42 CHEMICAL PHYSICS. 



above 0.7 per cent., abstract liquids from animal tissues when in con- 

 tact with them. 



Diffusion of gases. A diffusion similar to that of liquids takes 

 place also when two different gases are separated from each other by 

 some porous substance, such as burned clay, gypsum, and others. 



It has been found that specifically lighter gases diffuse with greater rapidity 

 than the heavier ones. The quantities of two different gases which diffuse 

 into one another in a given time are, as a general rule, inversely as the square 

 roots of their specific gravities. Oxygen is sixteen times as heavy as hydrogen ; 

 when the two gases diffuse, it will be found that four times as much hydrogen 

 has penetrated into the oxygen as of the latter gas into the hydrogen. This 

 regularity in the diffusion of gases is expressed in the Law of Graham, thus: 

 The velocity of the diffusion of any gas is inversely proportional to the square 

 root of its density. 



Indestructibility. All matter is indestructible i. e., cannot pos- 

 sibly be destroyed by any means whatever, and this property is known 

 as indestructibility. Form, shape, appearance, properties, etc., of 

 matter may be changed in many different ways, but the matter itself 

 can never be annihilated. Apparently, matter often disappears, as, 

 for instance, when water evaporates or oil burns; but these apparent 

 destructions indicate simply a change in the form of matter; in both 

 cases gases are formed, which become invisible constituents of the 

 atmospheric air, and can, therefore, not be seen for the time being, 

 but may be recoudensed or rendered visible in various ways. 



Not only is matter indestructible, energy also partakes of this 

 property. This is expressed in the Law of the conservation of energy, 

 which says that in a limited system of bodies no gain or loss of 

 energy is ever observed. But energy may be converted from one 

 form into some other form. Motion may be converted into heat, and 

 heat into motion, or this motion into electrical energy and chemical 

 energy. In fact, all the different forms of energy are convertible one 

 into the other, theoretically, without loss. This fact is spoken of as 

 the Law of the correlation of energies. 



QUESTIONS. Define matter, force, and energy. Describe the character- 

 istic properties of matter in the solid, liquid, and gaseous states. State the dif- 

 ference between amorphous, crystalline, polymorphous, and isomorphous sub- 

 stances. State the laws of Boyle and Avogadro. Explain the terms mass and 

 molecule. What are cohesion, adhesion, and gravitation? Mention instances 

 of their action. Give a definition of weight and of specific weight. Explain 

 construction and use of the mercury barometer. Define capillary attraction, 

 absorption, diffusion, and osmose ; give instances illustrating their action. 

 What is meant by saying that matter and energy are indestructible? 



