i6 SCIENCE REMAKING THE WORLD 



twenty able-bodied slaves waiting on us day and 

 night. 



This increment of energy, that has given to all of 

 us comfort and conveniences beyond the power of 

 petentates in former times, comes mostly from two 

 simple and similar chemical reactions, the union of 

 hydrogen and of carbon with oxygen, or in common 

 language, burning. The first reaction, the uniting of 

 hydrogen with the oxygen to form water gives more 

 heat than any other combination of elements. Hydro- 

 gen would, therefore, be the best possible fuel but for 

 two reasons. In the first place it is too expensive. It 

 is not found free in nature, except in natural gas, and 

 this is rare and running out. To get the hydrogen out 

 of water would require as much expenditure of energy 

 as we should get out of it by burning it back again to 

 water. Secondly, hydrogen is a gas and therefore not 

 convenient to carry around. It would not be conveni- 

 ent to have a big gas bag hitched to your car like a cap- 

 tive balloon. It is true hydrogen can be liquefied but 

 it does not stay so and it is then exceedingly cold. 



Carbon is tolerably abundant in many countries in 

 the form of coal. But carbon has less than one fourth 

 the heating power per pound that hydrogen has. 

 Carbon, being a solid, is handier to use than a gas like 

 hydrogen, but not so handy as a liquid would be. A 

 solid has to be shovelled. A liquid will flow. Coal 

 has to be mined and hoisted up from the ground. 

 Petroleum is so anxious to get out that it will blow off 

 the rigging when its rock prison is tapped. 



What, then, would be the ideal fuel if we could have 



