AOTES OK DIPPING FLUIDS. 131 



Gooch and Morris esthuation ('" Analyst," xxvi., 24), did not give with 

 u.s concordant results, particulai'ly with such dips which contained 

 phenols and sulphur compounds. As the precipitation of the arsenic 

 ais sulphide presented also many difficulties, we tried some of the dis- 

 tillation methods. The estimation of arsenic in various materials is 

 easily carried out b}' distillation as arsenious chloride. Odling 

 (■■ Chemical News," July, 1863) proposed a method of distillation with. 

 ferric chloride and hydrochloric acid. The method was improved by 

 P^mil Fischer (" Berichte," 1880, p. 1778), who uses ferrous chloride 

 iu the distillation. The process was modified by Dr. J. Clark, Riecker, 

 A. Gibb ("J.S.C.I.," March, 1901), and others so as to make it ap- 

 plicable for the estimation of arsenic and antimony. 



The process of distillation, which gave us the best results and was 

 tlierefore adopted, was carried out as follows: — 10 cc. of the dipping 

 fluid were boiled down to a few cc. in a distillation flask, 10 cc. of 

 cuprous chloride solution (containing 62 grammes dissolved in 200 cc. 

 HCl), and 10 cc. saturated CaCl solution, and '25 grammes copperfoil 

 were added, boiled and the distillate collected in an U-tube, containing 

 a few cc. of water, kept cool in a water bath. A second distillation 

 was caiTied on after the addition of 10 cc. HCl. Distillation was 

 carried on until the residue in the flask began to spurt. The distillate 

 was titrated with iodine solution in the usual way. 



Already Rohmer (" Berichte," 1901) has recommendetl the distilla- 

 tion of arsenic with hydrolji'omic acid, and he uses both gravimetric 

 and volumetric estimation of the arsenic in the distillate. Gooch and 

 Phelp ("J.C.S.," Abstr., 1894, II., 477) recommend the distillation 

 with KBr and HCl. On tiying this method we found it to be much 

 quicker than the other, but we again found that if the fluids contained 

 appreciable amounts of phenols and sulphides the distillate could not 

 be titrated directly with iodine solution for the estimation of the 

 arsenic. Norton and Koch (" J.A.C.S.," 1905) recommended Kjeldahl's 

 moist combustion with strong sulphuric acid for organic compounds 

 containing arsenic. As in the digested residue the arsenic could be 

 directly detenTiined by titration with standard peniianganate solution, 

 O. Kiihling ("Analyst," 1901), the digestion of the dipping fluids 

 with sulphuric acid proved an excellent and rapid method. The 

 titration with penuanganate solution requires a good deal of practice 

 to give good results, the peiTnanganate must be added to the boiling 

 hot liquid in certain amounts, and the liquid must be kept 

 boiling until the slight pink colour disappears, and the titration con- 

 tinued until the pink remains pennanent on continued boiling. 

 Occasionally it was found that the duplicates, which as a rule agreed ab- 

 solutely, did not agree, and came out lower than the gi-avimetric result. 

 This fact was caused by certain dips containing arseniate, unsuspected 

 at that time, which was not all changed into arsenite during digestion, 

 and in other cases by a slight oxidation of arsenite into arseniate 

 taking place in the digestion. No trouble was experienced in the 

 piesence of an excess of organic matters, and for this reason we 

 always add before digestion a small amount of pure starch or sugar. 



The titration with permanganate was also replaced by the much 

 easier and sharper titration with potassium bromate solution, using 

 methyl orange as an indicator, a method originally proposed by S. 



