« PreviousContinue »
respects the same elements, according to the same numbers of atoms, excepting that one contains the substance A, the other the substance B, and there are grounds for supposing that the former contains 1 At. A, or 2 At. A, &c.; then also must it be admitted that the other compound contains 1 At. B, or 2 At. B, &c. There being but one compound of aluminum and oxygen, viz., alumina, this compound might be supposed to contain 1 At.
etal + 1 At. oxygen; but alumina crystallizes in sapphire in acute rhombohedrons, just like those of peroxide of iron in specular iron ore and of artificially prepared oxide of chromium. These last mentioned oxides combined with sulphuric acid, potash, and water also form regular octohedrons, just as alumina does in common alum: all these salts contain 4 At. sulphuric acid, 1 At. potash, and 24 At. water. Alumina is then isomorphous with these oxides, and must therefore be made up of the same number of atoms. Since then, according to Principle 4, peroxide of iron is supposed to contain 2 At. metal + 3 At. oxygen, the same must likewise be the case with alumina. Now 100 parts of alumina contain 53.31 aluminum and 46.69 oxygen; and 46:69 : 53:31 = 24 : 27.4; hence with 24 (3 At.) oxygen there are combined 27:4 (2 At.) aluminum; and 1 At. aluminum - 13.7. Again, peroxide of tin in tin-stone crystallizes in the same form as oxide of titanium in rutile; and since, according to Principle 4, it was assumed as probable that peroxide of tin contains 1 At. tin with 2 At. oxygen, this relation must also be supposed to hold good with regard to oxide of titanium. Black oxide of copper forms compounds isomorphous with the analogous compounds of magnesia, oxide of zinc, and protoxide of iron, all of which are supposed to contain 1 At. metal with 1 At. oxygen; such then must also be the case with the black oxide of copper, a conclusion agreeing with that arrived at in 4. Further development of these relations will be found under the head of Isomorphism.
For the determination of the atomic weights of simple substances from their specific heats, vid. Heat.
The following table of the atomic weights of the elementary bodies is fou ded almost wholly on the analyses of their compounds performed by Bizelius, a labour as difficult as it was extensive, by which Berzelius has de ferred an everlasting obligation on chemical science.
Column A contains the names of the simple substances; B the +
bols introduced by Berzelius to denote them; C and D the atomic ghts, those, namely, which most probably belong to the several bodies
ording to the principles just developed ; column č, in which the atomic ght of hydrogen = 1 is that which will be used in preference in this rk; in D the atomic weight of oxygen = 100. The columns E and F htain the atomic weights according to Berzelius; in E the atomic weight hydrogen is assumed
0.5, that of a double atom of hydrogen = 1; F the atomic weight of oxygen is put = 100. The numbers of this t column are those which are adopted by the majority of chemists after example of Berzelius. The atomic weights of lanthanum and cerium
given according to the approximate determination of F. J. Otto. aham, Lehrb. 1, 222.)
8 1 6 10.8 31:4 16 40 126 78.4 35.4 18.7 14 39.2 23.2
100 12.5 75 135 392:5 200 500 1575 980 442.5 233.75 175 490 290
80 857-5 550 256.25 158.75 451.7 578.8
8:01 0.50 6.13 10.91 15.72 16.12 39.63 63.28 39.20 17.74 9:37
7.09 39.26 23.31
6.44 68.66 43.85 20:52 12.69
20:5 12.7 36.1 46:3
Oxygen Hydrogen Carbon.. Boron Phosphorus Sulphur Selenium Iodine Brominé Chlorine Fluorine Nitrogen Potassium Sodium Lithium Barium Strontium Calcium Magnesium Lanthanum Cerium Didymium Yttrium Erbium Terbium Glucinum Aluminum Thorium Zirconium Silicium Titanium Tantalium Niobium Pelopium Tungsten.. Molybdenum Vanadium Chromium Uranium Manganese Arsenic Antimony Tellurium Bismuth Zinc.... Cadmium.. Tin Lead Iron.. Cobalt Nickel Copper. Mercury Silver Gold Platinum Palladium Rhodium Iridium Osmium Ruthenium
