24 LUMSDEN: THE LIQUID VOLUME OF 111.-The Liquid Volume of a Dissolved Substance. By JOHN SCOTT LUMSDEN. THE following investigation was undertaken in order to obtain some information regarding the volume assumed by a solid, liquid, or gas when dissolved in a liquid on which it exerts no chemical action. It is well known that the values determined for atomic volumes and atomic refractions from experiments made on pure liquids hold with fair accuracy when applied to solids and liquids in solution; and the inference is, that a liquid retairis its own volume when dissolved and that a solid assumes in solution the volume which theA DISSOLVED SUBSTANCE. 25 same weight would have if it existed as a liquid at the same temperature. If that inference is correct, or if it can be proved to vary from exactness in a rational manner, a law of the li.quid volume of a dis- solved substance is revealed and the experimental results here recorded show that there is such a law, which holds, not only for the volume assumed by a solid or liquid, but also for the volume taken by a dissolved gas.A t the beginning of the investigation it was found necessary to exclude from consideration solutions in which water was the solvent, since solution in water is of the nature of combination and is always accompanied by a marked shrinking i n volume ; a further contraction also occurs if the dissolved substance becomes ionised. The first experiments were designed to prove that a dissolved substance behaves as a liquid and does not undergo any sudden change in volume as the temperature is raised above its normal melting point or boiling point.A number of substances of widely different composition were chosen ; these were dissolved in various solvents and the volume of the molecular weight in grams of each substance was measured at several temperatures. A quantity of substance was weighed in a short-necked, stoppered flask, the solvent was added and the flask was reweighed. A pyknometer was filled with the solution obtained in this way by inserting the point of the instru- ment into the flask and withdrawing the liquid, and a similar pykno- meter was filled with the solvent. The pyknometers were then placed together in a thermostat and after remaining a sufficient time a t the desired ,temperature they were removed, dried, and weighed.The capacity of each pyknometer was carefully determined at several temperatures and by interpolation the capacity a t any desired temperature was obtained. All the weighings were corrected to the weight in a vacuum and the densities are referred to water at 4O, thus making the number which expresses the molecular volume represent also the volume in cubic centimetres of the molecular weight in grams of the substance at the temperature given. The molecular volume in solution was calculated by the usual i- - ’ where M is the molecular weight formula : Vm = - D of the substance, D the density of the solution, d the density of the solvent, and s the weight of the solvent used to dissolve the molecular weight in grams of the substance. 2’26 LUMSDEN: THE LIQIJID VOI.CME O F Mol ecu 2 ~ 1 ' Yo Zzt me of Ntcphth ale ne i n To1 uene .2.7935 grams of naphthalene mere dissolved in 19.7216 grams of toluene : sp. fir. Temp. toluclle. 15" 0.8706 25 0.8612 40 0.8476 60 0.8296 so 0.8113 100 0.7931 Sp. v. 0.8885 0.8'791 0.8653 0.8473 0 8287 0-8104 solnt?on. Vol. of 128 g. nnphthalene. T I n solution. As liqiiid. 123.28 - 124.25 - 128.42 130'92 * 131'05 (98'4") 133'64 133'04 t 126.05 (79 .9") * Schiff, A.imcdeii, 1884, 223, 261. f Nasini, Gnxetta, 1885, 15, 84. Molecular Volunie of I'hen ylacetic Acid in Toluene. 3.1889 grams of acid were dissolved in 19.6646 grams of toluene : Temp. 15" 25 40 60 80 100 sp. 91.. toluene. 0.8706 0.8612 0-8476 0.8296 0,8113 0.7931 Vol. of 136.08 g. acid. A sp. 8''. / \ solntion.In solution. As liqnid. 0.8998 119.91 (7 6 '6") 0 '8 9 0 6 120.60 125.50 0*8770 122.04 O*S590 123.84 (86 *2"1 * 0.8405 125.88 i26.41' (89-5") 126.73 0'8223 127-90 -x Schiff, A~~nalen, 1884, 223, 260. iliolecular Yolume of llhynzol iq~. Benzene. 2-0108 grams of thymol were dissolved in 14.1864 grams of benzene : Temp. 15" 25 35 45 55 65 Vol. of 150 g. thymol. Sp. gr. Sp. gr. F A \ 0.8846 0'8943 154.74 0.8742 0'8842 156*01 0-8639 0'8740 157 -50 157'91 benzene. solution. I n solution. As liquid. * ( 49'3") 158.99 (58'3") 159.08 (64") 0.8638 0.8536 0'8432 0'8535 160 -58 0.8328 0.8432 162.26 159.78 * Schiff, Amalen, 1884, 223, 259.A DISSOLVED SUBSTANCE. 27 Jfolecular Volume of Dichlorobenxene in, Carbon Tetrachloride. 