350 
Sewage Disposal and Divers Pollution. 
de mieux, when land or filter beds are not available, as is the 
present case with London, it is no doubt defensible ; and in the 
very different case where the river itself into which the effluent is 
discharged is already used for irrigating watermeadows on its 
banks, it may be the best course to adopt. But there is now a 
pretty general agreement, even amongst the advocates of chemical 
treatment, that its proper function is as an adjunct to irrigation or 
filtration. 
Dr. Dupre himself, who, in conjunction with Mr. Dibdin, pre- 
scribed the proportions of chemicals used to precipitate the London 
sewage, admits in this discussion that “ no such chemical treatment 
would do more than clarify the sewage by removing the suspended 
matter, but would leave the matters in solution almost unaffected,” 
and that by the system followed in London “ the effluent produced 
was not such as could with safety be discharged into a relatively 
small river.” 
This being so, it is interesting to glance at the prospect of 
advance in the direction of exalting the purifying power of soil or 
other filtering material. 
“Actual practice shows that quantities varying from 2,000 to 
6.000 gallons per acre per day have generally been applied to sewage 
irrigation farms, and from 10,000 gallons to 60,000 gallons to farms 
laid out for irrigation combined with intermittent filtration where 
crops are cultivated.” The well-known laboratory experiments of 
Dr. Frankland, which led to the practice of intermittent downward 
filtration, showed that volumes of 43,000, 74,000, and 96,000 gallons 
per acre per day could be filtered through filters packed with six 
feet of porous surface soil, with complete purification. Although 
this estimate of Dr. Frankland’s led to much disappointment when 
it was first attempted to put intermittent filtration into practice, 
from the fact that the conditions obtainable were not such as existed 
in his experimental filters, it appears from the statement of Mr. 
Bailey Denton that when the soil is exceptionally favourable, as at 
Abingdon and Forfar, a near approach to these maximum figures 
has actually been obtained. At Abingdon, for example, the soil of 
which he regards as ideally favourable, it appears that although 
they have 274 acres for irrigation and 6 for intermittent filtration, 
3 only of the latter are sufficient to purify the whole sewage of the 
town (6,500 people), which gives an ordinary dry-weather flow of 
67.000 gallons to the acre. 
The experimental filters constructed by the Massachusetts Board 
of Health 1 are in some cases of neai’ly double this efficiency, and throw 
more light on the requisite conditions. These filters were 17 feet 
in diameter and 6 feet deep. The best result was obtained with 
5 feet of coarse clean sand, which filtered at the rate of 102,000 
gallons per acre per day ; extremely fine sand filtered only 34,000 
gallons, and garden soil only 8,600. The necessity of air spaces is 
thus clearly indicated, and is forcibly pointed out by the result 
1 Massachusetts State Board of Health, 19th and 22nd Annual Keports. 
