114 HISTORY OF CHEMISTRY. [LECTURE VII. 



they were then able to calculate the quantity of water pro- 

 duced by the combustion, and, therefore, the composition of 

 the compound. 



Gay-Lussac and Thenard carried out the analysis of twenty 

 substances in this way. Their results are moderately accurate, 

 but the method still left much to be desired. The combustion 

 was very violent ; it was accompanied by explosion, and was, 

 therefore, frequently incomplete. 



The next great step in the development of elementary 

 analysis was made by Berzelius in i8i4. n By carrying out the 

 combustion with a mixture of potassium chlorate and sodium 

 chloride, he secured the much more moderate progress of the 

 analysis. His method, also, differs very essentially and advan- 

 tageously from the earlier one, in so far that he did not gradually 

 introduce the substance intended for combustion into a red-hot 

 tube, but instead, put the whole quantity of the substance, 

 along with the oxidising material, into a tube which he gradually 

 heated to redness in a horizontal position. Further, he was 

 the first to weigh the water directly, which he did after having 

 absorbed it by means of calcium chloride ; whereas he deter- 

 mined the carbonic anhydride either by volume or by weight. 



This mode of carrying out the analysis already approximates 

 closely to the present method ; it was still further improved by 

 employing cupric oxide instead of potassium chlorate. This 

 was first used by Gay-Lussac for nitrogenous substances, 12 but 

 a year afterwards it was employed by Dobereiner in the com- 

 bustion of substances free from nitrogen. 13 



Analyses were carried out by this process for more than ten 

 years, until the method was modified by Liebig 14 in 1830, and 

 brought into the form now employed. As a consequence of 

 Liebig's investigations, elementary analysis became an easily 



11 Ann. Phil. 4, 330 and 401. 12 Ann. Chim. 95, 154; Ann. Phil. 

 7, 357- 13 Schweigger's Journal. 17, 369 ; compare also Chevreul, Re- 

 searches chimiques sur les corps gras d'origine animale (1823). 14 Pogg. 

 Ann. 21, i ; more fully in his " Anleitung zur Analyse organischer Korper." 

 Braunschweig (1837); English Translation, by Gregory: "Instructions 

 for the Chemical Analysis of Organic Bodies," Glasgow (1839). 