2.0677 grams were dissolved in 30.3615 grams of carbon tetra- chloride : Vol. of 146 -9 g.dichlorobenzene. s;). $"'. Sp. gr. A- Temp. CC1,. solation. I n solntion. As liquid. 15" 1 '6039 1.5794 113.93 - 25 1.5845 15608 114'77 - 35 1.5652 1'5435 45 1 *5462 15244 116.33 55 1.5275 1'5065 117.18 65 1.5075 1.4876 117.95 115.48 (5$ 117'63 (63") 118'36 ' Schitf, A?~?inlen, 1884, 223, 263. i I l o l e c d ~ r Voltone of o-iVhrophenol in Chlorofoma. 1.1628 grains of nitrophenol were dissolved in 12.9120 grams of chloroform : Vol. of 139 Q. nitrophenol. 'l'enip. CIECI,. solution. In solution. As liquid. sp. 6'. 81'. gr. r 2. \ 15" 1.4898 1 *4774 102.80 * (35") 106'48 25 1 *4721 1 '4605 103.56 35 1-4531 1 -4423 104'31 (45.2") 45 1.4344 1,4247 105-06 107.38 108'29 55 1.4163 1.4071 105'91 (55") + Schiff, Annalcn, 1884, 223, 263.Moleculur Qolunte of Chloroform in Toluene ; Vol. of 119.4 g. chloroform. Tciiil). toluene. solution. I n solution. As liquid. 4 0" 0'8472 0'9647 82-98 (20") 80.21 * 60 0.8290 0.9427 85.39 (40 ) 83-33 80 0'8105 0'9203 88.02 (60 ) 84.62 * Thorpe, Trans., 1880, 37, 196. Sp. gr. Sp. gr. c A > Moleculccr Volume of Bromine in Carbon Tetrachloride. 3.4716 grams of bromine were dissolved in 28.3596 grams of CCI, : Vol. of 79.96 g. bromine. Temp. CCl,. solution. I n solution. As liquid. 40" 1.5555 1.6379 27'70 26-22 * 50 1.5362 1-6178 27 '98 26'52 60 1.5173 1.5981 28-27 26.83 70 1'4969 1'5769 28-57 - 75 1.4892 1 -5687 28.74 * Thorpe, Trans., 1880, 37, 174. Sp. gr. Sp. gr. c A -I28 Temp. 15" 40 80 120 160 200 220 LUMSDEN: THE LIQUID VOLUME OF Molecukar Volume of Nap?&alene in, Quinoline : Vol. of 128 g.naphthalene. Sp. gr. /- h \ solution. I n solution. As liquid. SP. gr. quinoline. 1,0978 1.0887 123.73 130'34 1-0785 1-0691 126'40 1'0478 1.0378 130.85 (130.7") 1-0150 1.0057 134'61 136.78 (173'8") 141-99 0'9826 0,9735 139'20 0.9489 0.9394 144.93 (193 '6") 143'37 0.9319 0.9234 146'56 (217") 14757 (7G) * Lossen and Zander, Annnlen, 1884, 225, 111. These molecular volumes are represented by curves on the accampanying diagram and the continuity of the curves makes it apparent that with rise of temperature the increase of volume is regular and that no breaks occur at the normal melting points or boiling points of the dissolved substances. Liquids, such as bromine and chloroform, when in solution were raised to temperatures above their boiling points, but their volumes did not nndergo any sudden change ; similarly, solids such as naphthalene and thymol when in solution were raised to temperatures above their melting points, but their curves of volume are continuous ; and in the example given of a solution of naphthalene in quinoline, the change of temperature includes the regions a t which the naphthalene normally exists as solid, liquid, and gas, yet there are no breaks in the curve of volume.I n solution there is, therefore, only one phase, namely, the liquid phase, and a substance in solution a t any temperature behaves as a simple liquid. The next point on which information was sought was the relation between the volume of a pure liquid and its volume when dissolved.The substances employed in the foregoing experiments had in every case been examined by previous workers and their volumes determined in the liquid state a t several temperatures. From these measurements, the molecular volumes were calculated,and the values obtained aregiven in the last columns of the preceding tables and are indicated on the volume diagram by dotted lines. It is seen that naphthalene and phenylacetic acid dissolved in toluene have volumes in solution almost identical with their volumes as pure liquids ; bromine in carbon tetrachloride, thymol in benzene, and chloroform in toluene show greater volumes in solution, whilst nitrophenol in chloroform and dichlorobenzene in carbon tetrachloride have smaller volumes when dissolved. Two liquids may therefore be mixed without any change of volumeA DISSOLVED SUBSTANCE. 29 taking place, but usually mixing is attended either by a small con- traction or a small expansion.Some very accurate experiments on the mixing of carefully purified FIG. 1. Molecular volumes of various substances in solution. 10" 20" 30" 40" 50" 60" 70" 80" 90" 100" liquids are recorded by Young and Fortey (Trans., 1902, 81, 742 and 772; 1903, 83, 45), and by Thorpe and Rodger (Trans., 1897, 71, 367), and in order to indicate the extent of the change of volume30 LUMSDEN: THE IJQUID VOLUME OF accompanying mixing, I: giro the memnrements made by these investigators : Mixtures of Voln1mFs. Tolueiie and etliylbenzenc .................... Eqiiiiiiolt~q1:~r Hexniie and octane ............................. 