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An Introduction to Chemical Science

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CHAPTER LXI.

THEORIES.

339. The La Place Theory.--This theory supposes that at one time
the earth and the other planets, together with the sun,
constituted a single mass of vapor, extending billions of miles
in space; that it rotated around its center; that it gradually
shrank in volume by the transformation of potential into kinetic
energy; that portions of its outer rim were thrown off, and
finally condensed into planets; that our sun is only the
remainder of that central mass which still rotates and carries
the planets around with it; that the earth is a cooling globe;
that the other planets are going through the same phases as the
earth; and finally that the sun itself is destined like them to
become a cold body.

340. A Cooling Earth.--The sun's temperature is variously
estimated at many thousands, or even millions o£ degrees. Many
metals which exist on the earth as solids -e.g. iron- are gases
in the dense atmosphere of the sun. Thus the earth, in its early
existence, must have been composed of gases only, which in after
ages condensed into liquids and solids. So intense was the heat
at that time, that substances probably existed as elements
instead of compounds, i.e. the temperature was above the point of
dissociation. We have seen that Al2O3, CaO, SiO2, etc., are
dissociated at the highest temperatures only. If the temperature
were above that of combination, compounds could not exist as
such, but matter would exist in its elemental state. On slowly
cooling, these elements would combine. It is, then, a fair
inference that such compounds as need the highest temperatures to
separate them, as silica, silicates, and some oxides, were formed
from their elements at a much earlier stage of the earth's
history than were those compounds that are more easily separable,
such as water, lead sulphide, etc., and that the most infusible
substances were solidified first.

341. Evolution.--As the earth slowly cooled, elements united to
form compounds, gases condensed to liquids, and these to solids.
At one time the entire surface of our planet may have been
liquid. When the cooling surface reached a point somewhat below
that of boiling water, the lowest forms of life appeared in the
ocean. This was many millions of years ago. Most scientists
believe that all vegetable and animal life has developed from the
lowest forms of life. There is also a theory that all chemical
elements are derivatives of hydrogen, or of some other element,
and that all the so-called elements are really compounds, which a
sufficiently high temperature would dissociate. As evidence of
this, it is said that less than half as many elements have been
discovered in the sun as in the earth, and that comets and
nebula, which are less developed forms of matter than the sun,
have a few simple substances only.

It is easy to fancy that all living bodies, both animal and
vegetable, are only natural growths from the lowest forms of
life; that these lowest forms are a development, with new
manifestations of energy, from inorganic matter; that compounds
are derived from elements; and that the last are derivatives of
some one element; but it must be borne in mind that this is only
a theory.

342. New Theory of Chemistry. We have seen that heat lies at the
basis of chemical as well as of physical changes. By the loss of
heat, or perhaps by the change of potential into kinetic energy,
in a nebulous parent mass, planets were formed, capable of
supporting living organisms. Heat changes solids to liquids, and
liquids to gases; it resolves compounds, or it aids chemical
union. In every chemical combination heat is developed; in every
case of dissociation heat is absorbed. Properly written, every
equation should be: a + b = c + heat; e.g. 2 H + 0 = H2O + heat;
or, c - a = b - heat; e.g. H2O - 2 H = 0 - heat. Another
illustration is the combination of C and O, and the dissociation
of CO2, as given on page 82. C + O2 = CO2 + energy. CO2 - O2 = C
- energy. In fact, there are indications that the present theory
of atoms and molecules of matter, as the foundation of chemistry,
will at no distant day give place to a theory of chemistry based
on the forms of energy, of which heat is a manifestation.

Chapter, LXII.

GAS VOLUMES AND WEIGHTS.

343. Oxygen.

Experiment 134.--Weigh accurately, using delicate balances, 5 g.
KClO3, and mix with the crystals 1 or 2 g. of pure powdered MnO2.
Put the mixture into a t.t. with a tight-fitting cork and
delivery-tube, and invert over the water-pan, to collect the gas,
a flask of at least one and a half liters' capacity, filled with
water. Apply heat, and, without rejecting any of the gas, collect
it as long as any will separate.

Then press the flask down into the water till the level in the
flask is the same as that outside, and remove the flask, leaving
in the bottom all the water that is not displaced. Weigh the
flask with the water it contains; then completely fill it with
water and weigh again.

