March , 1923
INDUSTRIAL A N D ENGINEERING CHEMISTRY
265
The Electrophoresis of Chromic Solutions’ By F. L. Seymour-Jones DEPARTMENT O F CHEMISTRY, COLUMBIA UNIVERSITY, NEW YORK,N. Y.
R
-
ECENTLY, F. C. A recent the0r.y of chrome tanning postulates the existence of t i o n corresponding to trivalent chromium in a negatioe ion as the actioe tanning agent. C r ( O H ) (sod) and CrsThompson and W. R.AtkinZhave ten(OH)ds04)4. They found EIectrophoresis experiments on normal and basic solutions of chromic tatively suggested that in no chromium in that porchloride, sulfate, and chrome alum show that such a negatioe comtion migrating to the anode. chrome liquors as used in plex exists only in basic sulfcte solutions, and not in solutions of the Their work dealt with a tannil%& that Part of the chloride or alum. Since the basic chloride solutions tan, the theory special chromic solution, ChromfUm is resPo11cannot be of general application, but it was one designed to sible for tanning is present offer the possibility of the as a negatively charged complex, and they adduce evidence that such a complex exists formation of chromosulfates. With a view to testing the theory, electrophoresis experiin the case of chromium sulfate solutions. The critical test for its existence must be that of electrolysis or electrophoresis, ments were carried out with a number of chromic solutions. which would show the presence of either negatively charged A U-tube, provided with a stopcock in each arm a little above complex ions containing chromium or of negatively charged the bend, was used. The chromic solution was placed in the complex chromium colloidal particles. They cite work by bend, below and up to the top of the stopcock. Above this Bassett3 and Ricevuto4 that anodic migration occurs in such an approximately 0.05 M solution of sodium sulfate was placed. The U-tube was connected by stoppers with elecsolutions. For this theory to be acceptable, necessarily all solutions of trodes in small distilling flasks, copper in saturated copper chromic salts capable of tanning must contain this complex, sulfate serving as the cathode and platinum in saturated unless it be possible for chromic cation to be taken up by the sodium chloride as the anode. Diffusion of these solutions hide and changed to a negative complex thereon, which is was stopped by cotton-wool plugs. The ordinary house current, 110 volts, d. c., was used, passing through a lamp iinproba ble. Bassett3 electrolyzed solutions obtained by the reduction filament to reduce the amDeraae to a convenient amount. of potassium bichromate with sulfur dioxide, in which the The results are shown in Tible 1. chromium was present as a mixture of 94 to 95 per cent CrzTABLEI (S04)3and 5 to 6 per cent Cr2(Sz0&, together with K2S03. No. MIGRATION SOLUTION COMPOSITION Both to anode and t o 1 NazCrzOr reduced 2 3 9 . 9 g. CrzOa per liWith fresh, dilute solutions barium chloride and ammonium cathode ter. All excess Son with Son, 13 mo. hydroxide gave no precipitate in the cold, an indication of removed old T o cathode only 2 0 . 2 M , cold, green Crz(SOa)a, fresh the absence of sulfate and chromic ions. Bassett assumes To cathode only 0 . 2 M , green 3 No. 2 heated and the presence of complex chromosulfates of the type cooled ~ ~ $ > C r z ( S 0 4 ) , . When fresh green solutions containing- a slight excess of sulfur dioxide were electrolyzed under dilute sulfuric acid, a green boundary moved anodically and a violet boundary cathodically. With lapse of time the anodic migration decreased in speed, and after standing over night ceased altogether. The cessation of anodic migration on standing is important to the theory in that it implies the breaking up of the negative complex to potassium sulfate and sulfite and chromic sulfate, and consequently the absence of chromium in a negative complex in ordinary chrome liquors, Further, if the green solution is due to chromic anion and the violet to chromic cation, pure violet solutions should not tan. Ordinary violet solutions certainly contain some proportion of green chromic ion, but Burtons has shown that violet chrome solutions actually tan more rapidly than the green. Ricemto4 worked on chrome alum, but his conclusion, that chrome tanning is possible only in alkaline solution, obviously deprives his results of value. T. W- Richards and F. Bonnet6 tested the formation of complex negative chromosulfate complexes. They used green chromic sulfate solutions, freed from acid by shaking with chromium hydroxide, and of the approximate composi1
Presented before the Division of Leather Chemistry at the 64th Meet-
i n g of the American Chemical Society, Pittsburgh, P a , September 4 to S, 1922 2 J . Soc Leather Tiades’ Chem , 6 (1922), 207. J. Chem. SOC.(London), 85 (19031, 6 9 2 . 4 K o l l o t d - 2 , 3 (1908), 114 5 J. SOC.Leathev Trades’ Chem , 4 (1920), 205. 6 Proc A m Acad Arts S c i , 39 (1903),1; See also Z p h 2 s i k C h e m , 47
(1904), 29
4
No. 3 plus NaOH
5
”Tanners’ Zhrome crystals, fresh “Tanners’ Ehrome crystals, 34 mo. old CrCla plus NaOH, fresh, heated and cooled
6
7
8 9
10
Chrome alum, fresh No. 8 heated and cooled N o . 9 plus NaOH
Basicity corresponding to Cr(0H) (Sod Basic sulfate. 160 g. crystals per liter 166.5 g. CrzOt per liter
Both to anode and to cathode Both t o anode and to cathode Both to anode and to cathode
Heated with a little T o cathode only CrCla to dissolve. Basicity corresponding t o Cr(0H)Clz. 45 g. CrCb per liter To cathode only 0 . 2 M , cold violet To cathode only 0.2 M , green Basicity corresponding to Cr(0H) (SO4
T o cathode only
