CONCLUSIONS 



"S 



weights, or, in other words, the molecules of hydrogen and 

 nitrogen must each contain two atoms (H2 and Ng). 



This observation that the relative density is always half the 

 molecular weight is of use in determining the molecular com- 

 position of volatile substances. For instance, nitric oxide 

 might have the composition represented by either of the 

 formulae NO and NgOo. But the relative density is found 

 by experiment to be 15. Hence the molecular weight is 30, 

 and this corresponds with the formula NO. It also makes it 

 possible to calculate the weight of any volume of gas, if the 

 molecular weight be known, from the weight of a liter of hydro- 

 gen ( = .0896 grams when measured at 0° C. and 760 m.m.). 

 For instance, the calculated molecular weight of ammonia 

 (NHg) is 17. The weight of a liter of ammonia gas at 0° and 



760 m.m., will therefore be '^-^ — ^^±£. = .7616 grams. 



2 



In the foregoing studies it has been observed that the non- 

 metallic elements form compounds with hydrogen. These 

 substances differ in their composition : — 



Those elements which combine with one, two, three, and 

 four atoms of hydrogen are termed, respectively, univalent, 

 bivalent, trivalent, and quadrivalent. The metallic elements 

 have less tendency to combine with hydrogen, but they com- 

 bine with chlorine, which is univalent ; and they combine 

 with oxygen and sulphur, which are bivalent; so that their 

 valency is easily determined. Thus, sodium and potassium 

 are univalent, for they form the compounds Na'Cl', K'Cl', 

 Na2'0" and K/O". Calcium, barium, magnesium, zinc, lead, 

 copper, and mercury are bivalent, for they form the com- 

 pounds Ca"0", Ba"Cl2', Mg^lg', Zn"0", Pb"0", Cu'S", Hg-O". 



