WATER 



59 



The water is carried as vapor by the excess of hydrogen and 

 passes into the U-tube B. This tube contains calcium chloride, 

 a substance which absorbs water greedily and is used therefore 

 for drying gases. Here the water is all caught, while the hydro- 

 gen passes on. The tubes A and B with their contents are 

 weighed just before, and again just after, the experiment. The 

 loss of weight in A is the weight of the oxygen. The gain in 

 weight in B is the water. The difference between these numbers 

 is the hydrogen. It is found that the weights 

 of hydrogen and oxygen thus ascertained always 

 stand in a ratio close to 1 (Hyd.) : 7.94 (Ox.) or 

 1.008 : 8, the proportions accurately determined 

 by Morley. 



Measurement of the Composition by Vol- 

 ume. The proportions by volume in which 

 hydrogen and oxygen combine may be shown by 

 introducing the two gases into a tube, filled with 

 mercury and inverted in a cylinder of mercury 

 (Fig. 32). The volumes, at atmospheric pres- 

 sure, are read by lowering the tube, after the 

 introduction of each gas, until the levels of the 

 mercury inside and outside are alike. A spark 

 from an induction coil passed between the 

 platinum wires inserted at the top of the tube 

 causes the union of the gases. The water con- 

 denses to a slight dew and the volume of the 

 single gas which remains is measured. Thus, 

 if 19.5 c.c. of oxygen and 20 c.c. of hydrogen FlG - 32 



are taken, the volume of gas remaining is 9.5 c.c. and this gas is 

 afterwards found to be oxygen (test, p. 36). The volumes con- 

 sumed were therefore 19.5 - 9.5 = 10 c.c. of oxygen and 20 c.c. 

 of hydrogen. The ratio by volume is therefore 2 Hyd. : 1 Ox. 

 If these exact proportions are used, the mercury fills the tube 



