BORON AND FLUORINE. 23 



infusible, any columbic acid (a very weak acid) and sodium 

 hydroxide produced by a transient hydrolysis might find it par- 

 ticularly difficult to recombine and form the original columbate 

 and water. Hence, the prolonged ignition. 



In the special case of borax the last portion of water may also 

 be assumed to be held in a somewhat different manner, which 

 would not require the supposition of any hydrolytic action. 

 Borax, in a state of fusion, is often said to dissociate into sodium 

 metaborate and boric anhydride : 



Na 2 B 4 7 ^2NaBO 2 +B 2 O s 



This dissociation may conceivably commence before the water 

 has been driven out completely. The hygroscopic boric anhydride 

 would naturally combine with any water still present and thus 

 retard the final dehydration. 



This question of the complete dehydration of borax has been 

 discussed at some length here because previous investigators have 

 made extensive use of fused borax in atomic weight work without 

 fully realizing the difficulties presented by the dehydration of 

 this salt. The question, therefore, is all-important. The results 

 obtained in the present investigation, as previously indicated, 

 hinge upon this very point. 



BALANCE AND WEIGHING; CONSTANTS USED. 



All weighings were made on a Troemner balance No. 10, which 

 was kept in a double case and was easily sensitive to 0.02 mg. 

 The weights were carefully calibrated by the substitution method. 



Weighings were made by comparing the platinum bulb con- 

 taining the substance, by substitution, with a counterpoise con- 

 sisting of a stoppered platinum bottle which had approximately 

 the same weight and surface as the former. Weights from a 

 second set served as a tare on the other balance pan. The counter- 

 poise was also ignited (protected from the free flame, of course) 

 before each weighing; both objects, having nearly the same initial 

 temperature, were then allowed to cool, side by side, in a large 

 desiccator placed near the balance case for at least 4 to 5 hours. 

 The stoppers were inserted just before weighing was begun. When 

 the bulb had reached constant weight, which usually required 

 about an hour, it was substituted by the counterpoise, which had 



