OP ARTS AND SCIENCES. 43 



potassic nitrate, dried on the plate, burued over the plate, and the 

 residue washed ott* into an evaporating disli. The residue was then 

 treated with about 5 c. c. strong sulphuric acid aud evaporated until 

 sulphuric acid fumes appeared. To insure the complete expulsion of 

 nitric and nitrous acids, the mass was boiled down again, after addi- 

 tion of a little water. It was then taken up with hot water, hllerod, 

 and washed with hot water. The filtrate was kept at 60-70° for 

 half an hour, and sulphur dioxide passed through. After boiling the 

 reduced solution in the flask until sulphur dioxide was expelled, it was 

 made alkaline with sodic bicarbonate, cooled, and titrated. The results 

 obtained were far from satisfactory, but the analyses agreed closely in 

 three cases, which are given below. (Papers numbered 111, 395, and 

 42 in final table.) 



Next, instead of ignition with potassic nitrate, the paper was 

 treated exactly as in the Berzelius-Marsh method, with nitrosidphuric 

 acid (1-30), taking care to get rid of all nitric and nitrous acids. The 

 extract was reduced at 60-70° by sulphur dioxide, the excess of the 

 latter driven off by boiling, and the cooled solution made alkaline with 

 sodic bicarbonate, and titrated. In one case the arsenic was precipi- 

 tated from the extract by sulphuretted hydrogen, and the arsenious 

 sulphide converted to arsenious acid, and titrated. The amount of 

 time required for this, however, off"set any advantage from it. Al- 

 though by care this method can be employed, yet the details require 

 much time and the chances for error are many. Duplicate analyses 

 agreed closely in two cases which are given below. (Papers num- 

 bered 194 and 155 in final table). 



The method finally used was adapted from the well known process 

 of Schneider* and Fyfe.f A measured quantity of paper was cut 

 in*o small pieces and placed in a 500 c. c. distilling flask connected 

 with a cooler. Attached to the latter was a receiver with a second 

 tubulus carrying a long tube which served as an air cooler. About 

 100 c. c. of hydrochloric acid, diluted one half, were added to the 

 flask, and the mixture distilled, slowly, almost to dryness. It was 

 found by trial, that in nearly every case all the arsenic came over in 

 one distillation, and, if not, that a mere trace was left in the residue. 

 The distillate was transferred to a flask, potassic chlorate added, the 

 solution boiled down one half, transferred to an evaporating dish, and 

 evaporated to dryness, with the addition of a few drops of strong sul- 

 phuric acid. The residue was generally white. If dark, from pres- 



* Jahrb. d. Chem., 1851, p. 630. t Jour. f. prakt. Chetn., L V. 103. 



