SYNTHESIS OF MARSH-GAS. 87 



These four bodies the methyl varieties of hydrogen, hydro- 

 chloric acid, water, and ammonia are mutually convertible by a 

 variety of processes. Marsh-gas, in addition to its occurrence as 

 the chief constituent of coal-gas, as the fire-damp of coal mines, 

 and as the gas of stagnant ponds or marshes, has recently been 

 recognised by Pettenkofer as a normal ingredient of expired air. 

 Wood- spirit, again, is not only a product of destructive distilla- 

 tion, but occurs in nature as a constituent residue of the essential 

 oil of wintergreen, thus : 



Wintergreen-oil Water Salicicacid Wood-spirit 



C 8 H 8 3 -f H a O C 7 H 6 3 + CH 4 



Among other well-known methyl-compounds may be men- 

 tioned sarcosine, kreatine, caffeine or theine, theobromine, coniine, 

 narcotine, &c. &c. Methylamine I have already referred to on 

 several occasions. Associated with it we have trimethylamine 

 (CH 3 ) 3 N, a frequent constituent of stale brine in which herrings 

 and other fish have been pickled. 



(91.) The production of methylic from carbonic or formic 

 compounds may be effected in a variety of ways. Thus, prussic 

 acid, by hydrogenation, yields methylamine : 



Pruesio acid Hydrogen Methylamine 



CHK + H 4 CH 5 N 



Formiate of barium is decomposed by heat with production of 

 marsh-gas, thus : 



Barium formiate Barium carb. Carb-anhyd. Marsh-gas 



a] cH Ba O* = 2CBa"0 3 + CO, + CH 4 



Marsh-gas also results from passing a mixture of carbonic sul- 

 phide and sulphuretted hydrogen over metallic copper heated to 

 redness, thus : 



Carb. sulph. Hyd.sulph. Copper Cupr.sulph. Marsh-gas 



CS a + 2H,S + Cu 8 = 4Cu a S + CH 4 