7 , Carbon tetrachloride and benzene ............I , 7 ) ,, methyl alcoliol 1 , Ethyl acetate and ethyl propionate ......... 7 9 Benzene and tolnene ............................. > 7 Chlorobenzene aiid bromobenzene ........... ¶ I 9 , ... Beiizene and ethyl alcohol ..................... 31 per cent. alcohol Ether and chloroform ........................... 84 per cent. chlorofoi 111 Carbon disulphide and methyl iodide ..... 78.4 per cent. methyl iodide Il1stc~:Wl of Ob- 100 C . C . servers. 99.966 Y. & F. 99.966 ), 99.849 ,, 99'820 ,, 100*015 ), 100'161 ,, 100~000 ), 100~000 99.185 T. k R. 100*Pl7 ,, F I G . 2. M o l e c d a y voluwic of nnplzlhalelie iiz quinolinc. 150 i$ % 140 $ T5 u 5 130 2 120 0" 5 0" 100" 150" 200" I n no case do these measurements by Young and Portey indicate a change of volume on mixing as great as one-fifth of 1 per cent., and according to Thorpe and Kodger, a mixture of the two dissimilar liquids, ether and chloroform, is accompanied by a change which does not exceed 1 per cent.Referring again to the volume diagram it will be observed that the curve indicating the volume of the pure liquid at different temperatures runs parallel with the curve showing the volume of the substance in solution. One learns from this that whatever change takes place on mixing two liquicls a t one temperature, the same amount of change will take place on mixing them at another temperature. It also leads to a second important generalisation: if the volume of a pure sub- stance over the range of temperature when i t is liquid can be repre- sented by a curve which coincides with or runs parallel to the volume curve of the substance in solution, then, as the trend of the solution curve is regular, it may safely be concluded that if the pure substance remained liquid, its volume, at any temperature below or above the temperature of the normal liquid state, mould be represented by a point on an extension of the liquid volume curve continued parallel to the curve of the volume in solution.A DISSOLVED SUBSTAKCE.31 It follows directly from this that, if the two curves coincide, the conditions of the law of liquid volume are fulfilled, and the law may be stated thus : When cc substance in tibe liquid state dissolves without change of volume, tlhe same substance when in the stcde of solid OY US wild, when dissolved in the same solvent, chccnge to the volume which the same weight of it would have if it were a pure liquid at the temperature of solution.Should, however, the two curves run parallel, the deviation from the law may be expressed as follows : When a substtcnce in the liquid state, on being dissolved, changes in volume by cc certaiiz amount, the same substunce, when in the state of solid or gas, will, when dissolved, assume a volume which difers fyom tlhe volume which it would have if liquid at the sccme temperatum, by the same amount. These two definitions may be combined in a general statement: the volume occupied by a substance in solution is the same as that of the pure substance at the same temperature if it were liquid; or if it is not identical, it deviates by the same amount at all tempera- tures.When two pure liquids were mixed it was seen that the change in volume was very small, and the deviation from conformity with the law of liquid volume can in no instance be considerable, yet it seemed of interest to inquire further concerning the cause of the change of volume when two liquids are brought together. The cause must be looked for in the distribution of the particles of the solute throughout the solvent producing an adjustment of spacing, since it might be expected that molecules differing in size, shape, and weight, when mixed, will arrange themselves so that the new volume is not exactly the sum of the volumes added. The change, moreover, cannot entirely be ascribed to the dissolved substance; the solvent must also be affected, and if that is the case it is evident that the true volume which a substance occupies when in solution cannot be measured, since the amount of change of each constituent is unknown. From these considerations it was reasonable to predict that alteration of the amount of solvent and the employment of different solvents would give different values for the volume of a dissolved substance, and the following experiments were made to obtain information on these points.Solutions were prepared containing approximately 5, 10, and 20 molecules of naphthalene in 100 molecules of benzene, toluene, xylene, and carbon tetrachloride. Four pykno- meters were employed; one to contain the pure solvent, the others the three solutions made with this solvent.The pyknometers were heated in a thermostat to 1 5 O , removed a t the same time to ensure that they were all a t exactly the same temperature, dried, and weighed :32 Solvent. Benzene Toluene.. .... Xylene ...... Carbon tctra- chloride LUMSDEN: THE LIQUID VOLUME OF Mols. naph- thalene. i 5 10 20 5 10 20 5 10 20 5 10 20 Naph- thalene in grams. 