STEAM AND BRINES. 531 



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

 o-oocl, 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 dissolve 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 in molecule of each salt : — 



Salt Used. NaCl. KC1. BaCl 2 . (NH 4 ) 2 S0 4 . 



Temperature of Condensation | water, . 100-44° C. 100-44° 99-95° 99-40° 



of Steam on (salt, . . 108-98° 108-94° 104-46° 107-03° 

 AVeight of Steam Condensed for complete 



solution, .... grms., 299 25-9 64-0 25 



The least soluble of these salts is chloride of barium, requiring 64 grms. of condensed 

 steam for solution, and the most soluble is sulphate of ammonium, which requires only 

 25 grms. 



Apparatus and Method of Experimenting. — The apparatus, fig. 1. consists of 

 the lamp, A, the steam generator or boiler, 13, the U-tube or receiver, D, and the 

 connecting tube, G. In the laboratory a gas lamp was used, except when it was 

 wished to check the results by the fuel consumed, when a spirit lamp was used, 

 and it was weighed before and after the experiment. In the experiments at 

 high levels, where gas was not available, spirit was used. The lamp employed 

 was one of a French pattern, and forming a part of the Rechand d double jiamme forcee 

 of smallest size, which has a large sale for domestic purposes. It is the most 

 efficient pattern of spirit lamp with which I am acquainted, and as it is especially con- 

 structed for use in travelling, it was very suitable for my high-level work. It holds 

 about 250 c.c. of spirit. 



