212 WATER. 



water absorbs any other gas, the air which it contains is more or less ex- 

 pelled ; hence, gases confined over water, are soon contaminated in 

 this manner. In boiling water, the first portions expelled contain the 

 most oxygen ; the nitrogen comes more tardily, and, if after boiling 

 and air pump exhaustion have ceased to evolve any more gas, electri- 

 cal discharges be passed through water, more nitrogen will be evolved 

 along with oxygen and hydrogen, proceeding from the decomposition 

 of the water. 



2. Boiled water, absorbs a portion of every gas.* The quantity 

 absorbed is increased by pressure and by cold, and the facts will be 

 more particularly stated in giving the history of each particular gas. 



3. Water always exists in the atmosphere, in the driest weather. 



Sa.) Deliquescent substances attract it, as potash, sulphuric acid, 

 muriate of lime. 



(b.) Cold bodies condense it, in dew or hoar frost. 

 (c.) Porous bodies absorb water from the air. -Dry earth, dry oat 

 meal, and dry metallic filings, afford examples. 



4. Water, by combination becomes solid. This is seen in the hy- 

 drated alkalies, potash and soda,, in the hydrated oxides, and in many 

 crystals, especially artificial ones ; when crystals contain water, it is 

 always in definite quantity. 



5. Water, dissolves a great variety of bodies, more, probably, than 

 any other fluid acids, alkalies, salts, gum, sugar, alcohol, &c. 



It is the most general solvent to bring substances together, under 

 such circumstances as to promote the various chemical processes of 

 nature, and as it alters their properties very little, it is favorable to 

 chemical action by bringing many solids into a state of fluidity. But 

 in some cases, its chemical action is highly important. 



6. The solution of a solid in water generally produces cold. 

 Bi-carbonate of potash and caustic potash crystallized, produce cold ; 

 but caustic potash that has been recently ignited, or which after that 

 operation has not again absorbed water, dissolves with a rise of tem- 

 perature. 



7. Jlir is disengaged during the solution of bodies in water. It is 

 partly contained in the crevices of the bodies, and partly dissolved in 

 the water. 



8. Water, when pure, is perfectly transparent, tasteless, colorless, 

 and inodorous. According to Professor Robinson, a cubic foot of 

 water at the temperature of 55, weighs 998. 74f oz. Avoirdupois, or 

 62.42 Ibs. A cubic inch at 60, and at 30 inches pressure, weighs 

 252.525 grains. Pure or distilled water, at the temperature of 60, 

 is always taken as the unit, when we speak of the specific gravity of 

 other bodies. 



* See n table, Henry, Vol. 1, p, 225. i In round numbers 1000. 



