 

 AgCd 3 practically untouched (see fig. 8). The structure is developed 

 when sections are merely polished, the crystallites of AgCd 3 standing 

 out in relief. They diminish in number as the percentage of silver is 

 reduced. 



The results of the investigation may be summarised as follows : 



(1) Evidence is afforded of the existence of the compounds AgCd 3 > 

 Ag 2 Cd 3 , AgCd, Ag 3 Cd 2 , Ag 2 Cd, and Ag 4 Cd. 



(2) The alloys containing from 25 per cent, of silver consist, 

 when solid, of crystals of AgCd 3 set in a matrix of cadmium. Those 

 containing between 25 and 40 per cent, of silver consist of the com- 

 pound Ag 2 Cd 3 set in a matrix consisting mainly of AgCd 8 . The alloy 

 containing about 50 per cent, of silver consists of crystals of a silver- 

 rich body set in a matrix consisting chiefly of AgCd 3 . The matrix or 

 eutectic solidifies at 420, or nearly 300 below the freezing point of 

 the crystals. 



The alloys containing from 50 60 per cent, of silver consist, at 

 temperatures above 420, of mixtures of two different solid solutions,, 

 one of which is chiefly composed of the compound AgCd, and the other 

 of Ag 3 Cd 2 . Traces of the eutectic freezing at 420 are still visible. 



When more than 80 per cent, of silver is present, the alloys consist 

 of a mixture of two bodies at temperatures between the liquidus and 



