TRANSACTIONS OF SECTION B. 449 
If one mg. of lead is mixed with a quantity of radium D which gives 10,000 
units of activity in an electroscope, one-millionth part of this mixture is easily 
detectable by the radioactivity of radium D. In this way 10-® mg. lead is 
quantitatively determinable, 
By this method also the solubility of the difficultly soluble salts of lead such 
as the chromate and the sulphide has been determined. Further, the amount of 
lead chloride entrained by a precipitate of silver chloride after washing the 
latter thoroughly with water is measurable. 
Experiments on the electrochemical behaviour of small quantities of lead and 
bismuth have been begun. By means of these indicators a study may be made 
of the electrochemical behaviour of these metals for electrode potentials lying 
below the decomposition voltage, a problem which could not be investigated by 
any other means. 
Of especial use are the indicators for investigating the diffusion and mobility 
of ions in extremely small concentration, from which results we obtain informa- 
tion concerning the behaviour and the hydration of ions in very dilute 
concentration. Datas are already available on the diffusion rate of lead salts 
down to a normality of 10-", 
The following Papers were then read :— 
Puysican Division. 
1. (a) Neutral Salt Action. (b) Solubility and Distribution. 
By Dr. B. pe SzyszkowskI. 
2. Some Suggestions regarding the Nomenclature of Oplical Activity. 
By Dr. T. S. Parrerson. 
3. The Hydrogen Ion Concentration of the Sea and the Alkali Carbon 
Dioxide Equilibrium. By Dr. Pripeavx. 
METALLURGICAL DrvyisIon. 
4. The System Copper-Oxygen. By F. D. Farrow. 
_This paper presented in a concise form the results of the work on the melting- 
points and dissociation pressures of the system copper-oxygen, obtained by 
Heyn, Wohler, and by Slade and Farrow. Heyn has obtained melting-points 
of mixtures containing up to 1 per cent. of oxygen. He finds a eutectic point 
with an oxygen content of 0°39 per cent. at 1065° C., while the mixture con- 
taining 1 per cent. of oxygen melts at 1167° C. 
Slade and Farrow have shown that mixtures containing between about 2°3 
and 10°3 per cent. of oxygen when heated above 1195° C. melt and form two 
liquid layers, the upper of which is richer in oxygen than the lower. The 
composition of these layers is for all temperatures investigated about 2°3 per 
cent. of oxygen for the lower and about 10-3 per cent. for the upper. The 
compositions do not appear to approach each other with rising temperature. 
By extrapolating over a short distance the authors place the melting-point of 
cuprous oxide (11°26 per cent. of O) at 1210° C. 
The same authors have investigated systems whose composition lies between 
those of cuprous and of cupric oxide. They find two melting-point curves which 
intersect at about 1060° C. The eutectic mixture corresponding to this has a 
composition of 14:8 per cent. of oxygen. The melting-point of cupric oxide is 
found not to have been attained at a temperature of 1148° C., at which tempera- 
ture the dissociation pressure of the oxide exceeds 24 atmospheres. 
1913. aa 
