Apparatus and Methods 75 



APPARATUS AND TECHNIQUE USED IN THIS RESEARCH. 



The importance of securing the highest degree of accuracy in these 

 analyses led to a critical examination of all the forms of gas-analysis ap- 

 paratus of unusual accuracy now in use. Special attention was given to 

 the apparatus of Haldane, 1 Chauveau, 2 and Sonden-Pettersson. 3 After 

 a careful personal examination had been made of practically every form 

 of exact gas-analysis apparatus in existence, it appeared that the poten- 

 tialities for exact analysis were greatest with the Sonden apparatus. Ac- 

 cordingly I visited Stockholm to make arrangements for securing such an 

 apparatus, but on my arrival was much discouraged to find that none 

 thus far constructed was sufficiently exact for the research proposed. 

 Through the geniality and interest of Dr. Klas Sonden, however, I was 

 able to spend considerable time with him in discussing the conditions to be 

 met; as a result, he designed and superintended the construction of the 

 apparatus herein to be described, which, we believe, fulfills perfectly all 

 of the conditions outlined except the last, i. e., constancy in volume of the 

 liquid water above the mercury. 



Since Dr. Sonden had previously spent a great deal of time in ex- 

 perimenting with the hydrogen method for determining oxygen and the 

 results had been unsatisfactory, it was decided to use, as the absorbing 

 reagent, a strong solution of potassium pyrogallate, potassium hydroxide 

 being used to absorb carbon dioxide. To insure thoroughly controllable 

 temperature conditions, the entire apparatus, including both the two 

 measuring pipettes and the containers for the reagents, is immersed in a 

 water-bath, nothing but capillary tubing being exposed to the room tem- 

 perature. The apparatus is constructed entirely of glass, and neither the 

 reagent nor the gas is in contact with any other material. The gas 

 volumes are measured over mercury to avoid the solubility of the gases 

 in water, and a few drops of water above the mercury in the measuring 

 pipette insure saturation with water-vapor at the temperature at which 

 the gases are measured. 



In using the apparatus a volume of air is first measured, the tempera- 

 ture, pressure, and tension of aqueous vapor being exactly equal to a 

 confined volume of air in a compensating pipette. The air sample is then 

 passed into a strong solution of potassium hydroxide by means of which 

 the carbon dioxide is absorbed. The gas is next returned to the original 

 measuring-vessel and the apparent volume arbitrarily adjusted so as to be 

 the same as before the absorption of the carbon dioxide. There is then 

 a slightly decreased pressure of the confined air due to the volume of car- 



1 Foster and Haldane, The investigation of mine air, London, 1905. See, also, J. S. 

 Haldane, Methods of air-analysis, London, 1912. 



2 Chauveau's apparatus is described in detail by Tissot, Traite de physique biolo- 

 gique, 1, pp. 709-723. 



3 Pettersson, Zeitschrift fur analytische Chemie, 1886, 25, pp. 467 and 469; Pettersson 

 and Palmquist, Berichte der deutschen chemischen Gesellschaft, 1888, 21, p. 21-29; 

 Sonden, Zeitschrift fur Instrumentenkunde, 1889, 9, p. 472. 



