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June, 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
It is evident from this experiment that as the adsorption proceeds there is a gradual conversion of the initially adsorbed Nz04to nitric acid by water for which silica gel is known to have a pronounced selective action.8 The ratio of nitrogen oxides to water in the product recovered from the gel will, therefore, depend on the length of time it has been exposed to the gas containing Nz04 and water vapor. An experiment was therefore carried out in which recovery tests were made a t definite time intervals. A total flow of 200 cc. per minute of gas containing 5 per cent NZO4and 2 per cent water vapor was admitted directly to a 10-gram sample of Gel B at 0" C. This corresponds to a and 0.193 gram H20per hour. Adflow of 2.460 grams N204 sorption experiments of 4, 8, 12, 16, 20, and 25 hours' duration were made. No water vapor passed the gel during any of these tests. After each adsorption run the gel was given the following treatment: It was submitted to distillation a t 100' C. with condenser a t 0" C. for 30 minutes and the cona A recent observation of the selective adsorption of water by silica gel is that of Williams, J Soc Chem I n d , 45, 97T (1924) He found that benzene initially adsorbed on silica gel from a benzene water vapor mixture is gradually displaced by water on continued passage of the mixture through the gel.
densate (liquid
603
was weighed. It was then heated a t
-hJzo4)
200" C. for 30 minutes, followed by the passage of air for 5
minutes a t 20 cc. per minute. The condensate of nitric acid was weighed and its concentration determined. The gel was then brought back to its initial condition-that is, to its original weight-by heating a t 200" C. for 1 hour with air passing a t 20 cc. per minute. of T i m e of Adsorption on Relative A m o u n t s of NzOd a n d Water in Adsorbed P r o d u c t Concentra- Per cent of Duration of NzOi Hn0 NnOi "03 tion of adsorbed " 0 8 NzOd +H2 adsorption adsorbed recovered recovered Hours Grams Grams Grams Per cent recovered 4 3.612 1.723 1.653 74.1 93.3 8 4.936 1.313 3.331 72 6 94.1 12 6.122 1.107 4.858 68.7 97.3 16 7.662 0.61ga 6.895 67.8 98.0 20 8.882 0.360a 8.296 66.1 97.4 24 10 181 ...b 9.994 67.1 98.0 a These condensates were blue in color, due to the presence of a small amount of water. b Some condensate here, but it was believed to contain but little NzOd. This was carried on with the condensate from the next distillation.
T a b l e VI-Effect
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The results in Table VI show how the relative amounts of X204and water in the adsorbed product depend on the time of adsorption.
The Versatility of Ferrous Hydroxide' By Peter Fireman MAGNETIC PIGMENT Co., T R E N T O N N,. J.
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UPPOSE you have before you a tub holding, say, 6000 gallons and that you fill it to three-fifths of its - * capacity with a solution of ferrous chloride and then add a ton of slaked lime while passing air through the whole massq, Having done this, you may begin to make up your mind whether the product shall be black or yellow. If you decide that you want a black pigment, you turn on steam full blast and continue the oxidation a t a boiling heat until you get the right color. If you desire a yellow you operate for a while a t a low temperature but finally increase the heat to boiling. I n either case you obtain a valuable, readily marketable color. I n using soda ash as the precipitating agent the conditions are analogous. With an equal proportion of sodium carbonate you will obtain either a black or a yellow according as you use a high or low temperature while blowing in the air. Only when using lime you operate with an excess of ferrous chloride, but when using soda ash you operate with a considerable excess of alkali carbonate. If you diminish the excess of soda ash and carry on the oxidation a t an elevated temperature you produce a brown. A further decrease of the excess of soda enables you to obtain a red. I n all the reactions enumerated the first step is the precipitation of ferrous hydroxide, whose eagerness to take up oxygen is the cause of the formation of the various pigments. The remarkable feature of the reactions under consideration, however, is not so much the avidity of ferrous hydroxide for pxygen as its tendency to form a large number of substances varying in shade of color. This tendency to produce strikingly-different colors in response to slight changes in the conditions of the mother liquor may fittingly be characterized as the versatility of ferrous hydroxide. To restrain this tendency to react in many different ways and bring it under
S
1 Received April 2, 1925 Presented before the Division of Physical and Inorganic Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, .Md , April 6 to 10, 1925.
