of Iodine in Haloid Salts by Arsenic Acid. 339 



danger of bringing about the reduction of the arsenic by the 

 bromide. 



Messrs. Friedheim and Meyer contend that the redaction of 

 volume under the conditions should not be pressed beyond 

 50 cm 3 at the most, and cite in proof experiments in which 

 potassium bromide in amounts less than half as great as those 

 which we used caused an error on concentration to 35 cm 3 

 equivaTent to five or six milligrams of iodine. They recom- 

 mend boiling from 150 cm 3 to 50 cm 3 to remove the iodine 

 without disturbing bromine. Our former experiments are 

 sufficiently definite upon these points. We have, however, 

 determined directly and quantitatively the amounts of iodine 

 remaining unexpelled when solutions are boiled froml50 cm 3 to 

 50 cm 3 and found, in certain experiments, in which the addi- 

 tional iodine expelled in concentrating from 50 cm 3 to 35 cm 3 

 was collected in potassium iodide and estimated with sodium 

 thiosulphate, that about 0*0013 grm. remained when 0*5 grm. of 

 potassium iodide was originally taken, and 0*0003 grm. when 

 0'25 grm. of the iodide was present at the first. It is evident, 

 therefore, that concentration to 50 cm 3 is not sufficient when 

 the maximum amount of iodide may be present. We have 

 also made certain experiments — recorded below — in which the 

 bromine liberated at different degrees of concentration was 

 collected in potassium iodide and estimated by the iodine set 

 free. In our former work we inferred the loss of bromine 

 from the effects upon the arsenic acid in the residues. In these 

 experiments solutions of potassium bromine (free from iodine), 

 with 20 cm 3 of sulphuric acid (1:1), and 2 grm. of dihydrogen 

 potassium arseniate were boiled down in a flask connected by 

 ground glass joints with a cooled receiver containing potassium 

 iodide, or the iodine set free was estimated by standard sodium 

 thiosulphate. 





Initial 



Final 



Bromine in 



<r taken. 



volume. 



volume. 



distillate. 



grm. 



cm 3 . 



cm 3 . 



grm. 





( 150 



50 



trace 



0-5 



| 50 



40 



trace 





( 40. 



35 



... 0-0004 





( 50 



31 



o-ooio 



0-5 



] 31 



26 



23 



0-0064 





/ 26 



0-0072 





( 45 



... 40 



none 



0-25 



■} 40 



31 



21 



0-0004 





I 31 



... o-ooio 



0-25 .. 



50 



35 



0-0003 



o-i 



50 



30 



... 0-0003 



Am. Jour. Sci— Third Series, Vol. XLV, No. 268.— April, 1893. 

 24 



