5i6 THE POPULAR SCIENCE MONTHLY. 



only in two oi" three out of a hundred cases where the flasks had been 

 sealed at the top of the mountain, and to a proportionate extent in 

 those sealed at the intermediate elevations. What, now, did these 

 experiments prove ? Simply this, that the development of these or- 

 ganic forms was in direct proportion to the numher of germs in the 

 air. It did not settle the question of spontaneous generation, but it 

 showed that false conclusions had been deduced from the experiments 

 which had been cited to prove it. 



A still more striking illustration of the same method of question- 

 ing Nature is to be found in the investigation of Sir Humphry Davy 

 on the composition of water. The voltaic battery which works our 

 telegraphs was invented by Volta in 1800; and later, during the same 

 year, it was discovered in London, by Nicholson and Carlisle, that this 

 remarkable instrument had the power of decomposing water. These 

 physicists at once recognized that the chief products of the action 

 of the battery on water were hydrogen and oxygen gases, thus con- 

 firming the results of Cavendish, who in 1V81 had obtained water by 

 combining these elementary substances ; oxygen having been previ- 

 ously discovered in 1775, and hydrogen at least as early as 176G. It 

 was, however, very soon also observed that there were always formed 

 by the action of the battery on water, besides these aeriform products, 

 an alkali and an acid, the alkali collecting around the negative pole 

 and the acid around the positive pole of the electrical combination. 

 In regai'd to the nature of this acid and alkali there was the greatest 

 difierence of opinion among the early experimenters on this su^bject. 

 Cruickshanks supposed that the acid was nitrous acid, and the alkali 

 ammonia. Desormes, a French chemist, attempted to prove that the 

 acid was muriatic acid ; while Brugnatelli asserted that a new and 

 peculiar acid was formed, which he called the electric acid. 



It was in this state of the question that Sir Humphry Davy be- 

 gan his investigation. From the analogies of chemical science, as 

 well as from the previous experiments of Cavendish and Lavoisier, 

 he was persuaded that water consisted solely of oxygen and hydro- 

 gen gases, and that the acid and alkali were merely adventitious prod- 

 ucts. This opinion was undoubtedly well-founded ; but, great disci- 

 ple of Bacon as he was, Davy felt that his opinion was worth nothing 

 unless substantiated by experimental evidence, and accordingly he set 

 himself to work to obtain the required proof. 



In Davy's first experiments the two glass tubes which he used to 

 contain the water were connected together by an animal membrane, 

 and he found, on immersing the poles of his battery in their respective 

 tubes, that, besides the now well-known gases, there were really formed 

 muriatic acid in one tube and a fixed alkali in the other. Davy at 

 once, however, suspected that the acid and alkali came from common 

 salt contained in the animal membrane, and he therefore rejected this 

 material and connected the glass tubes by carefully-washed cotton 