2.4151 2.3258 2.0620 2.0382 2.1583 2.2576 1-9115 2.0811 3,8963 2,1084 2.7271 5.4420 Sol vc n t in grams. 32.0184 149250 7.0862 29'7285 15.8576 7'6144 30.8078 16'7844 17.7555 54'9772 32.8754 36 '236 3 sp. gr. solvent. 0.8848 Y > 7 ) 0.8712 7 ) 7 7 0.8678 9 ) > 9 1.6043 7 ) 9 ) Sp. gr. solution. 0.8938 0.9025 0.9150 0'8802 0.8883 0'9046 0.8761 0-8836 0.8940 15741 1.5425 1'5006 Vol.of 128 g. naph- thalene. 123 '90 123'63 123'48 123'43 123.30 123'17 123-88 123'69 123.55 121.23 121-46 121.98 These molecular volumes of naphthalene, calculated as before on the assumption that each solvent retains the volume it has in the pure state, show that there is in solutions in benzene, toluene, and xylene a distinct diminution in volume with increase of concentration, whilst in carbon tetrachloride the volume becomes greater as the amount of solvent decreases. Several experiments with carbon tetrachloride gave the same result : a diminution in the volume of the dissolved substance on dilution. The cause of these changes will be discussed later on. An experiment was then made in order to find the change in volume of the dissolved substance when different solvents were used. Solutions containing approximately 10 molecules of naphthalene to 100 molecules of benzene, toluene, xylene, and carbon tetrachloride were prepared, these were heated a t 154 removed from the bath at the same moment, and weighed : Naph- Vol.of thalene. Solvent Sp. gr. Sp. gr. 128 g. naph- in grams, in grams. solvent. solution. thalene. Benzene ..................... 2-8556 19'7194 0.8847 0'9014 123.52 Toluene ..................... 2.6164 25.8188 0.8708 0.8837 123.55 Xylene ..................... 2.3361 19'3979 0.8679 0-8832 123.67 Carbon tetrachloride ... 2.2266 27'4185 1.6043 1.5421 122.57 The volume of naphthalene is seen to be nearly the same in benzene, toluene, and xylene, but there is a great diminution when carbon tetrachloride is the solvent, These experiments prove that the volume occupied by a substance in solution a t any given temperature alters with the solvent employed and also wifh the concentration of tho solution. The foregoing results enable one to form a conception of what takes place when two liquids are mixed, If a pure liquid is a collection of like molecules which are i nA DISSOLVED SUBSTANCE.33 constant motion jostling each other and changing their direction and motion a t every moment, and that to permit of this jostling there are spaces between the molecules, then the question arises : is the inter- space per molecule at the same temperature the same for each liquid3 Kopp did not recognise the existence of interspaces, and in the atomic volumes deduced by him are included atom and space, and the sum of the atomic values make up the whole volume of the liquid ; but accord- ing to Horstmann and Traube there must be added to the sum of the values which they assign t o the atoms a co-volume of 25.9 C.C.a t 15' in order to obtain the molecular volume, and this co-volume has a. higher value as the temperature rises. Now it is very improbable that the molecular interspaces in different liquids should have the same dimensions. The molecules differ in size, shape, and weight, and any value for the co-volume must be an average number from which the real value may in any given case differ considerably. If, however, the co-volume be different in different liquids, then, when two liquids are brought together, an adjustment of the dimensions of the interspaces will sufficiently account for the change in volume.With regard to this adjustment, little can be inferred from the size and shape of the molecules, but considering only their mass, the direction of the change of volume may in many cases be explained. It was seen that when naphthalene was dissolved in carbon tetra- chloride the volume was smaller than when the solvent was benzene, and that, whilst in carbon tetrachloride the volume diminished on dilution, in benzene the volume was greater as the amount of solvent was increased. When the molecules of naphthalene were introduced amongst the heavier molecules of