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THE GENESEE FARMER. T5 



in the tube, and not rise to its liydrostatic or proper level. If tlie attraction of the par- 

 ticles of water for each other and for the glass be equal, the fluid will come precisely to 

 its level ; and if the attraction between the water and the glass be greater than between 

 atoms of water, the water will rise steadily in the tube. This explains the law oi cajnl- 

 lary attraction and circulation. 



A body, when acted on by an extraneous force, if brought into a smaller space, it is 

 said to be compressible ; if, when the pressure is removed, the body regains its original 

 volume by the mutual repulsion of its own particles, it is said to be elastic ; if, on the 

 contrary, it remains compressed, it is called inelastic. In nature there are but few bodies 

 perfectly elastic, and none which are perfectly inelastic. When the pressure is removed 

 from the so-called inelastic solids, if they have been compressed, a slight expansion 

 occurs ; while in gases and liquids the return to the original volume is complete. Solids 

 and liquids are so slightly compressible, that delicate tests are necessary to determine it. 

 A pressure of 400 lbs. upon a square inch of water diminishes it the 1-1000 part. The 

 compressibility and elasticity of gases are nearly perfect and uniform. Thus, air which 

 under a weight of 20 lbs. occupies 100 cubic inches, is reduced in volume to 25 inches 

 by increasing the pressure to 80 lbs. ; and it expands to 400 cubic inches if the weight 

 be reduced to 5 lbs. Barometers indicate variations in the weight of the atmosphere, 

 caused, doubtless, partly by the rotation of the earth on its axis and by its course round 

 the sun ; and partly by clouds, winds, mountains, vapors, oceans, continents, &c. The 

 essential difterance between a barometer and a thermometer is, that the former has a 

 column of mercury wdiich is exposed to the air at its base, having, like a thermometer, a 

 vacuum above the mercury. Hence, the least variation in the pressure of the air on the 

 mercury in the little cup, causes it to rise or fall in the tube. In a thermometer, the 

 mercury is hermetically sealed in the glass, and rises or falls as heat expands or cold 

 contracts the liquid metal. 



In some cases gases are brought within the cohesive forces of their particles, which 

 modify their compressibility. Thus, if a tube full of air and a tube full of sulphurous 

 acid gas be subjected to exactly the same pressure, the volumes will not diminish in the 

 same degree when the pressure becomes high, but as follows : 



The air as ICfiO a^? K9 814 



Sulphurous acid aa 1000 851 554 801 



In some other gases the same variation has been observed. (Kane.) 



Some gases have been liquified by great pressure, and frozen by their sudden expan- 

 sion when the pressure was taken off by gi^^ng vent. Other gases, such as oxygen, 

 hydrogen, and nitrogen, have been subjected to a pressure of 800 atmospheres, equal to 

 12000 lbs. to the square inch, without causing any change in their natural elasticity, or 

 other properties. 



Heat may be regarded as an antagonist power to that of cohesion, and tends to render 

 the molecules of a body repulsive to each other, and to separate them to greater dis- 

 tances than they had been before. "V^Tien a solid, like salt or sugar, is dissoh^ed in water, 

 the phenomenon is explained by saying that the particles in the solid have a greater 

 affinity for water than for each other. Hence, their previous cohesion is destroyed ; 

 they separate in the mass of liquid, which constitutes their solution, or the disappear- 

 ance of the solid. Substances are soluble or insoluble, according as the force of solid or 

 liquid cohesion, or attraction, prevails among their several atoms. Bodies insoluble in 

 water, like resins, dissolve in other fluids, such as alcohol, ether, and Seneca oil. 



Gt^ • — — — — r-;c) 



