BORON AND FLUORINE. 21 



only with great difficulty, although the salt is kept in a complete 

 state of fusion and although anhydrous borax is not particularly 

 hygroscopic. The rather artificial distinction between "water of 

 crystallization" and "water of constitution" can be of little 

 assistance in this case and amounts to begging the question. It 

 would lead to the rather extravagant conclusion that only about 

 -s^, or even less, of the water originally present was "water of 

 constitution." The experimental fact may be explained, it is 

 thought, in a much simpler and more reasonable manner. 



Practically nothing is known concerning the state or form in 

 which water, or the elements of water, exist in hydrated salts, 

 and it matters little in this discussion. Certain it is that such 

 water of crystallization escapes as vapor when the salt is heated, 

 and that in many instances when the loss of water begins at a 

 rather low temperature this water must pass through the liquid 

 state before escaping as steam. At some stage, then, during the 

 dehydration of borax there must be minute particles or globules 

 of water momentarily in contact with sodium borate, which would 

 mean, of course, so many droplets of dissolved borax in contact 

 with the solid. Now these droplets, or this "mist" of borax solu- 

 tion, distributed through the porous mass of partly dehydrated 

 borax, must have the properties of an ordinary borax solution; 

 hydrolysis, for example, must take place as usual. It is well 

 known that there are good reasons for assuming that borax in 

 water solution is extensively hydrolyzed, that is to say, that this 

 solution is the scene of such reactions as the following: 



Na 2 B 4 7 +H 2 ^2NaB0 2 +2HB0 2 

 Na 2 B 4 O 7 +3H 2 0^2NaOH +4HB0 2 



Such or similar reactions would naturally take place in the 

 "mist" referred to above; and it is true that hydrolysis gradually 

 decreases and finally disappears as we evaporate the solvent; in 

 the present case the metaborate or the hydroxide of sodium com- 

 bine again with the boric acid to form the original sodium borate. 

 Bearing in mind, however, that the complete combination of 

 sodium hydroxide and the very weak boric acid takes place quite 

 slowly, it is not unreasonable to suppose that in the evaporation 

 of the droplets of borax solution the expulsion of the water may 

 be comparatively rapid on account of the minute quantities 



