30 
MESSRS. C. T. HEYCOCK AND F. H. NEVILLE ON 
in the crucible with an insufficient supply oi air, deposited so much carbon that the 
crucible soon became full ; we were therefore obliged to employ hydrogen in such 
cases. 
Before and during the reading of the freezing point the metal was stirred by means 
of a plunging stirrer. This stirrer consisted of a carbon rod screwed into a semi- 
annular foot cut from a plate of gas-carbon so as nearly to fit the crucible. Without 
efficient stirring it is impossible to obtain sharp and consistent readings of the 
freezing point when the solutions are at all concentrated. The stirring was in some 
cases efiected automatically by means of a small water motor, but more often hand 
stirring was adopted. Hand stirring, though not so vigorous as an automatic stir, 
has the advantage that the person stirring can note the formation of precipitate and 
observe its character. 
The pyrometers employed were of the Callendar-Geiffiths type, in which the 
temperature is determined by the change in the electrical resistance of a platinum 
wire. Their constants were re-determined from time to time during the progress of 
the experiments, using as fixed points, ice, steam, and the vapour of boiling sulphur 
(444’53°). These three points are sufficient for reducing, by Callendar’s rule, the 
observed resistance to the temperature on the Centigrade-air scale. The justification 
for this rule is to be found in Callendar’s'* comparison with the air thermometer up 
to 600° C., and in the identity of the freezing point of copper, as determined by us 
and by Holborn and WiEN,t the latter observers virtually using the air thermometer. 
This point has also been discussed by Griffiths.;!; The exact accuracy of this reduc¬ 
tion to the Centigrade-air scale is not, however, of moment for the purpose of the 
present paper; it is sufficient that these pyrometers give consistent temperatures on a 
scale that nowhere differs much from the true scale. The additional experience 
gained in making the experiments described in the present paper has confirmed us in 
the opinion that such is the case. 
Section III. 
The Tables of Experimental Results. 
Each table gives the freezing points for a pair of metals. The weight of pure 
metal that we start with is given at the head of the table or section. 
Column (1) gives the total weight of the second metal present at the moment 
of taking the freezing point. 
Column (2) gives the percentage of the second metal present in the alloy. The 
percentage of the first metal present can be obtained by subtracting the numbers 
of column (2) from 100. 
* Callendar, ‘Phil. Trans.,’ A., 1887, p. 161; A,, 1891, p. 119. 
t Holborn and Wien, ‘Ann. Phys. Chem.,’ 1892, 47, 107. 
I Griffiths, ‘ Nature,’ November 14, 1895, and February 27, 1896. 