6.2398 76.44 136.20 196.14 201.17 494.58 789.75 489.15 221:33 116.90
88:52 489.92 290.90
80:33 856.88 547.29 256.02 158.35
Th Zr Si Ti Ta
17.7 13.7 59.6 22.4 14.8 24.5 185
331.26 171.17 744.90 420.20 277.31 303.66 1153.72
64 106.4 32.2 55.8 59 1038 27.2 29.6 29.6 31.8 101.4 108.1 199 98.7 53.4 52:1 98.7 99.6 51.7
1187.5 600 857.5 351.25 2712.5 345 940 1612.5
800 1330 402.5 697-5 737.5 1297.5 340 370 370 397-5 1267.5 1351.25 2487-5 1233.75 667.5 651.25 1233.75 1245 646.25
94.80 47.96 68.66 28.19 217.26 27.72 37.67 64.62 64.25 71.07 32:31 55.83 58.92 103.73 27.18 29.57 29.62 31.71 101.43 108.30 99.60 98.85 53:36 52.2 98.84 99.72
1183.00 598.52 856.89 351.82 2711:36 345.89 470:04 806.45 801.76 886.92 403.23 696.77 735.29 1294.50 339.21 368.990 369.68 395.71 1265.82 1351.61 1243.01 1233.50 665.90 651.39 1233.50 1244:49
The discrepancies between the numbers in C D and those in E F are explained by the following considerations. In C D it is supposed that the atomic weight of oxygen is exactly 8 times that of hydrogen, wbile in E F its value is 8:01 times (or more accurately 8·0083 times) that of the double atom of hydrogen: also in CD the fractions of the other numbers are shortened as much as possible. In E F the atomic weights of hydrogen, iodine, bromine, chlorine, fluorine, and nitrogen are, for reasons above mentioned, reduced one-half. In C D, according to Principle 2, the atomic weights of phosphorus, arsenic, and antimony are doubled ; according to CD, the phosphoric, arsenic, and antimonic acids contain 5 At. oxygen for every atom of phosphorus or metal; according to E F these acids contain 2 At. phosphorus or metal for every 5 At. oxygen. In CD it is supposed that glucina and zirconia contain 1 At. glucinum or zirconium with 1 At. oxygen: in E F they contain 2 At. metal to 3 At. oxygen. In CD it is assumed that silica contains 1 At. silicium, combined with 2 At. oxygen : in E F, 1 At. metal with 3 At. oxygen. In C D it is assumed, as was formerly supposed by Berzelius, and is now regarded by him as admissible, that oxide of 'bismuth contains 3 At. oxygen to every 2 At. metal: in E F it is supposed to contain 1 At. oxygen + 1 At. metal.
On comparing with one another the numbers in column C, we obtain the following results.
1. The atomic weights of the other simple substances are in many instances exact multiples of that of hydrogen, e. 9., carbon, oxygen, nitrogen, sulphur, selenium, strontium, molybdenum, &c. Is it then a law of nature, as Prout and Thomson suppose, that the atomic weights of all the elements are divisible by that of hydrogen? If we can entertain the notion that there is but one primary ponderable matter, we must suppose that body to be hydrogen, since hydrogen has the smallest atoms: and it must further be supposed that when these atoms unite in different numbers in such a manner that they are not separable by any method yet discovered, they produce the larger and heavier atoms of the other bodies, whose atomic weights are then necessarily divisible by that of hydrogen. But the atomic weights of most bodies exhibit deviations from this law of such magnitude that Berzelius regards the occasional near divisibility of these weights by that of hydrogen as merely accidental; indeed, according to him, they are never exactly divisible, as may by inspection of columns E, F. Nevertheless the later experiments of Dumas and Stass (A nn. Chim. Phys. 76, 1), which give the atomic weight of carbon exactly = 6, and those of Liebig and Redtenbacher (Ann. Pharm. 38, 113), which make it 6.088, show that the question is not yet decided.
