38 THE ATOMIC WEIGHTS OF 



consisting of sodium nitrate, was dried in a current of air (the 

 temperature finally reached was about 200) and weighed. This 

 gave the weight of the unfused salt, after which the sodium 

 nitrate was dissolved in a little water containing a few drops of 

 nitric acid, again evaporated and dried, and finally fused for a 

 moment at a temperature only slightly above the fusion point 

 of this salt (cir. 315). The weight of the product (the fused salt) 

 was determined again and found to be 0.1 mg. lower than the 

 first weight, that of the unfused salt. The mean of these two 

 weighings was assumed to be the true weight and was used in 

 the computation. The difference (0.1 mg.) between these weigh- 

 ings is considerably greater than permissible in the range of 

 "constant" weight for the other salts. However, the difference 

 did not seem excessive in the case of sodium nitrate, which can 

 not be kept fused for any length of time without decomposition. 

 The weight of the unfused salt, resulting after the evaporation of 

 the alcohol, was probably somewhat too high on account of a 

 trace of moisture; the weight of the salt fused after evaporation 

 with dilute nitric acid was a trifle too low, presumably, as a result 

 of a slight decomposition. Hence, "splitting the difference" 

 seemed permissible in this case. It may be added that the water 

 solution of the final product was neutral in reaction. 



The nitric acid used in this experiment was prepared as 

 follows: A good grade of sodium nitrate was recrystallized a 

 few times until it was free from chlorides. This salt was then 

 distilled with pure, concentrated sulphuric acid from a long- 

 necked retort; the first third of the distillate being rejected. 

 The middle fraction was redistilled with pure barium nitrate and 

 again rectified. Finally the acid was redistilled, just before use, 

 from a quartz distilling bulb. 



EXPERIMENT VIII: THE RATIO OF SODIUM TETRABORATE TO SODIUM CARBONATE. 



This interesting ratio may be arrived at in various ways. 

 Before giving the method finally adopted we may indicate at 

 least two other attempts which seemed to bid fair to lead to the 

 ratio desired. 



First it would have been possible to expel the boric acid in 

 the presence of formic acid and to change the resulting formate, 

 by strong ignition, to the carbonate, which is the final product 



