Gerhard? s Organic Chemistry. 171 



Art. XIV. — Review of the Organic Chemistry of M. Charles 



Gerhardt. 



(Concluded from p. 100.) 



We have already seen that M. Gerhardt halves the equivalents 

 of most substances, taking the equivalent of hydrogen to be rep- 

 resented by the weight of its atom. Chlorine, bromine and iodine 

 which unite with hydrogen, volume for volume, are also divided 

 so that their volumes correspond to that of oxygen. In many 

 reactions in which carbonic acid and water are evolved, they are 

 observed to be in the proportions C 9 4 and H 4 2 , or in quan- 

 tities double those which are regarded as equivalents in mineral 

 chemistry. It will also be observed that in the formulas of all 

 those substances which like alcohol and its derivatives are ordi- 

 narily represented by four volumes of vapor, the equivalents of 

 carbon and oxygen are divisible by two and those of hydrogen 

 by four. This has led many chemists to consider the oxygen in 

 organic compounds as having double the equivalent ascribed to 

 >t in mineral combinations. If we regard C 2 4 and H 4 2 as 

 representing single equivalents, it will then be necessary to double 

 me formulas of mineral chemistry in order to harmonize the two. 

 |f on the other hand these represent two equivalents, the formu- 

 las of organic compounds must be divided ; and this last course 

 has been adopted by M. Gerhardt. 



The protoxyds of the metals corresponding to water in their 

 composition, will hence be expressed by M, O, and the equiva- 

 fents of metals themselves will be one-half the number usually 

 adopted. The equivalents of organic acids are generally deter- 

 ged from their silver salts, and in the monobasic acids the 

 weight corresponding to one atom of silver is taken as the equiv- 

 alent of the salt ; thus the acetic acid is C, H 4 2 , and the ace- 

 tate of silver C, (H 3 Ag) O s , in which it is impossible to imagine 



me existence of water or oxyd of silver, which are H 3 O and 

 Ag 2 0. 



The equivalents of chlorine, bromine and iodine, will by this 

 arrangement, be like oxygen represented by a single volume ; 

 mose of nitrogen, phosphorus and arsenic, are also divided, while 

 carbon with sulphur and selenium are retained unaltered. The 

 equivalent of water is represented by H, O and equals two vol- 

 tes of vapor, hydrochloric acid is HCl = 2 vol. vapor, and ammo- 

 n, a m hke manner is NH 3 and its equivalent is expressed by two 



^^es— (Precis, Vol. I, pp. 47-53.) 



Mode of Combination. — Many compounds have the 

 exchanging one or more of their equivalents of hydrogen for a 

 J^a!, thus producing a series of compounds known as salts. All 

 01 those metals which unite with chlorine in single equivalents, 



power 



