I PHYSICAL PROPERTIES AND STATES OF MATTER 11 



itself to the shape of the vessel containing it, but the con- 

 ditions remaining the same, it keeps its own size or volume, 

 however much its shape may vary. JVTien it is not held by the 

 sides of a vessel it at onceflou-s. This is the commonest everyday 

 experience. You cannot get a pint of beer into a glass of half a 

 pint capacity. It does not matter what the shape of the bottle 

 or jug may be providing it holds a pint, as we say, or provided 

 its capacity is a pint, the quantity of beer taken to exactly fill it 

 is always the same. If we turn the jug upside down, the beer all 

 runs away because there is no part of the vessel to prevent it 

 from flowing. The surface of liquids, too, enclosed by a vessel 

 is always level. 



The Flow of Liquids. The power of flowing is not perfect in 

 liquids. The small particles making up the liquid always stick 

 to one another a little, and when any part of a mass of liquid 

 moves, it always attempts to drag the neighbouring particle, which 

 is at rest, with it. We can sum this up by saying that liquids 

 would flow perfectly if they possessed no viscosity. Those liquids 

 which have little viscosity, or, what is the same thing, are very 

 mobile liquids, are instanced by alcohol and water ; while treacle 

 and tar have little mobility, but are very viscous. Evidently, 

 then, there is a gradation in those forms of matter which have 

 as yet come before our notice. At one end we have very mobile 

 liquids, which as the viscosity increases flow less and less easily, 

 until at last there is no power of flowing at all, and we have the 

 solid form of matter. 



EXPT. 14. Procure specimens of treacle and pitch. Soften 

 the latter. Compare the consistency of the treacle and the 

 softened pitch with 

 that of water, and 

 note the gradual in- 

 crease in the vis- 

 cosity of the liquids, 



Liquids find their 

 Level. If several ves- 

 sels of the most varied 

 shapes (Fig. 5) are in 

 communication with 

 one another, and water 

 be poured into any one 



FIG. 5. Vessels of various shapes in communica- 

 tion. Water standing at same level in all. 



