A treatise on chemistry. Vol. III, The chemistry of the hydrocarbons and their derivatives, or, Organic chemistry. Part I / by H.E. Roscoe & C. Schorlemmer.

  • Henry Enfield Roscoe
Date:
1881
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on chemistry. Vol. III, The chemistry of the hydrocarbons and their derivatives, or, Organic chemistry. Part I / by H.E. Roscoe & C. Schorlemmer. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    tioa of the two theories of types and radicals. Dumas had already jjoiutcd out that hydrogen can not only be replaced by elements such as chlorine, but also by certain groups of atoms, such as NOg; and that these may be desig- nated as compound radicals. Gerhardt revived this view in 1839, but not e.xactly in the sense of the radical theory, ac- cording to which theory the radicals are closed groups of atoms and form the proximate constituents of comjMuijds. Here, however, it must be noticed that Liebig ^ had already pointed out that a radical is not to be considered as an unalterable quantity, and that it was not necessary that the existence of tlio radical must precede the formation of an organic compound. Gerhardt did not assume that a substitution must occur when an element is replaced by a compound body, but rather that a combination of tlie two residues takes place to form a chemical unit, and not a copulated compound. The group of atoms which can be assumed to be a radical was termed le rest or le restant. Then came his theorie des residus according to which such a residue possesses indeed the composition of a compound radic-al, but is not contained as such in the com- pound. Thus, for instance, the radical theory considers ethyl nitrate as nitrate of ethyl oxide, and the formula is written, with equivalent weights, C^EJJ.NO-^; this ether is obtained by the action of nitric acid on alcohol : CJ-IcO + HNO3 = C.H.NOg + H,0. According to Gerhardt the reaction which here takes jDlace is that the one compound gives up an atom of hydrogen, and the other the group or residue OH, and that these unite together to form water, whilst the two other residues form the chemical unit, ethyl nitrate. Gerhardt's theory of residues soon replaced the radicals of the old theory, and their assumption in the new theory of types brought about the union of the two theories. This was more especially effected by the discovery of the compound ammonias made by Wurtz^ in 1849. Liebig ^ had foreseen the possible existence of such compounds, inasmuch as he pre- dicted that by uniting the alcohol radical with amidogen, IMHg, compounds would be obtained possessing the characteristic properties of ammonias. Wurtz also assumed a corresponding 1 Ann. Pharm. xiv. 1G6 ; xviii. 323. ' Com.pt.cs Jlmdus, Aout. 13, 1849 ; rhil. Mag. [3] xxxv. 34. ^ Ilandwortcrb. i. C98.