512 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



A similar apparatus with no taps has been constructed by Gardner and 

 Buckmaster : it possesses the advantage that no leakage of air into the ap- 

 paratus through the taps can occur when the apparatus is evacuated. 



It consists of a vessel in the form of two bulbs surrounded by water 

 jackets, a condenser cooled by ice water, a drying chamber (test tube) contain- 

 ing sulphuric acid, a glass pump with a valve, a trough containing mercury, a 

 tube filled with mercury to collect the gases and a burette to introduce the 

 blood. The part between the burette and the bulbs also contains mercury. 



The whole apparatus is exhausted by first evacuating with a water pump 

 at the point where the burette is put and then raising the mercury so that 

 it fills the expanded portion and just runs out into the trough ; it is pre- 

 vented from reaching the rest of the apparatus by the valve. The mercury 

 is lowered ; gas is thus removed from the rest of the apparatus. It is raised 

 again ; the gas is driven out into the trough in front of the mercury. 

 When the mercury reaches the trough it is again lowered. This process 

 is continued until no more gas can be removed as is shown by the absence 

 of gas bubbles in the trough when the mercury is raised. The mercury 

 has to be raised and lowered some 10 or 20 times; this is conveniently 

 effected by water pressure as shown in the figure, p. 511. 



The blood is collected in the burette containing hirudin or oxalate by insert- 

 ing it in the artery or vein of art animal with the tap open. As soon as it has 

 filled and contains a proper sample of blood, the tap is closed. It is connected 

 to the bulb vessel and the mercury is displaced by blood. On turning the 

 tap to the bulb, blood rushes in ; the tap is closed again. The volume of 

 blood introduced is measured on the burette. The bulbs are heated by a 

 hot water current and the evolved gases are pumped out in the same way 

 as in evacuating, but instead of being driven into the air they are driven into 

 the gas tube which is placed over the end of the pump. The condenser and 

 sulphuric acid remove the water vapour, from the gases as they are collected. 

 The gas in the gas tube is transferred into a measuring tube, measured and 

 analysed. 



Analysis of the Gases. 



The analysis of the gases is carried out according to the general methods 

 of gas analysis ; the gas is measured in a graduated tube connected with a 

 levelling tube and enclosed in a vessel which is kept at a constant temperature 

 by running water. By raising the levelling tube the gas is driven into caustic 

 potash solution to absorb the carbon dioxide. It is returned to the graduated 

 tube and measured. The difference in volume is the amount of carbon 

 dioxide. By again raising the levelling tube it is driven into alkaline 

 pyrog illol solution to absorb the oxygen ; it is returned to the graduated tube. 

 The difference in volume is oxygen. The residual gas is nitrogen. 



The apparatus generally used for blood gas analysis is that of Haldane, 



Fig- 73- 



A gas burette (G) and a control tube (C) are contained in a vessel of water 

 to give a constant temperature. The gas burette is connected at its base 

 with the levelling tube ; at the top it has a 2-way tap (T) : (a) to the air and 

 for filling ; (b) to the absorption pipettes. The absorption pipettes (S and P) 

 are separated from one another and from the gas burette by a 3-way tap. 

 The absorption pipette (S) contains 20 per cent, caustic potash. It is con- 

 nected with a reservoir (R) and has a mark (f) on it and also by a side tube (Y) 

 ;o the control tube (C) through the tap (M). The absorption pipette (P) 

 contains pyrngallol solution (10 gm. pyrogallql in 100 c.c. saturated caustic 

 potash) and has a mark (II). 





