100 



ELEMENTARY GENERAL SCIENCE 



CHAP. 



Determination of Eelative Densities by a U -tube. A 



graphic method of showing the relative densities of liquids is 

 obtained by means of a glass tube bent in the form of a |J> and 

 tht'ivfore called a LJ-tube. 



EXPT. 97. Cut off two pieces of glass tube, each about 

 30 cm. long ; connect the tubes with india-rubber tubing about 

 18 cm. long, and fix them upright upon a strip of wood. Pour 

 mercury into one of the tubes until it reaches a horizontal line 

 drawn a little above the junctions (Fig. 44). Now introduce 

 water into one of the tubes by 

 means of a pipette, and notice that 

 the mercury on which the water 

 rests is pushed down ; afterwards 

 introduce sufficient water into the 

 other tube to bring the mercury 

 back to its original level. The 

 length of each column of water will 

 be found the same. Repeat the 

 experiment with varying amounts 

 of water. 



.Mercury 

 India-rubber 



FIG. 44. Determination of Re- 

 lative Densities by a U'tube. 



The mercury in the bend of the 

 LH-ube evidently acts as a balance, 

 which enables us to balance columns 

 of different liquids in the upright arms. 



EXPT. 98. Nearly fill one of the 

 tubes with methylated spirit, and 



balance it with water introduced into the other tube. Measure 

 the lengths of the two columns. 



As these two lengths of liquid balance one another it will be 

 evident that the shorter of the two columns, namely, the water 

 column, has a greater relative density than the longer column. 



If a column of liquid 40 cm. long balance a similar column of 

 water of half that length, would the liquid be double or half as 

 dense as the water ? 



By thinking over this question and the result of the experi- 

 ments you will be able to understand that the densities of two 

 liquids balanced in a U'tube are in inverse proportion to the 

 lengths of the columns ; in other words, the density of one 

 liquid is less than the density of the other in proportion as its 



