82 NON-METALS AND THEIR COMBINATIONS. 



cause disease. Boiling of water destroys these germs, and by subse- 

 quent filtering of the boiled water through sand, charcoal, spongy 

 iron, etc., an otherwise unwholesome water may be rendered fit for 

 drinking. 



It should be remembered that no filter can remain efficient for any 

 length of time, as the impurities of the water are retained by the 

 materials used as a filter, and this may become, therefore, a source of 

 pollution instead of a purifier. By heating to a low red heat the 

 materials used for filtering, these are cleaned and may be used again. 

 The methods applied to the analysis of drinking-water will be men- 

 tioned later. (See Index.) 



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 100 parts distilled over should 

 not be used, as they contain the gaseous constituents. The solids, 

 contained in the water are left in the undistilled portion, which should 

 not be less than 200 parts. 



Properties of water. Water is an inodorous, tasteless, and, in 

 small quantities, colorless liquid. Thick layers of water show a blue 

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

 both acid and basic substances. These compounds are usually called 

 hydroxides (formerly hydrates), such as NaOH, Ca(OH) 2 , etc. These 

 compounds are often formed by direct union of an oxide with water, 



thus : 



CaO -f H 2 O = Ca(OH) 2 . 



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 ; sodium sulphate is most soluble in water of 

 33 C. (91 F.), and some calcium salts are less soluble in hot than 

 in cold water. 



Many salts combine with water in crystallizing ; crystallized sodium 

 sulphate, for instance, contains more than half its weight of water. 

 This water is called water of crystallization, and is expelled generally 

 at a temperature of 100 C. (212F.). Some crystallized substances 

 lose water of crystallization when exposed to the air ; this property is 

 known as efflorescence. Crystals of sodium carbonate, ferrous sulphate, 

 etc., effloresce, as is shown by the formation of powder upon the crys- 

 talline surface. The term deliquescence is applied to the power of 



