LECTURE VIII.] HISTORY OF CHEMISTRY. 14! 



1. When a substance containing hydrogen is exposed to 

 the dehydrogenising action of chlorine, bromine, or iodine, for 

 every volume of hydrogen that it loses, it takes up an equal 

 volume of chlorine, bromine, etc. 



2. When the substance contains water, it loses the hydrogen 

 corresponding to this water without replacement. 



The second rule was advanced chiefly to explain the 

 formation of chloral, and at the same time to justify the 

 formula C 8 H 8 + 2H 2 O [C = 6] adopted for alcohol by Dumas 

 six years previously. According to Dumas, the phenomena of 

 substitution furnish a new proof of the difference of the hydro- 

 gen atoms, eight of which are united to carbon, and four to 

 oxygen. In the case of the former alone does replacement 

 occur, whilst the others are removed without replacement. 



Thus we have : 



(C 8 H 8 + 2 H 2 0) + 4 C1 - C 8 H 8 2 + 4 HC1 

 Aldehyde. 



C 8 H 8 O 2 + 1 2C1 = C 8 H 2 C1 6 O 2 + 6HC1 



Chloral. 



By means of various examples, Dumas further endeavours 

 to prove the general validity of the laws which he advances. 

 In establishing the correct composition of the Dutch oil, he 

 points out that the chloride of carbon obtained from it by 

 means of chlorine, and examined by Faraday, 33 supplies a new 

 argument in favour of the accuracy of his views. He also finds 

 similar support in the action of chlorine on hydrocyanic acid, 

 on bitter almond oil, etc. 



But Dumas is not satisfied with this. He goes a step 

 further still, and regards oxidations as cases of substitution, as, 

 for example, the conversion of alcohol into acetic acid. 34 In 

 this case every volume of hydrogen eliminated is replaced by 

 half a volume of oxygen. Accordingly we have : 



(C 8 H 8 + H 4 2 ) + 4 = (C 8 H 4 2 + H 4 2 ) + H 4 O 2 ; 

 Alcohol. Acetic Acid. 



33 Phil. Trans. 1821, 47. 34 Ann. Chim. [2] 56, 143. 



