298. Marsh-Gas Series.--The chemistry of the hydro-carbons depends on the valence of C, which, in most cases, is a tetrad. Take successively 1, 2, and 3 C atoms, saturate with H, and note the graphic symbols:-- H H H H H H | | | | | | H-C-H, or CH4. H-C-C-H, or? H-C-C-C-H, or ? | | | | | | H H H H H H Write the graphic and common symbols for 4, 5, and 6 C atoms, saturated with H. Notice that the H atoms are found by doubling the C atoms and adding 2. Hence the general formula for this series would be CnH2n+2. Write the common symbol for C and H with ten atoms of C; twelve atoms; thirteen. This series is called the marsh-gas series. The first member, CH4 methane, or marsh gas, may be written CH3H, methyl hydride, CH3 being the methyl radical. C2H6, ethane, the second one, is ethyl hydride, C2H5H. Theoretically this series extends without limit; practically it ends with C35H72. In each successive compound of the following list, the C atoms increase by unity. Give the symbols and names of the compounds, and commit the latter to memory:-- Boiling-point. 1. CH4 methane, or CH3H, methyl hydride, gas. 2. C2H6 ethane, C2H5H, ethyl hydride, gas 3. C3H8 propane, C3H7H, propyl hydride, gas 4. ? butane, ? ? 1 degree 5. ? pentane ? ? 38 degrees 6. ? hexane, ? ? 70 degrees 7. ? heptane, ? ? 98 degrees 8. ? octane, ? ? 125 degrees 9. ? nonane, ? ? 148 degrees 10.? dekane, ? ? 171 degrees Note a successive increase of the boiling-point of the compounds. Crude petroleum contains these hydro-carbons up to 10. Petroleumissues from the earth, and is separated into the different oils by fractional distillation and subsequent treatment with H2SO4, etc. Rhigoline is mostly 5 and 6; gasoline, 6 and 7; benzine, 7; naphtha, 7 and 8; kerosene, 9 and 10. Below 10 the compounds are solids. None of those named, however, are pure compounds. Explosions of kerosene are caused by the presence of the lighter hydro-carbons, as naphtha, etc. Notice that, in going down the list, the proportion of C to H becomes much greater, and the lower compounds are the heavy hydro-carbons. To them belong vaseline, paraffine, asphaltum, etc.