2 THE ATOMIC WEIGHTS OF 



acid seems inadvisable, since sodium acetate is not readily dehy- 

 drated. This objection does not apply to the other acids men- 

 tioned, i.e., to hydrochloric, sulphuric, and nitric acids. All of 

 these have been used in the present work. In addition carbonic 

 acid, or rather its anhydride, has been employed in converting 

 borax into sodium carbonate. 



The action of hydrofluoric acid seems to be not strictly analo- 

 gous to that of the acids just mentioned. Although sodium 

 fluoride and boric acid are undoubtedly formed at first, a number 

 of secondary reactions may take place between these primary 

 products and the excess of hydrofluoric acid, leading chiefly to the 

 formation of borofluoric acid and, possibly, of sodium boro- 

 fluoride. 6 It is true that the mixture thus obtained will give up 

 considerable portions of boric acid when evaporated with methyl 

 alcohol, but the quantitative elimination of boric acid by this 

 means, with reasonable quantities of methyl alcohol, seemed very 

 doubtful. Again, sodium borofluoride, upon ignition, will give 

 up boron trifluoride and leave sodium fluoride. However, at 

 the temperature required to effect this decomposition, appreci- 

 able quantities of the sodium salt itself may be volatilized. At 

 any rate, the conclusion w r as soon reached that the elimination of 

 boric acid as methyl borate in the presence of an alkali fluoride 

 and hydrofluoric acid could not be rendered sufficiently accurate 

 for an atomic weight determination, even if it should be possible 

 to expel boric acid completely by this method. 



Therefore, if the distillation method were to be applied to 

 borax with a view of obtaining sodium fluoride as an end-product, 

 the problem clearly resolved itself into this: An acid had to be 

 found which would react "normally" with borax and its sodium 

 salt would have to be readily transposed to the fluoride by means 

 of hydrofluoric acid. Formic acid was found to be such an acid. 

 It gave results that left little to be desired. 



Besides purity of materials, the essential prerequisites in 

 deriving an acceptable atomic weight ratio are definite and 

 weighable substances constituting the ratio sought and complete- 

 ness of the reaction correlating the two terms of that ratio. That 



6 See also Abegg, Fox, and Herz on possible reactions between boric acid, potassium 

 fluoride, and hydrofluoric acid. Z. anorg. Chem. 35, 129 (1903). 



