266 PHYSIOLOGY OF NUTRITION. 



cated by the thermometer T 7 , and hence also that of the research 

 material in R. 



The purified Hydrogen, free from Carbon dioxide, during its 

 passage through the worm is brought to the temperature of the 

 water. It then traverses the respiratory chamber proper from 

 below upwards, enters the stop- valve Sc~h, which contains a little 

 concentrated Sulphuric acid, and in the Pettenkofer's baryta tube 

 7?, containing 75 c.c. of baryta water, gives up the Carbon dioxide 

 received from the research material. The object of the valve is 

 to render impossible the passage of air into the respiratory space ; 

 the latter can, moreover, be completely isolated from the valve by 

 means of the stop-cock H n . The tube K ir , which contains frag- 

 ments of caustic potash, is intended to prevent the passage of air 

 containing Carbon dioxide from the aspirator into the baryta tube. 



Suppose an experiment on intramolecular respiration is to be 

 made, the apparatus is opened at Z, and we pass a rapid stream of 

 Hydrogen through it for an hour. Then I and o are connected by 

 means of a piece of glass tubing, and the current of Hydrogen 

 is continued for half an hour or an hour longer with the aspirator 

 in action, during which time the temperature in B, and the rate 

 of the current (3 1. per hour) must be carefully regulated. The 

 Oxygen being now displaced, as thorough investigation of the 

 method has taught, we insert the baryta tube between I and o ; 

 new tubes are put in every hour.* 



For success in the experiments it is naturally of the utmost 

 importance to have the apparatus absolutely air-tight at all points. 

 We use only carefully selected rubber stoppers and connection 

 tubing (the latter well greased), and well-ground glass stop-cocks, 

 and take care that the ends of the glass tubes are in contact at the 

 connections. The apparatus being in action, we can readily make 

 sure that all is tight by turning the stop-cocks H J or IV 11 . In the 

 former case, the flow of water at Ab must at once stop ; in the 

 latter the evolution of Hydrogen must cease. 



To prepare -the baryta water, we treat Barium hydrate and 

 Barium chloride with distilled water (to every litre of water, 

 21 gr. of Barium hydrate and 3 gr. of Barium chloride). The 



* To ascertain whether all the Oxygen has been driven out of the apparatus 

 by the Hydrogen, it is only necessary to connect the valve Sch with a bottle 

 containing some Phosphorus. To make sure that 75 c.c. of baryta water will 

 completely absorb the Carbon dioxide produced, it is sufficient to join on to the 

 baryta tube another vessel containing baryta water. This baryta keeps clear. 