Subtract the first weight from the second, and the result will
evidently be the weight of water that occupies the same volume as
the O collected. This weight, if expressed in grams, represents
approximately the number of cubic centimeters of water,--since 1
cc. of water weighs lg,--or the number of cubic centimeters of O.

At the time the experiment is performed the temperature should be
noted with a centigrade thermometer, and the atmospheric pressure
with a barometer graduated to millimeters.

Suppose that we have obtained 1450 cc. of O, that the temperature
is 27 degrees, and the pressure 758 mm.; we wish to find the
volume and the weight of the gas at 0 degrees and 760 mm.

According to the law of Charles--the volume of a given quantity
of gas at constant pressure varies directly as the absolute
temperature. To reduce from the centigrade to the absolute scale,
we have only to add 273 degrees. Adding the observed temperature,
we have 273 degrees + 27 degrees = 300 degrees. Applying the
above law to O obtained at 300 degrees A, we have the proportion
below. Since the volume of O at 273 degrees will be less than it
will at 300 degrees, the fourth term, or answer will be less than
the third, and the second term must be less than the first. 300 :
273 :: 1450 : x. This would give the result dependent upon
temperature alone.

By the law of Mariotte - Physics, - the volume of a given
quantity of gas at a constant temperature varies inversely as the
pressure. Applying this law to the O obtained at 758mm, we have
the following proportion. The volume at 760mm will be less than
at 758mm; or the fourth term will be less than the third; hence
the second must be less than the first. 760: 758:: 1450: x. This
would give the result dependent on pressure alone.

Combining the two proportions in one:--

300: 273 ):: 1450: x = 1316cc.
760: 758 )

1316cc=1.316 liters. It remains to find the weight of this gas. A liter of
H weighs 0.0896g. The vapor density of O is 16. Hence 1.316 liters of O
will weigh 1.316 X 16 X 0.0896 =1.89g.

(KClO3 = KCl + O3)
From the equation (122.5 48) we make a proportion,
( 5 x)

122.5: 5:: 48: x = 1.95, and obtain, as the weight of O contained in
5g of KClO3, 1.95g. The weight we actually,obtained was 1.89g. This
leaves an error of 0.06g, or a little over 4 per cent of error (0.06 / 1.95
= 0.03 +). The percentage of error, in performing this experiment,
should fall within 10.

Some of the liabilities to error are as follows:--


1. Impure MnO2, which sometimes contains C. CO2 is soluble m H2O.

2. Solubility of O in water.

3. Escape of gas by leakage.

4. Moisture taken up by the gas.

5. Difference between the temperature of the gas and that of the
air in the room.

6. Errors in weighing.

7. Want of accuracy in the weights and scales.

344. Hydrogen.

Experiment 135.--Weigh 5g, or less of sheet or granulated Zn, and
put it into a small flask provided with a thistle-tube and a
delivery-tube. Cover the Zn with water, and introduce through the
thistle-tube measured quantities of HCl, a few cubic centimeters
at a time. Collect the H over water in large flasks, observing
the same directions as in removing O. Weigh the water, compute
the volume of the gas, reduce it to the standard, and obtain the
weight, as before. Should any Zn or other solid substance be
left, pour off the water or filter it, weigh the dry residue, and
deduct its weight from that of the Zn originally taken. Suppose
the residue to weigh 0.5g. Make and solve the proportion from the
equation:-


Zn + 2HCl = ZnCl2 + 2H.
65 2.
4.5 x.


Compute the percentage of errcr, as in the case of O. If the
purity of the HCl be known, i.e. the weight of HCl gas in one
cubic centimeter of the liquid, a proportion can be made between
HCl and H, provided no free HCl is left in the flask. State any
liabilities to error in this experiment.

PROBLEMS.

(1) A gas occupies 2000cc.when the barometer stands
750mm. What volume will it fill at 760mm?

(2) At 750mm my volume of O is 4 1/2 liters. What will it be at
730mm?

(3) At 825mm?

(4) At 200mm?

(5) Compute the volume of a gas at 70 degrees, which at 30
degrees is 150cc.

(6) At 0 degrees I have 3000cc.of O. What volume will it occupy
at 100 degrees?

(7) I fill a flask holding 2 litres with H. The thermometer
indicates 26 degrees, the barometer 762mm. What is the volume of
the gas at 0 degrees and 760mm?

