INDUSTRIAL AXD EhTGINEERING CHEMISTRY
March, 1928 y1 = yo
-
[n
+
Pnxn (R
- P)XOl*
This gives the lowest value to which the concentration of solute vapor in the exit gas can be reduced if the oil is brought up to equilibrium with the entering gas. (111) P = r . For this case a t equilibrium y = 2, and it is therefore theoretically possible to have eauilibrium a t all points in the system, provided the capacity of the e q u i p ment is s u f f i c i e n t t o 0 carry out the absorpztion under a negligible Figure 5 driving force. The conditions for the three cases are given in Figure 5, the upper curve corresponding to stripping, the lower to ‘absorption, and the straight line between them to the special
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case of P = T. It is worth noting that in both stripping and absorption one normally operates on the unfavorable side of the equilibrium curve-i. e., it is theoretically impossible to secure equilibrium a t both ends of the operating line. Were one absorbing under conditions corresponding to the upper curve or stripping under those of the lower, the reverse would be true. However, this disadvantage is more apparent than real, because the height of the equilibrium curve corresponding to stripping conditions, secured by raising the temperature and lowering the pressure, far more than comDensates for its unfavorable shaDe. I , and the same is true of the advantages gained by lowering the equilibrium curve for absorption, through decreased temperature and increased pressure. While for many cases of absorption Raoult’s law does not apply, there are important instances, notably the absorption of hydrocarbons in oil, where it is a satisfactory approximation. Furthermore, even in those cases where the deviations are too wide to justify its quantitative use, it none the less gives a clear visualization of the qualitative effects of various factors upon operating results.
Molybdenum Tannage’ Joseph G. Niedercorn A. F. G4LLUN & SONS CO., MILWAUKEE, W1S.
H E analogy between the compounds of chromium and those of molybdenum seemingly becomes more firmly established as the true character of molybdenum is better understood. This consideration gives rise to the conception that salts of tervalent molybdenum should form, with hide substance, unhydrolyzable compounds very similar to those formed in chrome tannage. There are two sulfates of tervalent molybdenum, the purplered and the green. The green sulfate has been assigned the formula M O ~ O ( S O ~ ) ~ the ; ~ constitution J of the red salt is as yet undetermined. Both salts are best obtained by the electrolytic reduction of a solution of molybdic anhydride in sulfuric acid, using a diaphragm cell and smooth platinum electrodes.4 In hydrochloric acid solution molybdic acid is reduced as follows:6
T
Movr+ colorless
MoV+ emerald-green
MolI1+ purple-red
MolI1 olive-green
In sulfuric acid solution the emerald-green salt was not obtained unless the solution was more strongly acid than was desirable for tanning purposes, inasmuch as it would become loaded with sodium sulfate in adjusting the acidity; instead, molybdenum blue, MoaOa(?), was formed as intermediate product. I n solutions nearly neutral the reduction did not proceed beyond molybdenum blue; in strongly acid solution it sometimes stopped a t the red stage. No vivid green solutions, such as those that appear in the reduction of molybdenum salts with zinc in an atmosphere of hydrogen, were obtained. An attempt was made to determine the acidity of the solutions potentiometrically, but this method proved unPresented before the Division of Leather and Geldtin Chemistry a t the 74th Meeting of the American Chemical Society, Detroit, Mich., September 5 to 10, 1927. * Wardlaw, Nicholls, and Sylvester, J . Chem. SOL. (London), 126, 1910 (1924). * Chilesotti, Gal?. chim. itul,, 2, 33 (1903). Wardlaw, Law, and Sylvester, J . Chem. SOL. (London), 123, 969 (1923). Chilesotti, Z . Elekfrochem., 12, 173 (1906).
certain because of the oxidation-reduction potentials which made the hydrogen-ion concentration seem much greater than it really was, especially in the case of the red solution.jj6 According to Chilesotti,’ platinum black exerts a catalytic influence upon molybdenum solutions, causing them to be reduced in the presence of hydrogen and then causing them to be oxidized. Because of the strong reducing action of Note-Oxidation with the evolution of hydrogen takes place immediately upon the reduction of all the metal to what is apparently the tervalent state, and occurs even in an atmosphere of hydrogen.
the solution, indicators could not be effectively used, and therefore the acidities were controlled very inaccurately with the hydrogen electrode, making no allowance for oxidation-reduction potentials. Apparent acidities could be duplicated without difficulty. The green solution turned red upon standing, even if kept in a tightly stoppered bottle; it had no sharp precipitation point, but noticeable amounts of hydroxide appeared a t p H 3 and kept increasing. At pH 9 complete precipitation had not taken place. The solution tanned calfskin well a t apparent pH 2 to 2.5. Probably because of the greater oxidation-reduction potential, the red solution showed a greater acidity than the green (the opposite is true of the corresponding chromium salts), and precipitated sharply a t p H 2.5. It tanned very rapidly a t p H 1-1.5, but a t p H 2 it no longer penetrated into the skin. Both salts yielded a dark brown leather that could be boiled without altering its condition. However, upon standing in the air it gradually lost this property; even then no hydroxide was removed by boiling-the skin merely shrank and hardened. Experimental
A solution was made up by dissolving 40 grams of molybdic anhydride in 54 cc. of boiling sulfuric acid (sp. gr. 1.84) 6 Clark, “The Determination of Hydrogen Ions,” p. 242, Williams & Wilkins Co., Baltimore, Md , 1922. ’ 2 . Elekfrochem., 12, 146 (1906).
