150 NON-METALS AND THEIR COMBINATIONS. 



drinking-water. There are, however, good drinking-waters which 

 contain more of total solids than the amount mentioned above. 



Most objectionable in drinking-water are organic substances, espe- 

 cially when derived from animal matter, and more especially when 

 in a state of decomposition, because such decomposing organic matter 

 is frequently accompanied by living organisms (germs) which may 

 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. 



In nature water is rendered free from organic impurities by the 

 oxidizing power of atmospheric oxygen, which is taken up by the 

 water and is readily transferred upon organic matter present. 



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 puri- 

 fier. 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 mentioned 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 100 parts. 



Composition of water. Until the discovery of oxygen, water 

 was thought to be a simple substance. In 1781 Cavendish, of Eng- 

 land, discovered the qualitative composition of water when he 

 obtained it by causing hydrogen and oxygen to unite. Water was 

 thus produced synthetically. 



The proportion of hydrogen and oxygen in water has been determined 

 accurately by weighing the oxygen and the water formed by union with hydro- 

 gen, also by weighing both constituents and the water after union. The results 

 of the most accurate experiments showed that water contains 11.185 per cent. 

 of hydrogen and 88.815 per cent, of oxygen, or 2 parts by weight of hydrogen 

 to 15.88 parts, by weight, of oxygen. It has been ascertained that the mole- 

 cule of water is made up of two atoms of hydrogen and one atom of oxygen, 

 H 2 O. Hence, it follows that the atomic weight of oxygen is 15.88. By vol- 

 ume, hydrogen and oxygen unite in the proportion of 2 : 1 to form water. 