If the volumes of gases vary as above, it is evident that their
vapor densities must vary inversely. A liter of H at 0 degrees
weighs 0.0896. What will a liter of H weigh at 273 degrees? At
273 degrees the one liter has be- come two liters, one of which
weighs 0.0448 (= 0.0896 / 2). The vapor density of a gas is
inversely proportional to the temperature. Also, the vapor
density is directly proportional to the pressure, since a liter
of any gas under a pressure of one atmosphere is reduced to half
a liter under two atmospheres.

PROBLEMS.

(1) Find the weight of a liter of O at 0 degrees; then compute the
weight of a liter at 27 degrees.

(2) Find the weight of 500cc.of N2O at 60 degrees.

(3) Of 200 cc. of CO at -5 degrees.

(4) A given volume of O weighs 0.25g at a pressure of 750mm; find
the weight of a like volume of O at 758mm.

APPENDIX.

INDIVIDUAL APPARATUS.

Each pupil should be provided with the apparatus given below, but in
cases where great economy must be exercised different pupils may, by
working at different times, use the same set. The author has selected
apparatus specially adapted, as to exact dimensions, quality, and cheap-
ness, for performing in the best way the experiments herein described,
and sets or separate pieces of this, together with other apparatus and
chemicals, can be had of the L.E. Knott Apparatus Co., 14 Ashburton
Place, Boston, to which firm teachers are referred for catalogs.

4 wide-mouthed bottles (horse-radish size), with corks.
1 soda-bottle.
4 pieces window-glass (3 in. sq.).
2 pieces thick glass tubing (20 in. long, 4 in. outside diam.).
1 glass stirring-rod.
1 glass funnel (2 1/2 in. wide, 60 degrees).
2 pieces glass tubing (12 in. long; 5/8 in. diam.).
1 porcelain evaporating-dish (3 in. wide).
1 asbestus paper and 1 fine wire gauze (3 in. sq.).
1 iron (or tin) plate.
1 pair forceps.
1 triangular file and 1 round file.
1 copper wire (15 in. long).
6 test-tubes, and corks to fit.
1 wooden test-tube holder.
1 flask with cork (200cc).
1 Bunsen burner (or alcohol lamp).
1 iron ring-stand.
1 piece rubber tubing (18 in. long,
3/8 in. inside diam.).
4 reagent bottles (250cc), HCl, HNO3, H2SO4, NH4OH.
1 pneumatic trough.

Wherever in this work "Bunsen burner" or "lamp" is mentioned, if
gas is not to be had, an alcohol lamp may be substituted.

GENERAL APPARATUS.

The following list includes apparatus needed for occasional
use:--

Metric rules (20 or 30cm long).
Scales with metric weights (1-200 g).
Metric graduates (25 or 50cc).
Filter papers.
Metric graduates (500cc).
Reagent bottles (250 and 500cc).
Mouth blowpipes.
Platinum wire and foil.
Mortars and pestles.
Test-tube racks.
Thistle-tubes.
Filter-stands.
Beakers.
Glass tubing (3/16 in., 1/4 in., and 1 in. outside).
Rubber tubing (1/8 in., and 3/8 in. inside).
Hessian crucibles.
Porcelain crucibles.
Electrolytic apparatus, including 2 or more Bunsen cells.
Ignition-tubes.
Steel glass-cutters.
Wire-cutters.
Calcium chloride tubes.
Water baths.
Thermometers.
Barometers, etc.

APPENDIX.

CHEMICALS.

