t 541 J 



"Native guano ", which is mixed with super to make it a 

 richer manure. 



868. Another process applied is that of cultivating de- 

 odorising bacteria in tanks protected from sunlight through 

 which the sewage is made to run. Electric processes have 

 been also applied with more or less success in purifying 

 sewage. 



869. In England it has been estimated that for every head 

 of population 40 to 60 tons of sewage is formed per annum. 

 This is not absolutely wasted as the fish and sea-weeds are 

 nourished by it. These 40 to 60 tons consist mainly of water, 

 solid and liquid excrements forming only small proportion 

 of the sewage. This quantity contains only about 10 Ibs. 

 of N calculated as Ammonia. The conclusion drawn. from 

 experiments conducted in sewage-farms in England is, that by 

 the use of 5,000 tons of sewage per acre 30 tons of grass 

 may be expected, and the value of sewage has been calculat- 

 ed at \d. to id. per ton. Leguminous plants are killed out 

 in a pasture manured with sewage water. Weight for weight 

 unsewaged grass is better fodder than sewaged grass, but 

 for equal weights of dry matter the sewaged grass which is 

 richer in N has a better nutritive value. Milk increases in 

 quantity but is reduced in quality with sewaged grass, but 

 cows kept on sewaged grass, if they are given some oil-cake 

 every day thrive beautifully and give good quantities of rich 

 milk. From 5000 tons of sewage applied judiciously to I 

 acre, about 75 maunds of milk may be expected per annum, 

 as 30 tons of green grass would keep 3 cows for i year, 

 each Cow being allowed 30 seers of green grass and one seer of 



,30 tons x 28 mds. x 40 srs. . , , , 



oil-cake per day (- = about 3) and the 



30 srs. x 365 



average yield per cow (if a select class is kept) may be taken 

 at 5 seers per day for 200 days per annum. The rent of the 

 land being calculated at Rs. 10 and'the value of the oil-cake 

 (3 srs. x 365 days) at Rs. 60 and the cost of irrigation 



