THE EEASON WHY. 37 



" I will both lay me down in peace and sleep : for thou, Lord, only, makest mo 

 dwell in safety." PSALM iv. 



60. What proportion of carbonic acid gas is dangerous to 

 life ? 



Any proportion over the natural one of 1 per cent, may bo 

 regarded as injurious. But toxicologists state that five per cent. 

 of carbonic acid gas in the atmosphere is dangerous to life. 



Gl. Wliat are toxicologists ? 



Persons who study the nature and effects of poisons and their 

 antidotes. 



62. IVhich kind of combustible used for lighting tends 

 most to vitiate the air ? 



Assuming all the lights to be of the same intensity, the degree in 

 which the substances burnt would vitiate the atmosphere may be 

 gathered from the number of minutes each would take to exhaust 

 a given quantity of air. This has been found to be : rape oil, 71 

 minutes ; olive oil, 72 ; B.ussian tallow, 75 ; town tallow, 76 ; sperm 

 oil, 76 ; stearic acid, 77 ; wax candles, 79 ; spermaceti candles, 83 ; 

 common coal gas, 98 ; canal coal gas, 152. Thus it is shown that 

 rape oil is most destructive of the atmosphere, and that coal gas is 

 the least destructive. 



63. Is an escape of hydrogen gas from a gas-pipe dangerous 

 to life ? 



It is dangerous, first, by inhalation. There are no less than 

 six deaths upon record of persons who were killed by sleeping in 

 rooms near to which there was a leakage of gas. 



It is dangerous, secondly, by explosion. 



[In 1848, an explosion of gas occurred in Albany-street, Regent's-park, 

 London. The gas accumulated in a shop for a very short time only. It had 

 been escaping from a crack in the nic-ter for about one hour and twenty 

 minutes. The area of the room was about 1,620 cubic feet. When the gas 

 exploded, it blew out the entire front of the premises, carried two persons 

 through a window into an adjoining yard, and forced another person on to the 

 pavement on the opposite side of the street, where she was killed. The effect 

 of the explosion was felt for more than a quarter of a mile on each side of the 

 house, and most of the windows in the neighbourhood were shattered. The 

 iron railings over the area of the house directly opposite were snapped asunder ; 

 and a part of the roof, and th back windows of another house, were carried to 

 a distance of from 200 to 300 yards. The pavement was k.rn up for a considerable 





