CHEMISTRY OF THE NINETEENTH CENTURY. 613 



chlorine and hydrogen do as a matter of fact unite, it follows that a 

 volume of hydrogen contains the same number of atoms of hydrogen 

 as an equal volume of chlorine, and hence the weights of hydrogen and 

 chlorine atoms will be proportional to the weights of equal volumes 

 of the gases. The specific gravities (or densities) of the gases would 

 therefore have indicated how many times the atom of chlorine ex- 

 ceeded in weight the atom of hydrogen ; but these inferences were 

 not made at the time. Yet shortly before Gay-Lussac published his dis- 

 coveries, an Italian chemist named AMADEO AVOGADRO (17 . . 18 . .) 

 suggested, as a means of accounting for certain properties of gases, 

 an hypothesis which involved the relation in question. The properties 

 he sought to explain were, that all gases expand in the same degree 

 by heat, and follow one law (Boyle's, page 231) of relation between 

 volume and pressure. Avogadro's supposition was that in the same 

 volume of different gases, whether simple or compound, the same 

 number of particles are contained, the gases being taken, of course, 

 under the same circumstances of pressure and temperature. This idea 

 appears to have attracted no attention at the time, and though it was 

 revived by Ampere in 1814, it was not until many years afterwards 

 that Avogadro's hypothesis met with the recognition it deserved. In 

 applying the hypothesis, not a little confusion has arisen from con- 

 founding the particles or molecules of a body with its ultimate atoms. 

 Every molecule of any given elementary gas may contain two particles, 

 or three, or four, or any greater number of atoms, or it may consist of 

 but a single atom, without affecting the statement of Avogadro's pro- 

 position. The same is true of the molecules of a compound gas, 

 except only that here each molecule must necessarily comprise at 

 least two atoms. 



The scientific reputation of Sweden has been ably sustained in the 

 present century by the labours of the celebrated chemist, JACOB 

 BERZELIUS, who was born at Wafnersunda in West Gothland, 1779, 

 and died at Stockholm in 1848. His career was marked by an in- 

 dustry truly astonishing, and he worked to the last. He was rewarded 

 for his labours with every academic and public honour which could 

 be bestowed upon a man of science, and he obtained also wealth and 

 position, which less frequently fall to a philosopher's lot. The chemical 

 work of Berzelius is distinguished rather by its extent and accuracy 

 than by depth or brilliancy of theoretical conceptions. Nevertheless, 

 the discoveries he made were neither few nor unimportant. It was 

 he who first imported exactness into the methods of analysis, and 

 fitted it to become the instrument of fresh discoveries. It was he 

 who first made known several of the rarer elements, and separated 

 silicon from its oxide. He contributed perhaps still more to the pro- 

 gress of the science when he placed in the hands of chemists an in- 

 strument so effective as the Symbolic Notation, which is "to the chemist 

 what the symbols of algebra are to the mathematician. 



