72 PROCEEDINGS OF THE AMERICAN ACADEMY. 



pounds are also present. Free hydrogen, carbon monoxide, hydrogen 

 sulphide, and oxygen do not occur. 



It is a difficult matter to single out any of the constituents of natural 

 gas as specially suited for a series of determinations having for their 

 purpose to ascertain whether fluctuations actually occur in its composi- 

 tion. One of its constituents — nitrogen — seems to be less prone than 

 the others to enter into chemical changes locally in the rocks, and there- 

 fore less likely to undergo diminution in the original gas as it is stored 

 in the interstices of the sandstones and limestones of the Devonian forma- 

 tion. It might be proper to begin such a study with nitrogen. 



Under the term nitrogen is here understood the incombustible residue 

 obtained when natural gas is burnt in such manner as to prevent the 

 admixture of air or oxygen with the products. That the element nitro- 

 gen is actually contained in natural gas has been frequently shown by 

 passing the gas over heated magnesium. The magnesium, on being 

 afterwai'ds moistened, yielded ammonia, recognizable by its odor and 

 reactions, and indicating the presence of nitrogen in the original gas. 



The method employed for the determination of nitrogen consisted in 

 burning a measured volume of natural gas by passing it over heated 

 copper oxide. The resulting steam was condensed and the carbon 

 dioxide absorbed by potassium hydroxide solution, leaving the residual 

 nitrogen to be measured over mercury. This adaptation of the Dumas 

 ifcethod has been proposed by Stockmann for the determination of nitro- 

 gen in coal gas.* Arth has described an apparatus for a similar purpose, 

 the gas measurements being made over water. f 



Description of the Process. 



The gas sample was collected in a glass cylinder of from 150 to 

 400 c. c. capacity, and having stopcocks at both ends. In the drawing 

 of the apparatus A represents the gas sample vessel with its stopcocks 

 and capillary endings; Vessels of 150 c. c. proved sufficiently large for 

 the determination, although in the later work, where it was desirable 

 to collect a larger volume of the residual incombustible gas, vessels of 

 350 to 400 c. c. were used. These vessels were calibrated by weighing 

 the mercury required to fill them. They were filled with gas under 

 slight excess of pressure (about two ounces). With a view to deter- 

 mining by calculation the volume at 0° and 760 mm. pressure of the 



* Zeitschrift fiir Analyt. Chemie, 1875, p. 46. 

 t Bull. Soc. Chim., 1897, p. 30. 