control has been the problem in the utilization of the reaction in question. The task is an attractive one. You start out with very common, cheap raw materials. You obtain pigments of fine structure, desirable shades, of great tinctorial power, and permanent in color. A gratifying feature in the production of these pigments is that you may utilize a waste liquor-namely, the spent acid obtained in cleaning iron wire or plates. It may be noted that during the last two decades there has been developed in this country a new industry based on the manufacture of precipitated iron oxides. A brief discussion of some of these pigments follows. Precipitated Ferro-Ferric Oxide
This black oxide of iron is produced by precipitation from either a solution of ferrous chloride by slaked lime or a solution of ferrous sulfate by soda ash. I n both cases a lively current of air and a rapid stream of steam are introduced. The mass soon becomes a greenish blue, but gradually loses its bluishness and becomes lighter, greener. As the boiling temperature is being approached the color darkens to a grayish brown. During the remaining few hours of the operation the black color becomes more and more pronounced. The oxidation is kept up until the ratio of the ferric to ferrous iron becomes 1.2:l to 1.5:l. The washed ferro-ferric oxide is best dried with the exclusion of air. Two typical analyses will show the composition of the black pigment. From FeClz and Ca(OH)z FeO 23.09 Fez03 76.52 coz 13 99.74
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From FeSOi and NalC03 25.90 72.40 1.14 99.44
Considerable oxidation takes place during the drying. With suitable precautions this can be held in check, but it is of no particular moment whether the ratio of ferric to ferrous iron is a little greater or bss as long as it does not fall much
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604
INDUSTRIAL A Y D ENGI-VEERILVG CHE-MISTRY
below 2: 1 or does not much exceed 3: 1. Anyway, there does not seem to be any particular virtue in the ratio 2:l that corresponds to the formula FeO.FezOs. I n the oxidation of freshly precipitated ferrous hydroxide by air no sudden change of physical or chemical properties takes place when the composition of the magnetic oxide of iron is reached. Precipitated ferro-ferric oxide is a black pigment of impalpably fine structure, strongly magnetic. It is adaptable for working in oils and varnishes, for use in paints and printing inks. Notwithstanding its fineness of structure it possesses remarkable polishing qualities, imparting to glass, in particular, a bright luster. At a low red heat these black oxides are converted into bright reds, which are greatly sought by the rubber, leather, paint, and asbestos-board manufacturers.
Summary
Yellow Oxide from Ferrous Chloride and Soda Ash
I n this process a considerable excess of soda ash is required. The temperature during the oxidation is a t first kept low. The change of colors here is blue, green, brown-yellow, and yellow. The entire operation is more rapid than when lime is used in making a yellow. The resulting product is also a hydrated ferric oxide of the composition Fez03.Hz0. It carries usually from 3 to 5 per cent carbon dioxide which, in part a t least, is contained in the pigment as sodium carbonate. This yellow is somewhat deeper, of orange shade, and very voluminous. Brown Oxide from Ferrous Chloride and Soda Ash
Here a moderate excess of the precipitating agent is used. The temperature is raised rather rapidly. On addition of the soda ash the color of the mass is a t first light greenish blue, but soon loses the bluishness, becoming lighter and lighter, greener and greener. Then for a considerable time the green remains unchanged; thereupon a sudden darkening takes place, the color turns gray brown with a yellowish cast, then brown black, and finally lightens to a decided brown. The oxidation is continued until the product is all ferric oxide. The brown pigment is impalpably fine, sometimes with a reddish cast and sometimes with a yellowish one. Its composition is FeZO3. It has no water of hydration. It is greatly prized in rotogravure printing and is much used in paints and leather. Gray, Green, Red, and Purple Oxides of Iron
These pigments we will only mention here as having been produced, but their description must be left for another occasion.
