262 HYDROGEN. 



Oxygen . 88.9 or 100 or 8.009 



Hydrogen . 11.1 12.48 1. 



100 112.48 9.009 



The oxygen and hydrogen are therefore very nearly, if not 

 exactly, in the proportion of 8 to I, as appears by the propor- 

 tions of the last column. This experiment serves not only to 

 determine rigorously the composition of water, but it offers also 

 the best method of ascertaining the composition of such metallic 

 oxides as are de-oxygenated by hydrogen. 



Properties. When cooled down to 32 water freezes, if in a 

 state of agitation, but may retain the liquid condition at a lower 

 temperature, if at rest (page 40) ; the ice, however, into which it 

 is converted cannot be heated above 32 without melting. Ice 

 is lighter than water, its specific gravity being 0.916 ; and the 

 form of its crystal is a rhomboid, very nearly resembling iceland 

 spar. Water is elastic and compressible, yielding according to 

 Oersted 53 millionths of its bulk to the pressure of the atmo- 

 sphere, and, like air, in proportion to the compressing force for 

 different pressures. The peculiarities of its expansion by heat 

 while liquid, have already been fully described (page 8). Under 

 a barometric pressure of 30 inches, it boils at 2 1 2, but evapo- 

 rates at all inferior temperatures. Its boiling point is elevated 

 by the solution of salts in it, and the temperature of the steam 

 from these solutions is not constantly 212, as has been 

 alleged, but that of the last strata of liquid through which the 

 steam has passed. When mixed with air, the vapour of water 

 has a tendency to condense in vescicles, which inclose air; 

 forming in this condition the masses of clouds, which remain 

 suspended in the atmosphere form the lightness of the vescicles, 

 the substance of mists and fogs, and " vapour " generally, in 

 its popular meaning. The vescicles may be observed by a lens 

 of an inch focal length, over the dark surface of hot tea or 

 coffee, mixed with an occasional solid drop which contrasts 

 with them. According to the experiments of Saussure, 

 made upon the mists of high mountains, these vescicles gene- 

 rally vary in size from the l-4500th to the l-2780th of an 

 inch, but are occasionally observed as large as a pea. They are 

 generally condensed by their collision into solid drops, and fall 

 as rain ; but their precipitation in that form is much retarded 

 in some conditions of the atmosphere. 



