July 4, 1884.] 



SCIENCE 



in a similar way, there might not be alcohols 



derived from two molecules of water, 2 \ jj 2 , 



by substituting some group for two hydrogen 

 atoms. He soon discovered the first mem- 

 ber of this 

 group of bod- 

 ies, viz., gly- 

 col, which he 

 showed to be a 

 compound in- 

 termediate be- 

 tween ordinary 

 alcohol and gly- 

 cerine. He rep- 

 resented it by 

 the formula, 



° 2 IH 2 

 Probably the 

 most important 

 result of this 

 discovery was 

 the fact that the 

 attention of 

 chemists was 

 directed to the 

 differences be- 

 tween the radi- 

 cals C 2 H 5 in 

 ordinary alco- 

 hol, C 2 H 4 in 

 glycol, and 

 C 3 H 5 in glycer- 

 ine. In the 

 first the radical 

 takes the place 

 of one atom of 

 hydrogen , in 

 the second one 

 radical replaces 

 two atoms of 

 hydrogen, and 

 in the third the 

 radical replaces 

 three atoms 

 of hj'drogen. 

 Here, then, in 

 the polyatomic 

 radicals, we 



have the beginning of the conception of va- 

 lence. Just as radicals exist which can re- 

 place one, two, or three hydrogen atoms, so 

 similar differences exist between the elements. 

 Regarding the discovery of glycol, Ladenburg, 

 in his ; Entwickelnngsgeschichte der chemie,' 

 says, " Seldom has the discovery of a single 

 body exerted such an influence on the devel- 



opment of chemistry, seldom has a single com- 

 pound given rise to such a series of beautiful 

 and useful investigations, as glycol." 



The ideas suggested by the investigations on 

 the substituted ammonias and the polyatomic 



radicals were 

 followed up by 

 Wurtz and oth- 

 ers, and the re- 

 sult is the chern- 

 istiy of to-day. 

 Wurtz has been 

 an active par- 

 ticipator in all 

 important dis- 

 cussions re- 

 garding funda- 

 mental matters, 

 and has ably 

 and vigorously 

 defended the 

 modern views 

 against the at- 

 tacks of Ber- 

 thelot, St. 

 Claire Deville, 

 and others in 

 France. One 

 of the last of 

 these discus- 

 sions was car- 

 ried on only a 

 few years ago. 

 It pertained to 

 the question 

 whether Avoga- 

 dro's hypothe- 

 sis is valid or 

 not. Many of 

 the most promi- 

 nent French 

 chemists refuse 

 to accept it, 

 and, in defence 

 of their posi- 

 tion, tauntingly 

 refer to two or 

 three apparent 

 exceptions. 

 The particular 

 case which gave rise to the discussion referred 

 to is that of chloral hydrate. Wurtz claimed 

 that the reason wiry this compound does not 

 conform to the hypothesis is, that, when heated, 

 it breaks up into water and chloral. This his 

 opponents strenuously denied. Both sides in- 

 troduced very delicate and skilful experiments ; 

 but, as is usually the case, no final conclusion 



