i8o GREAT MEN OF SCIENCE 



Since then, the atomic weight has not only been deter- 

 mined with very greatly increased accuracy through the 

 further refinement of quantitative chemical analysis, but it 

 was soon learned, by the use of determinations of molecular 

 weight and other methods, how unknown multiples could be 

 avoided with complete certainty. A somewhat longer time, 

 about fifty years, was necessary before the movements of the 

 molecules in bodies, particularly in gases (kinetic theory of 

 gases), were understood, and this then led to our learning the 

 actual sizes of the molecules, and also their absolute weight 

 (in ordinary units); and the knowledge in detail of molecules 

 and atoms, which internally are worlds in themselves, is still 

 being rapidly advanced. 



Klaproth was born at Wernigerode in the Harz mountains, 

 went to school there, and then became apprenticed, and later 

 assistant, to an apothecary in Quedlinburg; but he did not 

 become acquainted with good textbooks of chemistry until 

 his twenty-third year, in Hanover. This awakened his 

 desire to find a position in which he could learn more; he 

 went to Berlin, where he became an assistant in, and finally 

 manager of, an apothecary's business. In the year 1780 he 

 was able to set up his own laboratory, from which a very 

 large number of exact researches issued. He was the first to 

 introduce the custom of stating, as the result of a quantitative 

 analysis, not corrected values, but the data actually obtained 

 by experiment. The loss or excess which almost always re- 

 sults in an analysis, had hitherto always been corrected by the 

 analyst himself according to his own notions, which were 

 often aff^ected by preconceived ideas; and the result of obser- 

 vation stated was not the actual result of the experiment, 

 but almost always only the conclusion which it was supposed 

 possible, with more or less justification, to draw from the 

 experiment. Klaproth was the first to introduce the custom 

 of not only publishing one's own convictions regarding the 

 composition of a compound, but also of giving full details of 



