24 THE ATOMIC WEIGHTS OF 



been exposed to the same conditions for the same length of time. 

 The difference between the objects was thus determined. 



The densities used in the reductions to vacuum for the various 

 substances involved are given below. They refer to the fused salts. 



Density. Density. 



Na 2 B 4 7 2.357 Na 2 CO, 2.533 19 



NaCl 2.161 l7 NaF 2.804 



Na 2 SO< 2.698 18 Brass 8.40 



NaNO, 2.255 



The density of sodium borate (which had been fused in a 

 double platinum crucible for several hours) was determined in 

 toluene. It was found that 3.8607 grams of the salt displaced 

 1.4103 grams of toluene at 25. The density of the toluene at the 

 same temperature was 0.8610, referred to water at 4. From 

 these data 2.357 20 is deduced as the density of fused borax. 



The density of fused sodium nitrate was determined in a 

 similar way. It was found that 8.2077 grams of this salt displaced 

 3.1344 grams of toluene at 25. This yields 2.255 for the density 

 of fused sodium nitrate. 



For fused sodium fluoride, 5.1199 grams displaced 1.5739 

 grams of toluene at 25; 6.6544 grams displaced 2.0414 grams of 

 toluene. Hence, the density of the salt was found to be 2.801 

 and 2.807, respectively. The average, 2.804, was taken as the 

 density of fused sodium fluoride. The weights given in these 

 determinations refer to the vacuum standard. 



The antecedent atomic weights used in calculating the atomic 

 weights of boron and fluorine are the following: 



=16.000 S =32.069 



Na = 22.997 N = 14.010 



Cl =35.457 C= 12.005 21 



17 Baxter and Wallace, J. Am. Chem. Soc. 38, 261 (1916). 



18 Richards and Hoover, Ibid. 37, 111 (1915). 



19 Ibid., p. 105. 



20 For present purposes this agrees well with the value 2.367 found by Filhol (Ann. 



chim. phys. (3) 21, 415 (1847)). Ramsay and Aston (J. Chem. Soc. 63, 210 

 (1893)), found 2.29; this seems to indicate that the sodium borate was not 

 entirely free from water. 



21 This value has been questioned by E. Moles (J. chim. phys. 15, 51 (1917)). It is 



the value obtained by Richards and Hoover, J. Am. Chem. Soc. 37, 106 (1915). 

 As other determinations on record also point to a somewhat higher value than 

 12.00, it seemed safe enough to use the value given above. 



