io6 SEWAGE AND ITS PURIFICATION 



may accompany a hydrolytic change due to bacterial activity. 

 He recognises that, as shown by Sonstadt,^ crystalloids as 

 well as colloids are separated from solutions by surfaces, but 

 insists on the importance of the natural tendency of colloids 

 to flocculation, especially in contact with surfaces, as aiding 

 and determining bacterial decomposition of albuminoids. 



2. The Fermentation of Urea. — In the ordinary hydrolysis 

 by B, urecB and M. urece — CO(NH2).2+ H20 = C02 + 2NH3 — the 

 COg and NH3 combine to form carbonate of ammonium, which 

 dissolves ; therefore none is evolved as gas, and no oxygen is 

 required beyond that derived from the water, even for the 

 bacteria, since these are facultatively anaerobic. M. urece^ for 

 example, grows equally well in oxygen and hydrogen, and we 

 know that urine putrefies in closed bottles. Miquel found that 

 several water bacteria readily converted urea into ammonium 

 carbonate, and that M. urecB was constantly present in the 

 atmosphere. 



3. The Disposal of Amido- Compounds derived from Albu- 

 minous Bodies. — It will be seen from the table (p. 98) that 

 either nitrogen or ammonia can be produced by bacterial 

 action. That both transformations occur is proved by the 

 composition of the gases from a closed tank, and also by the 

 liberation of H and CO2 in anaerobic cultures.^ 



Every 8 parts by weight of oxygen absorbed from water g 

 would involve the liberation of an equivalent, or i part by 

 weight of hydrogen, so that the weights, if increased by one- 

 eighth, give the weight of water taking part in the hydrolysis. | 

 Both the transformations given in the last two columns of the 

 table on p. 98 occur in sewage purification. The first or more 

 complete change is one in which the gases evolved are entirely 

 without odour, but the N, being in the free state, is lost. In 

 the second or less complete anaerobic change the gas will have 

 an ammoniacal odour, and would be offensive if allowed to 

 escape into the air. The effluent also will contain combined 

 N in the form of NH3 and compound ammonias, and make it 

 absolutely necessary to insure that adequate nitrification should 

 follow. In this case the final effluent theoretically contains all 



1 journal of the Chemical Society, Ixxxix., 339, 



'^ Hugounenq and Doyon found that under these conditions B. coli comuiitnis 

 generated H and CO2 (the gas bubbles), B. tctani also H and CO2, B. typhosus 

 N and CO2 [Ann. Chim. Fhys. 1898, vii., 45). According to Pennington and Kiisel, 

 B. coli evolved in per cents. 62 to 70 H, 23 to 34 CO2, i to 4 methane (not formed 

 when O excluded), and i to 5 N {Journal of the American Chemical Society, 1900, 

 xxii., 556), See also Pakes and Jolly man (loc. cit.). 



