( 761 ) 
85 0, Sn or 16 % Sb and 84 0/, Sn by whirling at a constant 
temperature of 270° (the commencing solidifying points of the alloys 
are 284° and 290°) are partly found loose (fig. 2); near the narrowing 
of the tube they are partly united to a loose cake by the adhering 
motherliquor. 
By mixing with 1 % of Ag it could be ascertained how much 
motherliquor had been retained by the crystals (VAN BYLERT, |. c.). 
The amount of Ag in the loose crystals was so small that it 
could not be estimated. In the loose crystalline cake 8 °/, of mother- 
liquor was found. 
The crystals contain 32.5 °/, of Sb, Sb Sn, contains 33,6 0/, of Sb. 
In the case of Sn Cu crystals (fig. 3) which were obtained by whirl- 
ing at 300° an alloy containing 4.5 °/, of Cu, the amount of loose 
erystals is much smaller and insufficient for analysis. 
Several alloys containing 4.5 °/) of Cu were therefore whirled 
and the loose erystais (fig. 3) collected as far as possible and analysed. 
Found 67,9 °/, of Sn, calculated 65 °/, of Sn. 
The erystals cannot therefore be completely freed from mother- 
liquor by whirling, but by operating in this manner it will be as 
a rule easy to ascertain whether pure metals, compounds or mixed 
erystals are deposited from the alloy. 
If a change takes place in the composition of the alloy, the separ- 
ated erystals in the first two cases will remain of constant compo- 
sition within a few per cent, while in the case of mixed crystals a 
gradual change will be observed. 
Physics. — Communication n? 78a from the Physical Laboratory 
at Leiden: ‘“Isotherms of diatomic gases and their binary 
mixtures. II. The determination of density with the piezometer 
of variable volume for low temperatures”. (By Prof. H. KaMER- 
LINGH ONNEs and H. H. Francis HYNDMAN). 
§ 7. The measurements. 
These are of two kinds. 1st. The density being given in terms of 
the normal density dy (at 0.0° C. and 1 At.) the quantity of gas 
contained in the piezometer tube is determined by measurements of 
the normal volume Vy. 2"¢. The volume of the compressed gas 
is measured under known conditions of pressure and temperature. 
The measurements of Vy are made both before and after the measu- 
rements at higher pressure. In general this is very desirable and 
50* 
