547 87.5 215 Sodium 1437 23 Rubidium. 533 85 4 350 561 152 152, Bunsen 107 1 171119 11911181,Crookes; 11 862, Lamy 671, Marchand and Scheerer; 6·7, Karsten; 6697, Schröder 1144, Berzelius; 1135, Herapath; 1133, Kupffer; 1136, Reich 2008 625 6.25, Berzelius 21 34 984 988, Thénard; 983, Herapath; 9.8, Marchand and Scheerer 312 (liquid) 2'99, Löwig; 2'97, Balard 138 (liquid) (133 about), Faraday 25.6 495 495, Gay-Lussac 34'56 254 254, Bunsen [0985, Schröder 1475 2360 0972 0972, Gay-Lussac and Thénard 243'7 39 281 44'96 0.865 0.865, Gay-Lussac and Thénard از The column headed calculated sp. gr. indicates the numbers which, if used as divisors of the atomic weights, yield the numbers adopted as the atomic volumes of the elements. 958 ATOMIC VOLUMES OF SOLIDS. : instrument is to be used it is to be filled up to the mark o° on the stem with water, with oil of turpentine, or with some liquid which exerts no solvent action on the body. It is then inclined to one side, the stopper removed, and a weighed quantity of the solid under experiment is carefully introduced the stopper is then replaced, and the number of divisions which the liquid is raised in the stem indicates in grains the quantity of water which has been displaced. Thus, if 56 grains of iron (the number of grains corresponding to the atomic weight of the metal) be introduced, the liquid will rise 7'1 divisions in the stem of the instrument, indicating the atomic volume by simple inspection. If the quantity of the substance employed be greater, say three or four times the atomic weight in grains, the rise in the stem, when divided by 3 or by 4, as the case may be, indicates the atomic volume of the body under experiment. The same experiment also furnishes the data for determining approximatively the specific gravity of the body, since the weight of the substance used, when divided by the number of divisions which the liquid has risen (corresponding to the weight of the bulk of water equal to the solid), will, of course, give the specific gravity. Schröder, Kopp, and many of the chemists who have worked upon this subject, have made their calculations upon the oxygen scale of atomic weights; but recently Kopp and others have adopted calculations from the hydrogen unit; both sets of numbers are therefore given in the table to facilitate reference. From the foregoing table, it is apparent that several groups of isometric elementary bodies (that is to say, bodies possessed of equal atomic volume), exist; and that between many of these groups, multiple relations of a simple kind occur; for example : 1. The atomic volume of the group containing cobalt, copper, iron, manganese, and nickel, is double that of carbon, as found in the diamond. 2. The atomic volume of the group containing aluminum, molybdenum, and tungsten, is to that of the iron group as 3: 2. 3. The atomic volume of lead is double that of platinum and its congeners. 4. There are indications of an equality in the atomic volume of the halogens-chlorine, bromine, and iodine; but the specific gravities of these bodies are not known with sufficient accuracy to admit of a satisfactory comparison. That of chlorine is only an approximation, and it was in the liquid form, whereas, iodine, with which it is compared, was in the solid state. 5. It has been supposed that the atomic volume of potassium is double that of sodium; but if this be so, the specific gravities INFLUENCE OF ISOMORPHISM AND DIMORPHISM. 959 of the two metals obtained by experiment must be inaccurate. If that of sodium were 0.99, and that of potassium o'84, the ratio of their atomic volumes would be as 290: 580, or as 23'2: 46'4. (1732) Influence of Isomorphism and of Dimorphism on Atomic Volume.-Kopp has further shown that the coincidence in atomic volume first observed by Dumas in the case of certain isomorphous metals, holds good very generally with isomorphous bodies; so that, when the volumes occupied by equivalent weights of such bodies are compared together, the volumes, allowing for errors of observation, are identical. This law is found to hold good both with elementary and with compound bodies. A close approach to isomorphism in compound bodies does not, however, necessarily indicate the isomorphism of all their corresponding constituents. Zincic sulphate, for example, is isomorphous with ferrous sulphate, but metallic zinc and metallic iron are not isomorphous, nor do they possess the same atomic volume; and indeed, strictly speaking, the salts are not identical in form, for though the crystals resemble each other in their geometrical figure, yet when their angles are accurately measured, considerable differences are detected. The solid volume of the crystallized sulphates of zinc and iron differs but little; the atomic volume of zincic sulphate, according to Filhol's experiments, being 724, and that of ferrous sulphate 73.6, and since so large a proportion of the mass of the salt is in each case made up by substances which are identical, the same general form is preserved in both salts. In the case of dimorphous substances, the specific gravity of the body in one of its forms is greater than it is in the other form; consequently, such substances possess two different atomic volumes. The following table contains the specific gravity and atomic volume of a few dimorphous substances : 960 DISTURBING INFLUENCE OF TEMPERATURE. (1733) Disturbing Influence of Temperature.