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I*VDUSTRIA L AND ENGINEERING CHEMIX T RY
component liquid system. I n practice liquids are used which contain several components. With such liquids the above described treatment would not hold. An extension of this investigation would be necessary in order to be able to predict the type of results t o be expected with such systems. This investigation has shown that liquid absorption is approximately proportional to the specific surface and, therefore, to the degree of fineness of a pigment. This appears to justify the use of a simple method for determining the approximate specific surface of a pigment. Suppose the liquid absorption value has been obtained with a pigment of known specific surface and one wishes t o determine the specific surface of another sample of the same kind of pigment. All that is necessary is to determine the liquid absorption of the latter. The ratio of the two liquid absorption values is approximately the same as that of the specific surfaces of the two pigments. From this the approximate particle size of the second pigment may be calculated. Further it would seem to be possible to specify the approximate degree of fineness to which a pigment must be ground in order that it may have some desired liquid absorption value with a given liquid. It would only be necessary to know the liquid absorption value of a sample of the same kind of pigment of known specific surface. The specific surface corresponding to the desired liquid absorption of the pigment could be found from the simple ratio pointed out above. From this the particle size required to give the desired liquid absorption value could be readily calculated. It should again be pointed out that the above statements apply to pure liquids only and to liquids and solids between which no reactions occur. They do not, for example, cover cases in which two-component liquid systems are used nor those in which chemical reactions between pigment and liquid occur. Summary of Results 1-The liquid absorption values of a series of zero contact angle liquids with polar solids increase linearly with increase in interfacial tension values of those liquids against water. 2-The liquid absorption values of a series of zero contact angle liquids with carbon, a non-polar solid, decrease line-
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arly with increase in interfacial tension values of these liquids against water. 3-The order of decrease in free surface energies which occurs when a polar solid is wetted by each of a series of zero contact angle liquids is the same as the order of the decrease in free surface energies which occurs when vater is brought into contact with the same series of liquids. 4-The liquid absorption values of contact angle liquids with any solid bear no apparent relationship to the interfacial tension values. They are much lower than liquid absorption values obtained when zero contact angle liquids of correRponding interfacial tension values are used. 5-JThen an air-dried powder is heated and evacuated, the liquid absorption values obtained with it are practically the same as those obtained with the powder before this treatment. 6-The liquid absorption values obtained with a given solid powder and with a given liquid system were found t o be approximately proportional to the specific surface of the powder. 7-Liquid absorption data obtained using different solids of the same particle size indicate that the solids used in this investigation form two distinct groups. One group consists of barium sulfate, fluorite, and silica; the other group includes the sulfides. The members of the former group were more highly wetted by liquids than were those of the latter. It has been indicated that such data might be useful in determining the relative degrees of wetting of a single liquid against various solids. Literature Cited Baldwin, IND. ENG. CHEM.,21, 2326 (1929). Barnard, Paint, 012 Chem. Rev., 70, 8 (1920). Bartell and Greager, IND. ENG. CHEM.,21, 1248 (1929). Blom, Farbcn-Zlg., 33, 1969 (1928). Gardner and Coleman, Paint Mfrs.Assocn. LJ. S., Tech. Circ. 86. Grohn, Farben-Zlg., 33, 1660 (1928). Harkins, IND. ENG. CHEM.,22, 901 (1930). Hoek, Van, Farben-Zlg., 34, 1784 (1929). Hougen and Hentzen, Chem. M e t . Eng., 29, 840 (1923). Klumpp, Farben-Zlg., 32, 2306 (1927). Klumpp, Ibid., 34, 2130 (1929). Ruchti, Ibid., 34, 1754 (1929). Waele, de, and Lewis, Kolloid-Z., 48, 126 (1929). Wagner and Pfanner. Farben-ztg., 34, 2513 (1929).
The Observation of Cataphoresis in Nitrocellulose Solutions’ E. A. Lantz and 0. A. Pickett HERCCLESEXPERIMENTAL STATION,HERCULES POWDERCo., KENVIL,S . J.
