OF TWO LIQUIDS. 37 



unequal mobility of the particles of one or the 

 other liquid has a favourable or unfavourable in- 

 fluence on the result. 



When the one liquid is heavier than the other, by un- 



equal mo- 

 and of tough, viscid consistence, a much longer biuty, and 



time elapses before the ingredients of the tougher 

 or heavier liquid reach the surface from the bottom 

 of the vessel ; and in this case the greater density 

 and the less mobility of the particles are obstacles 

 to the mixture. 



On the other hand, if the heavier or more viscid 

 liquid be placed above the lighter, the mixture 

 takes place rapidly ; at the points where both liquids 

 are in contact is produced a mixture, which, being 

 heavier, descends, whereby the heavier liquid above 

 is continually brought in contact with new surfaces 

 of liquid. 



The very same phenomenon is observed in solu- Effect of 

 tion. A fragment of sugar, when covered with 



water at the bottom of a narrow cylinder, dissolves 

 very slowly, while, if suspended just below the sur- 

 face, it rapidly disappears. In the former case there 

 is produced round the sugar a thick syrupy viscid 

 solution, which protects the undissolved part of the 

 sugar for a long time from contact with the water ; 

 in the latter there is formed at the surface a solution, 

 which descends in striae, and gradually disappears, 

 while by the change of place thus induced, new 

 portions of water are constantly brought in contact 



