22 DIFFUSION AND OSMOTIC PRESSURE 



equivalent" and "gram-molecule" are synonymous terms 

 in the case of monovalent compounds, and that a gram- 

 equivalent of a bivalent compound is one half of its gram- 

 molecule, of a trivalent compound one-third, etc. 



A solution made up so as to contain in one liter a single 

 gram-equivalent of solute is termed an equivalent normal, 

 or simply a normal, solution. Unfortunately there is a usage 

 which terms a molecular solution normal, thus giving rise 

 to ambiguity for all but monovalent solutes. This ambi- 

 guity can be avoided only by the careful definition of the 

 term "normal" by each author using it. 1 For all neutral 

 organic compounds, such as the sugars, and also for monova- 

 lent electrolytes, a gram-equivalent is the same as a gram- 

 molecule, and a normal solution must be a gram-molecule in 

 a liter volume. Thus the sugar solutions described in a pre- 

 vious paragraph are both normal solutions. No ambiguity 

 can arise from the use of the term in reference to such com- 

 pounds. 



Regarding acid salts (such as KHSO 4 , for example), there 

 is a difference of opinion as to what should be denoted by 

 gram-equivalent. Some hold (e. g., Kahlenberg) that in 

 the salt just mentioned gram-equivalent and gram-molecule 

 are identical. Thus, such a salt might be regarded as a 

 monobasic acid. On the other hand, Button, Fresenius, 

 Dandeno, and others regard a gram-equivalent of KHSO 4 

 as one-half a gram-molecule. Thus, an equivalent solution 

 of this salt would contain only one-half gram of hydrogen; 

 the salt is to be regarded as a monobasic acid, one-half of 

 whose hydrogen has been replaced. It seems that the latter 

 is the more truly scientific position. 



1 For an account of confusion (partly imagined) which has arisen from a lack of 

 attention to such definition of these terms, see J. B. DANDENO, " The Application of 

 Normal Solutions to Biological Problems," Bot. Gaz., Vol. XXXII (1901), pp. 229-37. 

 Also see "Open Letters," one from Louis KAHLENBEEG, and an answer from DAN- 

 DENO, ibid., p. 437. 



