198 



follow attempts to drain the marshes and bogg}- places. The injury to 

 meadows should be considered especially in this connection on account of 

 the frequent use of injurious marsh and boggy water for irrigation. The 

 conversion of irrigated meadows into marshes by overfilling the soil with 

 sewage may be considered only in passing. 



The statements of Bischof and Popoff' should be cited in connection 

 with the exhalation of gases. The gases produced are often rich in hydro- 

 carbons, especially methane or marsh gas (CH^). Popoff investigated the 

 gas developed in a cylinder which contained a slimey mass consisting of 

 kitchen refuse and substances of similar character. This slime was kept 

 3J^ weeks in the cylinder, at first at 17° C, later at 7 to io°C., and gave 

 gas mixtures of the following percentages of composition in the successive 

 investigations which took place usually at intervals of 2 to 4 days: — - 



4.71 O. 81.06 N. 



81.70 



0.0 O. 35-98 N. 

 0.0 " 1.65 " 



0.0 " 1.30 " 



0.0 " 0.0 " 



0.0 " 0.1 " 



These figures show that at the beginning of the experiment part of the 

 air found in the cylinder was driven out, and part used up, while the oxy- 

 gen oxidized the organic fragments in the slime. So long as free oxygen 

 w'as present, the formation of carbon dioxid exceeded that of marsh gas, — 

 on the other hand, this proportion was reversed as soon as the oxygen was 

 exhausted. 



Proceeding with the hypothesis that it is the cellulose in the slime 

 which is decomposed, assisted by the action of the lower organisms, Popoff 

 put clean filter paper with a small quantity of slime into a flask. On investi- 

 gating the gas formed after some little time, he found its composition to be 

 34.07 per cent, carbon dioxid, 37.12 per cent, marsh gas, 1.06 per cent, hy- 

 drogen and 27.75 per cent, nitrogen. 



Near marshes, however, we also frequently detect the odor of hydrogen 

 sulfid. This comes partly from the decay of protein bodies which form 

 leucin, tyrosin and other substances by their decomposition and finally car- 

 bon dioxid, marsh gas, ammonia, etc. Erismann's- observations, cited by 

 Detmer, make possible the determination of the quantitative composition of 

 the gas given off in 24 hours from 18 cubic m. of excrement placed in a 

 poorly ventilated cess pool. 



The whole mass gave 11. 144 kg. carbon dioxid, 2.040 kg. ammonia, 

 0.033 ^S- hydrogen sulfid and 7.464 kg. marsh gas. In this decomposition 

 oxygen and nitrogen were also set free. 13.85 kg. of oxygen are said to have 

 been taken up by the 18 cubic m. in 24 hours. 



1 Bischof's Lehrbuch der chemischen unci physikalischen Geologie, 2n(l. 

 Popoff in Pfliiger's Archiv f. Physiologie, Vol. X., p. 113. 

 - Zeitschr. f. Biolog-ie, Vol. XI, pp. 233 ff. 



