of Physicians and Surgeons at Glasgow, are particularly interesting. 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 experiments 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 different 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.
| GAS. | Old water-closet trap (A). | Kitchen trap (B). | ||
| Grains. | Grains. | |||
| Soil-pipe open at the top | Carbonic acid | 7·084 | 7·084 | |
| 10·470 | ||||
| Ammonia | 1/217, 1/250, 1/330, 1/400 | 1/100, 1/200 | ||
| Sulphureted hydrogen | 1/200 | 1/200 | ||
| Soil-pipe closed at the top. | Carbonic acid | 32·032 | 17·063 | |
| Ammonia | . . . . . . . . . . . . . | 1/400 | ||
| Sulphureted hydrogen | 1/90 | . . . . . . . . . . . . . | ||
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 increased, but was still extremely small. And this represents the worst possible condition that can exist in houses which are properly 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 ordinary 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 lemonade 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-
