SOLUBILITY OF MANNITOL, PICRIC ACID, AND ANTHRACENE. 1217 CXIII.-The Solubility of J4annitoZ, Picric Acid, and A nthracene. By ALEXANDER FINDLAY. IN connection with another investigation dealing with a method of extrapolating the solubility curve of a substance, it became necessary for me to determine the solubilities of one or two substances at differ- ent temperatures and in different solvents. The substances and solvents chosen were: mannitol in water, picric acid in water and in benzene, and anthracene in benzene. It has recently been shown by the author (Proc. Roy. Xoc., 1902, 69, 471) thatif the solubility of a substance be determined at two, or, better, at three different temperatures lying fairly wide apart, the entire solubility curve can be calculated with a fair degree of accuracy by comparison with a known solubility curve (6 comparison curve '), by VOL.LXXXI. 4 M1218 FINDLAY: THE SOLUBILITY OF means of the relationship T,/Z”, = T2/P2 + c(t‘ - t), where T./T’, and F2/T2 are the ratios of the absolute temperatures at which the two substances have equal solubilities, c is a constant, and t’ and t the temperatures a t which one of the substances has the two values of the solubility in question. This relationship, which is analogous to that shown by Ramsay and Young to hold for the vapour pressures of substances (Phil. Mag., 1886, [v], 21, 33), may also be made use of even when the solvents are different. The solubility of the above- substances was determined at several temperatures between 25’ and 60’. From the values so obtained, the solubility at temperatures below 25’ and above 60’mas calculated by comparison with known solubility curves in the manner previously given by the author (loc.cit.). From theoretical considerations,* it is best to choose as the comparison curve one which is similar in form to the solubility curve of the substance in question. For the purpose of extrapolating the solubility curves of mannitol and of picric acid in benzene, the solubility curve of potassium chlorate, constructed according to the values of the solubility obtained by Gay-Lussac (Arm. Chim. Phys., 1875, [v], 11, 314) and by Tilden and Shenstone (Trans., 1879, 35, 345) was employed as comparison curve. The solubility curve of CaCrO,,$H,O as determined by Mylius and v. Wrochem (Bey., 1900, 33, 3639) was employed in order to calculate the solubility curve of picric acid in water, and the latter curve then used as the comparison curve for extrapolating the solubility curve of anthracene.Although, therefore, only those values of the solubility lying between the above limits of temperature can be regarded as experimentally determined, it appeared to be worth while to give the extrapolated values as well, since they may be taken as sufficiently accurate for all practical purposes at least. The figures given in the following tables were read from curves con- structed according to t6e above method, and the solubility is expressed both in grams of substance in 100 grams of solvent (percentage solu- bility), and as number of gram-molecules or moles of substance in 106 moles of solvent (percentage molar solubility).The vdues enclosed in brackets were determined experimentally. Solubility of Mannitol ilz Water, No complete set of solubility determinations has been made in the case of mannitol, but the following values of the percentage solubility have been found at isolated temperatures: 15.6 per cent. at 18’; 18.5 per cent, at 23‘ (Bertbelot, Ann. Chim, Phya., 1856, [%I, 47, * A theorotical discussion of the above relationship will appear ahortly in the Zeihchr~t far physikalische Chemie.kiNNiTOL, PlCRIC ACID, AND ANTaRACENE. 1219 361); 13.0 per cent. a t 14O (Krusemann, Bw., 1876, 9, 1467) ; 16.07 per cent, at 16.5O (Erlenmeyer and Wanklyn, Trans., 1862, 15, 456). The following are the values of the solubility determined experi- mentally and calculated by the above method : Percentage solubility.Temperature. Percentawe molar solubi'li ty. 0" 6 10 15 20 (24 ' 5 ) 25 30 (35.8) 40 50 (50.8) 60 70 80 90 100 7 *59 9-41 11.63 14.38 17-71 (20.96) 21 *39 25 '40 (29 -93) 35-40 47'01 (46'69) 60.01 74.50 91-50 110.8 133'1 0.75 0.93 1.15 1-42 1.75 (2.07) 2-11 2'51 (2'96) 3.50 4 *65 (4'63) 5 94 7-35 9 '04 10-96 13.17 Pic& Acid in Water. The solubility of picric acid in water was determined many years ago by Marchand (J. pr. Chem., 1855, 64, 91). As, however, the method employed was precipitation by strong acids, it appeared advis- able to redetermine the solubility by titrstion with barium hydroxide, using lacmoid as indicator. The values obtained are practically identical with those found by Marchand between the temperatures of 15O and SOo, but the value of the solubility at 5*, as given by Marchand, is almost certainly too low, The solubilities as newly determined and calculated are as follows : Temperature.Percentage solubility. 0" 6 10 15 30 25 (28.5) 1-05 1.07 1 . l o 1.16 1 -22 1.37 (1.42) Percentage molar solubility. 0 ,082 0 '084 0 *086 0'081 0'096 0.108 (0 -11 2) 4 M 21220 SOLUBILITY OF MANNITOL, PICRIC! ACID, AND ANTHRACENE. Temperatare. Percentage solubility. 30 (38.4) 40 (44'6) 50 60 70 80 90 100 (58.7) 1 *55 ( 1 -90) 1 '98 (2.17) 2 '53 (3.14) 9.17 3 '89 4 '66 5'49 6 -33 Percentage molar solubility. 0'122 (0.149) 0-156 (0.170) 0.199 (0.247) 0-249 0.306 0'366 0.432 0'497 Picric Acid in, Benzene. The only statement I have been able to find regarding the solubility of picric acid in benzene is that at the ordinary temperature benzene dissolves 8-10 per cent.of picric acid (Beilstein). The following are t h e newly determined and calculahed values : Temperature. 5" 10 15 20 25 (26 '5) 35 (38.4) 45 55 (58.7) 65 75 Percentage molar soliibili ty Percentage solubiiity. 3 9 0 5 '37 7.29 9 '56 12-66 (13 '51) 21 -38 (26.15) 33'57 50'65 (58'42) 71.31 96-77 1'26 1'83 2.48 3-25 4 '30 (4'60) 7 *26 (8'8s) 11'40 17'21 (19 -8.7) 24.20 3292 Anthracene in Benzene. According to Versmann (Jahresber,, 1874, 423), the solubility of anthracene iri benzene is 1.661 per cent. at 15O, a value rather greater than that which I have found. The complete solubility curve is re- presented by the following figures :McCRAE : DI-SEC.-OCTYL TARTRATE. 1221 Temperature. 5" 10 15 20 25 30 40 (44 '6) 50 60 70 80 (26%) (35'4) Peroen tage solubility. 0.979 1,118 1.532 1'830 (1'951) 2-175 (2 -7 7 3) 2-987 (3'368) 3.928 4.941 6.041 7-175 ' 1'296 Percentage molar solubility. 0.429 0-491 0.567 0.673 0'803 (0.856) 0.954 (1 *213) 1-312 (1'473) 1,727 2.164 27349 3-143 CHEMICAL DEPARTMENT, UNIVEKSITP COLLEGE, LONDON.