94 ELEMENTS OF LABORATORY WORK 



possible. Finally, no region contains x alone and no region 

 contains y alone at any rate, so far as we can yet analyse. 



This action may be readily shown by placing a small flask 

 containing alcohol within a large cylinder (fig. 30), and filling 

 the cylinder gradually with water, which is denser than the 

 alcohol, until its level is about 2 inches above the top of the 

 flask. A glass bulb, blown so as to just float in water, and 

 placed in the cylinder, will be found to sink lower and lower 

 as the density of the liquid in the cylinder diminishes with the 

 progress of the diffusion. When the diffusion is complete, the 

 density of the liquid in the flask will be found, 

 on removal and examination, to be the same as 

 that in the cylinder. That is, the liquids will 

 be evenly mixed by a process which cannot be 

 directly traced nor explained, unless we admit 

 that it is by the imperceptible movement of 

 very minute particles of each liquid. 



This action may also be illustrated by 

 placing, by means of a fine pipette, a coloured 

 liquid, such as a solution of potassium bichro- 

 mate, at the bottom of a cylinder already 

 filled with water. With care, little disturbance 

 of the water will ensue. The diffusion may 

 "rig. soT then be observed bv tne gradual change to a 

 uniform tint throughout. Other methods will 

 suggest themselves. The rate of diffusion varies with the 

 kind of matter used ; but in all cases the rate increases 

 with the temperature. 



63. When a Solid and a Liquid are placed in Contact, the 

 Solid tends to gradually diffuse throughout the Liquid, in 

 Amount dependent upon their Relative Quantity and their 

 Nature and Temperature. If water is the liquid selected, and 

 sodium chloride the solid, it will be found that a small 

 quantity of the solid, introduced into the liquid, will rapidly 

 disappear or dissolve. A further quantity may be added and 

 the same change ensues, and so on until a limit is reached. 

 The solid does not then dissolve, but sinks to the bottom. 



