41 6 RESPIRATION 



When it is desired to determine the COg content of the blood the 

 procedure must be modified, as sodium carbonate cannot be used, and 

 2 cc. of blood would give too much COg for the capacity of the burette, 

 apart from other causes of error. Therefore only about i cc. of blood 

 should be taken. This is delivered under 1.5 cc. of a solution of 4 parts 

 of ordinary strong ammonia solution (sp. gr. .88) to a liter of boiled 

 distilled water, and a trace of saponin added. To avoid the presence of 

 any carbonate in the ammonia the strong solution is first shaken up with 

 some unslaked lime and allowed to settle. The stock of dilute solution 

 is kept tightly corked. As soon as the ammonia solution is placed in the 

 flask, the latter is kept tightly corked until the blood is added, otherwise 

 a considerable amount of CO2 may diffuse in and cause error. The blood 

 is shaken up to lake it, and .25 cc. of ferricyanide afterwards added to 

 liberate the oxygen, since if this were not done some oxygen might be 

 liberated by the acid. After all the liberated oxygen has been shaken off, 

 the small glass tube containing .25 cc. of 20 per cent solution of tartaric 

 acid is inserted and the burette read off after the gauges are steady. The 

 tartaric acid solution is then spilt into the blood solution and the flask 

 agitated under water till the CO2 has completely ceased to come off, as 

 shown by the gauge. The burette is then adjusted and read off and the 

 volume of gas given off reduced to its dry volume at 0° and 760 mm. 

 and calculated per 100 cc. of blood. Part of the COg however, remains 

 dissolved in the liquid in the flask, and must be allowed for. This liquid 

 is exactly the same as in the case of determination of COg by means of 

 the constant- volume apparatus described by Barcroft and myself, so the 

 correction is made in a similar manner. At a temperature of 13° the 

 coefficient of absorption of CO2 in this liquid was found to be i.oo. Hence 

 if we know the total volume of the flask as compared with the volume 

 of gas in it when the liquid is also present, and the temperature of the 

 bath is 13°, the total CO2 liberated from the blood will be to the amount 

 shown by the burette as the total capacity of the flask to the volume of 

 gas in it when the liquid is also present. The capacity of the flask to the 

 cork is about 20 cc. Let us suppose that as determined by weighing with 

 the cork in place it is 20.5 cc, including the capacity of a piece of glass 

 tubing of about 4 mm. bore and two inches long which passes through 

 the cork. The volume of liquid in the flask is 3.0 cc. Hence if the tempera- 

 ture of the bath is 13° the total volume of CO2 liberated is obtained by 



20. tj 

 multiplying the corrected volume actually read off by — — or adding 



175 

 17 per cent. If the temperature is above or below 13° a fortieth must be 

 subtracted from or added to this addition, since the solubility of CO2 

 diminishes by about a fortieth for each degree above 13°, and increases 



