THE MODERN THEORY OF CHEMICAL TYPES. 



161 



IV. Bases. 



CnH(„_5)N) 

 Aniline CiaH^ N 



Toluidiue... CuHg N 

 Xylidine ... CieHuN 

 Cumidine ... Ci8 H13 N 

 Cy midine ... C20 H15 N 



V. Hydrocarbons. 



CuH(n_6) ) 



Benzole do Hg 



Toluole Ci4 Ha 



Xylole CieHio 



Cumole Cig H12 



Cymole C20 H^ 



III. Alcohols 



C,H(u+2^02) 



Formylic C2 H4 0> 



Ethylic C4 He O2 



Propylic .... Cg Hg 0. 



Butylic Cg Hio 0. 



Amylic do H12 0. 



Aetbalic C32 H34 O2 



The most remarkable phenomenon connected with homologous series is not 

 the uniform law according to which the formulae are developed ; but that the 

 successive increment of the atoms C2 H2 contributes to a certain regularity of 

 physical and chemical character ; thus, neighbors in the series have greater 

 analogy to each other than to more distant members. The acids and alcohols 

 quoted advance (at the normal temperature) by degrees from liquids to solids; 

 and chemically, formic and acetic acids on the one hand, and palmitic and ste- 

 aric acids on the other are analogous. The boiling points increase with regu- 

 larity ; for example, in series II and III every addition of C2 H2 adds 19° C. 

 to the boiling pointr. Though this regularity of boiling point applies to other 

 series, the difference is not the same for all ; thus in series V every increment 

 of C2 H3 adds 24" C. to the boiling point. 



It would create too great a diversion from the main object of the present 

 article to enter further upon the nature of homologous series. The curious law 

 may, however, be cited with respect to certain series of acids, ethers, and alco- 

 hols, viz : that if two of them have an equal number of hydrogen and oxygen 

 atoms, and one has X more atoms of carbon, the latter will boil at X 14.5 degrees 

 centigrade higher. For example : 



Benzoic acid, C^ Hq O4 ; boiling point, 253- 

 Propionic acid, Cg Hg O4 ; " 137 



Difference, 



Angelica acid. 

 Butyric acid. 



C 



IIG'^ 



8 X 14.5 



Cio H3 O4 ; boiling point, 185- 

 d H8O4; " 15G = 



Difference, C2 



2 X 14.5 = 29- 



On the other hand, if the number of atoms of carbon and oxygen is the 

 same, and one compound contains X equivalents less of hydrogen, its boiling 

 point will be X 5 C.° higher. 



Angelica acid, Cio H3 O4 ; boiling point, 185'° 

 Valerianic acid, Cio Hio O4 ; " 175° 



Difference, 



H, 



2X5 



10 



Not only are the members of the same series subjected to one and the same 

 law, but some of the series are connected with each other. The importance of 

 this foct is very great, since it enables a systematic grouping of chemical com 

 pounds. From the character of well-studied bodies, and from the analogies 

 alluded to, we are able to pronoinice a judgment upon the chemical constitution, 

 nature, and beha""::.:- of new bodies. 



This connexion of the scries is as follows : 



From alcohol C4 Hg O2 we may obtain by the addition of oxygen, and by the 



subtraction of hydrogen, acetic acid, (C4 Ilg O2) -f- O4 = (C4 H4 O4) -f 2 H 0. 



Hence, in general terms, if from the series (Cu H(n-j-2) O2) we subtract H2, and 



add O2 = (Cu Hu O4,) we obtain an acid analogous to acetic acid. Moreover, 



11 s 



