299. Alcohols.--The following replacements will show how the symbols for alcohols, ethers, etc., are derived from those of the marsh-gas series. Notice that these symbols also exhibit the molecular structure of the compound. In CH3H by replacing the last H with the radical OH, we have CH3OH, methyl hydrate. By a like replacement C2H5H becomes C2H5OH, ethyl hydrate. These hydrates are alcohols, and are known as methyl alcohol, ethyl alcohol, etc. The common variety is C2H5OH. How does this symbol differ from that for water, HOH? Notice in the former the union of a positive, and also of a negative, radical. Complete the table below, making a series of alcohols, by substitutions as above from the previous table. 1. CH3OH, methyl hydrate, or methyl alcohol. 2. C2H5OH, ethyl hydrate, or ethyl alcohol. 3. ? ? ? 4. ? ? ? 5. ? ? ? Continue in like manner to 10. The graphic symbol for CH3OH is--- H | H-C-OH; | H for C2H5OH it is-- H H | | H-C-C-OH. | | H H Write it for the next two. 300. Ethers.--Another interesting class of compounds are the oxides of the marsh-gas series. In this series, O replaces H. CH3H becomes (CH3)2O, and C2H5H becomes (C2H5)2O. Why is a double radical taken? These oxides are ethers, common or sulphuric ether being (C2H5)2O. Complete this table, by substituting O in place of H, in the table on page 176. 1. (CH3)2O, methyl oxide, or methyl ether. 2. (C2H5)2O, ethyl oxide, or ethyl ether. 3. ? ? ? 4. ? ? ? 5, etc. ? ? ? Graphically represented the first two are:-- H H H H H H | | | | | | (1) H-C-O-C-H. (2) H-C-C-O-C-C-H. | | | | | | H H H H H H 301. Substitutions.--A large number of other substitutions can be made in each symbol, thus giving rise to as many different compounds. In CH4, by substituting 3 Cl for 3 H,-- H Cl | | H-C-H becomes H-C-CI, or CHCl3,the symbol for chloroform. | | H Cl Replace successively one, two, and four atoms with Cl, and write the common symbols. Make the same changes with Br. For each atom of H in CH4 substitute the radical CH3, giving the graphic and common formulae. Also substitute C2H5. Are these radicals positive or negative? From the above series of formulae, of which CH4 is the basis, are derived, in addition to the alcohols and ethers, the natural oils, fatty acids, etc. 302. Olefines.--A second series of hydro-carbons is represented by the general formula CnH2n. The first member of this series is C2H4 or, graphically,-- H H | | C = C. | | H H Compare it with that for C2H6, in the first series, noting the apparent molecular structure of each. H H | | C = C - C - H, or C3H6 is the second member. | | | H H H Write formulae for the third and fourth members.