32 Mr Berry, Notes on the volatilization of 
Cadmium and magnesium. On heating an alloy containing 
excess of cadmium in vacuo both metals volatilized together, but no 
definite relation between the composition of the distillate and the 
residue was established. From the form of the equilibrium 
diagram which was worked out by Grube (Zeitsch. anorg. Chem. 
1906, 49, 72) it is probable that the compound CdMg which forms 
solid solutions with both constituents would dissociate on melting. 
It is clear that this pair of metals belongs to Group V in Turner’s 
classification. 
Magnesium and lead. Since these two metals are both 
moderately volatile in high vacua at temperatures of the order 
of 600° according to the researches of Krafft and his collaborators, 
it was thought that the compound Mg,Pb might under suitable 
conditions be volatilized unchanged as had already been observed 
in the case of the compound MgZn,. The existence of the com- 
pound Mg,Pb has been proved by the work of Grube (Zeitsch. 
anorg. Chem. 1905, 44, 117) and confirmed by Kurnakoff and 
Stepanoff (abid. 1905, 46, 177). This compound does not form 
mixed crystals with either of its constituents. In the experiments 
of the present author, alloys containing the two metals in 
approximately equivalent proportions were distilled in vacuo at a 
temperature of about 680°. It was found that the distillate 
consisted chiefly of magnesium with mere traces of lead. In no 
case was it possible to isolate a homogeneous portion of the 
distillate for quantitative analysis. Under the microscope, steel 
blue crystals embedded in a matrix of magnesium or magnesium 
silicide from the glass were plainly visible, and these portions of 
the distillate underwent rapid corrosion on exposure to the air 
with formation of a black powder—a property of the compound 
Mg.Pb noted by Grube (loc. cit.). It is noteworthy that the 
coolest portions of the tube where the distillate condensed were 
practically free from lead. According to Krafft and Bergfeld 
(Ber. Deutsch. Chem. Ges. 1905, 38, 254) lead commences to 
volatilize at 335° in a cathode ray vacuum, while Knocke (ibid. 
1909, 42, 206) has shown that magnesium under similar con- 
ditions commences to volatilize at 415°. One might, therefore, 
expect that at a temperature of 680° both metals would readily 
vaporize and condense in the cooler parts of the apparatus. It 
must be borne in mind that magnesium vapour would diffuse 
nearly three times as rapidly as lead vapour, and further, although 
the volatilization point of lead is apparently lower than that of 
magnesium it does not follow that the same order would obtain 
with regard to the vapour pressures of these two metals at higher 
temperatures. In a special experiment in which 77 grams of 
assay lead were heated for about five hours at 680° in a vacuum 
produced by cold charcoal, it was found that only a very small 
