SANITARY SCIENCE. 



723 



for communities, there is chance of neglect and 

 a consequent risk to health, while the cost of 

 conveying the fresh earth and removing the 

 waste material becomes a burden. The dry- 

 earth system has been tried in certain sea-side 

 and other summer communities, and under com- 

 petent supervision has proved successful. But 

 for settled communities the water-carriage sys- 

 tem is by general consent considered more 

 economical and safe. The popular impression 

 that the waste products of a town or city are 

 of sufficient value to pay for their removal is 

 a mistake, and the question of drainage must 

 always be considered from its sanitary aspect 

 rather than with any hope of profits. 



The second method of domestic drainage is 

 what is known as the sub-irrigation system. 

 It has been adopted to a considerable extent 

 for draining small places in the country, and 

 on a large scale for disposing of the sewage 

 of towns and even cities -abroad. This method 

 consists in utilizing the absorbing powers of 

 the soil in taking up liquid sewage, and also 

 the oxidizing powers of the atmosphere in de- 

 stroying the products of fermentation. Instead 

 of pouring a mass of fluid matter into a pit, and 

 saturating the ground to a point beyond ab- 

 sorption, the sewage is spread over a wide area 

 by means of small pipes carried just below the 

 surface of the ground, with their joints open 

 to permit the contents to leach freely into the 

 soil, while it is further absorbed by the roots 

 of grass and oxidized by the air that penetrates 

 the interstices of the soil. A single acre will 

 serve to dispose of the waste products of an 

 ordinary household. The vegetation growing 

 on it will be benefited, and the cost of the ar- 

 rangement will not greatly exceed that of build- 

 ing and constantly cleaning an ordinary cess- 

 pool. Drain-pipes two inches in diameter are 

 preferred. They are laid so as to be easily in- 

 spected, and about once in three years they 

 may need to be taken up, cleansed of grease 

 that may accumulate at the joints, and relaid. 

 A prime feature of this plan is, first to convey 

 all the drainage into a settling- tank, so as to 

 collect the grease and to dissolve other solid 

 materials, which are then by the automatic ac- 

 tion of a siphon discharged in considerable vol- 

 ume, and the sewage distributed throughout 

 the whole area of the branching drains. Oth- 

 erwise, the discharge would be a mere dribble, 

 and would not extend throughout the pipes, 

 while the area of soakage would be confined 

 to a small section. The sub-irrigation system 

 works best in a gravelly, porous soil. Where 

 the ground is retentive, it is desirable to pro- 

 vide under-drainage. Mainly through the ef- 

 forts of Col. George E. Waring, this system 

 bas been widely made known and extensively 

 adopted. In the neighborhood of Orange, N. 

 J., about fifty houses are thus drained, while 

 at Lenox, Mass., and at the Sherburn (Mass.) 

 Reformatory, the system has been applied on 

 a larger scale. So perfect is the purifying ac- 

 tion of the soil, that it is said the foulest sew- 



age will flow at the outer end of an irrigating 

 pipe seemingly as pure as the best drinking- 

 water. 



Sewer-Gas. Ordinary sewer-air contains less 

 oxygen than the atmosphere, as some of it 

 combines with the carbon of putrefying organ- 

 ic matter to form carbon dioxide. The low- 

 est amount of oxygen reported in se\ver-air, 

 upon analysis, was 17 parts in 100. The 

 average amount of carbon dioxide was 2 to 

 100 parts. Sulphureted hydrogen was found in 

 inappreciable quantities, and some other gases 

 of trifling amount. The proportion of nitro- 

 gen was about the same as in the atmosphere. 

 Carbonic oxide is sometimes found in minute 

 quantities, and is usually traced to leaky gas- 

 mains (Gerhard). The ferry-boats at certain 

 New York slips where sewers empty their 

 contents have their copper bottoms blackened 

 by the sulphureted hydrogen. The silver ta- 

 ble-ware on ocean-steamers whose wharves 

 are in this vicinity is acted upon in a like man- 

 ner, and silver door-plates have shown the 

 same effects. Sewer-gas is exceedingly pene- 

 trating ; it escapes readily through the smallest 

 openings in walls and partitions. Menzies 

 says, u I have known it to pass through floors 

 and through chinks in two-foot walls." It will 

 find out the minutest crevice in a pipe that 

 will give it a chance of getting to the heat or 

 open air. It will readily pass through breaks 

 in cellar ceilings where plumbing pipes are car- 

 ried. Pettenkofer's experiments with ground- 

 air show that neither brick, stone, nor concrete 

 is a barrier to gases under heavy pressure. 



The following are among the chief sources 

 of sewer-gas : 



1. Foul and un ventilated sewers, usually 

 badly constructed with rough interior sur- 

 faces, and made too large for proper flushing 

 except in heavy rain-storms, so that the ordi- 

 nary flow of sewage covers only a small por- 

 tion of the surface, and the remainder be- 

 comes coated with slime, which decomposes 

 and throws off vast volumes of foul air. A 

 cubic ton of sewage, it is estimated, creates 

 its own bulk of sewer-gas every twenty-four 

 hours. 



2. Tightly sealed cess-pools carefully hidden 

 underground and filled to overflowing with 

 putrefying filth, whose gases have no means 

 of escape except through the house-drains 

 connecting directly with living-rooms. 



3. Small and clean sewers, which when tide- 

 locked or gorged with rain from their defi- 

 cient size, as in Brooklyn, force foul gases into 

 houses. 



4. Defective drains under or near houses, 

 which have not proper flush or pitch, and hence 

 become mere elongated cess-pools. 



5. Soil-pipes full of sand-holes, or lead soil- 

 pipes honeycombed by corrosion or eaten by 

 rats. 



6. Bad workmanship, as making joints with 

 cement or putty, instead of calked molten 

 lead. 



