SOLUTIONS 



87 



Condenser 



When the pressure under which water boils is less than 760 mm., 

 the boiling point is less than 100 C. (cf. Appendix, Table VIII). 

 Sugar refiners make use of this fact in boiling off the water from dilute 

 syrup. If the water were removed at the ordinary pressure, the syrup 

 would boil so high that the sugar would be spoiled. By the use of 

 evaporating vessels called "vacuum pans," which are covered with 

 tight hoods (Fig. 73), 

 this is avoided. If 

 the air is removed 

 from the pans until 

 its pressure is only 

 233 mm., the water 

 boils off at 70 C. 

 without injuring the 

 sugar. Salt is ob- 

 tained from salt brines 

 in the same way. 



The boiling point 

 of water falls about 

 1C. for every 960 

 feet we ascend above 

 sea level. Thus, at 

 the city of Mexico, 



7,500 ft. above the sea, water boils at 92.3 C., while at Denver, 5,000 

 ft. high, it boils at about 95 C. 



91. Solutions. If we put salt or sugar into water, the 

 solids disappear. We say they dissolve in the water. They 

 have really been mixed with the water, for they give their 

 taste and other properties to the water. We call the 

 water the solvent, and the dissolved substance the solute. 

 The mixture of solute and solvent is called a solution. 

 Solutions in which alcohol is the solvent are called tinc- 

 tures. If the solute is of some other color than white, 

 its water solution will usually be colored. A minute 



FIG. 73. 



Vacuum Pan. Water is being distilled at 

 "reduced pressure." 



