SANGER. — VOLATILE COMPOUNDS OF ARSENIC. 129 



starch paste, with wall paper containing arsenite of copper, so that 

 in the surface exposed there were about 400 mgr. of arsenious oxide. 

 These cardboards were then placed in a specially constructed tight 

 box with glass windows, arranged so that air could be drawn from 

 end to end. The air entering the box passed through a dilute solu- 

 tion of sodic hydroxide. On leaving it passed through a chloride of 

 calcium tube filled with cotton wool, next through a Liebig bulb tube 

 with 5°f argentic nitrate protected from the light, and finally through 

 bulbs filled with nitric acid (sp. gr. 1.12). Air was drawn through 

 the system for two and a half months, averaging seven hours per 

 day. At the end of this time a large amount of mould had formed 

 on the paper. The cotton wool gave a marked test for arsenic, but 

 the silver solution did not show the slightest trace. The nitric acid 

 evaporated with sulphuric acid was also free from arsenic. 



8. The box used in No. 2 remained over four years in the cellar 

 of the laboratory, and had become filled with mould, the windows 

 being covered with moisture. A similar series of absorbents was con- 

 nected, and air was drawn through the system for a week, night and 

 day. The cotton wool, silver solution, and nitric acid were tested as 

 in No. 2, but in no case was any arsenic found. 



The evidence presented above, with the exception of the experi- 

 ments of Fleck and the earlier work of Hamberg, was collected after 

 my first series of experiments was completed. These, which were 

 intended to repeat the work of Fleck and Hamberg, and which were 

 based on the assumption that the volatile compound, if formed, would 

 be arseniuretted hydrogen, are given below. On account of the nega- 

 tive results they are not presented in as much detail as originally 

 intended, for the conclusion derived from them at that time was 

 shown to be erroneous by the results of the second series. 



First Series op Experiments. 



Fermentation in Solution. — Experiment 1. — 20 grams potassic ar- 

 senite dissolved in water were mixed with syrup, flour, and part of a 

 yeast cake, and placed in a large flask fitted with a double bored cork. 

 Through one hole reaching to the bottom of the flask, passed a right- 

 angled tube connected with the tubulus of a side-neck test-tube (A) 

 the latter being half filled with a 2of solution of argentic nitrate and 

 fitted with a cork through which passed a right-angled tube to the 

 bottom of the test-tube. In the second hole of the stopper of the 

 vol. xtix. (n. s. xxi.) 9 