INDUSTRIAL AND ENGINEERING CHEXISTRY
258
to which had been added a few drops of nitric acid, and then diluting to 1 liter. The solution was then electrolyzed in a diaphragm cell, using a current density of 8 amperes per square decimeter a t 15 volts. When it had assumed a deep purple-red color, the solution was removed and showed an apparent p H < 0. This was not compatible with the quantity of acid added originally. If the reduction were allowed to proceed to the green stage, the solution would show an apparent pH 0.5, which obviously was not its true acidity, although the figure is somewhat more reasonable than the one preceding. To reduce the acidity, 1 M sodium carbonate solution was slowly added to the green molybdenum solution until apparent pH 2 was reached; in like manner the red solution was brought to pH 1-1.5.
Vol. 20, No. 3
No further neutralization was necessary during tannage; the pieces of skin were simply immersed in the solution and in about 24 hours tannage was complete. Conclusion The fact that tervalent molybdenum salts behave in this manner supports the chemical theory of tannage and indicates that tanning power is dependent upon the chemical properties of the salts involved. Acknowledgment The author is greatly indebted to J. A. Wilson, without whose kind interest and fertile suggestions this work would not have been accomplished.
Migration of Cane-Wax Complex through Stations of a Refinery’ C. F. Bardorf ST. I,A\i’RHSCE SI 0 \ R REFISERIES, LTD.,? I r O S T R E A L ,
N HIS “Report (No. 13) on a Preliminary Inves-
I
C.LSAD.3
Waxlike substances are extracted from refinery sugar liquors, raw sugar, blackstrap, etc., and by comparing the composition of t h e extracts it is endeavored to show t h a t they pass through all stations of a refinery. The methods of gathering t h e wax complex are described and tables show how t h e composition of t h e extracts may vary when passing from t h e raw sugar to the final products, and t o what extent the complex may be retained by Filter-Cell paper pulp, etc. Finally, i n a brief discussion of t h e significance of the data presented, it is pointed out that certain constituents of t h e complex, rather than t h e whole complex, should be considered as influencing refinery products.
tigation of the Colloids of Cane Juice and Molasses,” R. G. W. Farnell gives thirtythree references which convey a fair idea of the general interest and wide field of research that colloidal matter in sugar products of different origins has aroused in recent years. I n the closing paragraph of the report four lines of investigation are indicated, and it is to the third of these-viz., “the examination of the Fax present in juice, sirups, and molasses and its effect on manufacture”-that the data presented herein refer. Indeed, the nature of non-dialyzable substances in raw sugar is, no doubt, directly traceable to methods of defecation and subsequent operations in its manufacture; and in this respect not only is the quantity but also the composition of this wax complex of signiiicance as a factor influencing refinery processes. Through the recognition that this wax complex appears at different stages of refining operations, a series of preliminary ‘expairper& was undertaken. These experiments are necessarily but the “raw material” upon which subsequent investigations may be based. Most of the examinations were made with a view of explaining certain phenomena observed during the refining of the raw sugars listed in Table I. All these sugars were “centrifugals” of approximately 96 degrees polarization, but they exhibited very different qualities, irrespective of color or grain structure, in afhation and press and char filtration Methods of Isolating Wax Complex
For the purpose of isolating the waxlike material in these sugars, and also the sirups and liquors produced from them, three methods were tried.2 1 Presented before the Division of Sugar Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1976 Received September 27, 1927. 2 Farnell, Iiatern Sugar J , 26, 420 (1924).
SoLuTIox-Little need be said upon the possibility of extracting waxlike m a t e r i a l by the solvent action of alcohol, ether, benzene (CsH6), carbon tetrachloride, or ethyl acetate. None of these solvents are of value when acting on the whole raw sugar; most of them dissolve an appreciable quantity of sugar, which cannot be separated r e a d i l y f r o m t h e extract. Furthebore, with the exception of hot acetone and hot alcohol (denatured 96.0 per cent) they are poor solvents of the cane-wax complex. Acetone and alcohol are, however, valuable for fractional separation of the constituents of the wax complex. TRAPPING-This method consists of trapping the finer suspended matter by means of the flocculent precipitates of zinc or aluminum hydroxide or that caused by trisodium phosphate. In this work zinc hydroxide was used. The zinc precipitate settles rapidly, carrying down with it most of the suspended matter at the first addition of the precipitate. This can be washed by decantation, so that after the first three washings the precipitate is fairly free of sugar. The washed zinc hydroxide is then dissolved with a minimum of hydrochloric or sulfuric acid. The suspended matter so separated is treated for further examination. DIALYsIs-This method has proved most satisfactory in that the sugar can be completely diffused and all the colloidal and suspended matter conveniently gathered for subsequent treatment and examination. The diffusion bags were made in 100-cc. test tubes and the collodion was prepared as prescribed by Holmes.s The dialysis of a lot of sugar, in from 20 to 25 bags, each holding about 50 cc. of sirup (30”to 40” Brix), required from 24 to 36 hours. The bags were hung in a trough through which a current of hot water (80” to 85” C.) was flowing a t the rate of about 10 liters per hour. At the end of this time the contents of the bags were free of sugar. Sacks of fish membrane are not very satisfactory. If 3
“Laboratory 3Ianual of Colloidal Chemistry.”
