It is at this point that the serious error of a false assumption is so frequently made. The truth is, that sewer-air does not come into our houses in any appreciable quantity through the water seals of traps. On the contrary, it passes through the trap when the seal has been lost—when the water has been accidentally withdrawn or forced out. The broad principle of the efficiency of water-seals is not affected by these apparent failures. The difficulty is in maintaining the seals—in keeping them intact and secure against all the various adverse influences that may affect them. And here the aid of sanitary science must be sought; for the plumber's art has been powerless to devise traps that will protect our houses from the foul air of the sewers. Every failure in this attempt has been from a disregard of principles that have been well established by competent authorities. What are these principles?
For many years, skillful chemists, devoting themselves to sanitary work, have been carrying on careful investigations regarding the possibility of the passage of sewer-air and disease-germs through the water-seals of traps. The definite determination of this question is necessary in order to establish proper means of defense against the dangers we have already considered. It is evident that the form of traps and other apparatus to be used for this purpose will depend upon a conclusive demonstration of the truth or falsity of the views of those who have maintained that water as a resisting medium gives no protection in this particular The evidence which we have upon this point is clear and conclusive.
As long ago as 1877, Naegeli, an eminent scientific authority in Munich, established conclusively that disease-germs can never be given off from a liquid at rest in any ordinary temperature. Later researches by Carmichael, Wernich, and Miquel, chemists and sanitarists of world-wide reputation, corroborated the truth of Naegeli's demonstrations in every respect.
In 1880 the United States National Board of Health, through the efforts of Colonel George E. Waring, Jr., secured an appropriation for the purpose of investigating the same subject. Two able chemists. Prof. Raphael Pumpelly and George A. Smyth, Ph. D., were employed to conduct the investigations. A long series of careful and delicate experiments was made, extending through several months, and the published report of the results forms a valuable contribution to the literature of sanitation. The conclusions in this instance are precisely the same as those of the other authorities above referred to—viz., that disease-germs can not be given off to the air from any quiescent liquid at a normal temperature.
The experiments of Dr. Neil Carmichael, Fellow of the Faculty