2. The elements may be arranged in groups, the members of which exhibit similar physical and chemical relations. Whether, as Döbereiner supposes (Pogg. 15, 301), such groups necessarily consist of 3 elements arranged in a triad, is a question which we shall not undertake to decide. The atomic weights of such corresponding elements usually bear a simple relation to each other: sometimes they are nearly equal, sometimes exact multiples one of another, or at all events increasing in some simple proportion. The following are similar to one another and have nearly equal atomic weights: chromium 28:1, manganese 27.6, and iron 27:2; cobalt 29:6 and nickel 29•6; zinc 32-2, copper 31:8; platinum 987, iridium 98.7, and osmium 99.8. The atomic weights of oxygen, sulphur, selenium, tellurium, and antimony are 8, 16, 40, 64, 129, there
fore as 1:2:5:8:16. The atomic weights of fluorine, chlorine, bromine, and iodine are 18.7, 35-4, 78:4, and 126, which are nearly as 2:4:9:14. Again, half the sum of the atomic weights of chlorine and
35.4 + 126 iodine gives nearly that of bromine,
= 80-7, and we find
2 that bromine, in all its physical and chemical relations, holds the middle place between chlorine and iodine. The atomic weights of lithium,
6.4 + 39.2 sodium, and potassium are 6:4, 23.2, and 39:2; and
2 the atomic weight of sodium is therefore almost exactly the mean between those of lithium and potassium, just as sodium in other respects holds the middle place between lithium and potassium. The atomic weights of magnesium, calcium, strontium, and barium, are 12.7, 20:5, 44, and 68:6; therefore, nearly as 3 : 5 : 11 :17: in this instance also by adding the atomic weights of barium and calcium, and dividing by 2, we get nearly the atomic weight of strontium, an element which in all its other relations is intermediate between barium and calcium; 20:5 + 686
= 44:55. The atomic weight of lanthanum is nearly 3 2 times that of magnesium. The atomic weights of silicium, zirconium, and thorium are 14:8, 22:4, 59, which = 2 :3 : 8 nearly. Those of titanium, molybdenum, tungsten, and tantalium are 24.5, 48, 95, 185 = 1:2 : 4 : 8 nearly. The atomic weight of manganese is 27.6, of uranium 217, which = 1:8 nearly. That of chromium is 28:1, of vanadium 68-6, nearly = 2 : 5. That of phosphorus 31.4 + that of arsenic 75.2 gives 106:6, nearly that of bismuth 106.4. That of palladium is 53.4, of silver 108.1, nearly = 1: 2. Even if some of these relations should be accidental, and disappear when the atomic weights are determined with greater precision, it may, on the other hand, be expected that the greater number of them will, in such case, come out with mathematical exact
RELATIONS BETWEEN THE ATOMIC WEIGuts or SIMPLE SUBSTANCES
AND THEIR SPECIFIC GRAVITIES. The greater the number of atoms of a body in a given space, and the greater the weight of those atoms, the greater must be the specific gravity of the body; hence the specific gravity is the product of the atomic number and the atomic weight; and the specific gravity divided by the atomic weight gives the Atomic number, that is to say, the number of atoms in a given volume. With bodies which contain equal numbers of atoms in equal volumes, the specific gravity must vary as the atomic weight.
1. In Elastic Fluids. The atomic weight of elastic fluids, whether permanent gases or vapours, bears a simple relation to their specific gravity, that of air=1, and pressure and temperature being constant. The following table contains in column A the names of certain elements, in B their tomic weights, in the specific gravities of their gases, in D their atomic numbers obtained by dividing the sp. gr. by the atomic weight; E* gives the reduced atomic number obtained on the supposition that 1 volume of hydrogen gas contains 1 atom of hydrogen, the numbers in this column being the quotients obtained by dividing the several numbers in colu'nn D
by the atomic number of hydrogen = 0.0693. The last column F gives the specific gravities of the gases, that of hydrogen = 1, by which the simple relation between the specific gravity and the atomic weight becomes still more apparent.
According to this table elementary bodies in the gaseous state contain in a given volume either 1.3 or 2 . x or 6 . x atoms.
Heuce they may be divided into the following classes.
a. Hexatomic gas. Sulphur.
c. Monatomic gases. Hydrogen, iodine, bromine, chlorine, nitrogen, mercury.
In compound elastic fluids we also meet with ź, }, š, and L-atomic gases.
When a body assumes the gaseous state, its atoms become surrounded with heat-spheres, whose volumes are as 1 (in the 6-atomic gases); 3 (in the 2-atomic gases); 6 (in the l-atomic gases); 9 (in the 2-atomic gases); 12 (in the atomic gases); 18 (in the }-atomic gases); 24 (in the -atomic gases. Hence the magnitude of the gas-spheres increases in the simple proportion of 1:3:6: 9:12 : 18 : 24. The smaller the gas-spheres of any substance, the greater will be the number of them contained in a given space, e. 9., of the gas-spheres of sulphur 6 times as many as of the gas-spheres of hydrogen, which are 6 times as large. The cause of the different magnitude of the calorific envelopes in different substances is not known.
The last column of the table, in which the sp. gr. of hydrogen = 1, shows that in all monatomic gases the specific gravity and atomic weight coincide, because the sp. gr. of hydrogen which belongs to this class is assumed = 1; also that the sp. gr. of the 2-atomic gases is twice, and that of the 6-atomic gases 6 times as great as the atomic weight.
In order to bring together two gaseous bodies in equal numbers of atoms, equal volumes of the gases must be taken if the gases belong to the same class; but if one of them contains more atoms than the other in the same volume, then a larger volume of the latter must be taken than of the former; e.g., equal measures of hydrogen and chlorine gases because both are monatomic: on the contrary, 2 measures of hydrogen and 1 of oxygen, because the first is monatomic and the second 2-atomic; similarly, 6 measures of lıydrogen gas and 1 of sulphur-vapour, because the former is monatomic and the latter 6-atomic, &c. &c. If it were required