RTCHARDS AND STULL. — BROMINE AND OXALIC ACID. 



323 



bottles completely, for, if a free space be left above tbe solution, 

 bromine vapor will pass into this space and thus cause grave uncer- 

 tainty in the reacting concentration. 

 After a definite time had elapsed, the 

 bottle was taken from the thermostat, the 

 contents were treated with a solution of 

 potassium iodide, and the liberated iodine 

 was titrated with sodium thiosulphate. 

 The thermostat was covered with a black 

 cloth in order to prevent any reaction 

 between the bromine and water, although, 

 as will be noted later in this paper, this 

 precaution was necessary only when 

 working at higher temperatures. 



Although there was little probability 

 that the reaction is reversible, yet it 

 was thought advisable to test this point 

 experimentally. For this purpose the 

 rate of reaction of bromine on a solution 

 of oxalic acid in pure water was compared 

 with the rate when bromine acted upon 

 an oxalic solution charged with carbon 

 dioxide. The same quantities of bromine 

 and oxalic acid were present in each case 

 and the time allowed for reaction was one 

 hour. The residual bromine, where car- 

 bonic acid was present, was equivalent to 

 10.29 c.c. of T "o thiosulphate solution. In 



the absence of carbon dioxide the bromine remaining corresponded to 

 10.31 c.c. of T "jj thiosulphate. The reaction evidently possesses an over- 

 whelming tendency in one direction. 



That bromine does not act on water, at ordinary temperature, to any 

 great extent is shown by the following experiment. Three bottles, each 

 containing bromine equivalent to 17.97 c.c. T "jj thiosulphate, were tightly 

 stoppered and exposed in the thermostat, at a temperature of 23° C, to 

 the influence of diffused light. At the end of four hours the contents 

 were treated with potassium iodide and the free iodine titrated. The 

 quantities of iodine found corresponded to 17.95 c.c; 17. 9G c.c; and 

 17.98 c.c of t "q thiosulphate. The average 17.96 is essentially equal to 

 the previous value 17.97. For the purposes of this study we may there- 



Figitre 1. 



