20 THE ATOMIC WEIGHTS OF 



tically non-hygroscopic under ordinary conditions. Beads of this 

 substance were exposed to the air for months without losing their 

 luster, and a sample fused in a crucible and spread around the 

 sides gained only 0.006 per cent, when exposed for 3 hours; even 

 after 20 hours it had gained only 0.014 per cent. 



The final dehydration of borax by fusion to constant weight 

 is of the greatest importance in the present work. It accounts 

 very largely, if not entirely, for the new value found for the 

 atomic weight of boron, for it will be shown that if the analyses 

 in the present investigation had been referred to the roughly 

 dehydrated "borax glass," the apparent atomic weight of boron 

 would have been practically 11.0 (see p. 43). The method of 

 dehydration noted above was strictly adhered to in each case and 

 constitutes one of the most important steps in the analysis. In 

 this manner pure anhydrous sodium pyroborate was probably 

 obtained for the first time without the loss of some of the salt 

 itself by volatilization. It is of interest to observe that the com- 

 pletely dehydrated product could be kept fused in the bulb for 

 hours without appreciable change in weight, even when a slow 

 current of air passed through the apparatus. It would seem that 

 anhydrous borax is one of the most stable alkali salts under these 

 conditions. 



CONCERNING THE COMPLETE DEHYDRATION OF BORAX. 



That borax, even in a state of fusion, should retain appreciable 

 quantities of water is noteworthy and suggestions as to the reason 

 for this peculiar behavior may properly be offered at this time. 

 Substances which part with the last portions of water only upon 

 prolonged ignition and at elevated temperatures are, of course, 

 well known, and the difficulties involved in the complete dehydra- 

 tion of certain minerals, of silica and alumina (to mention only 

 a few), are known to every analyst. Such substances as these, 

 however, are "infusible"; hence, the difficulty just referred to is 

 not entirely unexpected. 



Salts, on the other hand, may, as a rule, be considered com- 

 pletely dehydrated as soon as a state of fusion has been reached. 

 Not so with borax. Here the analyst is confronted by the peculiar 

 fact that about 99.8 per cent, of the water of hydration can be 

 driven off with ease, whereas 0.2 per cent, or less is removed 



