TRANSACTIONS OF THK SECTIONS. 57 



drogen, or instead of liydrogen two atoms of chlorine or bromine, and form the 

 compounds CII4, C H^ CL^, (J H^ Br.^, respectively. Meth)'lene, therefore, being- 

 equivalent to two atoms of b ydrou'en, is termed divalent. The radical C H, left 

 after the abstraction of three atoms of hydrogen from marsh-gas, is able to reproduce 

 with three atoms of hydrogen one molecule of marsh-gas, or to combine with throe 

 atoms of chlorine, and form chloroform, C H CI3. The residue, C H, is thus triva- 

 lent, or equivalent to three atoms of hydrogen. In tlie same manner carbon is 

 found to be tetravalent or equivalent to four atoms of hydrogen ; but carbon, for- 

 men [C H], methylene, C H,, methj-l, C H3, not only combine Avith hydrogen, 

 chlorine, or other elements according to their equivalence, but also amongst them- 

 selves, and thus produce the so-caUed hydrocarbons, native as well as artificial. 

 Methyl combines with methyl and produces dimethyl, or better known as ethylic 

 hydride, C H.,-}-C H.,=C'2 H,, ; methylene combines with methylene and forms 

 ethjdene, C Ho-|-0Il2=C2 Hi. Methylene is divalent and metlijd monovalent; 

 therefore methylene combines with two equivalents of methyl and forms propylic 

 hydride, C;) H^, C H2-I-2 C H^ = C3 H,. Six equivalents of formen are supposed to 

 be contained in benzol [C,. Hg], 6C H— Cc H^. 



What has been said of marsh-gas also applies to ammonia and water. Ammonia, 

 N H3, minus one atom of hydrogen, forms the monovalent radical, N II.„ minus two 

 atoms of liydrogen, the divalent radical, N H, and nitrogen itself is trivalent, that is 

 to say, it can replace three atoms of hydrogen in compounds, or can combine with 

 tliree atoms of hydrogen. Water minus one atom of hydrogen produces the mo- 

 novalent radical hydroxyl, H 0, and water without both atoms of hydrogen gives 

 us divalent oxygen. These radicals, X H2, N II, N, H O, and O, can combine with 

 each otlier, and with methyl, methylene, formen, and carbon respectively, in dif- 

 ferent proportions. Thus methyl, methylene, and hydroxyl are contained in com- 

 mon alcohol. The union of methyl, carbon, oxvgen, and hydroxyl gives acetic 

 acid, C,H,0.,, 



C H3-f C+O-m 0=0, H, 0,. 



GlycocoU is considered as a combination of methylene, amidogen [N H J, car- 

 bon, oxygen, and hydi'oxyl : 



CH,-l-NIL+C+0-f-nO = 0,H,N03=glycocoll. 



The radicals C, C H, C II,, C H3, H 0, 0, N, N H, N 11^, and C are considered 

 to form the proximate constituents of the most important organic compounds. It 

 often happens that, from the union of the same radicals, two or more bodies of the 

 same composition, but ditlering from one another in properties, result. GlycocoU 

 as well as glycolamide contain the radicals methylene, hydroxyl, carbonic oxide, 

 and amidogen, N H,. In such cases the nature of the compound depends on tho 

 arrangement of the radicals, as may be seen by the following formulae : — 



C IT, . N H, . C . H 0=C, H, N 0,=glycocoll, 



C H, . H . C . N H,=C^H3 N 0,= glycolamide. 



Now the great problem with whose solutions scientific chemists are occupied^is — 

 To determine fjirsf, ichat sort of radicuh of the above nature are contained in a given 

 crfianic body, and, second, /tow these radicals are f/roupcd amongst each other. 



There are several ways of solving this problem. The molecule may be built up 

 by placing the radicals which are supposed to exist in it under suitable conditions 

 in contact. Two molecules of iodopropionic acid placed together with metallic silver 

 will lose their iodine, and the residues of the two molecules remain united. A new 

 acid, called adipic acid, is thus formed. 



(CO. HO 



Iodopropionic acid ■! C H 



CH,I 



COIIO 

 OIL 



1CII,I 

 Iodopropionic acid l C H., 



(COHO 



-)- Ag, =2AgI+ { g {{2 adipic acid. 



CII, 

 C II 



