78 WATER, 



It is rapidly dissolved by water. If passed into a solution 

 of nitrate of silver, it produces a white precipitate which 

 soon blackens on exposure. It is given out occasionally by 

 volcanoes.* 



CLASS II.— WATER. 



Water (oxyd of hydrogen) is the well known liquid of our 

 streams and wells. The purest natural water is obtained by 

 melting snow, or receiving rain in a clean glass vessel ; but 

 it is absolutely pure only when procured by distillation. It 

 consists of hydrogen 1 part by weight, and oxygen 8 parts. 

 It becomes solid at 32° Fahrenheit, (or 0° Centigrade) and 

 then crystallizes, and constitutes ice or snow. Flakes of 

 snow consist of a congeries of minute crys- 

 tals, and stars like the annexed figure may 

 often be detected with a glass. Various 

 other allied forms are also assumed. The 

 rays meet at an angle of 60 °, and the 

 branchlets pass off at the same angle with 

 perfect regularity. The density of water is 

 greatest at 39° 1 F. ; below this it expands as it approaches 

 32°, owing to incipient crystallization. It boils at 212 F. 

 A cubic inch of pure water at 60 3 F. and 30 inches of the 

 barometer, weighs 252*458 grains. A pint, United States 

 standard measure, holds just 7342 troy grains of water, 

 which is little above a pound avoirdupois (7000 grains troy.) 

 Water as it occurs on the earth, contains some atmos- 

 pheric air, without which the best would be unpalatable. 

 This air, with some free oxygen also present, is necessary 

 to the life of water animals. In most spring water there 

 is a minute proportion of salts of lime, (sulphate, chlorid 

 or carbonate,) often witfi a trace of common salt, carbo- 

 nate of magnesia and some alumina, iron, silica, phospho- 

 ric acid, carbonic acid, and certain vegetable acids. These 

 impurities constitute usually from ^ to 10 parts, in 10,000 

 parts by weight. The Long Pond water, used in Boston, 



Of what does water consist ? What is said of snow and ice ? What 

 of the density of water ? its boiling temperature ? the weight of a pint 1 

 What are the usual impurities of common spring or river water i 



* Carbonic acid and sulphurous acid gases, are described, one undei 

 tarbon, and the other under sulphur. 





