of Iodine in Haloid Salts by Arsenic Acid. 



337 



starch solution prepared by Gastine's formula* (5 grin, starch, 

 O01 Hgl 2 , 1 liter of water) gave the starch blue with a single 

 drop of decinormal iodine at all dilutions below 300 cm 3 . The 

 results of these experiments are given in the following table. 





Iodine 



Iodine 



Iodine 



Iodine 









taken in 



found in 



found in 



found in 









form of 



residue by 



distillate 



distillate by 



Error in 



Error in 





KI. 



our method. 



by As 2 O s . 



Na 2 S a Og. 



residue. 



distillate. 





grm. 



grm. 



grm. 



grm. 



grm. 



grm. 



( 1) 



0-4054 



0-4052 







0-0002 — 





( 2) 



0-4057 



0-4055 







0-0002 — 





( 3) 



0-4054 



0-4052 







0-0002- 





( 4) 



0-4054 



0-4052 







0-0002 — 





( 5) 



0-4042 



0-4046 



0-4046 





0-0004 + 



0-0004 + 



( 6) 



0-4050 



0-4052 



0-4040 





0-00O2 + 



o-ooio- 



( *) 



0-4050 



0-4052 





0-4039 



0-0002 + 



o-ooii- 



( 8) 



0-4058 



0-4052 





0-4051 



0-0006- 



0-0007- 



( 9) 



0-4054 



0-4046 





0-4051 



0-0008 — 



0-0003 — 



(10) 



0-4042 



0-4046 





0-4039 



0-0004 + 



0-0003- 



(11) 



0-4055 



0-4U52 





0-4057 



0-0003 — 



0-0002 + 



Experiments (1) to (4) were made exactly in accordance with 

 the directions of our former paper, the mixtures being simply 

 boiled in an Erlenmeyer flask trapped to prevent mechanical 

 loss by hanging in the neck of the flask, with the larger end 

 downward, a straight, two-bulbed drying tube cut off so as to 

 leave the larger tube about 4 cm. in length. These four ex- 

 periments all gave the same result, which differed from the 

 theory by 0*0002 grm. — . The mixtures of the remaining ex- 

 periments were treated in a flask connected with a cooled 

 receiver and absorbtion tubes for condensing the distilled 

 iodine (all joints being of glass and carefully ground) and car- 

 bon dioxide was passed through the apparatus in slow current 

 to facilitate the transfer of iodine and quiet boiling. In ex- 

 JDeriments (5) and (6) the iodine was received in an alkaline 

 solution of standard arsenious oxide and titration was effected 

 with standard iodine after addition of starch. The residue 

 was treated by our method. It will be observed that the resi- 

 dues, which contain the large amounts of salts, yield results 

 by titration practically identical with those obtained by treat- 

 ing the distillates which do not contain the large masses of 

 salts. In experiments (7) to (11) the iodine distilled was re- 

 ceived in potassium iodide and estimated by standard sodium 

 thiosulphate, itself standardized against the iodine whose value 

 in terms of the standard arsenious oxide was also known. The 

 residues were treated by our method. It is evident that the 



*Bull. Soc. Chim., 1, 172. 