T
HE detection of cataphoresis in colloidal systems in which the dispersion media are non-aqueous is not nearly so easy as in aqueous systems. I n the latter case the solutions are generally good conductors of the electric current, are more or less colored, and generally of low viscosity. These factors combine to make the observation of electric charge on the sol relatively simple. Sitrocellulose solutions, however, are poor conductors, colorless, and generally of high viscosity. A method was recently devised by Humphrey and Jane (1) for the observation of cataphoresis in colorless, non-aqueous Received September 19, 1930. Presented before the Division of Paint and Varnish Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. 1
colloidal solutions. The sol was made to flow downward between two electrodes immersed in the dispersion medium. To make the sol visible, use was made of the difference between the refractive indices of the sol and the medium by applying the Toepler “Schlieren” method (2). The course of the stream of the sol flowing between the two electrodes is very sharply defined and any motion of the boundary of the sol can be clearly seen when a potential is applied to the electrodes. Apparatus The method employed by Humphrey and Jane in the study of cataphoresis in rubber-benzene systems has been used in
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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this work with only slight modification. The experimental arrangement in the original apparatus is shown in Figure 1. A vertical straight edge, V , is placed on the axis of the lens L and is illuminated by the lamp S. A real image of this edge is produced at V,, and the light passing by the edge of the image is just intercepted by a second vertical straight edge, V2. I n the path of the rays from the lens there is placed the glass cell, C , having polished glass sides and filled with the dispersion medium. Two parallel metal electrodes, E, 2.0 x 2.5 em., are immersed in the liquid and are supported so that they do not come in contact with the sides of the glass cell.
Figure I-Orlglnai AppBrntuB for Study of Catwhoresia
The distance between the electrodes in the liquid is less than that between the leads in air. The sol is made to flow through the buret tip, T,drawn out to a h e capillary, the end of which is placed between the electrodes where the field is most uniform. Observations are made at the point A . The thin stream of sol flowing downward through the dispersion medium is seen as & thin, bright hand. A known difference of potential is then applied and the movement of the sol noted. The potentials can be reversed by a reversing switch so as to eonfirm any movement toward either electrode. This original apparatus was modified slightly so that observations were less difficult and tedious. The method adopted is shown in Figures 2 and 3. The source of illumina, tion was an arc light, L , the light being diffused by a groundglass shield, S. The straight edge V was placed in the vertical position as before so as to intercept half the light passing through the glass cell C . In this ease no lens was used to illuminate the cell. Observations were made on the ground glass of the camera, V , (which was focused on the electrodes, E ) . When the sol flowed downward tbrongh the dispersion medium, i t could very easily be observed on the ground glass. A vertical straight line was drawn on the s o u n d glass and the camera was so placed that the image of the sol stream just
of nitrocellulose, purity of solvent, etc., on the electric charge and on the nitrocellulose in solution. Results
In all cases where nitrocellulose solutions were examined for cataphoresis, the electrodes were placed about 1 cm. apart. The potential applied to the electrodes was supplied by a bank of radio B-batteries and w&s generally of the order of 90 to 180 volts, depending on the conductivity of the solvent mediam. The results usually indicated a definite negative charge on the nitrocellulose in solution, hut in a few eases the charge was so small as to he almost imperceptible. EFFECTOF SOLUTION CONCEN'llZATION-A1k other faCtOr8 being equal, the more concentrated solutions showed the greatest charge. TYPEOF SoLvEm-Many solutions were made and tested. The results showed a change in intensity of charge from solution to solution prepared and tested under identical conditions, save for solvent. The solvents used were acetone, ethyl acetate, ethyl acetatetoluene, butyl acetate, and amyl acetate. The effect was greatest in acetone, next greatest in ethyl acetate, and so on to amyl acetate, in which the effect was least.
