184 DIFFERENT LIQUIDS IN COMMUNICATING VESSELS. 



between the horizontal plane a b and c is 40 cm . The 

 surface at which both liquids are in contact experiences 

 from below an upward pressure, which is equal to the 

 weight of a column of water, having a base of 300 

 square centimetres, and a height of 40 cm , that is, a 

 pressure of 40 x 300 = 12,000 CC water, or 12,000 gr . 

 Equilibrium can only exist if the surface of contac 

 supports an equal downward pressure from above. 





FIG. 132 (^ real siae). 



The volume of a column of paraffin -oil which weighs 

 12,000^ is easily found, for its specific gravity bein< 

 0*8, l cc of the oil weighs 0^*8, and therefore the numbei 

 of cubic centimetres of it that are required to make u 

 together a weight of 12,000 Fr is equal to the number ol 

 times that 0*8 is contained in 12,000, that is, we requir* 



15,000 CC . The volume of the liquid columi 

 o 



and the area of its base being known, the heighl 

 may be calculated; for the volume is the product oi 

 the area of the base into the height, and hence the 

 height is found by dividing the volume by the base. 



In our case it is 1 = 50 cm . The height of the 



