Six parts of sulphate of iron.... Slight arrest of decomposition. One part of saturated solution of sesquichloride of iron, Three and one-half parts carbolic acid, ......Evolution of gas entirely and permanently stopped. The carbolic acid used is known as No. 2 in commerce, and contains forty-six per cent. of real acid. The effect of a large amount of sulphate and sesquichloride of iron was not permanent nor entirely effective, while the effect of the three and one-half parts per 1000 of carbolic acid was entirely effective in arresting decomposition and evolution gas. of The carbolic acid acts by its presence, and not like the mineral salts which directly combine with the products of decomposition. The cost of the largest amounts of the above named disinfectants which were added to the sewage mud, at the present wholesale prices, is as follows: It is well known that some kinds of decomposition are favored by an alkaline condition, and hindered or arrested by an acid condition of the substance decomposing, but this is not the case with sewer mud. I found in the experiments above referred to, that an amount of sulphate of iron sufficient to cause an acid reaction in the sewer mud did not arrest decomposition in the sewage. The effect of a large amount of running water in rendering harmless the products of decomposition, is as powerful as that of the best chemical disinfectants. When clear water is used for flushing offensive draining canals or sewers, the effect is wonderful. The water has not only the mechanical effect of removing decomposing matter, but the no less important one of destroying organic matter by the rapid combination with it of the oxygen, which all water holds in solution, and which it has absorbed from the air: motion of the water favors the absorbtion of oxygen from the air, so that in a running stream containing sewage the oxygen which is continually uniting with the organic matters present, is continually being replenished by the absorbtion of more oxygen from the air. The following extracts are taken from reports by Mr. Bazalgette, Civil Engineer, of London, Dr. A. W. Hoffman and Dr. Taylor, to the British Parliament, on the sewage discharge into the Thames : It is estimated by Mr. Bazalgette that ninety-five millions (95,000,000) of gallons of sewage are discharged each day from London into the Thames, and that the volume of water into which it is poured is fifty times that quantity, so that the dilution of the sewage in the river is about one in fifty. According to the analysis of Professor A. W. Hoffman, the Thames water contains two and twenty-nine one hundredths (2.29) grains of organic matter per gallon; at London Bridge, nearly the centre of London, two and seventy one hundredths, showing that the immense quantity of sewage poured into the river only increases the amount of organic matter fourtenths of a grain per gallon, so rapidly is it destroyed. Below London, after a flow of a few miles, the amount of organic matter which the river has received from the sewage has decreased one-fourth. An offensive black mud is deposited by the sewage where it flows into the river, forming mud banks, of which the above mentioned report says: "It would appear that the black mud from the sewage contains a considerable quantity of organic matter, which is most deleterious. An immense mass of this fetid mud has ac 129 cumulated in the bed and on the banks of this river, and is continually supplying to the water large amounts of soluble matter, in a state of putrescence, and contaminating the atmosphere with most offensive emanations. It is probable that the unhealthy condition of many of the towns on the sea coast is caused by deposits of this character. "We cannot but emphatically assert that the formation of this mud deposit in the river appears to us by far the most serious evil which results from the discharge of the London sewage into the river. These mud banks are covered during high tide, but are exposed to the sun daily during low tide." These remarks will exactly apply to the abundant deposits of sewage mud which fill our draining canals especially, and with the rise and fall of water in them, are exposed alternately to the influence of the sun and water. I have quoted so largely from the English reports on the subject, as it has been more thoroughly examined by that government for a series of years, and their experience is more valuable on the subject than any other in the world. Very respectfully, ALFRED W. PERRY, M. D. |