( 759 ) 
to approximately determine the composition of the crystals and 
motherliquor by testing the etchingliquor and the grindings of the 
protruding crystals (BEHRENS). An accurate quantitative analysis 
by this process is, however, an impossibility. 
2. Determination of the solidifying curve (LE CHATELIER, 
ROBERTS-AUSTEN, ia). From the course of this curve, the exis- 
tence of chemical compounds may often be traced and indications 
found as to the crystallising of mixed crystals. This determination 
by itself is, however, rarely conclusive. Guided by the modern 
ideas about the equilibria of phases (Bakuuts RoozeBoom, Zeit. 
phys. Chem. 30, 385) which occur in alloys, Heycock and NEVILLE 
have succeeded, by combining the two above-mentioned methods, 
in obtaining almost positive certainty about the very complicated 
relations which occur in alloys of copper and tin. The circum- 
stances that the crystals which separate on solidification may be 
readily fixed by chilling and that the heat-effects which occur 
on solidification and transformation are large have materially con- 
tributed to make this possible. 
3. The separation of the crystals which are deposited from the 
alloy on cooling. 
The methods used for this purpose are: 
a. The draining of the motherliquor when solidification sets in ; 
the amount of motherliquor adhering to the crystalline mass is tien 
determined by adding a third metal (Van Byer, Zeit. phys. 
Chem. 8, 358); 
b. by pressure between hot plates; the still adhering mother- 
liquor is dissolved in an acid which does not attack the crystals 
(Benrens, Verslag Kon. Akad. 1898, 58); 
c. filtration (KEMP on amalgams, Zeit. anorg. Chem. 17, 284 
and 25, 1). 
The last method can only be applied to alloys which have a 
very low melting point and gives a very incomplete separation of 
crystals and motherliquor. 
In cases where different chemical compounds or mixed crystals 
are likely to be deposited from an alloy during its solidification, 
the first two methods must be objected to because the temperature 
is not constant. They are, moreover, only applicable to alloys 
which have a comparatively low melting point and oxidise but 
little in contact with the air; it is also by no means sure that on 
dissolving the motherliquor in an acid the crystals are not attacked. 
In addition to the determination of the solidifying curve and the 
microscopic test, the isolation of the Fe from the partly solidified 
50 
Proceedings Royal Acad. Amsterdam Vol. IV. 
