16 PHYSICAL CHEMISTRY 



weight of a substance may change upon solution, the weight 

 in grams as given in the chemical formula (mol) is usually taken, 

 and the solution of this in a liter is called formal but is designated 

 here as mol in order to save space. When attention is especially 

 directed to an element that occurs more than once in the formula, 

 the molecular weight is divided by the number of times this sub- 

 stance occurs in the molecule (= gram equivalent weight), and 

 the solution of this in i liter is then called normal. The effects 

 of temperature are eliminated by using weight normal solutions, 

 in which the formal or normal (gram equivalent) weight of the 

 substance is dissolved in iooo grams of the solvent, but such 

 solutions require a new standardization before use in burettes. 

 The requirements of volumetric analysis are satisfied in the 

 method used in titrating the chloride content of sea water. The 

 results are expressed as grams of CI per kilogram of sea water. 

 The volumetric apparatus is standardized with a bottle of stand- 

 ard sea water at the temperature at which the titrations are to 

 be made. It is then necessary merely to have a relative calibra- 

 tion of the divisions on the burette. 