'4
, iy
1-Freshly precipitated ferrous hydroxide, in underboing oxidation through the action of the air, gives rise to the f rmation of a long series of well-defined colored pigments, n dependence on slight changes in the composition and conditions of the mother liquor. 2-In general, the oxidation a t low temperatures leads to the formation of hydrated oxides of iron yellow in color, whereas the oxidation a t higher temperatures leads to the formation of anhydrous oxides of iron. 3-Black ferro-ferric oxide, yellows of the composition Fez03.Hz0,and browns of the composition Fez03are briefly described.
P
Nickel Table Tops for Laboratories'
Yellow Oxide of Iron from Ferrous Chloride and Lime
The raw materials are brought together in the same proportions as in the making of magnetic black oxide, but after precipitation the temperature is kept low while the air is admitted full blast. By the time all the lime is introduced the mass is dark blue; the color soon becomes deeper and deeper, then begins to lighten, turning dark green; the green persists for some time, though gradually assuming lighter and lighter shades, and finally gives place to yellow, which becomes more and more pronounced. At this stage a brown sometimes sets in, which after a period of increasing intensity gradually disappears, whereupon at a boiling temperature the final, clear, light yellow color slowly comes to full development. This pigment is a clearly defined compound of the composition Fez03.Hz0. It is a bright light yellow, very voluminous, and of exceeding fineness of structure. It has great color strength and has proved to be a valuable color for paints, paper, leather, and rubber. At a red heat it forms a bright yellowish red. The voluminousness of this red is four to five times that of the reds made by furnacing copperas.
V d . 17.. N0. 6
By 0. B. J. Fraser INTERNATIONAL NICKELCo.,BAYONNE, N. J.
H E service conditions to which laboratory tables are exposed are probably more severe and more diverse than any similar article of equipment is called upon to withstand. Satisfactory materials for surfacing laboratory tables, which are easy to keep clean, resist effectively all of the common corrosive reagents, and a t the same time are fire and heat resistant and capable of surviving mechanical abuse, especially in commercial laboratories, are very few in number. Moreover, none of the materials of which table tops are usually built possesses all these desirable properties. Wood, even when chemically treated, leaves much to be desired on almost all of these points, and asbestos compositions also are weak on many. Soapstone has proved more serviceable than either of these, but it disintegrates%mw . what under the action of concentrated mineral acids and its surface is not sufficiently hard to withstand abu pecially from hard objects with sharp corners and dges. .e&&' It is remarkable that pure nickel, which for many years has been used so largely for such important and harshly used pieces of apparatus as crucibles, evaporating dishes, tongs, spatulas, combustion boats, etc., has not been long recognized as a material highly suited for surfacing laboratory tables. Pure sheet nickel combines in itself more of the properties desired for table tops than the more commonly used, nonmetallic materials. With such metal, in sufficient thickness to avoid buckling, a table surface is provide4which is hard, resistant to abuse, and not affected by expopre to heat. It has a pleasing, bright color and resists taraishing and staining remarkably well. Chemical work bench tops covered with sheet nick4 have been in constant use for more than a year in the research laboratory of the International Nickel Company. Their service record has been excellent and all that has been necessary to keep their fine appearance a t its best has been an occasional scouring with one of the common household cleansers. There are very few of the chemical reagents usually met with in commercial analytical or research laboratories which attack nickel appreciably, and with these the rate of attack is slow. Of the mineral acids, nitric acid in its higher ~22-rr centrations is corrosive, but its activity is not m a r h d a r ordinary temperatures. Because of the passivity of nickel, even this acid can be considered harmless. Thc max'. a i m effect it may have is a moderate etching of the metal. #Itis scarcely necessary to point out that the average chemist will not permit pools of acid to lie on his working tabfsfor longer than a very few minutes.
9,
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Received April 17,1925.
