the union of carbon with oxygen, but the proportion of oxygen is less in the former than in the latter compound. Carbonic oxide, though a dangerous gas, need not be considered at length here, as it does not, I believe, exist in sewers, and is very seldom found in houses.* It cannot, like sulphuretted hydrogen, be detected by its smell, as it is inodorous as well as colorless and tasteless. Carbonic oxide burns with a blue flame, which probably most people have noticed at some time or other, either playing over burning charcoal or dancing upon an ignited lime kiln.

The quantity of air required by a man varies with the state of his body. Thus a man at hard work or violent exercise may require even five times as much air as the same man when asleep.

* In America, where hot-air furnaces are much more used than in England, and cheap ones at that, carbonic oxide is not unknown in houses. It is one cause of the dislike to furnace heating. It is very injurious, even in small quantities, and should never be allowed to escape. The proper remedy is good stoves and furnaces, with good drafts.

J. L. G.

This amount of air has been variously estimated, but I think we may safely take the following calculation by Box to be correct. He states that an ordinary man takes 20 respirations per minute, of the capacity of 40 cubic in. each, thus vitiating 28 cubic ft. per hour. Added to this, there is the quantity of air saturated by the moisture evolved to be considered. According to Dumas, this quantity in the form of vapor equals .0836 of a pound of water per hour, which is sufficient to half saturate, for air should not be more than half saturated to be pleasant-187 cubic ft. of air at 62 deg. Fahr.

We thus see that to be in good health a man must have 215 cubic ft. of air per hour for his own use. Sick persons require very much more than this.*

There is one more source of contamination of the air of our houses, which often forces itself unpleasantly upon our notice. I mean the foul gases which escape from drains and water-closets. is not too much to say that if architect

*See next note.

It

and builder always did their duty, no foul air from any drain or closet ought ever to enter a house, and that the negligence of one, and the ignorance, or worse, of the other, must be charged with a greater destruction of human life and with causing more disease every year than has been produced by the bloodiest battle. recorded in history.

If is impossible to estimate correctly the air contaminated from this source, but I hope to show how such contamination. may be avoided.

As a summary of results we see, that in a room of the net cubic capacity of 3,800 ft., having a fire burning, inhabited by, say, six persons, and lighted by three gas-lights, there will be required every hour, so that the inmates may be healthy, 1,694, or say 1,700 cubic ft. of fresh air at 60 deg. F.

But air expands, or 0.00204, of its volume for every degree F. it is heated; it is obvious from this that, assuming the temperature of the outer air to be 32 deg. F., we shall not require to admit so much

cold air into the room by about 100 cubic ft., but exit must be provided for the full quantity.*

*The editor of this second edition of Mr. Butler's book must here be allowed to differ from him radically. He cannot feel that the reasoning which leads up in this case to a supply of 1,700 cubic ft. of fresh air per hour is founded upon correct premises. What are the conditions? A room with six people sitting in it, and exhaling their breath to mingle with the air of the room. Three gas-lights also throwing their products of combustion into the surrounding air, and an open fire that requires for practical combustion 296 cubic ft. of air per hour. What were the conditions assumed in arriving at the supply of 1,700 cubic ft per hour? In the first place, the supply of 108 cubic ft. per hour for the gas jets can only be sufficient on the supposition that the products are immediately carried off, as has been already explained. In a similar manner, Mr. Box's estimate of 215 cubic ft. of air per hour for each person is based on the actual amount of air that goes into the lungs in an hour, and takes no account whatever of the fact that the returning vitiated breath must be disposed of. If people could be induced to take in a supply of air, and then go to a hole in the outer wall and breathe it out, or, if they could be arranged somewhat on the plan of ventilating gas-lights, this supply might be sufficient. It is true that Mr. Box makes an allowance for the diffusion of moisture from the breath, but it is a mere bubble in the volume that is needed. The fact is, that the supply decided upon as sufficient is based upon conditions not met with in any room. If it were possible that the inmates could "be done for," as it has been expressed, as definitely as the gas-lights can be managed,

I am aware that any proposal to admit cold air into a room will meet with opposition, and were houses built upon prin

then the conditions of this theory and of practice would harmonize. As it is, they evidently do not. Practical conditons require enough supply of fresh air not only to fill the lungs, but also to dilute the breath to an extent compatible with health. This, for really healthy breathing, should be taken at not less than 1,800 cucic ft. per hour per person for average circumstances, an amount far below what most sanitarians now recommend.

The thought may occur, why don't the people suffocate, then, in such a room as mentioned? They probably would, or reach a point very close to it, if the assumed conditions were rigidly existing; if the fire took all its allowance of 296 cubic ft of fresh air, if the gas-burners were all lighted, the six inmates in full operation, and if the supply of air was absolutely restricted to 1,700 cubic ft. per hour.

In any ordinary case, the open fire, as was pointed out by Mr. Butler, draws its supply from the air of the room, and thus aids to ventilate it; but, particularly, the people are saved from suffocation by the insensible ventilation that takes place through the walls, and in every way besides the recognized channels.

If this be the case, and if rooms that are theoretically unventilated, without inlets and outlets, may not be suffocating, or even unhealthy, because of this insensible ventilation, in spite of the large air allowance specified by modern sanitary science, it may be asked, is it not excess of refinement to calculate an air supply upon the number of people present? The answer seems to be, that where rooms are to contain a large number of people, in proportion to their size, such a