ANAEROBIC RESPIRATION 



67 



bell jar rests a dish, the proper form of which may be learned 

 from the figure. This dish is filled with small sticks of the 

 purest metallic zinc. The purity of the metal is controlled as 

 follows. After immersing the sticks in pure dilute sulphuric 

 acid without copper sulphate only a very insignificant generation 

 of gas should occur. This becomes vigorous only after the 

 addition of copper sulphate. Only such sticks of metal should 

 be used for accurate experiments; otherwise the research mate- 

 rial may be poisoned. This has actually occurred in the experi- 

 ments of various investigators. 





K m//////////{ yzMzz^ 



cQi;3=x 



^.__ 



Fig. II. — The Bardeleben apparatus. 



The gas needs only to be passed through an alkaHne solution 

 of pyrogallol if the reagents are sufficiently pure. The wash 

 bottle shown in Fig. 1 1 is closed with a three-hole rubber stopper. 

 The right-angled entrance tube passes through one hole and is 

 connected with the exit tube of the Bardeleben apparatus. Into 

 another hole is placed the T-tube fitted with two glass stop- 

 cocks by means of which the gas current may be passed through 

 at least two plant containers and two series of absorption tubes. 

 A funnel with a glass stopcock goes in the third hole. The 

 expansion of the neck of the flask above the stopper is filled with 

 mercury. The flask is next supplied with concentrated caustic 

 potash, and hydrogen is passed through for a time until all the 

 oxygen is driven from the flask. Then a concentrated solution 

 of pyrogallol is run in through the funnel. A little of it is left 

 in the funnel above the stopcock in order to isolate more securely 