-There can be no doubt that the atomic volume of a body is a character as definite as is its specific gravity, or its atomic weight; but the determination of its precise amount is opposed by some peculiar and considerable obstacles. One of these arises from the difficulty of accurately determining the specific gravity of a solid, under circumstances which shall be properly comparable. Since the bulk of all bodies varies with the temperature, and increases as the temperature rises, the specific gravity, as taken in the ordinary method, will be liable to variation according to the temperature. This would be of little consequence, however, if the amounts of expansion produced by equal increments of heat were alike in all bodies; but experiment distinctly proves that this is not the case, and the great extent of this variation amongst many of the simple bodies may be seen by the subjoined table: Cubic Expansion of some of the Metals from 32° to 212°. Supposing that the expansion quantity of each of the metals taken in proportion to its atomic weight (as represented by its atomic volume), were in the multiple ratio represented in the sixth column of the table, the cubic expansion should be such as is indicated in the seventh column. The cubic expansion is calculated by multiplying by 3 the linear expansion of the different metals. (1734) 2. Atomic Volume of Compounds.—In a few instances, when solid bodies unite, the resulting compound possesses an atomic volume equal to the united volumes of its components: thus, in the case of sulphide of copper, 16:16 being the atomic volume of sulphur, 7.1 that of copper, 23:26 is that of the sulphide; for it is found by experiment, that the specific gravity of this sulphide is 41, and its atomic weight is 955: now 95'5÷4'1= 23.29. But this simple relation between the bulk of the com ATOMIC VOLUME OF COMPOUNDS. 961 Con pound, and that of its components, is of rare occurrence. densation, however, appears to occur according to certain laws, though they are by no means so simple as those which regulate the act of combination amongst gases. Schröder observed that when from the atomic volume of a series of analogous combinations, such as the oxides, the volume of the metal which each compound contains is deducted, the same number is frequently obtained as a representative of the volume of those constituents which are common to all the members of the class. When from the analogous sulphates, for instance, the atomic volume of the metallic oxide contained in each is deducted, the residue for sulphuric anhydride remains the same. Kopp extended these views, and supposed that he had deduced from them additional arguments in support of the binary theory of salts; but the results of observation, as Filhol has shown (Ann. de Chimie, III. xxi. 429), may be equally well explained upon the older view, and, indeed, even better; for I have found, by a very slight modification of one of the values for sulphuric anhydride, that numbers are obtained with which the results of experiment accord quite as well as with the numbers assumed by Kopp, as will be seen almost immediately. The oxides may be subdivided into four classes, in each of which the oxygen must be supposed to undergo a different amount of condensation. In the first class, the atomic volume of oxygen is assumed by Kopp to be 16, the metal retaining its original volume; in the second and more numerous class, the metal retains its original volume, but that of oxygen is 32; in the third class the volume of oxygen is 64. In the fourth class, assuming the volume of oxygen to be 32, the metals undergo condensation in the act of combining: thus, I find that aluminum, calcium, and strontium are condensed into exactly half their volume. The specific gravity of barium is not known with certainty, but it is probable that it likewise belongs to the same class. The condensation experienced by sodium and by potassium is such, that they occupy very nearly one-third of the volume which they possess in the uncombined form; thus, if the atomic volume of these two metals be divided by 3, we have for sodium 293÷3-98; by observation of the density of soda, it is 102, when combined with oxygen of an atomic volume of 32; and for potassium, 562 ÷ 3=187; whilst by observation of the density of potash it is 184. The tables which follow are based upon those given by Kopp, but they include many new data, and several of the results have been re-calculated from the values more recently assigned to the |