64 Biological Chemistry. 



may be considered as derivatives of the hydrocarbons 

 methane, ethane, propane, butane, and pentane (see p. 54), 

 in which one hydrogen atom is replaced by a " hydroxyl " 

 group ; and it will be seen later that there is a justification 

 in giving the above formula to these compounds, in that 

 one hydrogen atom (that is, the hydrogen of the hydroxyl 

 group) behaves differently to the other hydrogen atoms in 

 the molecule. These, with the carbon atoms, form groups 

 which are designated " alkyl " or alcohol radicles. These 

 radicles, methyl, ethyl, propyl, etc., will be repeatedly 

 referred to in the succeeding pages, and it will be seen 

 that the grouping of atoms which they designate can 

 remain intact through many series of operations. The 

 monohalogen derivatives mentioned above are liquids, of 

 which the boiling points show progressive rises with 

 increasing molecular weights. The bromides have higher 

 boiling points than the corresponding chlorides, and the 

 iodides boil at higher temperatures than the bromides. 

 Certain of the halogen derivatives are of technological 

 interest. 



Methyl chloride, or monochlormethane, which boils at 

 24 under the pressure of 1 atmosphere, is used for the 

 production of low temperatures, being supplied in the form 

 of a compressed gas which absorbs heat on evaporation. 

 It is also largely employed as a reagent in various manu- 

 facturing processes. It is manufactured by heating crude 

 trimethylamine hydrochloride (see p. 124). 



Methyl, ethyl, and other iodides are prepared generally 

 by the action of red phosphorus and iodine on the corre- 

 sponding alcohols. 



Chloroform or trichlormethane, which is largely used 

 as an anaesthetic, is prepared commercially by the action 

 of bleaching powder on alcohol, methylated spirit, or 

 acetone. It can also be readily obtained by this method 



