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 oŁ 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.