CHEMICAL SUMMARY 189 



freed are used to connect the two carbon atoms. In a similar way pro- 

 pane, C s H a , and butane, C t H I0 , and an indefinite number of higher com- 

 pounds are formed. 



In the paraffins all of the valences of the carbon atoms are filled and 

 no more hydrogen atoms can be attached to the molecule without splitting 

 it between two carbon atoms, and therefore these compounds are said 

 to be saturated. In the unsaturated hydrocarbons, however, more hydro- 

 gen atoms may be attached without splitting the molecule, which is 

 thereby converted into a saturated compound. There are no free valences 

 in the unsaturated compounds but two carbon atoms are united by more 

 than one bond, and by opening up one bond two free valences are formed 

 for the attachment of two hydrogen atoms. Thus in ethylene, 'CoH 4 , there 

 is a double bond between the carbon atoms and acetylene, C 2 H 2 , there is 

 a triple bond between the two carbon atoms. 



The first products of the oxidation of the paraffines are the alcohols, 

 methyl alcohol, CH.OH, ethyl alcohol, C,H B OH, propyl alcohol, ;C 3 H 7 OH, 

 and so on. Alcohols may combine with bases, but where water is formed 

 by the combination the compound may decompose again. If the presence 

 of water be eliminated the compound is relatively stable. Thus when 

 metallic sodium is dropped into ethyl alcohol, sodium ethylate is formed 

 with the evolution of hydrogen. 



C 2 H B OH + Na = QHsONa + H and 2H = H 2 . 



The combination of an alcohol with an acid forms an ester, thus : 

 QH.OH + H 2 S0 4 = C 2 H B HSO, + H 2 0. 



If an ester is warmed with a strong base, the base combines with the 

 acid and the alcohol is set free, a process known as saponification, thus : 

 C 2 H 5 HS0 4 + Ca(OH) 2 = C 2 H B OH + CaS0 4 + H 2 0. 



The alcohols with one OH group, like the ones given above, are called 

 monatomic. The highest monatomic alcohol found in cells is cholesterol, 

 CjrHaOH, a waxy substance, insoluble in water and crystallizing in plates. 



Alcohols with three OH groups are called triatomic. The one found in 

 cells is glycerol, C s H 5 (OH) 3 , which is soluble in water, and its esters 

 with fatty acids are called fats. 



By oxidation of alcohols we obtain aldehydes. Methyl alcohol gives 

 form-aldehyde, thus : 2CH s OH + 2 = 2HCHO + H 2 0. In the alde- 

 hyde group, CHO, the oxygen is united with the carbon by a double bond, 

 which makes the aldehyde capable of further oxidation, in fact it has such 

 an affinity for oxygen as to be a mild reducing agent. The product of 

 such an oxidation of an aldehyde is a fatty acid and the aldehyde is 

 named for the acid that it forms and not for the alcohol from which 

 it is formed, where there is a different name for the alcohol and acid. 

 Thus we have methyl alcohol, formaldehyde and formic acid and we have 

 ethyl alcohol, acetaldehyde and acetic acid, but propyl alcohol, propyl- 

 aldehyde and propionic acid. 



The CHO group of the aldehyde contains the terminal carbon atom 

 of the chain. If an intermediate carbon atom of the chain hears the 

 double bond we have a CO' group, and the substance is called a ketone. 

 Thus, CH 3 CH 2 CHO is propyl aldehyde, hut CH„COCH 3 is dimethyl ke- 

 tone (acetone). 



The carbohydrates are aldehydes or ketones of polyatomic alcohols, in 

 which the hydrogen and oxygen are usually in the proportion to form 

 water. Aldehydes have a tendency to polymerize or combine to form 

 larger molecules. Formaldehyde in alkaline solution polymerizes to form 

 a series of sugars with six carbon atoms. This seems also to be the 

 mode of formation of sugar in the green plant. The carbonic acid, 

 H 2 C0 3 , is reduced by the action of sunlight and the fluorescent chlorophyll 

 to HCHO, the oxygen removed from the carbonic acid combines with 



