60 THE ATOMIC WEIGHTS OF 



boric acid and 5 grams of pure, neutral sodium chloride, and an 

 equal volume of pure water both liquids containing the same 

 amount of the indicator required practically equal amounts of 

 dilute hydrochloric acid for the production of the same tint. He 

 naturally concluded from these results that boric acid was neutral 

 to the indicator. It should be remembered, however, that Rim- 

 bach's hydrochloric acid was approximately half-normal; for he 

 distinctly states that this acid was used in these tests. Now, an 

 acid of this concentration is not sufficiently dilute to detect, with 

 certainty, any slight difference in reaction between the two solu- 

 tions, that is to say, between the boric acid solution and the 

 "blank." This may be gathered from the following simple 

 experiment: 



A beaker contained a solution of 9.7 grams of pure H 3 B0 3 in 

 450 cubic centimeters of distilled water. This approaches the 

 quantity and concentration of the boric acid produced in the 

 titration of about 15 grams of crystallized borax, the largest 

 single portion used by Rimbach. A similar beaker contained the 

 same volume of distilled water which came from the same source 

 and the same container as that used in the first beaker. Ten 

 cubic centimeters 13 of a methyl-orange solution, containing 0.010 

 gram of the dye per liter, were added to the contents of each beaker. 

 The tints produced in the two vessels, when viewed separately, 

 indicated neutrality or, possibly, a slight alkalinity in each case. 

 When the boric acid solution and the blank were placed side by 

 side, however, a distinct difference was noticeable: The boric 

 acid solution was slightly acid with reference to the blank. In 

 fact, this difference could easily be measured. The water con- 

 taining only the indicator required the addition of 0.5 c.c. of 

 hydrochloric acid solution. It will be observed that this hydro- 

 chloric acid is much more dilute than that used by Rimbach in 

 a similar test. A second experiment involving the same quanti- 

 ties gave like results. Finally 5 grams of pure sodium chloride 

 were dissolved in the solution containing th e boric acid ; a change 

 in color was not to be observed, which shows that the sodium 

 chloride, produced in the titration of borax, does not perceptibly 



18 Contrary to what might be expected, this amount gives only a faint color under the 

 conditions and probably represents a practicable minimum. The indicator was 

 prepared and used as directed by Rimbach. 



