204 SEWAGE AND ITS PURIFICATION 



water, and the influence of ozone and hydrogen peroxide. His 

 investigations were published in 1885/ and show that 



" When left standing, and after agitation with air, the self-purifica- 

 tion only took place if the water had not been sterilized through 

 boiling, and had not been protected against the entrance of germs 

 during the period of observation. If, however, sterilized water was 

 afterwards fully exposed to the air, or if it was afterwards infected 

 with ordinary water, the same changes took place in it as in non- 

 sterilized water exposed to air, viz., the quantity of potassium per- 

 manganate required for the oxidation of the organic matter, and the 

 amount of ammonia, decreased with the formation of nitrous and 

 nitric acid. A direct oxidation through the oxygen of the air did not 

 take place, and even one brought about by ozone and hydrogen 

 dioxide plays only an unimportant part compared with that played 

 by the biological process." 



All this had main reference to oxidation, which, as we have 

 seen in earlier chapters, is only a later part of the cycle of 

 changes in the course of purification. The first hydrolytic, or 

 dissolving, stage had been conducted from very early times in 

 a leaky and objectionable way in the old cesspools, which, how- 

 ever, when well managed and under favourable conditions, were 

 quite capable of giving a good result. I have mentioned in 

 Chapter I. an example in 1858. 



About 1865 Dr. Alexander Mueller had come to the following 

 conclusions:^ 



" The contents of sewage are chiefly of organic origin, and in 

 consequence of this, an active process of decomposition takes place 

 in sewage, through which the organic matters are gradually dissolved 

 into mineral matters, or, in short, are mineralized, and thus become 

 fit to serve as food for plants. To the superficial observer this pro- 

 cess appears to be a chemical self-reduction ; in reality, however, 

 it is chiefly a process of digestion, in which the various — mostly 

 microscopically small — animal and vegetable organisms utiHze the 

 organically fixed power for their life purposes. . . . The decomposi- 

 tion of sewage in its various stages is characterized by the appear- 

 ance of enormous numbers of spirilla, then of vibrios (swarming 

 spores), and, finally, of moulds. At this stage commences the re- 

 formation of organic substance, with the appearance of the 

 chlorophyll-holding protococcus, etc." 



Mueller recognised the importance of a preliminary change, 

 and later patented a process (German patent 9,792 of 1878) 

 for utilizing the micro-organic life in sewage in its purification, 

 which was actually in operation at one time to purify the 



1 Monatshefte, vi., 77; Chem. Centralblatt, 1885, 333. 



2 Landwirthschaftliche Versuch-stationen, xvi. , 273. 



