December, 1929
INDUSTRIAL A N D ENGINEERING CHEMISTRY
temperatures noted in the preceding section have been used again. The remaining values, found by Buchler and Graves (except those for C22H46and CaHB2,which were interpolated), are in general slightly below the melting points given in the International Critical Tables. The molal entropies of fusion, as calculated by the equation, appear in the third column. These values, when multiplied by the absolute temperature of the melting point and divided by the molecular weight, give the data of column 4. The heats of fusion thus obtained, though not experimental, are probably good to about 2 per cent in most instances; and could no doubt be used for all practical purposes. When we come to consider the branched paraffin hydrocarbons, no similar quantitative regularities are evident. Qualitatively we can say that the entropy of fusion apparently decreases progressively with an increase in the amount of branching; but this fact does not enable us to predict the fusion value. This lack of quantitative regularity in the fusion entropies of branched hydrocarbons is undoubtedly due to the fact that they possess a variety of crystal structures. Hence the melting process involves the overcoming of molecular attractive forces which differ greatly in character and magnitude from
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one compound to the next. On the other hand, the x-ray evidence indicates that we are probably dealing with the same general type of crystal structure as we proceed up the series of the normal compounds. Accordingly, the fusion process is essentially the same throughout, and it is not surprising that the energy required to overcome the crystal forces varies in regular fashion with the molecular weight and the melting temperature. Acknowledgment
The writers wish to thank the Ethyl Gasoline Corporation and the Standard Oil Company of Indiana for the loan of valuable hydrocarbon samples. They also desire to acknowledge their indebtedness to Hugh M. Huffman, of this laboratory, for assistance on several occasions during the course of the investigation. Literature Cited (1) (2) (3) (4)
Buchlerand Graves, IND. ENG.CHEM.,19, 718 (1927). Eucken and Karwat, Z. phys. Chem., 112, 467 (1924). Marker, Engineer’s Thesis, Stanford University, 1926. Parks, Paper presented before the Division of Petroleum Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
Wetting of Pigments and Its Relation to Various Paint Characteristics’ Elliott L. McMillen THE N E W
JERSEY ZINC
COMPANY, PALMERTON, PA.
H E wettingofpigments This paper presents preliminary data upon one phase f o r m e d in small additions is of interest to the of a comprehensive investigation of the factors ine a c h a d d i t i o n being compaint manufacturer in fluencing the consistency of pigment-vehicle mixtures. pressed by means of a hydrauThe method of Bartell has been applied to the study of lic press a t 200 atmospheres. two respects: (1)The time of wetting of pigments by various liquids and oils. ExFrom the weight of pigment wetting dependsupon wetting forces, viscosity of vehicle, perimental data correlating wetting forces of Pure used and thevolume of the reand the amount of mechaniliquids with Plastic Properties of lithopone-liquid sulting cake, the ratio of the cal work done upon the mixmixtures shows that flocculation and Plasticity are volume of voids to the volume more pronounced the better the liquid wets the Pigof solid was calculated, thus ture; (2) the forces of wetment. These results are in accord with recent theories insuring uniform packing in t i n g between pigment and vehicle have decided influence of the plasticity of paint which are discussed. successive determinations. Liquid from the reservoir, B, u p o n s u c h properties of a was allowed to flow into the end of the compressed pigment and paint as consistency, leveling, settling, etc. By “wetting force” is meant the spontaneous force with out of capillary tube C. With the stopcock to the reservoir which a liquid tends to spread upon and wet a solid when the B closed, the movement of the liquid into the pigment could liquid is brought into contact with the solid, no external be observed in the capillary tube, C. On account of the work being supplied. The method of Bartell ( 2 ) furnishes very slow movement of the viscous liquids, a thermometer the only method of quantitatively measuring the force of tube with its graduations was found very convenient. Gasewetting or adhesion tension of a liquid toward a powdered ous pressure was applied through tube D to oppose the flow solid. Good wetting is characterized by high adhesion ten- of liquid into the pigment. By gradually increasing the pression and low angle of contact between the solid and liquid. sure a point could be reached when the flow of liquid would This investigation presents measurements of wetting forces cease. This pressure was measured by means of a calibrated upon pigments using Bartell’s method. The data so obtained Bomdon test gage. Leather packing a t E rendered the cell are correlated with consistency data obtained by means of leakproof. The surface tensions of the various liquids used a modified Bingham and Murray vacuum plastometer (6). were measured by means of the du Nouy (9) surface tension The Bartell method of studying wetting involves measur- apparatus, applying the correction given by Harkins ( 7 ) . ing the pressure developed when a liquid displaces a gas Methods of Calculating Results (or another liquid) from a compressed cake of powdered Bartell (2) has shown that the pores in a compressed powsolid. Figures 1 and 2 show the apparatus used for this purpose. In Figure 1 the pigment cake is shown held in dered solid may be considered as a bundle of small capillary position by the perforated disks, A . The pigment cake was tubes and the formula for the rise of a liquid in a capillary due to its surface may be 1 Presented before the Division of Paint and Varnish Chemistry a t
T
the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 to 13, 1929.
