IRRIGATION AND SEWAGE FARMS 



145 



lours at a time," by the ridge and farrow system, with intervals 

 of eighteen hours per day for rest and aeration, crops of cabbages 

 being grown. The works were suggested by the experiments 

 of Sir E. Frankland in the laboratory of the Royal Commission. 

 It is reported that the crops at Merthyr were healthy and 

 luxuriant, and were valued in 1872 at £^2 to ^45 per acre, also 

 that no nuisance had arisen. From Frankland's analyses of the 

 effluents in 1871-1872 I have calculated the following averages, 

 adding also his " proposed standards of purity ": 



In the use of land by any system there is always a variable 

 dilution with rain and subsoil water, so that the improvement 

 effected by soil, as indicated by the quality of sewage and 

 effluent, would appear to be greater than it is, unless we take 

 this feature into account. Frankland^ applies the formula 



a + c 

 c + b 



" in which a, b, and c represent the amount of chlorine in 

 100,000 parts of sewage, subsoil water, and effluent respectively, 

 and X the required volume of the subsoil water which has thus 

 become commingled with each volume of the original sewage." 

 In this case he finds that each gallon of the sewage had 

 become mixed with from 1*9 to 2*2 gallons of subsoil water, 

 and probably also with some rain, as the mean dissolved solids 

 of the sewage and subsoil water are about the same as those in 

 the effluent, while the chlorine in the effluent is less than half 

 that in the sewage. But even with this allowance the result 

 justifies Frankland's statement that " the effluent water on all 

 occasions was purified to an extent much beyond that required 

 by the standards of pollution suggested by us as those below 

 which refuse liquids should not be permitted to enter rivers." 

 The analyses are of further interest at the present time, as we 

 ^ " Experimental Researches," p. 763. 



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