20 INTRODUCTION. 



energetically in statu nascendi, or in the presence of 

 certain substances, particularly of spongy platinum. 

 When it acts at all, it is either added directly to the 

 compound, or the hydrogen contained in the com 

 pound is oxidized to form water, or both of these 

 changes take place together. At times a more mate 

 rial decomposition takes place. At a red heat, all or 

 ganic substances burn in oxygen, forming carbonic 

 acid, water, and nitrogen. 



Hydrogen, especially in statu nascendi, likewise trans 

 forms very many organic compounds, either a direct 

 addition of hydrogen, or an elimination of oxygen, or 

 both at the same time taking place. In most cases in 

 which hydrogen acts upon compounds containing chlo 

 rine, bromine, or iodine, these elements are eliminated 

 and replaced by hydrogen. Hydriodic acid and sul 

 phuretted hydrogen act similarly to free hydrogen. 

 At times, bodies containing iodine or sulphur result, 

 but generally the iodine or sulphur is set free, and 

 merely the hydrogen acts. 



Chlorine and bromine act very energetically upon 

 organic bodies. Non-saturated organic compounds 

 (those in which the carbon atoms are united by means 

 of more than one of each of their four affinities), usu 

 ally combine directly with these elements, and take up 

 as many atoms as are sufficient to produce saturated 

 bodies, the simple union of the carbon atoms being re 

 established. In this way are formed from ethylene, 



CH 2 CH Cl 



C 2 H 4 = || , the compounds C 2 H 4 CP = I and 



CH 2 CIPC1 



CH 2 Br 

 C 2 H 4 Br 2 = I . With saturated compounds, how- 



CH 2 Br 



ever, the action generally takes place in such a man 

 ner, that a certain number of atoms of hydrogen are 

 eliminated, and replaced in the compound by an equal 

 number of atoms of chlorine or bromine ; for instance: 



C 2 H 4 2 + 201 = CWCIO 2 + C1H 



Acetic acid. Chloracetic acid. 



