T H E J O c‘ R N A L 0 F I N D U S T RI A L A N D ELVGINEERING C H E M I S T R Y
7P1
Chevreul has been disproved, t h a t alkaline solutions are in no sense detergents in the absence of free f a t t y acids or soap.’ Water solutions of sodium hydroxide, sodium carbonate and trisodium phosphate. in t h e concentrations studied. showed very little changes in drop numbers with alterations in concentration. Within t h e limits of error of our observations. t h e changes in surface tension were about the same for chemical equivalents of the three solutions mentioned. The d a t a for all are about as shown for sodium carbonate in the bottom row of Fig. I . Along with the facts mentioned, these results show t h a t within the field examined t h e greater t h e quantity of alkali added t o a soap solution, t h e better t h e detergent properties. This is limited in practice b y the harmful effects on fabrics of large concentrations of the hydroxyl
Vol. 8, N O . 9
droxide is of no practical interest, because it is, for obvious reasons, seldom used in power laundries, These facts indicate t h a t , of t h e alkaline salts of weak acids, one is as efficient as the other as a wash-room reagent, excepting. of course, sodium bicarbonate, which. in cold solutions, does not affect t h e drop number of soap a t all. This conclusion is in harmony with the findings of Jackson, cited above. From the foregoing data, one is able t o eliminate all of the mystery in the “trade name” washing sodas mentioned. This is a preliminary report on work being conducted in t h e Rlellon Institute of Industrial Research for the Laundrymen‘s National Association of America, and it is the intention of the authors t o study further the field outlined above as t o t h e effect of these solutions on the breaking strength of cloth. M E L L O N INSTITUTE O F I N D U S T R I A L
RESEARCH
PITTSBURGH
300
,
,
,
,
,
,/‘
i1G.E
,
Effe cts of
Equivalents of Sodium Car bonote, Ti-isodium Phosphate and Sodium Hydroxide on +he Drop Number3 of Soap Solu+ions
a t 100‘ G . All AlKalies used
in Concentrations Equivoient 0.1 per
to
cent
Sodium Carbonate.
Not
tbbe compared
numerieaMy data ;n
Per
whh
FIG 31
cent Soap
ion; Faragher has shown t h a t these effects are almost negligible in t h e case of sodium carbonate and cotton. u p t o a I per cent solution of sodium carbonate. provided careful rinsing is employed. This figure is from j t o I O times t h e amount usually employed in power laundries. I n Fig. I1 there are shown t h e effects of equivalents of sodium carbonate, trisodium phosphate and sodium hydroxide on the drop numbers of soap solutions a t a temperature of 100’ C. Because of a change in the dropping pipette, these d a t a are not t o be compared numerically with those presented in Fig. I , b u t they show t h a t the values of equivalent weights of sodium carbonate and trisodium phosphate arc equal, while t h a t of sodium hydroxide is different within the field studied. The case of sodium hy1 See Faragher, Rogers and Aubert’s “Industrial Chemistry,” 2nd Ed ; Hillyer. O p . cif.. and Jackson, O p sit.
NOTES ON SOME PHYSICAL CHARACTERISTICS OF PIGMENTS AND PAINTS By HENRYA . GARDNER
Received August 4, 1916
HIDING POWER O F PIGMENTS
The opacity or hiding power (covering ability) of a paint pigment depends upon its fineness, refractive index, and oil absorption. These physical properties are responsible for the fact t h a t a coat of white lead in oil hides a dark surface better t h a n a coat of silica in oil. FIXEXESS-Paint pigments. if produced i n sufficiently large size particles, would be more or less transparent like a lump of glass, since all such products allow the light t o be transmitted in varying amounts. If any one of them, however, is broken down and powdered, the finely divided particles reflect t h e light in all directions and only a small amount of light is transmitted; the powdered substance thus appears opaque. Therefore, it may be stated t h a t the o p a c i t y of f i g m e n t s i n c r e a s e s w i t h fineness of d i v i s i o n . With some pigments, however (produced b y t h e fume process), there may be a point beyond which increasing fineness may result in a lowering of opacity. REFRACTI0P;-The refractive index of a pigment determines t h e amount of light t h a t will be transmitted b y it. The higher the refractive index. the greater t h e reflection and consequent hiding power. A layer of white lead will reflect more light t h a n a layer of finely ground silica, since t h e refractive index of t h e lead is higher t h a n the refractive index of silica. When either of these pigments are ground in water, t h e same phenomenon holds true. b u t both arc less opaque t h a n in dry form because water has a higher refractive index than air. A s the refractive i n d e x o j the vehicle a p p r o a c h e s that o j the p i g m e n t , o p a c i t y d i m i f t i s h e s , an optical condition being produced by t h e film around the particles, t h a t allows t h e passage of light, thus decreasing t h e reflection. When turpentine is used as a binding medium, t h e pigments show the same relative differences in hiding power, b u t both are less opaque t h a n when in water, since turpentine is more highly refractive t h a n water. When
