CHAPTEVER LIV. ORGANIC CHEMISTRY.

295. General Considerations.--Inorganic chemistry is the
chemistry of minerals, or unorganized bodies. Organic chemistry
was formerly defined as the chemistry of the compounds found in
plants and animals; but of late it has taken a much wider range,
and is now defined as the chemistry of the C compounds, since C
is the nucleus around which other elements centre, and with which
they combine to form the organic substances. New organic
compounds are constantly being discovered and synthesized, so
that nearly 100,000 are now known. The molecule of organic matter
is often very complex, sometimes containing hundreds of atoms.

In organic as in inorganic chemistry, atoms are bound together by
chemical affinity, though it was formerly supposed that an
additional or vital force was instrumental in forming organic
compounds. For this reason none of these substances, it was
thought, could be built up in the laboratory, although many had
been analyzed. In 1828 the first organic compound, urea, was
artificially prepared, and since then thousands have been
synthesized. They are not necessarily manufactured from organic
products, but can be made from mineral matter.

296. Molecular Differences.--Molecules may differ in three ways:
(1) In the kind of atoms they contain. Compare CO2 and CS2. (2)
In the number of atoms. Compare CO and CO2. (3) In the
arrangement of atoms, i.e. the molecular structure. Ethyl alcohol
and methyl ether have the same number of the same elements,
C2H6O, but their molecular structure is not the same, and hence
their properties differ.

Qualitative analysis shows what elements enter into a compound;
quantitative analysis shows the proportion of these elements;
structural analysis exhibits molecular structure, and is the
branch to which organic chemists are now giving particular
attention. `

A specialist often works for years to synthesize a series of
compounds in the laboratory.

297. Sources.--Some organic products are now made in a purer and
cheaper form than Nature herself prepares them. Alizarine, the
coloring principle of madder, was until lately obtained only from
the root of the madder plant; now it is almost wholly
manufactured from coal-tar, and the manufactured article serves
its purpose much better than the native product. Ten million
dollars' worth is annually made, and Holland, the home of the
plant, is giving up madder culture. Artificial naphthol-scarlet
is abolishing the culture of the cochineal insect. Indigo has
also been synthesized. Certain compounds have been predicted from
a theoretical molecular structure, then made, and afterwards
found to exist in plants. Others are made that have no known
natural existence. The source of a large number of artificial
organic products is coal-tar, from bituminous coal. Saccharine, a
compound with two hundred and eighty times the sweetening power
of sugar, is one of its latest products. Wood, bones, and various
fermentable liquids are other sources of organic compounds.

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.

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.

Write the common formulae for the first ten of this series. This
is the olefiant-gas series, and to it belong oxalic and tartaric
acids, glycerin, and a vast number of other compounds, many of
which are derived by replacements.

303. Other Series.--In addition to the two series of hydro-
carbons above given, CnH2n+2 and CnH2n, other series are known
with the general formulm CnH2n-2, CnH2n-4, CnH2n-6, CnH2n-8,
etc., as far as CnH2n-32, or C26H2O. Each of these has a large
number of representatives, as was found in the marsh-gas series.
Not far from two hundred direct compounds of C and H are known,
not to mention substitutions. The formula CnH2n-6 represents a
large and interesting group of compounds, called the benzine
series. This is the basis of the aniline dyes, and of many
perfumes and flavors.