August 1, 1902.] 



SCIENCE. 



167 



condition be examined, every individual 

 piece is seen to be coated over with a slimy 

 growth, which if removed and dried cuts 

 like a jelly. Under the microscope the 

 slime is found to be chiefly composed of 

 bacteria. 



It is on the presence of this slimy mate- 

 rial that the action of the bed depends ; the 

 greater in amount, up to a certain limit, 

 the greater the efficiency. If, however, this 

 limit is over-reached, the void spaces be- 

 tween the particles of the filling material 

 become filled up and the liquid capacity 

 is so diminished that the bed becomes 

 spongy and will not allow the water to 

 drain away. 



Can this growth of organisms be regu- 

 lated so that the bed will do its proper 

 work and at the same time not lose its 

 liquid capacity? Further, is serious trou- 

 ble to be apprehended from the deposition 

 of the non-putrescible part or ash of organic 

 substances 1 



These are the two points about which 

 there is a great difference of opinion among 

 English sanitary engineers. Many believe 

 from the results obtained at Manchester 

 that the growth of organisms can be regu- 

 lated and that no serious trouble will be 

 caused by the ash of organic substances. 

 Others, being influenced by the experi- 

 ments at Leeds, take the opposite view and 

 believe that the loss of liquid capacity de- 

 pends as much on the retention of the ash 

 of organic substances similar to the humus 

 of the soil, as to the growth of organisms, 

 and that consequently the loss in liquid 

 capacity, or the clogging up of the beds, 

 cannot be prevented no matter how care- 

 fully the process is worked. They regard 

 this as so serious a matter as to prevent 

 the contact method from being a practical 

 process with many kinds of sewage, espe- 

 cially those containing iron liquors and 

 acid waste. 



My own opinion, after careful study of 



the whole question, is that crude sewage 

 cannot be successfully treated by the con- 

 tact-bed method, and should never be at- 

 tempted, that clarified sewage, sewage 

 from which the solid matter has been re- 

 moved by chemicals, or sewage which has 

 undergone fermentation in the septic 

 tank, can be successfully purified on con- 

 tact beds, and that with such sewage the 

 contact method offers a solution to the 

 problem of sewage purification for to'wns 

 or cities where large areas of sand do not 

 occur. It is not, however, a process which 

 can be run successfully without care and 

 attention, and to be successful requires, as 

 does a slow sand- water filtration plant, the 

 personal oversight of a well-trained sani- 

 tary chemist or engineer. 



A very large contact bed plant for 

 treating 15,000,000 gallons of sewage per 

 day, costing about $1,500,000, is now being 

 built at Manchester, England, and a few 

 pictures showing the construction of these 

 beds, as well as pictures of some plants in 

 operation, may be of interest. 



Continuous Filtration. — "With the diver- 

 sity of opinion regarding the practical suc- 

 cess of the contact method of treatment, 

 there has arisen in England during the past 

 two years a growring interest in the so- 

 called continuous filtration methods and 

 the one question you are sure to be asked 

 in England is, "V^liat is your opinion re- 

 garding continuous filtration of sewage?' 

 Continuous filtration is an attempt to still 

 further increase the amount of sewage that 

 can be treated on a given area, to treat two 

 to three million gallons in place of 500,000 

 gallons per acre per day. 



The methods by which this is attempted 

 are all based on the idea that if air is sup- 

 plied to the filter at the same time that the 

 sewage is being run upon the filter, and 

 the filter is of such a construction and so 

 drained that fresh air continuously re- 

 mains in the filter, there is no necessity for 