The following estimate is for twenty pupils: -
Alcohol 1 pt
Alum 1 oz
Ammonium chloride 1/2 lb
Ammonium hydrate 1 lb
Ammonium nitrate. 1/2 lb
Antimony (powdered metallic) 1/2 oz.
Arsenic (powdered metallic) 1/2 oz.
Arsenic trioxide..... 1 oz.
Barium chloride..... 1 oz.
Barium nitrate..... 1 oz.
Beeswax....... 1 oz.
Bleaching-powder.... 1/4 lb.
Bone-black...... 1/2 lb.
Bromine....... 1/4 lb.
Calcium chloride.... 1 lb.
Calcium fluoride (powdered) 1 lb.
Cannel coal 1 lb
Carbon disulphide 1/4 lb
Chlorhydric acid 6 lb
Cochineal 1 oz
Copper (filings) 2 lb.
Copper nitrate 1 oz
Copper oxide 1/4 lb.
Ether (sulphuric) 1/4 lb
Ferrous sulphide 1 lb.
Ferrous sulphate 1/4 lb
Indigo 1/4 lb
Iodine 1 oz
Iron (filings or turnings) 1 lb.
Lead (sheet) 4 lb
Lead acetate 1 oz
Lead nitrate 1/4 lb
Litmus 1/2 oz
Litmus paper 3 sheets
Magnesium ribbon.... 3 ft.
Manganese dioxide.... 2 lb.
Mercurous nitrate.... 1/2 oz.
Nitric acid 3 lb.
Oxalic acid 1/4 lb
Phosphorus 1/4 lb
Potassium (metallic) 1/8 oz
Potassium bromide 1/4 lb.
Potassium dichromate 1/4 lb.
Potassium chlorate 2 lb.
Potassium hydrate 1/4 lb.
Potassium iodide 2 oz
Potassium nitrate 1/4 llb
Silver nitrate 1 oz.
Sodium 1/8 oz.
Sodium carbonate 1/4 lb
Sodium hydrate 1 lb.
Sodium nitrate 1/2 lb
Sodium silicate..... 1/2lb
Turkey red cloth.... 1/2yd
Sodium sulphate..... 1/4lb
Turpentine(spirits). 1/4lb
Sodium sulphide..... 1/4lb
Zinc(granulated).... 2lb
Sodium thiosulphate. 1/4lb
Zinc foil........... 3ft
Sulphur............. 2lb
Sulphuric acid...... 12lb

Additional Material

These substances are best obtained of local dealers.

Calcium carbonate(marble)..... 1lb
Molasses...................... 1pt
Calcium oxide(unslaked lime).. 1lb
Sodium chloride(fine)......... 1lb
Charcoal...................... 1lb
Sodium chloride(coarse)....... 1lb
Sheet lead.................... 4lb
Sugar......................... 1/2lb

FOR EXAMINATION

Those in capitals are most important

Rocks and Minerals.
ARGILLITE,
ARESENIC,
ARSENOPYRITE,
Barite,
CALCITE,
CASSITERITE,
CHALCOPYRITE,
CHALK,
CINNABAR,
COPPER (native),
Corundum,
Dolomite,
EMERY,
FELDSPAR,
Flint,
GALENITE,
GRANITE,
GRAPHITE,
GYPSUM,
HEMATITE,
Hornblende,
Jasper,
LIMONITE,
MAGNESITE,
MAGNETITE,
MALACHITE,
Meerschaum,
MICA,
OBSIDIAN,
Orpiment,
PYRITE,
QUARTZ,
Realgar,
SAND,
SERPENTINE,
SIDERITE,
SPHALERITE,
Talc,
ZINCITE

Metals and Alloys.

Aluminium, Iron (cast),
Aluminium bronze. Pewter,
Bell metal, Solder,
Brass, Steel,
Bronze, Type metal,
Copper, Tin foil,
Galvanized iron, Tin (bright plate and terne plate),
German silver, Zinc (sheet).
Iron (wrought)

Additional Compounds, for Examination:

Copper acetate, Lead carbonate,
Copper arsenite, Red lead,
Copper nitrate, Magnesia alba,
Copper sulphate, Smalt,
Lead dioxide, Vermilion.
Lead protoxide,

TABLE OF SOLUTIONS.

Number of grams of solids to be dissolved in 500cc of water.

AgNO3......... 25 K2Al2(SO4)4...... 50
BaCl2......... 50 KBr.... 25
Ba(N0 3)2........ 30 K2Cr207........ 50
CaClz......... 60 KI.......... 25
Ca(OH)2...... saturated KOH....... 60
CaS04....... saturated NaICOS........ 50
CUC12 50 NaOH 60
Cu(N03)......... 50 NalSl03....... saturated
FeS04......... 50 NH,N03........ 50
HgC12......... 30 Pb(C2H302)2...... 50
HgN03..... 25 + 25 HN03 Pb(NOs)2....... . 50


Other solutions....saturated.

Indigo solution (sulphindigotic acid) is prepared by heating for
several hours over a water bath, a mixture of ten parts of H 2SO4
with one of indigo, and, after letting it stand twenty-four
hours, adding twenty parts of water and filtering.



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