856 DR S. M. JOHNSTON ON THE BOILING AND FREEZING POINTS OF 



vacuum tubes, ether and solid carbon dioxide, or ether, solid carbon dioxide, and liquid 

 air. The solid carbon dioxide was added to the ether, and a freezing temperature 

 obtained approximately as desired. When very low freezing temperatures were 

 desired, of — 70° Centigrade or more, the temperature of the ether was reduced to over 

 — 60° Centigrade by the use of solid carbonic acid, and the further reduction was effected 

 by means of liquid air blown into a tube inserted in the mixture of ether and carbonic 

 acid. The evaporation of the liquid air quickly produced the degree of cold desired, 

 and there was no difficulty in freezing any of the solutions used. Three Beckmann 

 thermometers and two pentane thermometers were used to give the temperatures of the 

 various freezing solutions. Two of the Beckmann instruments read to one-hundredth 

 of a degree, the third had a range of 12° and read to one-fiftieth of a degree. Two of 

 these instruments were certified correct as to scale reading by the Reichsanstalt. One 

 of the pentane thermometers used had a range of — 65° Centigrade and read to one-fifth 

 of a degree, and was made by Goetze ; the other had a range of — 100° Centigrade, and 

 was made by Hicks. Neither was certified, but they were compared with the standard 

 Beckmann's for the range of temperature of the latter. The readings were taken with 

 the aid of a Beckmann reading glass. 



Conductivity experiments at 0° Centigrade were made with the aid of a bath kept 

 at about 0° Centigrade. The cells used were of the Arrhenius and Kohlrausch 

 patterns, and their electrodes, which were of stout platinum foil, were platinised. 

 For measuring resistances, Hartmann and Braun's form of the Kohlrausch bridge was 

 used, with a Bell's telephone and an induction coil by the same makers.* The current 

 was supplied from a two- volt storage cell. The salts used were Messrs Merck & Co.'s 

 " Purest," and water-free salts were used when these were obtainable. From 20 to 30 

 cubic centimetres of solution were used for an experiment. 



The deci-normal solutions of the chlorides, bromides, and iodides were tested 

 volumetrically by a standardised solution of silver nitrate, potassium chromate being 

 used as indicator. The silver nitrate solution was standardised by titration against a 

 tenth normal solution of potassium chloride. The concentration of the acids used was 

 found by volumetric analysis, with the aid of a solution of sodium hydrate, which was 

 standardised by titration against a tenth normal solution of oxalic acid, phenylphthalein 

 being used as indicator. The other salts were analysed gravimetrically. 



The following tables contain determinations of elevation per gramme equivalent 

 which have been made from my own observations, and the results are given graphically 

 in fig. 1, p. 859, by curves for which gramme equivalents per litre have been plotted 

 against elevation per gramme equivalent. The curves usually show a minimum point, 

 which occurs at a point corresponding to a concentration of from '5 to 1 gramme 

 equivalent per litre or thereabout. In a very few instances the curves do not present 

 any minimum point. For higher concentrations than that corresponding to the 

 minimum point, there is for nearly all the salts considered an increase of elevation 



* JVied. Ann., 10, 326 (1880). 



