CHAPTER VII 

 CHEMICAL UNITS OF WEIGHT. FORMULAE 



As we have seen (p. 60), when the volumes occupied by sub- 

 stances in the gaseous condition, rather than the weights, are 

 taken as the basis of measurement, the combining proportions are 

 simple and are expressible by small whole numbers (Gay-Lussac's 

 law). This shows that there must be some relationship, connected 

 with chemical combination, between the amounts of different sub- 

 stances contained as gases in equal volumes. It suggests that 

 we might do well to take such amounts (weights of equal volumes) 

 as the standard or unit quantities for chemical purposes. Now 

 this is precisely what the chemist has found it in practice most 

 convenient to do, and the present chapter deals with the units of 

 material based upon comparing equal volumes. 



Illustrations of Gay-Lussac's Law. Let us first famil- 

 iarize ourselves with the volume-measuring point of view in 

 chemical actions. The following are a few observed facts, begin- 

 ning with the union of hydrogen and oxygen already discussed 

 (p. 59): 



(1) Hydrogen (2 vols.) + Oxygen (1 vol.) > Steam (2 vols.). 



(2) Hydrogen (1 vol.) + Chlorine (1 vol.) Hydrogen chloride 



(2 vols.). 



(3) Chlorine monoxide (2 vols.) > Chlorine (2 vols.) + Oxy- 



gen (1 vol.). 



(4) Mercuric oxide (not volatile) > Mercury (2 vols.) + Oxy- 



gen (1 vol.). 



(5) Phosphorus (1 vol.) -f Oxygen (5 vols.) - Phosphorus 



pentoxide (1 vol.). 



(6) Zinc (at 1000, 2 vols.) + Sulphur (at 1000, 1 vol.) -* 



Zinc sulphide (not volatile) 

 72 