Plgure 3-Assembly
I
U
Figure 2-ModlBad
ApplPlturi for Study of Cataphoresis
coincided with this line. Any slight movement of the stream could he detected very easily. Observations could readily he made photographically, if desired, by inserting a plate holder and making an instantaneous exposure. Types of Solutions Examined The first solutions to he tested for charge were prepared without any defmite plan of procedure other than the detection of cataphoresis in nitroeellulose solutions. When the preliminary teats gave promising results, a definite program of attack was followed to determine the effect of various factors, such as solution concentration, type of solvent, type
of Modl6ed Cataphorerilr. Appsratua
TyPE OF NITROCELLULOs~olUtionSprepared from Iowviscosity types of nitrocellulose showed less charge than those prepared from the higher viscosity types providing eoncentrations and solvents were the same. PUEITYOF S o ~ v ~ ~ ~ - - - S o l u tprepared ions from the same types of solvent but from different grades showed that the charge was greatest in the ones of lowest purity. A few photographic illustrations of the observations are given in Figure 4. I n all cases a reversal of potential confirmed the bend toward the positive electrode. Permanency of Charge and Effect of Added Electrolytes The solutions examined for Cataphoresis were generally tested Soon after solution of the nitrocellulose was complete. On several occasions solutions were tested which had been allowed to remain unmolested for several weeks. Under tbese conditions only a slight charge remained on the sol. Confirmatory experiments proved that the greatest charge was present immediately after solution of the nitroeellulose bad been vigorously shaken and that the charge decreased BB the solution aged. In some eases, if a solution which was allowed to stand until the charge was at a minimum WBB
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INDUSTEIAL A N D ENGINEERING CHEMISTRY
shaken vigorously, an increase of charge was noted after this treatment. Some of the solutions of nitrocellulose in acetone, which showed a definite negative electric charge on the sol, were treated by adding a small amount of electrolyte such ~a potassium iodide. An immediate test before and after this addition shoumd that addition of the electrolyte caused a great decrease in the charge. Viscosity measurements taken on the same solutions showed the viscosity of the solution
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liewise to be greatly decreased. It is probable that the drop in viscosity of nitrocellulose solutions as they are aged is related to this loss in electric charge over the same period of time. Literature Cited (1) Humphrey and Jane. T,,,,,~. Pnrndoy sot., 4 ~ , 4 2 0(1926). (2) wmd, "Phyriea: optics:' p. 94 (1011).
When Agriculture Enters the Chemical Industry'
I
F WE look upon agriculture as an organic chemical ac-
tivity, which it is solely and nothing more, we shall have little difficulty in understanding the real needs of the farmer and directing his chemical labors so as to bring him assured prosperity. At the outset we must recognize that prosperity has come to the organic chemical industry in this country primarily by reason of the adaptation for distinct use of every single component found to arise in the course of any of its manufarturing processes. Roughly speaking, this may be termed "the utilization of all byproducts;" as a matter of fact. it is such control of manufacturing processes that by-products may become mainproducts a t will and to profitable turn. The farmer markets no pure organic chemical compound. He confines himself, and rightly so8 to the production of organic chemical mixtures, consisting chiefly of proteins, fats, and carbohydrates. A large portion of the carbohydrates (cellulose, starch, and sugars), consumed on the farm, he markets in the form of livestock (mixtures of proteins and fats). That particular portion, however, which has not found use in the feeding of livestock and in the supply of present-day demands of various processing companies is generally characterized as surplus. Such surplus may go into export or may lie in storage, but in all events I
Received October 9. 1930.
* Director. Organic Chemical Research, The D o a Chemical Company.
i t operates as a price depressant on the market for whatever staple it happens to be. Agricultural Overproduction of Today Opening Door to Prosperity
I n this surplu+tl:at is, in our present-day overproduction of farm staples-it is chemically consistent to establish all agriculture on a profitable basis. Not, however, in an overproduction a t random of a perishable mixture can we look for this prosperity, but in a high production of individual organic chemical mixtures, that will meet tremendous demands in an advancing civilizxtion. can we see this greatest opportunity of promoting agriculture. In this way agriculture is brought directly into the organic chemical iudustry. The surplus of today may be mxde to serve as a bridge, as it were, between the old medieval custom of growing agricultural products for an indiscriminate market and the new advanced practice of growing agricultural products primarily for well-defined and distinct markets, where contractual agreements concern themselves only with acreage under cultivation. The growing competition between the industries making use of organic chemical products manufactured directly from farm staples by a group of industries, whicii we shall call "the carbohydrate industries," makes incumbent upon these latter that they seek cheaper and cheaper sources of their own raw materials--that is, farm staples.
