330
ANALYTICAL CHEMISTRY
Table 11. Effect of Time of Heating a t 70" C. on Development of Color Complex i n Solutions Containing 3 P.P.M. of Molybdenum Time of Heating, Minutes 10
Light Transmittancy,
70 20 5
20
20.5
20 3 20.3
30 40 50
20 .5 20.3
60
rapid fading is still encountered at concentrations of 1 p,p.m. of molybdenum. The acetone reduction method has given color stability a t concentrations up to 20 p.p.m. of molybdenum for a period of 48 hours. As in previous methods, the acidity of the solution in Tvhich the molybdenum determination is carried out must be carefully controlled when acetone is used as the reducing agent. I t was found that the final solution should be betneen 1.2 and 2 S in respect to hydrochloric acid or other nonoxidizing acids in order to obtain accurate results. This is essentially the same as determined by Hurd and Allen ( 2 )using stannous chloride. Iron is the only interfering element that has been encountered by the authors in their experimental work. However, i t is assumed that elements interfering with the determination of mo-
lybdenum as the thiocyanate by other reducing methods n ill also interfere with the acetone reduction. Grimaldi and Wells ( I ) have devised a method for eliminating the interference of tungsten and vanadium. They have also found that phosphates interfere with the color reaction when tungsten is present in appreciable amounts and that large amounts of nitrates cause excessive color fading. Table I1 compares transmittancy values obtained after various periods of heating during the reduction process. ,Inexamination of the table seems to indicate that heating for 10 minutes is sufficient for color development. I t is recommended that heating be continued for 20 minutes to ensure full color development. This allows for the reduction of small amounts of ferric iron, and also allows for a range of temperature> fiom GO" to 70" C. during the period of heating. The temperature of the solutions a t the time of reading may vary from 15' to 40' C. without affecting the transmittancy values. Considerable variations in room temperature are, therefore, allo\vable. LITER4TURE CITED
(1) Grinialdi, F. S.,and Wells. K. C., ISD. EXG.CHEM.,A s ~ r , ED., . 15, 315 (1943). (2) Hurd, L. C., and Allen, H. O., Ibid.,7, 396 (1935). R E C E I V E .luguet D 1 , 1949. Contribution 411, Department of Agronomy, Kansas Agricultural Experiment Station
Estimation of Solubility of Solids in Liquid Ammonia and Liquid Sulfur Dioxide GEORGE W. WATT, WILLIAM A. JENKINS, AND CECIL V. ROBERTSON C'niversity of Texas, Austin, Tex.
A convenient and rapid method for the estimation of the solubility of solids in liquefied gases is described, and data therehj- obtained are compared with earlier results obtained by other methods. Solubility data at 25" C. for sodium chloride and rubidium chloride i n liquid ammonia, and sodium iodide, potassium bromide, and twelve alkaline earth halides in liquid sulfur dioxide are given.
