18 THE ATOMIC WEIGHTS OF 



a platinum tube was inserted, thus making the device resemble a 

 Rose crucible. It was set into a plate of asbestos board covered 

 with sheet nickel and was heated by means of a ring-burner which 

 supplied the heat mainly to the sides of the vessel. In this manner 

 the crucible and contents were kept at a gentle heat for several 

 hours, while a steady stream of dry air free from carbon dioxide 

 was passed through the apparatus. Finally the heat was increased 

 sufficiently to melt the porous, silky mass to a clear glass. The 

 residue was then again fused completely over a direct flame and 

 allowed to flow toward the edge of the crucible. The mass thus 

 collected on the side cracked sufficiently of its own accord on 

 cooling, and a convenient sample could easily be removed for 

 further treatment. The exclusion of carbon dioxide in the dehy- 

 dration and fusion of this salt is probably not essential, because 

 any absorption of this gas would be counteracted by the boric 

 acid under these conditions. Nevertheless it seemed best to 

 exclude this gas as much as possible. 



This clear, flawless mass, often called "borax glass," is gen- 

 erally assumed to be anhydrous sodium tetraborate. A portion 

 of such borax glass, however, weighing 1.22243 grams, was 

 transferred to the platinum bulb already described and was kept 

 fused for about 15 minutes; it then weighed 1.22191 grams. This 

 process of re-fusing and re-weighing was repeated a few times 

 until the weight finally became constant at 1.22106 grams, show- 

 ing that the borax glass had given up fully 0.1 per cent, of volatile 

 matter. As will be seen, this loss usually amounted to about 

 0.2 per cent. At least an hour of actual fusion was required for 

 a 1-gram sample to reach constant weight. 



The question naturally arose whether this decrease in weight 

 was to be attributed to the loss of water. It certainly was not 

 due to the volatilization of borax or some other compound of 

 sodium, for during the entire fusion a sodium flame could not 

 be obtained at the mouth of the bulb a most delicate test which, 

 by actual experiment, was found to show unweighable amounts 

 of borax, unless the lower part of the bulb was heated almost to 

 a white heat and the air current accelerated considerably. 15 



18 This "flame test" was applied as follows: From time to time a small, pointed 

 Bunsen flame was played across the mouth of the platinum bulb. The gas was 

 filtered through cotton wool before reaching the burner, which was constructed 



