148 



Confirmation of the Formula? C1 2 and H 2 . According to 

 Avogadro's hypothesis, there are equal numbers of molecules in 

 equal volumes of these gases. Let the rectangles represent small 

 volumes, containing 1000 molecules each: 



Hydrogen Chloride Hydrogen Chlorine 



1000 I I 1000 



It appears from this that 2000 molecules of hydrogen chloride 

 come from 1000 molecules of hydrogen and 1000 molecules of 

 chlorine. Now, each molecule of hydrogen chloride contains 

 at least one atom of hydrogen, so that the 1000 molecules of hydro- 

 gen must have given at least 2000 atoms of hydrogen, one for 

 eaoh molecule of the compound. Hence each molecule of hydro- 

 gen contains at least two atoms. The same is true of each mole- 

 cule of chlorine. We have no reason, however, for supposing 

 that there are more than two atoms in either molecule; no sub- 

 stance is known which contains less than 1.008 g. hydrogen or 

 35.46 g. chlorine in its unit weight (p. 75). Hence the con- 

 clusion is confirmed which we reached before (p. 79), namely, that 

 the formulae of the free gases are H2 and C^, and that single atoms 

 of the elements occur only in combination (as in Nad, HC1, etc.). 



CALCULATIONS 



Calculations Involving Volumes of Gases. For such cal- 

 culations the simplest method is always to use the gram-molecular 

 volume the 22.4-liter cube. 



Relative Densities of Gases. What are the relative weights 

 of equal volumes of chlorine and hydrogen chloride? The for- 

 mula record the weights of 22.4 liters: C1 2 = 2 X 35.46 = 70.92, 

 and HC1 = 1.008 + 35.46 = 36.468. The required relation is 

 70.92 : 36.468, so that chlorine is almost twice as heavy, bulk for 

 bulk, as hydrogen chloride. 



