of Frozen Electrolytes at very Loiv Temperatures. 395 



form of the dielectric temperature curve is not unlike the magnetisa- 

 tion curve of a ferro-magnetic body or a vapour tension curve. 



In most of the curves there is within a certain range of tempera- 

 ture a fall more or less sudden from a high value of the dielectric 

 constant to a low value. 



As regards the value of the dielectric constants of frozen electro- 

 lytes at the temperature of liquid air, the salts employed by us may 

 be divided into three broad classes : — 



I. Those which, when added to water in percentages from 5 to 50, 

 do not much affect the dielectric constant of the water when it 

 is frozen ; and which, at the temperature of liquid air, have 

 dielectric constants not far from 25, or lying between 2 and 3. 

 Such salts are sodic bicarbonate, sodic bisidphate, potassic bi- 

 chromate, potassic bicarbonate, sodic chloride, baric chloride, 

 potassic iodide, sodic nitrite, hydropotassic sulphide, cupric 

 carbonate. These include the acid salts and halogen salts. 



[I. Those salts which, when added to water in percentages from 

 5 to 50, raise the dielectric constant of the water somewhat and 

 which yield frozen electrolytes, having, at the temperature of 

 liquid air, dielectric constants lying between 3 and 10, that 

 of pure ice at the same temperature being 2' 5. Such salts 

 are potassic chromate, sodic sulphate, sodic chlorate, cadmic boro- 

 tungstate, sodir> acetate, potassium aluminic sulphate, plumbic 

 nitrate. These are all highly oxygenated salts. 



III. Salts which, when added to water in percentages from 5 to 50, 

 yield electrolytes which, if frozen, have immensely greater 

 dielectric constants, than pure ice at the temperature of liquid 

 air, viz., values from 30 to 70. 



Such salts are sodic carbonate, sodic biborate, sodic hypo- 

 sulphite, sodic silicate, hydrodisodic phosphate, potassium ferro- 

 cyanide. 



It will be noticed that whenever we have tested a normal salt and 

 an acid salt of the same base, such as a carbonate and a bicarbonate, 

 a chromate and a bichromate, a sulphate and a bisulphate, the acid 

 salt always has the low r er dielectric constant of the two at the tem- 

 perature of liquid air. 



With the exception of sodium carbonate, potassium ferrocyanide, 

 and hydrodisodic phosphate, the whole of the dielectric curves seem 

 to be tending downwards in such a way as to show that at somewhat 

 lower temperatures than we have at command, the whole of these 

 frozen electrolytes would have dielectric constants not far from that 

 of pure ice. In other words, would be reduced to values probably 

 near 2 or 3. 



There seems now a fair amount of evidence to show that with a 



