154 On Steam and Brines 



to fall in the same way as that of a freezing mixture begins 

 to rise. Operating in this way it is possible to obtain definite 

 and perfectly constant temperatures with most of the ordinary 

 soluble salts of the laboratory. They are, however, not all 

 equally good, and there are some that are of no use for 

 boiling mixtures. 



The effect produced when steam meets a salt depends on 

 the properties of the salt, especially on its solubility in boiling 

 water and on the thermal effect of its solution. Generally 

 speaking, the greater the solubility of the salt the greater is 

 the elevation of the condensing point of steam which it 

 produces. At ordinary temperatures salts commonly dis- 

 solve in water with absorption of heat, which tends to 

 increase the condensation of steam. The absorption of heat 

 may be so great that the brine produced by the salt dissolving 

 in the condensed steam is unable to rise to its boiling-point 

 until all the solid salt has disappeared. 



Amongst anhydrous salts nitrate of ammonium is a good 

 example of this. An experiment was made with 60 grammes 

 of the salt. In 2\ minutes after the steam reached the salt 

 it was all dissolved, and the temperature barely rose to that 

 of boiling water. Twelve grammes of steam had been 

 condensed. 



Of salts containing water of crystallisation, acetate of 

 soda is a good example amongst those which dissolve with 

 great absorption of heat. Sixty-two grammes of this salt 

 treated in the same way as the nitrate of ammonium were 

 completely dissolved in 2\ minutes after the steam reached 

 the salt, and the temperature had only reached 60 C. These 

 and similar salts are not suitable for boiling mixtures. 



The following are one or two examples of the solubilities 

 observed at the boiling-point of the saturated solution for 

 one-fifth gramme-molecule of each salt : 



Salt used Nad KC1 BaCl 2 (NH 4 ) Z SO 4 



Temperature of Conden-) water ioo'44 C. ioo'44 99'95 99* '40 



sation of Steam on f salt loS^gS io8'94 IO4'46 io7'O3 

 Weight of Steam Condensed 



for complete solution grms. 29^9 25*9 64^0 25 



