20 THE STORAGE OF ENERGY 



a legacy of potential energy laid by in former times. He has 

 devised detachable limbs (machines and tools) able to utilise the 

 energy of coal, petrol, etc., of which he could not avail himself 

 without their aid. This made possible an enormous increase in 

 the world's work work done no longer by human beings and 

 beasts of burden, but by inanimate machines using the energy 

 of fire, electricity, etc. To-day, a single machine does the work 

 of an army of men. In this way he conserves present-day solar 

 energy and lives on the banked income of past ages. Some time 

 in the future he may learn how to synthesise food from inorganic 

 constituents by the use of any form of available energy. Then 

 and only then will he be able to dispense with plant life. Steps 

 in this direction have been made. Moore and Webster have 

 synthesised formaldehyde by exposing an aqueous solution of 

 CO 2 to ultra-violet lignt (Chap. XI.) in the presence of inorganic 

 colloids (Chap. VIII.). They have also shown that dilute solutions 

 of nitrates exposed to ultra-violet rays are converted into nitrites 

 with an absorption of energy. One gram molecule of nitrite 

 formed from nitrate transforms about 10,000 gram-calories of 

 radiant energy into the potential state a strong endothermic 

 reaction. This is similar to the change taking place in the plant 

 in the formation of nitrogen compounds the first stage in protein 

 anabolism. 



