XVII 



MOLECULAR ARCHITECTURE 



393 



tion; potassium chlorate, not mixed with the substance, was 

 placed at both ends of the combustion-tube, in order to 

 provide an ample supply of oxygen (i) to complete the burn- 

 ing, (2) to drive the products of combustion forward into 

 the absorption-apparatus. Extreme care was needed to dry 

 perfectly all the materials with which the combustion-tube 

 was charged. 



Berzelius analysed nine organic acids in the form of 

 their lead salts, and four carbohydrates, thus covering much 

 the same ground as Gay-Lussac and Thenard. But, unlike 

 them, he was able to check his analyses by the requirements 

 of the newly-established atomic theory and to express the 

 composition of his compounds by means of formulae. 

 Berzelius's formulae for the acids are usually those of the 

 lead salt minus lead oxide, or of the acid minus water ; 

 apart from this, they agree very well with those adopted 

 to-day, the few differences that occur being due to an over- 

 estimation of the hydrogen. This is shown by the following 

 comparison : 



Rerzelius's 



Modern formulae. 



C 6 H 8 7 -H 1 = C.H 6 6 



C 4 H 6 6 -H 2 = C 4 H 4 5 



C 2 H 2 O 4 -H 2 O = C 2 O 3 



C 4 H 6 4 -H,0 = C 4 H 4 0. 



2C 2 H 4 2 -H 2 = C 4 H 6 3 

 C 6 H 6 3 (pyrogallol) 

 C 6 H 10 



C 7 H 6 2 



C 12 H 22 O 

 C B H 10 B 



wso 

 = [CH 2 0] 12 



Combustion by means of metallic oxides, It should be 

 noticed that metallic oxides were used for the quantitative 

 combustion of organic substances by Lavoisier, who used red 

 lead (p. 146), as well as by Berzelius, who used the brown 

 peroxide in his earlier analyses. The oxides of leads were 

 discarded in favour of potassium chlorate, because they 