Where there was anodic migration, it appeared to be of a pure green color, while the cathodic migration was of a bluish green hue. The basic chromium chloride solution, wliich,showed no anodic migration, was used to tan some hide powder, which it did quite normally. One-bath chrome tanning in practice is carried out in solutions of chromic salts rendered basic by the addition of soda. Chromic sulfate, either as chrome alum or by reduction from bichromate, is usually used, together with neutral salts. Add to this the fact that chromic salts exist in green and violet modifications, and the equilibrium in such a solution is obviously very complicated. Thompson and Atkin’ in their theory of chrome tanning postulate the presence of a negatively charged complex containing chromium in all chrome liquors. The hide collagen in chrome liquors, which have an acidity of from [H+] = to is positively charged. They consider, therefore, that chrome tanning is brought about by the neutralization of these opposite 7
Lac ai
INDUSTRIAL A N D ENGINEERIATG CHEMISTR.Y
266
charges and the resulting combination of the chromium and the collagen. But, as has been shown, all chrome liquors capable of tanning do not contain this negatively charged chromium complex, and consequently this theory cannot hold generally, if indeed at all. That a negatively charged chromium complex exists in certain basic chromium sulfate solutions is established, but that it is responsible for tanning has not yet
Vol. 15, No, 3
been proved. It is proposed to investigate the chemical nature and the tanning properties of the chromium-containing, negatively charged complex, as time and opportunity permit. ACKNOWLEDGMENT The writer's thanks are due to Prof. Arthur W. Thomas for his kind advice and criticism in the course of this investigation.
A New Absorption Bottle for Carbon Dioxide and Moisture' By William E.Morgan COLUMBIA UNIVERSITY, NEW YORK, N. Y.
HE SUBJOINED sketch illustrates an absorption bottle for moisture and carbon dioxide determinations, which has been found very convenient in organic chemistry work a t Columbia University. The dominant aim in designing this new bottle was to retain the advantage of employing a solid absorbing agent, such as soda lime, without undue complication of manufacture and consequent high-selling price, or excessive weight of container and consequent inconvenience and inaccuracy in weighing. The simplicity of the design is manifest. The weight empty is somewhat under 50 g., which permits filling two-thirds with moist soda lime and one-third with calcium chloride without exceeding generally a filled weight of 80 g.; filled with calcium chloride it is generally less than 70 g. I n order to charge the bottle for carbon dioxide absorption, it is set, bottom up, on its flat top, the requisite amount of soda lime is introduced, a cotton or perforated rubber diaphragm is inserted, if desired, and the calcium chloride added. The ground joint a t the base is greased, the cup base adjusted, and the bottle, when inverted, is ready for use. The gas current is led in a t the top, and passes out through the long tube embedded in the charge. Two combustions can always be made with such a filling, and checks may be obtained even when the charge materials have remained in contact for several days. For example, on the same filling the following results were obtained a t this laboratory:
T
Date November 21 November24
the soda lime rather than inside a tube surrounded by soda lime,, tends t o minimize temperature fluctuations in the absorption efficiency of the calcium chloride corresponding to the temperature changes of the reacting soda lime. With ordinary care the bottle is more durable than other heavier vessels, since the small diameter and absence of protuberant stopcock handle on the top permit a firm grasp of the sidearms while attaching rubber connections, thus obviating breakage a t the seal-in of the side arms-a frequent accident with beginners. The full bottle may be handled by the upper half without danger of the cup base falling off, provided the ground-glass joint has been properly greased. The absence of external attachments facilitates wiping to constant weight. If stuck, all joints are conveniently accessible to the loosenIng action of warm water.
Found Calcd HnO Con H C H C Sample G. G. % % % % 0.1998 0.1039 0,4992 5.69 68.14)5.73 68,26 0.2700 0.1372 0.6760 5.69 68.28
And ' on another filling, three. successful combustions were made. as follows: Found Calcd. coz C C
Date December 12 December 14 December 16
Sample 0.2348 0.2249 0.2159
G. 0,4753 0.4191 0.4191
%
%
55.21 52.84 52.94
55 26 52.72 52.72
A cotton diaphragm divided the charge materials in these runs, Nothing could better illustrate the practical uselessness of introducing ground-glass valves, with their attendant weight, difficulty of fitting, and liability to sticking, for the purpose of separating calcium chloride and soda lime between runs. Special experimental work with a perforated-rubber septum also shows that the migration of water from soda lime to calcium chloride may be ignored. Other advantages of the simplified bottle may be briefly mentioned. The accessibility of every part of the container to vigorous mechanical action facilitates removal of the exhausted charge. The position of the calcium chloride, below 1 Received
January 23, 1923.
It is then believed that this bottle represents a distinct improvement over other existing designs with respect to ( a ) lightness of weight , combined with reasonable capacity of chamber, (6) simplicity of manufacture, (c) convenience in filling, emptying, wiping, and manipulating generally, and (d) durability under ordinary conditions of use. For continuous work involving the absorption of relatively large amounts of carbon dioxide, as in organic combustions, it has given entire satisfaction.