carbon tetrachloride they would be subjected to greater pressure than if they existed as liquid naphthalene, since the mass attraction between the molecules of carbon tetrachloride is greater than between naphthalene molecules.This cause would lead to a diminution of volume. At the same time the carbon tetrachloride molecules would be separated from each other by the intrusion of the naphthalene molecules ; their mutual attraction would be diminished and expansion would result. The latter action must be the smaller since the experiment showed a contraction on mixture. When more solvent was employed, the separated naphthalene molecules would be subjected to still greater attraction by the heavy carbon tetrachloride molecules and thus prcjduce the diminution which was noticed on dilution, I n the case of naphthalene in benzene, the dissolved molecules are the heavier, they would be under less pressure than if in liquid naphthalene, and this would permit expansion; at the same time the 'VOT,.XCI. D34 THE LIQUID VOLUME OF A DISSOLVED SUBSTANCE. naphthalene molecules would be separated from each other, their mutual attraction would be diminished, and further increase of volume would take place. On adding more solvent the naphthalene molecules would become still more widely separated, their attraction for each other mould again be lessened, and the expansion which was noticed on dilution mould be brought about. Observed changes in volume may thereFore in many cases be accounted for by the mass attraction between the molecules of solvent and solute, but the shape and size of the molecules which are brought together must also affect the adjustment.Speaking generally, when the molecules of two substances resemble each other in size, shape, and weight, there will be little change on mixing, but when there is marked difference in the structure and weight of the molecules a con- siderable change may be expected. The following is an illustration: methyl iodide was dissolved in carbon tetrachloride and in benzene and the molecular volumes deter- mined : Vol. of wt, of 141.97 g. methyl Wt. or Sp. gr. Sp. gr. methyl Solvent, iodide. solvent. solvent. solution. iodide. Benzene ..................... 10.0459 26.5893 0.8847 1.0607 63'37 Carbon tetrachloride .., 6.8050 39.5385 1'6043 1.6778 62.09 ............ - 2'2924 - 61-93 Methyl iodide - The volume of the pure methyl iodide is seen to differ very little from its volume in carbon tetrachloride, but the increase in volume is very marked when solution is in the much lighter liquid benzene.One point in the preceding investigation demands notice: it was assumed as true that the curve of the volume of the subjtance in solution coincided with or ran strictly parallel to the curve of volume of the pure substance. The experimental results indicate that this is the case, and the examination of some measurements made by Thorpe and Rodger (Trans., 1897, 71, 367) on the densities of mixtures of carbm tetrachloride and benzene and carbon disulphide and methyl iodide leads also to the conclusion that when definite weights of two liquids are mixed the amount of change of volume which occurs a t one temperature is the same as the change a t another temperature. But it is improbable that any such regularity shonld hold ; for when two liquids have different rates of expansion the amount of change of vdume on mixing must vary somewhat with the temperature. As this variation has not been experimentally noticed, one must conclude that it is very small, more especially when the dissolved substance bears no great proportion to the total volume, and it cannot be of sufficient- magnitude t o invalidate the law of liquid volume which is based on the parallelism of the volume qurves.THE INFLTJENCE OF LIGHT ON DIAZO-REACTIONS. I. 85 In the foregoing discussion, proof has been adduced that the true volume of a dissolved substance cannot be known, and that the volume varies with the solvent and with the concentration of the solution ; but it has also been shown that the change i n volume when two liquids are mixed is very small, and that the volume assumed in solu- tion by a solid, liquid, or gas is never far removed from the volume that the same weight would occupy if liquid a t the same temperature. The law of the liquid volume of a dissolved substance is therefore seldom strictly accurate, but it deviates so little from the truth that it deserves a definite position as a guide when dealing with problems relating to solutions in liquids where dissociation cannot take place. UNIVERSITY COLLEGE, DUNDEE.