338 



Prof. W. M. Thornton. 



[Jan. 12, 



voltage. The effect is similar to that produced by the passage of ozone 

 through water, and being chemical rather than electrical is not considered 

 here in detail. It provides, however, an effective means of sterilising potable 

 water, using carbon electrodes, which might be of service where electrical 

 power can be had at low rates. 



On Milk. — In order next to examine the influence of direct current on 

 milk, and as before to keep the gases at the electrodes from the central 

 portion, a glass cell was made consisting of two circular pole-pits 4 cm. 

 diameter, joined by a tube 1*5 cm. diameter. Flat platinum foil electrodes 

 were used, the distance between them being 10 cm. Filled with fresh milk 

 and connected to a 100-volt supply from secondary cells, a current of 

 0"15 ampere passed. The current density at the poles was then - 03, and at 

 the centre of the connecting tube - l ampere per square centimetre. After 

 a few minutes the milk in the neighbourhood of the positive terminal began 

 to curdle, whilst that at the negative pole did not, though the surface became 

 covered with a fine froth. After a quarter of an hour the milk in the 

 positive pole-pit was a complete mass of hard curds, that at the negative 

 a yellowish whey with no sign of curdling. In the centre tube the milk 

 remained fresh and sweet to the taste ; the taste of the curdled milk was 

 strongly acid, and of the whey unpleasantly metallic. 



These effects were due to direct ionisation, not to the passage of the 

 current, or to the gases liberated, for on passing oxygen or hydrogen from 

 storage cylinders for long periods through milk no curdling or separation 

 resulted, and the milk in the centre tube carried the whole of the current 

 without change, even with 500 volts across the cell. The formation of curds 

 at the positive pole is in agreement with Hardy's conclusion* that coagula- 

 tion is set up by contact with ions of the opposite sign to that of the liquid. 

 In the present case the negative charge, though this is not so uniformly 

 distributed as in blood cells, can be directly observed under the microscope, 

 using a thin layer of milk and a strong electric field.f 



These results show that unidirectional currents can be passed through milk 

 without curdling it except quite near to the electrodes. As a practical 

 process of sterilisation this would, however, be very inefficient on account 

 of the large proportion wasted, and to attempt it at all, voltages of the order, 

 of 1000 to 2000 would have to be employed. 



* See Whetham's ' Theory of Solution,' p. 399. 



t See ' Eoy. Soc. Proc.,' 1910, B, vol. 82, p. 638, 2, for the method. 



