POPULAR SCIENCE. 17 



India. To have recognised small home specimens as a natu- 

 ral product was one thing ; to have mastered the conditions 

 of its formation, and generated it at pleasure in quantities 

 large enough to supply the needs of French revolutionary 

 armies, was another. Very soon after the pressure of the 

 need, the thing was done, and for many years every pound of 

 saltpetre entering into French gunpowder was home-made. 



The importance of this discovery became apparent to other 

 continental nations. Remembering that they might be sub- 

 ject by fortune of war to conditions of exclusion, just as the 

 French had been, they took measures to insure a home supply. 

 The government of Sweden to this day imposes a saltpetre 

 tax, payable in kind, 011 every Swedish farmer. A certain spe- 

 cified amount of this sinew of war must be rendered periodic- 

 ally to the collector. The Swedish government will accept no 

 money-equivalent the saltpetre must be paid in kind. An- 

 other chemical manufacture to spring out of the revolution 

 under the pressure of the times was that of sugar from beet- 

 root. The French are, and always have been, a sugar-eating 

 people ; but English command of the ocean was so vigilant, 

 that during a period of the revolutionary war no sugar from 

 the colonies could be obtained. Some years previously it hap- 

 pened that a Prussian chemist had demonstrated the presence 

 of sugar in white Silesian beetroot, but the discovery had been 

 turned to no practical account. The French applied them- 

 selves to the commercial problem, and ultimately with com- 

 plete success as the large importation to this country of 

 beetroot-sugar testifies. At first, however, they were unsuc- 

 cessful. And here again we find an instance of inventors 

 men of practice correcting a doctrinal error. A com- 

 mission of French philosophers came to the conclusion that, 

 although sugar did exist in beetroot, it could not be extracted 

 at a commercial profit. The doctrinaires were wrong. Less 

 connected with the revolutionary pressure, but associated with 

 it to some extent, was the manufacture of soda from sea-salt. 



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