Vapours of Boiling Saline Solutions, 



483 



fixed by the stops i; the 

 cover is conical, so that 

 any liquid formed from 

 condensed vapour on its 

 under surface may trickle 

 down into the annular 

 channel which surrounds 

 it, and thence be discharged 

 through the small tube /, 

 which also gives exit to the 

 steam. Through the necks 

 fjf thermometers fixed in 

 perforated corks may be in- 

 serted. 



A saturated solution of 

 common salt was prepared 

 which was found to boil at 

 109°. The vessel a was 

 filled with this brine to the 

 level of the dotted line g, 

 and was caused to boil gently 

 by the spirit-lamp m. The 

 neck/' being closed with a 

 cork, the thermometer 1 was 

 inserted in the neck/. The 

 small conical screen of covkk 

 fitting tightly on the stem of 

 the thermometer, prevents 

 moisture from above from 

 trickling down on the bulb, 



which it also shields in a degree from radiation in that direction. 

 When steam was issuing freely from the small pipe I, the thermo- 

 meter indicated 109°. The liquid was now drawn off slowly by the 

 stopcock e into a measure previously adjusted, so that the sur- 

 face of the liquid in a would remain approximately at the level h, 

 and thus the thermometer was left in an atmosphere of steam 

 with the bulb and the lower part of the stem with its cork screen 

 wet with brine. The double screen n, with holes not opposite to 

 each other, shields the thermometer from particles of brine which 

 may be thrown upwards by the boiling liquid. The flame of 

 the lamp was now kept steady, so as to cause a constant current 

 of steam to issue gently from the tube /. The surfaces of the 

 shell b above the level of the remaining brine would also have 

 been left wet with the same brine. The upper part of the vessel 

 a would now be full of steam under atmospheric pressure. 



Here we have a thermometer suspended in an atmosphere of 



21 2 



