76 PROCEEDINGS OF THE AMERICAN ACADEMY. 



discharged of its contents by the tube ss dipping into the beaker S. 

 The tube B serves to discharge carbon dioxide through a Liebig's bulb 

 having a water seal, when the apparatus is being cleared of air prepara- 

 tory to a determination. The various forms of stopcocks used are suffi- 

 ciently indicated by the sketch. The time required for a nitrogen 

 determination was from one and a half to two hours when 150 c. c. of gas 

 were used. Two or three days were sometimes occupied in expelling 

 the last traces of air from the apparatus by the slowly passing carbon 

 dioxide stream preparatory to a series of determinations. 



The potassium hydroxide solution was of 1.258 specific gravity, as 

 recommended by Kreusler, * and the measurement of the nitrogen was 

 always made with a little of the fresh solution resting upon the mercury 

 in the eudiometer. The mercury reservoirs, H, M, were attached to sup- 

 ports sliding vertically in wooden frames (not shown), and the reservoir 

 connected with the eudiometer could be adjusted by screw movement so 

 as to bring the mercury in the reservoir and that in the eudiometer to the 

 same level. Readings were made by an accurate cathetometer. The 

 pressures of mercury columns were all calculated at 0°. 



A very high temperature was found to be necessary for the complete 

 combustion of the hydrocarbons of natural gas, under the conditions of 

 the method, the excess of carbon dioxide produced causing retardation. 

 No difficulty was experienced, however, as repeated tests demonstrated 

 that the residual gas did not contain carbon monoxide or free hydrogen. 

 Moreover, it was repeatedly found that on passage of the residual gas for 

 a fourth and fifth time through the copper oxide, and absorption of the 

 carbon dioxide, no further reduction of volume was produced. The con- 

 stantly increasing amount of reduced copper in the porcelain tube, as 

 combustion goes on, serves to prevent the escape undecomposed of any 

 oxides of nitrogen, should such compounds tend to form during the 

 process. 



In order to procure pure carbon dioxide for the Dumas method of 

 nitrogen determination in organic bodies, it has been recommended that 

 the marble to be used be first pulverized and then boiled in water before 

 its carbon dioxide is liberated by the action of an acid. Bernthsen f 

 frees the pores of the marble from air by exhaustion with an air pump. 

 In experiments tried with a view to producing pure carbon dioxide these 

 methods have not always proved satisfactory. The carbon dioxide stored 



* Zeitschrift fiir Analyt. Cliemie, 1885, p. 445. 

 t Zeitschrift fur Analyt. Chemie, 1882, p. 63. 



