ELEMENTARY GENERAL SCIENCE CHAP. 



EXPT. 1. Filter some muddy water through a filter paper 

 placed in a funnel (Fig. 1). The particles of water are small 

 enough to pass through the pores of the paper, but the solid 



particles of mud are too large, 

 hence they are left behind. 



EXPT. 2. Procure a piece 

 of chamois leather ; make it 

 into a bag, and pour some 

 mercury into it. Increase the 

 pressure on the mercury by 

 twisting the leather. The 

 mercury is forced through 

 the pores. This is a common 

 FIG. 1. Funnel and Filter-paper. wa y o f filtering mercury. 



EXPT. 3. Half fill a baro- 

 meter tube with water ; then gently add alcohol until the 

 tube is nearly full. Make a mark on the tube at the level 

 with the top of the liquid column, and afterwards shake the 

 tube so as to mix the water and alcohol well together. 

 Observe that the volume of the mixture has diminished, the 

 reason being that some of each liquid has filled up pores 

 between the particles of the other. 



Compressibility. This property follows as a natural conse- 

 quence of that just described. If pores exist between the 

 indivisible small particles of which matter is built up, it ought 

 to be possible, by the adoption of suitable means, to make 

 these particles go closer together. This is found to be the case. 

 By pressing upon the body from outside it can be made smaller. 



This is very well known to be the case in gases, which can 

 actually be made to become successively one-half, one-quarter, 

 one-eighth, and so on up to at least one-hundredth of their original 

 size. 



The same thing holds true in the case of solids, though to 

 a much smaller extent. A familiar example of the compression 

 of solids is seen when a druggist presses a cork between two 

 pieces of iron in order to make it fit a bottle for which it was 

 previously too large. But, generally, in the case of solids the 

 pressure exerted has to be very great to bring about even a 

 small compression. 



It was believed for a long time that liquids could not be com- 

 pressed, but it is now known that they can be very slightly 



