384 Gooch and Hodge — Detection and Separation of 



condensed in 10cm 3 of a mixture of strong hydrochloric acid 

 and water in equal parts. The iodine evolved during the dis- 

 tillation was bleached by the addition to the distillate of stan- 

 nous chloride dissolved in hydrochloric acid of half-strength, 

 and hydrogen sulphide was passed to precipitate the arsenic if 

 present. The residue in the flask was treated with 10cm 3 of 

 the strongest hydrochloric acid and the process of distillation 

 was repeated, but this time the distillate was condensed in 

 10cm 3 of water in order that the final acidity of the liquid 

 should be that of acid of half-strength, and so, after bleaching 

 by stannous chloride, immediately available for the test for 

 arsenic by hydrogen sulphide. Subsequent treatments of the 

 residue were carried out similarly until arsenic ceased to appear 

 in the distillate. 



The results of experiments (1) to (5) show that four succes- 

 sive distillations of 10cm 3 portions of the strongest acid are 

 enough to transfer 0*01 grm. of arsenic completely to the dis- 

 tillate, while a single distillation appears to be sufficient to 

 volatilize anything less than 0*003 grm. 



Experiments (6) to (9) made similarly with antimony, taken 

 in the form of purified tartar emetic and oxidized by iodine 

 in alkaline solution previous to treatment, either alone or with 

 arsenic, show that antimony is discoverable in the residues 

 when even so little as 0*0001 grm. of that element is originally 

 introduced, though it was very evident that a portion of the 

 antimony may pass to the distillate when much of it is present 

 in the flask. Indeed when large quantities of antimony are 

 treated the appearance of the brownish-red fumes of antimo- 

 nious iodide in the distilling tube may serve as a very good 

 indication that the concentration should go no further, since 

 the antimonious iodide may, if it reaches the receiver in quan- 

 tity, impart to the distillate a color which is not discharged, by 

 the stannous chloride used to bleach the iodine and which 

 makes it necessary to look subsequently for a precipitate of 

 arsenious sulphide in a liquid of its own tint. The amount of 

 antimony volatilized seems to be proportioned to the amount 

 present, and, if the distillation is properly conducted, enough 

 antimony remains in the residue to be found if it was origi- 

 nally present in discoverable quantity. 



The results of similar work with tin alone, and with tin and 

 arsenic, are recorded in experiments (10) to (15), and the evi- 

 dence goes to show that, though like antimony it may pass to 

 the distillate under the conditions, enough tin always remains 

 to be found in the residue, if the amount originally taken was 

 discoverable. 



