38 THE REASON WHY. 



" O Lord, our Lord, how excellent is thy name in all the earth ! who hast set thy 

 glory above the heavens. PSAXM vm. 



length, and the damage done to 103 houses was afterwards reported to amount 

 to 20,000. Other serious explosions have taken place. The explosions of " coal 

 damp" which frequently occur iu mines, are of a similar character.] 



64. WTiat proportion of hydrogen gas with atmospheric air 

 will explode ? 



According to the researches of Sir Humphrey Davy, seven or 

 eight parts of air, to one of gas, produce the greatest explosive 

 effect ; while larger proportions of gas are less dangerous. A mix- 

 ture of equal parts of gas and air will burn, but it will not explode. 

 The same is the case with a mixture of two of air, or three of air, 

 and one offfas; but/owr of air and one of gas begin to be explosive, 

 and the explosive tendency increases up to seven or eight of air and 

 one of gas, after which the increased proportion of gas diminishes 

 the force of the explosion. 



65. WTiat is the lest method of preventing the explosion of 

 gas ? 



Observe the rule, never to approach a supposed leakage with a 

 light. Fortunately the gas, which threatens our lives, warns us of 

 the danger by its pungent smell. The first thing to be done is to 

 open windows and doors, and to ventilate the apartment. Then 

 turn the gas off at the main, and wait a short time until the accu- 

 mulated gas has been dipersed. 



66. Does "hydrogen gas rise or fall when it escapes ? 



Being twelve times lighter than common air it rises, and there- 

 fore it would be better for ventilation to open the window at the 

 top than at the bottom. But all gases exhibit a strong tendency to 

 diffuse themselves, and therefore they do not rise or fall in the 

 degree that might be anticipated. 



67. What proportion of hydrogen in the air is dangerous to 

 life, if inhaled? 



One-fiftieth part has been found to have a serious effect upon 

 animals. The effects it produces upon the human system are those 

 of depression, headache, sickness, and general prostration of the 

 vital powers. It is therefore advisable to observe precautions in the 

 use of gas. 