rhag
y =
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e
(1)
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1929
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Figure 3-Consistency Curves for Lithopone in Various Liquids Volume percentage of pigment = 17.5%
Lewis. I n a private communication t o the author, J. S. Long has also proposed, from theoretical considerations, that flocculation and the plastic properties of paint are a result of good wetting. De Waele, Lewis, and Haller have arrived a t the above views by indirect reasoning without any measurements of wetting forces or angles. The experimental data presented in this paper are in complete accord with their ideas, however. Good wetting (high adhesion and small angle of contact) results in flocculation, high yield value, and low mobility, while very poor wetting is seen t o cause practically no yield value and high mobility. Settling was observed to be greatest in those liquids which are the poorest wetters, and practically no settling occurs in good wetters such as Nujol or benzene. This study of pigment wetting has thus far been confined mainly to pure liquids. When the liquid contains two or more components, the problem becomes more complicated. It has been observed, however, that t.he addition of small amounts of materials which act as wetting aids lowers the contact angle and increases adhesion tension of the liquid for the solid without a corresponding increase in yield value, but instead produces a decrease in yield value with increase of mobility. De W-aele considers that in such a case the thickness of the liquid layer about the particle has been decreased. The study of the effect of wetting of these two component liquids upon the properties of the resulting pigment-vehicle mixture presents an interesting field for further investigation. Literature Cited
Flocculation is pictured as due to a force operating through the liquid-as, for example, two particles sharing to some extent their tightly held liquid layers. De Waele and Lewis cite the following effects due to this tightly held liquid layer: (1) high oil absorption values, (2) yield value in solid liquid systems, (3) low mobility, (4) restricted settling under the influence of gravity. Haller (6) discusses the same phenomenon under the name of lyosorption, and his views agree with those of de Waele and
(1) Bartell and Miller, IND.ENG.CHEM.,20, 738 (1928). (2) Bartell and Osterhof, I b i d . , 19, 1277 (1927). (3) Bartell and Osterhof, Colloid Symposium Monograph, Vol. V, p. 113 (1928). (4) Green, IND. EXG. CHEM.,15, 122 (1923). (5) Gregory, Rassweiler, and Lampert, J. Rheology, 1, 30 (1929). (6) Haller, Kolloid-Z., 46, 366 (1928). (7) Harkins, Colloid Symposium Monograph, Vol. VI, p. 39 (1929). (8) Jolly, J. Oil Colour Chem. Assocn., 11, 361 (1928). (9) Noiiy, du, J. Gen. Phrsiol., 1, 521 (1919). (10) Sulman, Bull. Insl. Mining Met., No. 182 (1919). (11) Waele, de, and Lewis, Kolloid-Z.,48, 126 (1929).
due t o flocculation of pigment, which he attributes to incomplete or partial wetting. Jolly (8) also considers flocculation of pigment particles to arise from poor wetting of the pigment by the vehicle. On the other hand, de Waele and Lewis (11) present plastometric data which indicate that flocculation is a result of strong forces of adhesion between the solid and the liquid. They consider that each particle of pigment in a vehicle is surrounded by a layer or shell of liquid, very much thicker than a monomolecular layer and tightly held by the particle, this layer of liquid being in a pseudo-solid compressed condition and exhibiting totally different properties from the liquid in bulk. They also consider the surrounding liquid near this tightly held layer to be influenced to some extent so that its viscosity is increased, thus picturing a gradual decrease in viscosity from the surface of the tightly held liquid layer to the surrounding liquid. ~~~
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Fusion Curve of System Alpha-NaphthylamineBeta-Naphthylarnine' Ivan Gubelmann and Henry J. Weiland THE NEWPORT COMPANY, CARROLLVILLE, WIS.
LPHA-NAPHTHYLAMINE, a basic dyestuff intermediate, is used in large quantities as a starting material in the preparation of dyestuffs, as well as a starting material in the preparation of intermediates. According to "Raw Materials and Container Guide Book," 1929 issue, a-naphthylamine is a white crystalline solid with a melting point of 50" C. and a boiling point of 300" C. Jts uses include intermediates, organic chemicals, azo dyes, laboratory reagent, toning photographic prints, petroleum, deblooming agent, and developing agent in dyeing. From a consideration of these uses, together with other known uses, it is obvious that a-naphthylamine is an extremely important organic product. It is highly important for both buyers and sellers to know the quality of such a product or to know how to determine its
A
1 Presented before the Division of Dye Chemistry at the 78th Meeting of the American Chemical Society, Minneapolis, Minn., September 9 to 13, 1929.
quality. The study upon which this paper is based was begun for the purpose of determining the quality of various technical a-naphthylamines. In conducting research on any compound it is usual to consult the literature, with the idea of ascertaining all known physical constants and, more particularly, the melting points of the compounds involved. If the product under consideration is an old one, the melting points reported probably will vary considerably, and it is difficult to decide which is the most reliable. It appears that in the earlier days of physical chemistry, melting point determinations were not always carried out with the precision and care used today. As a result, errors were frequently introduced into the literature. The melting point of a-naphthylamine has been carried in the literature from about 1871 to the present time as 50" C. All handbooks report the melting point as 50" C. Presumably all the reports are based upon the same original source,
