72 NOX-METALS AND THEIR COMBINATIONS. 



Another method to prove the presence of organic matter is 

 the addition of a solution of potassium permanganate. On 

 heating 100 cc. of water, acidulated with 10 cc. of diluted sul- 

 phuric acid to the boiling-point, and adding enough of a dilute 

 solution of potassium permanganate (1 in 1000) to impart to the 

 liquid a decided rose-red tint, this tint should not be entirely 

 destroyed by boiling for five minutes, as, otherwise, organic or 

 other oxidizable matter is present. 



Distilled water, Aqua destillata. The process for obtaining 

 pure water is distillation in a suitable apparatus. From 1000 

 parts of water used for distillation, the first 50 parts distilling 

 over should not be used, as they contain the gaseous constituents. 

 The solids contained in the water are left in the undistilled 

 portion. 



Properties of water. Water is a colorless, inodorous, tasteless 

 liquid. It is perfectly neutral, yet it has a tendency to combine 

 both with acid and basic substances. These compounds are 

 usually called hydrates. Water is the most common solvent, 

 both in nature and in artificial processes. As a general rule, 

 solids are dissolved more quickly and in larger quantities by 

 hot water than by cold, but to this there are many exceptions. 

 For instance : Common salt is nearly as soluble in cold as in 

 hot water; sulphate of sodium is most soluble in water of 33, 

 and some calcium salts are less soluble in hot than in cold 

 water. 



Many salts combine with water in crystallizing; crystallized 

 sulphate of sodium, for instance, contains more than half its 

 weight of water. This water is called water of crystallization, 

 and is generally expelled at a temperature of 100 C. 



Hydrogen dioxide, H 2 2 . This compound may be obtained by 

 the action of carbonic acid on barium dioxide suspended in 

 water, when carbonate of barium and hydrogen dioxide are 



formed : 



Ba0 2 -f H 2 + CO 2 = BaCO 3 + H 2 2 . 



The liquid, separated by decantation from the insoluble car- 

 bonate, may be concentrated under the receiver of an air-pump 

 and is, when thus obtained, a colorless liquid of a specific 



