296 



THE POPULAR SCIENCE MONTHLY. 



of Physicians and Surgeons at Glasgow, are particularly interest- 

 ing. They were conducted, with rare skill and an honest endeavor 

 to ascertain the worst conditions existing ordinarily in houses 

 containing the usual forms of plumbing fixtures. Dr. Carmichael 

 attached his experimental apparatus to the traps of two common 

 water-closets connected with a foul soil-pipe leading into an old 

 sewer. The outlet of this sewer, some three hundred yards away, 

 was submerged at high tide, so that sewer air or gases were forced 

 back toward the houses. The top of the soil-pipe used for the ex- 

 periments was ventilated by a two-inch pipe passing through the 

 roof to the outer air ; and, to impose the most severe conditions 

 possible, some of the experiments were conducted with the soil- 

 pipe tightly closed at the top. The average result of many dif- 

 ferent experiments by Dr. Carmichael is given in the following 

 table : 



Quantitative Determination of Gases which passed through Water-Traps (A and 



B) in Twenty-four Hours. 



Putrid organic vapors, if present, are included in the ammonia. 



With the top of the soil-pipe closed, it will be seen that the 

 amount of gases passing through the water was considerably in- 

 creased, but was still extremely small. And this represents the 

 worst possible condition that can exist in houses which are prop- 

 erly protected by traps having water-seals. 



The deductions of Dr. Carmichael from these experiments are 

 here given in his own words, taken from the " Proceedings of the 

 Philosophical Society " of Glasgow : 



" These are the quantities of the only sewage gases existing in 

 the soil-pipe in estimable quantities which pass through an ordi- 

 nary water-closet trap in twenty-four hours. Diffused into the 

 atmosphere of a house during this time, these quantities are, from 

 a health point of view, quite inconsiderable — perfectly harmless. 

 Thirty -two grains (the largest quantity of carbonic acid) is less 

 than the quantity of the same gas given off when a bottle of lem- 

 onade is opened. A man exhales in the same time about four 

 hundred times the amount which passes through the trap from 

 an unventilated soil-pipe." 



Dr. Carmichael then explains in detail his experiments in re- 



