19G KEY. S. M. JOHNSTON 



of asbestos paper E. It was supported on a piece of wire gauze by a retort-stand. 

 The wire gauze and asbestos paper preserved the tube from the direct action of the 



flame, the latter being used as the source of heat, the heating being direct. 



To ward off draughts a circular cylinder of zinc was used in two pieces, one of 

 winch could be removed when desired. Three sizes of boiling tubes were used, one 

 for dilute solutions capable of containing 50 cubic centimetres of solvent or solution 

 to the height indicated; the others were a 25 cubic centimetre and a 15 cubic centi- 

 metre tube for moderately dilute and concentrated solutions, each being so arranged 

 that the liquid, solvent, or solution reached the same height, and that the same platinum 

 cylinder suited all three. 



With the apparatus arranged in this way, a steady boiling temperature was quickly 

 attained. 



A Beckmann reading-glass was used for making the readings, the thermometer 

 being slightly tapped before the readings were made. In that way it was possible to 

 read to one-thousandth of a degree. Notwithstanding the delicacy of the thermometer, 

 it was possible to bring it to a perfectly steady position, not unfrequently for several 

 minutes. 



The water used was redistilled to guard against impurities. The filling material 

 after each series of experiments was thoroughly cleansed with boiling water and dried 

 before being used again. The platinum foil in addition was heated in a Bunsen 

 flame. 



In order to find the change in concentration due to boiling, experiments were made to 

 determine the amount of vapour present in the tube during ebullition. The determina- 

 tion was founded upon specific gravity observations made by means of a pyknometer, 

 and using in the boiling tube a quantity of the solution of known weight, the volume 

 corresponding to that to be used in experiments. The specific gravity of the solution 

 was first measured at 15° Centigrade before being placed in the boiling tube, and then 

 after boiling in the tube for some time. In the latter case the boiling solution was 

 withdrawn from the boiling tube in a pipette, in which it was cooled with as little loss 

 of vapour as possible. From these data the percentage compositions were determined 

 graphically by the aid of tables.* These being known, the vapour determination was 

 readily made. The amount was found to vary from "3 to '56 of a gramme, and was 

 allowed for. 



Series of solutions were made by the addition of compressed pellets of salt succes- 

 sively to the solvent or solution during ebullition. The pellets were made at first by 

 the aid of a steel press, but later by one with ivory fittings, to safeguard their purity, 

 this being specially important where deliquescent salts were the subject of research. 



The procedure adopted was to bring the solvent to a steady boiling temperature, 

 which was noted. Then pellet after pellet of salt was added at intervals of from 

 twenty to twenty-five minutes, the boiling temperature of the successive concentra- 



' B. A. Reporl on the Present. State of our Knowledge of Electrolysis and Electro-chemistry (1893). 