C
ONSIDERSBLE effort has been expended in the develop-
ment of methods for the determination of the solubility of solids in liquefied gases in general and liquid ammonia in particular (1, 5-5, 8-12). All the methods thus far employed are characterized by more or less elaborate equipment and involved manipulative procedures designed to provide highly accurate rcsults. In connection with certain work in progress in these laboratories there has arisen the need for a simple and rapid method for the estimation of the solubility of a \vide variety of solid compounds in solvents such as liquid ammonia and liquid sulfur d i o d e . For these purposes i t is usually sufficient to know the relative order of magnitude of the solubilities. Accordingly, attention has been directed toward the development of a method characterized by its simplicity and rapidity of application. EXPERIMENTAL
Materials. Commercial liquid ammonia was dried and dispensed as described by Johnson and Fernelius (7). Sulfur dioxide from a commercial cylinder was dried by passing the gas through concentrated sulfuric acid, then through phosphorus pentoxide. The gas \vas condensed in a trap cooled with dry ice and acetone,
and subsequently distilled into the tulles used in the solubility determinations. -411solids used in solubility determinations were prepared and/ or purified, dried, and analyzed ( 11 ) before use. Procedure. A weighed sample of the solid (approximately 0.1 gram) is introduced into one end of a glass filter tube about 18 em. in length, with a n inside diameter of 5 to 10 mm., and with a fritted-glass disk (porosity C or D, 2 ) a t the mid-point. This end of the tube is sealed and cooled, and the tube and its contents are weighed. The tube is flushed out with the anhydrous gas, after which the open end of the tube is attached to the source of anhydrous gas. The end of the tube containing the solid is immersed in a dry ice-acetone bath at a temperature of approximately - 7 5 " C. and a suitable quantity of solvent (0.8 to 1.0 gram) is condensed on the solid sample. The open end of the tube is then sealed off under conditions that permit determination of the weight of the glass removed in making the seal. (This is done by use of a weighed glass rod, determination of the weight of rod plus glass removed, and getting the weight of the latter by difference. The net weight loss involved in this procedure has been found not to exceed 0.8 mg. and is usually of the order of 0.4 mg.) The sealed tube is allo\\-ed to warm to room temperature, weighed, and agitated in a thermostat (25.0' * 0. I ") for 48 hours. The tube is removed from the thermostat, inverted, and centrifuged at 2000 r.p.m. for from 3 to 5 minutes, thus effecting a separation of the saturated solution and the excess undissolved solid. The end containing the saturated solution is cooled to
331
V O L U M E 22, NO. 2, F E B R U A R Y 1 9 5 0 -75', and the other end is diavr-n out to a fiiie capillary through which the solvent is allowed to escape. Thereafter, the tube is evacuated at about 10-3 nun. of mercury for from 1 to 2 hours. This procedure permits one to determine the weight of solute in the saturated solution by (1) chemical analysis, (2) removal of that portion of the tube which contains the sample of the solid that n a s dissolved, and determination of its >\eight before and after removal of the solid, or (3) the similar determination of the weight of excess solid, and the weight of the dissolved portion by diffei tanre. All three methods have been employed; although they lwd to substantiall!. the same results, the second is pref ~ l r e dfiom the standpoint of rapidity and simplicity. The first method must be used if it IS desired to establish the composition of solvates or the absence of solvol>tic reactions. The weight of solvent may be measured by (1) determination of the n eight of the tube assembly before and after introduction of the solvent and application of the correction for the ueight of glass removed, (2) determination of the n-eight of the tube assembly before and after evaporation of the solvent, or (3) collection and subsequent determination of the solvent volatilizede.g , collection of ammonia in standard hydrochloric acid, folloned by titration of excess acid. IIethods 1 and 2 gave results that were in consistently good agreement, vheieaq method 3 proved to be the m w t time-consuming and the least reliable; method 1 is P I C fer] ed Solubility of Sodium Chloride in Liquid Ammonia. Data from six independent determinations of the solubility of sodium chloride led to a value of 4.2 * 0.2 grams of sodium chloride per 100 grams of ammonia. Solubility of Rubidium Chloride in Liquid Ammonia. Four measurements gave a value of 0.22 * 0.03 gram of rubidium chloride per 100 grams of ammonia. Solubility of Sodium Iodide in Liquid Sulfur Dioxide. The solubilitv v a s found to be 2.1 + 0.2 grams of sodium iodide Der 100 grams of sulfur dioside (six measui~ements). Solubility of Potassium Bromide in Liquid Sulfur Dioxide. Five determinations gave a value of 0.38 * 0.05 gram of potassium bromide per 100 grams of sulfur dioxide.
Table I. Salt
Solubility of Alkaline Earth Halides in Liquid Sulfur Dioxide a t 25" C. Solubility, C. Salt/100 G. SO? 0.08 0.02
1
0.02
+ 0.01 10.2
1.8
0.01
0.01
0.01 0.02
