62 THE ATOMIC WEIGHTS OF 



To summarize regarding Rimbach's determination : The main 

 factors to be considered in his work are the following : Absorption 

 of carbon dioxide by the borax; improper water-content of the 

 salt; and a slight acidity of boric acid toward the indicator. As 

 no definite conclusions can be reached as to the extent, if any, 

 of the first two factors, it is not possible to say whether Rimbach's 

 result may be high or low. Any errors due to the standardization 

 of the hydrochloric acid, by means of silver chloride, are probably 

 of a different order and of smaller significance than those just 

 mentioned. At any rate, it is interesting that Rimbach's result 

 (10.917, as recalculated by the writers) agrees tolerably well with 

 the value (10.900) found in the present investigation. 



The above test for the slight acidity of boric acid toward 

 methyl orange would, of course, be utterly useless if the boric 

 acid were contaminated by traces of other acids, such as sulphuric 

 acid. Unfortunately the acid prepared from methyl borate had 

 all been used in the preparation of borax; hence, for the above 

 tests the boric acid was prepared as follows : A good commercial 

 grade of boric acid (which did contain a bare trace of sulphuric 

 acid) was twice recrystallized from water. It was then fused in a 

 platinum dish and recrystallized once more from pure water. The 

 product was again dissolved in boiling water and, after complete 

 solution, a few cubic centimeters of redistilled ammonium hydrox- 

 ide were added. The mother liquor from the crystals of boric 

 acid separating out from this solution was strongly alkaline to 

 methyl orange, due to the formation of some ammonium borate. 

 The boric acid thus obtained was recrystallized four times from 

 water. Centrifugal draining and washing were resorted to 

 throughout. The final product, in concentrated solution, was 

 again distinctly acid to methyl orange. It seems unlikely that 

 this acidity was due to anything but the boric acid itself. This 

 preparation was used in the quantitative tests. 



An exhaustive study of the accurate titration of borax was 

 not considered to be within the scope of the present paper. 15 



The two titrations of borax carried out by Armitage do not 

 require a lengthy discussion. This investigator modified Rim- 

 bach's method by substituting fused borax (supposedly anhy- 



16 It may be added that according to Joly (Compt. rend. 100, 103, 1885) solutions of 

 boric acid, dilute or concentrated, are neutral to methyl orange. 



