256 TiMEHRl. 



exceeded, it is necessary that 3000 cubic feet of fresh 

 air be supplied to each person inhabiting a room per 

 hour. The organic matter excreted has been found to be 

 in dire6t ratio to the quantity of carbonic acid gas, so 

 that by watching the amount of this gas in the air we 

 can prevent the organic matter accumulating in our 

 rooms So the simple rule has been laid down that we 

 should keep inhabited spaces in such a state that a 19I oz. 

 bottle full of its air shaken with ^ an ounce of clear lime 

 water gives no precipitate, or, put in other words, that the 

 carbonic acid gas is not in such quantity as to combine 

 with the lime to form sufficient carbonate or common 

 chalk to be visible. Immediately the proportion of '06 

 of carbonic acid is exceeded the precipitate becomes 

 visible. By the odour of the organic matter, only per- 

 ceptible to one entering from the fresh air, we always 

 have a rough but very reliable test for the amount of the 

 carbonic acid gas. If we can smell organic matter we 

 know we have excess of carbonic acid present ; and if on 

 testing, as given above, we can see a white cloud form 

 in the lime water, we know we have too much organic 

 matter. In either case, at once, additional means of 

 ventilation should be provided. Further, if 3 room is 

 used continuously at night, allowance must be made for 

 the impurity arising from the lights used. An ordinary 

 lamp for example produces a little more than half a cubic 

 foot of carbonic acid in an hour, and for the complete 

 combustion of one pound of oil, from 140 to 160 cubic feet 

 of air are required. We fortunately here have few fa6lo- 

 ries, so that our air is free from many impurities found in 

 manufafturing towns of Europe, such as compounds of 

 sulphur, chlorine, nitrogen and phosphorus. We get 



