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List Of Contents | Contents of An Introduction to Chemical Science
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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.

Chapter LV.

ILLUMINATING GAS.

304. Source.--The three main elements in combustion are O, H, C.
Air supplies O, the supporter; C and H are usually united, as
hydro-carbons, in luminants and combustibles. H gives little
light in burning; C gives much. The fibers of plants contain
hydro-carbons, and by destructive distillation these are
separated, as gases, from wood and coal, and used for
illuminating purposes. Mineral coal is fossilized vegetable
matter; anthracite has had most of the volatile hydro-carbons
removed by distillation in the earth; bituminous and cannel coals
retain them. These latter coals are distilled, and furnish us
illuminating gas.

Experiment 129.--Put into a t.t. 20 g. of cannel coal in fine
pieces. Heat, and collect the gas over H2O. Test its
combustibility. Notice any impurities, such as tar, adhering to
the sides of the t.t., or of the receiver after combustion. Try
to ignite a piece of cannel coal by holding it in a Bunsen flame.
Is it the C which burns, or the hydrocarbons? Distil some wood
shavings in a small ignition-tube, and light the escaping gas.

305. Preparation and Purification.--To make illuminating gas,
fire-clay retorts filled with coal are heated to 1100 degrees or
more, over a fire of coke or coal. Tubes lead the distilled gas
into a horizontal pipe, called the hydraulic main, partly filled
with water, into which the ends of the gas-pipe dip. The gas then
passes through condensers consisting of several hundred feet of
vertical pipe, through high towers, called washers, in which a
fine spray Fig. 60. Gas Works.

A, furnace; C, retorts containing coal; T, gas-tubes leading to
B, the hydraulic main; D, condensers; O, washers, with a spray of
water, and sometimes coke; M, purifiers-ferric oxide or lime; G,
gas-holder. In C remain the coke and gas carbon. At B, D, E, and
O, coal tar, H2O, NH3, CO2, and SO2 are removed. At M are taken
out H2S and CO2.of water falls, into chambers with shelves
containing the purifiers CaO or hydrated Fe2O3, and finally into
a gas-holder, whence it is distributed. At the hydraulic main,
condensers, washers, and purifiers, certain impurities are
removed froth the gas. Coke is the solid C residue after
distillation. Gas-carbon, also a solid, is formed by the
separation of the heavier hydro-carbons at high temperature, and
is deposited on the sides of the retort.

Coal gas, as it leaves the retort, has many impurities. It is
accompanied with about 3 its weight of coal tar, 1/2 its weight
of H2O vapor, 1/50 NH3, 1/20 CO2, 1/20 to 1/50 H2S, 1/300 to
1/600 S in other forms. The tar is mostly taken out at the
hydraulic main, which also withdraws some H2O with other
impurities in solution. The condensers remove the rest of the
tar, and the H2O, except what is necessary to saturate the gas.
At the main, the condensers, and the washers, NH3 is abstracted,
CO2 and H2S are much reduced, and the other S compounds are
diminished. Lime purification removes CO2 and H2S, and, to some
extent, other S compounds. Iron purification removes H2S. Fe2O3 +
3 H2S = 2 FeS + S + 3 H2O.

The FeS is revivified by exposure to the air. 2 FeS + O3 = Fe2O3
+ 2S. It can then be used again. H2S, if not separated, burns
with the gas, forming H2S03, which oxidizes in the air to H2SO4;
hence the need of removing it. CO2 diminishes the illuminating
power.

306. Composition.--Even when freed from its impurities coal-gas
is a very complex mixture, the chief components being nearly as
follows:--


Percent	                 Diluents, having little C, give
H	45)	         very little light. Notice the small
CH,	41) diluents.	 percentage of luminants, or light-
CO	5 )	         giving compounds, also the proportion
C,HB	1.3)             of C to H in them.
C,H6	1.2)luminants.
CZH4	2.5)	         Cannel coal contains more of
C02	2) impurities.   the heavy bydro-carbons, CnH2n,
N, etc. 2)	         etc., than the ordinary bituminous
        100	         coal. Ten per cent of the coal should be
cannel; naphtha is, however, often employed to subserve the same
purpose, one ton of ordinary bituminous coal requiring four gallons
of oil.

In Boston, 7,000,000 cubic feet of gas have been burned in one
day, consuming 500 tons of coal; the average is not more than
half that quantity. Of the other products, coke is employed for
heating purposes, gas carbon is used to some extent in electrical
work, and coal-tar is the source of very many artificial products
that were formerly only of natural origin. NH3, is the main
source of ammonium salts, and S is made into H2SO4.

307. Natural Gas occurs near Pittsburg, Pa., and in many other
places, in immense quantities. It is not only employed to light
the streets and houses, but is used for fires and in iron and
glass manufactories. It is estimated that 600,000,000 cubic feet
are burned, saving 10,000 tons of coal daily in Pittsburg, Only
half a dozen factories now use coal. More than half the gas is
wasted through safety valves, on account of the great pressure on
the pipes as it issues from the earth.

These reservoirs of natural gas very frequently occur in
sandstone, usually in the vicinity of coal-beds, but sometimes
remote from them. In all cases the origin of the gas is thought
to be in the destructive distillation, extending through long
geological periods, of coal or of other vegetable or animal
matter in the earth's interior.

Natural gas varies in composition, and even in the same well,
from day to day; it consists chiefly of CH4, with some other
hydro-carbons.

CHAPTER LVI.

ALCOHOL.

308. Fermented Liquor.

Experiment 130.--Introduce 20 cc.of molasses into a flask of 200
cc, fill it with water to the neck, and put in half a cake of
yeast. Fit to this a d.t., and pass the end of it into a t.t.
holding a clear solution of lime water. Leave in a warm place for
two or three days. Then look for a turbidity in the lime water,
and account for it. See whether the liquid in the flask is sweet.
The sugar should be changed to alcohol and CO2. This is fermented
liquor; it contains a small percentage of alcohol.

309. Distilled Liquor. Experiment 131.--Attach the flask used in
the last experiment to the apparatus for distilling water (Fig.
32), and distil not more than one-fifth of the liquid, leaving
the rest in the flask. The greater part of the alcohol will pass
over. To obtain it all, at least half of the liquid must be
distilled; what passes over towards the last is mostly water.
Taste and smell the distillate. Put some into an e.d. and touch a
lighted match to it. If it does not burn, redistil half of the

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