SCIENTIFIC CULTURE. 



517 



fibre : when, on submitting the water as before to the action of tlie 

 voltaic current, and continuing the experiment through a great length 

 of time, no muriatic acid appeared ; but he still found that the water 

 in the one tube was strongly alkaline, and in the other strongly acid, 

 although the acid was, chiefly at least, nitrous acid. A part of the 

 acid evidently came from the animal membrane, but not the whole, 

 and the source of the alkali was as obscure as before, Davy then made 

 another guess. He knew that alkali was used in the manufacture of 

 glass ; and it occurred to him that the glass of the tubes, decomposed 

 by the electric current, might be the origin of the alkali in his experi- 

 ments. He therefore substituted for the glass tubes cups of agate, 

 which contains no alkali, and repeated the experiment, but still the 

 troublesome acid and alkali appeared. Nevertheless, he said, it is pos- 

 sible that these i:roducts may be derived from some impurities exist- 

 ing in the agate cups, or adhering to them ; and so, in order to make 

 his experiments as refined as possible, he rejected the agate vessels 

 and procured two conical cups of pure gold, but on rejDeating the ex- 

 periments the acid and alkali again appeared. 



And now let me ask who is there of us who would not have con- 

 cluded at this stage of the inquiry that the acid and alkali were essen- 

 tial products of the decomposition of water ? But not so with Davy. 

 He knew perfectly well that all the circumstances of his experiments 

 had not been tested, and until this had been done he had no right to 

 dravv such a conclusion. He next turned to the water he was using. 

 It was distilled water, which he sujiposed to be pure, but still, he said, 

 it is possible tliat the impurities of the spring-water may be carried 

 over to a slight extent by the steam in the process of distillation, and 

 may therefore exist in my distilled water to a sufiicient amount to 

 have caused the difiiculty. Accordingly he evaporated a quart of this 

 water in a silver dish, and obtained seven-tenths of a grain of dry 

 residue. He then added this residue to the small amount of water in 

 the gold cones and again repeated the experiment. The proportion 

 of alkali and acid was sensibly increased. 



You think he has found at last the source of the acid and alkali 

 in the impurities of the water. So thought Davy, but he was too 

 faithful a disciple of Bacon to leave this legitimate inference unverified. 

 Accordingly he repeatedly distilled the water from a silver alembic 

 until it left absolutely no residue on evaporation, and then with water, 

 which he knew to be pui-e, and contained in vessels of gold from 

 which he knew it could acquire no taint, he still again repeated the 

 already well-tried experiment. He dipped his test-paper into the 

 vessel connected with the positive pole, and the water was still de- 

 cidedly acid. He dipped the paper into the vessel connected with the 

 negative pole, and the water was still alkaline. 



You might well think that Davy would have been discouraged 

 here. But not in the least. The path to the great truths which 



