“If we could get the genuine article,” said the Doctor, “it would be worth $4 a ton. But, as a rule, it is mixed with water, and dirt, and stones, and bricks, and rubbish of all kinds. Still, it is unquestionably a valuable fertilizer.”
“In the dry-earth closets,” said I, “such a large quantity of earth has to be used to absorb the liquid, that the material, even if used several times, is not worth carting any considerable distance. Dr. Gilbert found that 5 tons of absolutely dry earth, before using, contained 16.7 lbs. of nitrogen.
| After being used once, | 5 tons of the dry earth contained | 24.0 lbs. |
| After being used twice, | ””” | 36.3 lbs. |
| After being used three times, | ””” | 44.6 lbs. |
| After being used four times, | ””” | 54.0 lbs. |
| After being used five times | ””” | 61.4 lbs. |
| After being used six times, | ””” | 71.6 lbs. |
Dr. Vœlcker found that five tons of dry earth gained about 7 lbs. of nitrogen, and 11 lbs. of phosphoric acid, each time it was used in the closets. If we consider each lb. of nitrogen with the phosphoric acid worth 20 cents a lb., 5 tons of the dry earth, after being used once, would be worth $1.46, or less than 30 cents a ton, and after it had been used six times, five tons of the material would be worth $11.98, or about $2.40 per ton.
In this calculation I have not reckoned in the value of the nitrogen the soil contained before using. Soil, on a farm, is cheap.
It is clear from these facts that any earth-closet manure a farmer would be likely to purchase in the city has not a very high value. It is absurd to talk of making “guano” or any concentrated fertilizer out of the material from earth-closets.
“It is rather a reflection on our science and practical skill,” said the Doctor, “but it looks at present as though the only plan to adopt in large cities is to use enormous quantities of water and wash the stuff into the rivers and oceans for the use of aquatic plants and fishes. The nitrogen is not all lost. Some of it comes back to us in rains and dews. Of course, there are places where the sewage of our cities and villages can be used for irrigating purposes. But when water is used as freely as it ought to be used for health, the sewage is so extremely poor in fertilizing matter, that it must be used in enormous quantities, to furnish a dressing equal to an application of 20 tons of stable-manure per acre.”
“If,” continued the Doctor, “the sewage is used merely as water for irrigating purposes, that is another question. The water itself may often be of great benefit. This aspect of the question has not received the attention it merits.”
PERUVIAN GUANO.
Guano is the manure of birds that live principally on fish.