174 THE ATOMIC WEIGHTS. 



Na^B^O,. AgCl. Ratio. 



5.3118 7.5 2 59 70.580 



4.7806 6.7794 70.517 



4.9907 7.0801 70.489 



4.7231 6.6960 70.53 6 



3.3138 4-693 1 70.610 



Mean, 70.546, .0146 



Rimbach * based his determination of the atomic weight of boron upon 

 the fact that boric acid is neutral to methyl orange, and that therefore 

 it is possible to titrate a solution of borax directly with hydrochloric 

 acid. His borax was prepared from carefully purified boric acid and 

 sodium carbonate, and his hydrochloric acid was standardized by a series 

 of precipitations and weighings as silver chloride. It contained 1.84983 

 per cent, of actual HC1. The borax, dissolved in water, was titrated by 

 means of a weight-burette. I give the weights found in the first and 

 second columns of the following table, and in the third column, calcu- 

 lated by myself, the HC1 proportional to 100 parts of crystallized borax. 

 Rimbach himself computes the percentage of Na 2 O and thence the atomic 

 weight of boron, but the ratio Na 2 B 4 7 .10H 2 : 2HC1 is the ratio actually 

 determined. 



Na^B^O-f.wH^O. HCl Solution. Ratio. 



10.00214 103.1951 19.0853 



15.32772 158-1503 19.0864 



15.08870 155-7271 19.0917 



10.12930 104.5448 19.0922 



5.25732 54-2571 19.0908 



15.04324 155-2307 19.0883 



15-04761 I55-2959 19.0908 



10.43409 107.6602 19.0868 



5.04713 52.0897 i9-9 I 5 



Mean, 19.0893, d= .0006 , 



Obviously, this error should be increased by the probable errors in- 

 volved in standardizing the acid, but they are too small to be worth 

 considering. 



The following ratios are now available for boron : 



(1) Percentage of water in Na 2 B 4 O 7 .ioH 2 O, 47.1756, =h .0066 



(2) 3Ag : BBr 3 : : 100 : 77.425, .0017 



(3) Na 2 B 4 O 7 : 2NaCl : : 100 : 57-933, .0074 



(4) 2AgCl : Na 2 B 4 O 7 : : 100 : 70.546, + .0146 



(5) Na 2 B 4 O 7 .ioH 2 O : 2HC1 : : 100 : 19.0893, .0006 



* Berichte Deutsch. Chein. Gesell., 26, 164. 1893. 



