388 



SCIENCE 



[N. S. Vol. XXXVI. No. 926 



lieve so. The above estimate of the total 

 production of organic matter over all the 

 solid surface of the earth, that is, of 32 bil- 

 lion tons a year, has for its basis the old 

 calculation of Liebig of 2.5 tons per hec- 

 tare. This may be considered even to-day 

 the average production for all the earth. 

 According to A. Mayer, through intensified 

 culture the production may be increased to 

 10 tons per hectare, and in tropical climates 

 it may reach 15 tons. On a square kilo- 

 meter it would be 1,500 tons, correspond- 

 ing to 840 tons of coal, while the solar 

 energy received in a year by a square kilo- 

 meter would be equivalent to about 300,000 

 tons of coal, the part of the total energy 

 stored up by the plants being about %oo- 

 A great deal remains to be done, but if we 

 consider that since Liebig, largely by 

 adopting the methods proposed by him, 

 the production has been at least quad- 

 rupled, we may hope to do much more in 

 the future especially if we are spurred on 

 by necessity or even by convenience. 



By increasing the concentration of car- 

 bon dioxide up to an optimum value (1 to 

 10 per cent, according to Kreusler) and 

 by using catalyzers, it seems quite possible 

 that the production of organic matter may 

 be largely increased, making use, of course, 

 of suitable mineral fertilizers and select- 

 ing localities adapted to the purpose owing 

 to the climate or the condition of the soil. 

 The harvest, dried by the sun, ought to be 

 converted, in the most economical way, en- 

 tirely into gaseous fuel, taking care during 

 this operation to fix the ammonia (by the 

 Mond process for instance) which should 

 be returned to the soil as nitrogenous fer- 

 tilizer together with all the mineral sub- 

 stances contained in the ashes. "We should 

 thus get a complete cycle for the inorganic 

 fertilizing substances, the only waste being 

 that common to all industrial processes. 

 The gas so obtained should be burnt en- 



tirely on the spot in gas engines and the 

 mechanical energy thus generated should 

 be transmitted elsewhere or utilized in any 

 way that seems advisable. We need not 

 go into details. The carbon dioxide, re- 

 sulting from the combustion, should not be 

 wasted but should be returned to the fields. 

 Thus the solar energy, obtained by rational 

 methods of cultivation, might furnish low- 

 priced mechanical energy, perhaps better 

 than through the systems based on mirrors, 

 because the plants would be the accumu- 

 lators of the energy received by the earth. 



But the problem of the utilization of 

 plants in competition with coal has another 

 and more interesting side. First of all we 

 must remember the industries which have 

 their basis in agriculture: the cotton and 

 other textile industries, the starch indus- 

 try, the production of alcohol and of all 

 fats, the distillation of wood, the extrac- 

 tion of sugar, the production of tanning 

 substances and other minor industries. All 

 these industries are susceptible of improve- 

 ment not only by the introduction of more 

 advantageous technical devices in the treat- 

 ment of the raw materials but also by a 

 largely increased production of the raw 

 materials. Let us think for an example of 

 the progress made in the production of 

 beet sugar. 



The plants are unsurpassed masters of 

 — or marvellous workshops for — photo- 

 chemical synthesis of the fundamental sub- 

 stances, building up from carbon dioxide 

 with the help of solar energy. They also 

 produce the so-called secondary substances 

 with the greatest ease. These latter are 

 usually found in the plants in small quan- 

 tity and are of value for special reasons. 

 The alkaloids, glucosides, essences, cam- 

 phor, rubber, coloring substances and 

 others are of even greater interest to the 

 public than the fundamental substances on 

 account of their high commercial value. 



