OF ARTS AND SCIENCES. 29 



of hydrogen during the analysis. The latter objection is partially 

 remedied by some such contrivance as that of Lehmann* or of Blond- 

 lotjt both of whom regulate the current bj' raising or lowering the 

 zinc by a glass rod working through the cork of the flask. Chitten- 

 den and Donaldson J regulate the evolution by the successive use of 

 acids of increasing strength. Both difficulties are, however, obviated 

 by the use of a constant hydrogen generator by which the air of the 

 flask may be swept out and the flow of the hydrogen controlled, 

 thus assuring the uniform rate of deposition of the arsenic, on which 

 the success of the process as a quantitative one largely depends. 

 This idea of a constant generator was apparently first proposed by 

 Verryken,§ and has been used also in 1888 by Wolff || in a modifi- 

 cation of Bloxam's electrolytic method. *[[ Any form of generator can 

 of course be used. To the delivery tube is attached a distributing 

 tube, which may be two-way or three-way, according to the number of 

 reduction flasks used. For two flasks an ordinary Y tube suffices, 

 each end of the Y being fitted with a thick rubber connecting tube 

 and a screw clamp, so that the supply of hydrogen may be shut off 

 entirely or controlled for each flask. The reduction flask is a wide- 

 mouthed bottle of about 75 c. c. capacity, fitted with a rubber stopper 

 pierced with three holes. Through one hole passes a right-angled 

 tube reaching to the bottom of the flask, the other end being con- 

 nected with the distribution tube of the generator. Through the 

 second hole passes the right-angled delivery tube, reaching just below 

 the rubber cork. The third hole serves for the introduction of acid 

 and extract. Through it passes to the bottom of the flask a tube 

 with the bore at the lower end somewhat reduced by melting.** In 

 the top of this tube is set a very small funnel. 



To the delivery tube of the reduction flask is attached by a rubber 

 stopper a straight bulb drying tube filled with fused calcic chloride 

 (App., 5. a), and to the drying tube is connected by a short thick 

 rubber tube the reduction tube, which should be of the hardest and 

 best quality of Bohemian glass (App., 5. ^), and of as uniform bore as 



* Pharm. Zeitschr. f. Russland, 1888, XXVII. 193. 

 t Memoires de la Soc. Roy. de Sci., Lett, et Arts de Nancy, 1845. 

 i Loc. cit. 



§ Ref. by DragendorfE, Ermittelung von Giften, 1876, pp. 337 and 317, to Jour, 

 de Pharm. d'Anvers, 1872, pp. 193 and 241. 

 II Fresen. Zeitsclir., XXVII. 125. 

 TF Ibid.; also Biyth, loc. cit., p. 533. 

 ** That the fluid introduced may not carry any air with it into the flask. 



