hy the Direct Action of ArHenious Acid. 289 



the amount required bj theory. The balancing error due to 

 the evohition of iodine by the action of atmospheric oxygen 

 upon the acidified sokition of the iodide was found by experi- 

 ment to vary with the strength of the acid and the time of 

 exposure, from 0*0001 grm. to 0*0003 grm. expressed in terms 

 of the bromate, and these vahies are not greater than the 

 differences observed between parallel determinations of the 

 same sort. Probably, therefore, all the errors as shown in the 

 table should really be increased a trifle to approximate the 

 truth, notably those of the experiments allowed to stand the 

 longest period, twenty-two hours. 



The average apparent error of the process as applied to this 

 particular sample of bromate is 0*0009- grm. ; and 2*5^™^ of 

 sulphuric acid of half-strength (1:1) or the equivalent amount of 

 hydrochloric acid, 4^°^^ of the acid of sp. gr. 1*18, in the 

 presence of about 3 grms. of potassium iodide, complete the 

 action within a half hour, at a dilution of 100'^°'^ as far as it 

 will go under any of the conditions tried. The phenomenon 

 noted by Ostwald,^ that small amounts of hydrochloric acid 

 tend to force the reaction more rapidly than equivalent 

 amounts of sulphuric acid, does not appear in these experi- 

 ments, no doubt because the action was pushed to the limit by 

 the smallest amount of the weakest acid employed. 



The error of deficiency shown again appears to be due to 

 impurity in the sample of bromate rather than to incomplet- 

 ness of the reaction. If the reaction were incomplete it would 

 be natural to look for the cause in the possibility of the 

 inhibiting influence of the iodine set free,t but it was 

 found in three parallel experiments that the introduction 

 of '5 grm. of free iodine dissolved in potassium iodide 

 failed to influence the error appreciably. For the present pur- 

 pose, however, the absolute purity of the bromate is not a 

 matter of moment, if, as seems to be the case, Kratchmer's 

 reaction indicates its value with accuracy, as the basis of experi- 

 mentation. It seems safe to assume, then, that the average 

 result of experiments (3) to (22) will give a very fair value for 

 the sample of bromate investigated. That is to say, the 

 experiments show an average deficiency in bromate amounting 

 to 0*0009 grm., or to 0-64 per cent. 



Portions of this bromate were taken for reduction by 

 arsenious acid. Solutions not exceeding 200*^""^ in volume, 

 containing the bromate and a considerable excess of arsenious 

 oxide acidified with sulphuric acid of half-strength, were boiled 

 for periods varying from ten to forty-five minutes, neutralized 

 with potassum acid carbonate, and titrated with iodine. The 

 results are shown in Table III. 



*Loc. cit., p. 131. f Judson and Walker, loc. cit,, p. 411. 



