TEMPERATURE OF VAPOUR FROM BOILING SALINE SOLUTIONS. 223 



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2) the vapour arising from the boil- 

 ing solution passed up the central 

 column, and then down the outside 

 space before entering the condenser 

 tube K, to the top of which a glass 

 condenser was attached. The con- 

 densed water was led by a tube L back 

 to the bottom of the hypsometer and 

 thus kept the solution at constant 

 concentration. A brass coil S was 

 inserted in the bottom of the hypso- 

 meter in order that steam could be 

 blown in if required. The addition of 

 steam of course altered the concen- 

 tration. Two thermometers were 

 inserted into the centre column of 

 vapour. The bulb of one A, was just 

 halfway down the column, and was 

 about ten inches above the level of the 

 boiling solution, the other B, was 

 nearer the cork and opposite the pas- 

 sage into the outer space. In the 

 above arrangement the inner column 

 Fl S- 2 * of vapour arising from the boiling 



solution is jacketed by the vapour outside, which is of course 

 at a lower temperature, so that although radiation losses are 

 minimised, a certain loss of heat from the inner vapour to 

 the outer must take place. There is, therefore, no possi- 

 bility of the vapour in the outer jacket supplying heat to 

 that in the centre column. Superheating of the vapour in 

 the jacket was effectually prevented by placing the hypso- 

 meter on a large piece of asbestos cardboard, provided with 

 a small hole in the centre through which the flame of the 

 bunsen burner impinged on the bottom of the hypsometer. 

 There is still the possibility that heat may have been con- 