Sept., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
linseed oil is used as a medium, still less opacity is shown by t h e resulting paints, as linseed oil has a greater refractive index t h a n turpentine. T h e resulting silica paint will now be practically transparent, since t h e refractive index of t h e medium is substantially t h e same as t h a t of t h e pigment. The lead paint, however, will still be opaque, since white lead has a refractive index greater t h a n t h a t of t h e oil. OIL ABsoRPTIoN-Opacity increases inversely w i t h the amount of oil absorbed b y the p i g m e n t . This is shown by comparing t h e hiding power of lead a n d zinc whites. These pigments have substantially t h e same refractive index a n d theoretically should hide equally. A s a matter of fact. however, a workable lead paint has greater hiding power, since it may be produced b y grinding 70 parts of lead in 30 parts of oil, while a workable zinc paint will contain jo parts of zinc a n d jo p a r t s of oil. More light will pass through a film of the zinc paint t h a n through t h e lead paint, on account of t h e greater quantity of oil presentintheformer. This accounts for t h e difference i n t h e hiding power of t h e two paints. The preponderance of oil in t h e zinc paint, however, accounts for t h e much greater durability of those paints which contain zinc oxide in combination with lead pigments, since abundance of oil is recognized as a necessity in exterior paints. I t is apparent from t h e above considerations t h a t t h e hiding power of a white pigment is measurable b y determining its physical characteristics. Various methods for determining fineness a n d oil absorption have been in use, b u t no method has apparently been adopted for determining t h e refractive index of pigments. I t occurred t o t h e writer t h a t some application of t h e petrographic microscope might be made for this purpose. A series of pigments were therefore prepared a n d submitted t o test, t h e readings being made b y D r . Frederick E. Wright, of t h e Carnegie Geophysical Laboratory of Washington. Small particles of the pigment under observation were rubbed u p with media of known refractive indices, covered with glass, a n d submitted t o examination. Some of t h e readings are shown below: Quartz silica.. . . . . . , . , . 1 . 5 5 Barium sulfate. . , . , , . . . 1 , 6 Zinc oxide. , . , , . , , , , . . . 1 . 9 f
Basic carbonate-white lead 2 . 0 Basic sulfate-white lead. . . 2 .O Zinc sulfide. . . . . . . . . . . , . . 2 . 2 to 2 . 3 7
.
.
OPAQUE ADSORPTION PIGMENTS
One of t h e most interesting pigments examined was lithopone. Difficulty was experienced in getting a n exact reading, as it consists of a submicroscopic mixt u r e of aggregated particles. I t is possible t h a t t h e average refractive index might be considered as being between 1.9 a n d 2 . 0 . This pigment is prepared b y the resulting interaction o€ chemically equivalent amounts of zinc sulfate a n d barium sulfide solutions. The precipitated pigment is calcined, quenched, washed a n d dried. I t consists of approximately 7 0 per cent barium sulfate a n d 30 per cent zinc sulfide. When barium sulfate, which has a refractive index of 1.6, a n d zinc sulfide, which has a refractive index of 2 . 2 t o 2.4, are m i x e d in t h e above named proportions, a pigment is produced which is deficient in hiding power. It is apparent, therefore, t h a t t h e precipita-
795
tion process of preparing these pigments produces some physical change which is of great importance. I t is t h e writer’s opinion t h a t t h e effect is due t o adsorption of t h e zinc sulfide b y t h e barium sulfate particles. Microscopical examination tndicates t h a t each particle of finely divided barium sulfate is coated over b y adsorbed particles of opaque zinc sulfide. Experiments have been made with varying strengths of barium sulfate and zinc sulfide liquors in varying amounts, t o determine whether it would be possible t o produce even more opaque types of lithopone b y increasing t h e amount of t h e zinc sulfide present. When lithopones are made containing as high as jo per cent zinc sulfide, t h e hiding power has not been found substantially greater t h a n t h a t of lithopone which contains from 28 per cent t o 38 per cent of zinc sulfide. Below 2 8 per cent of zinc sulfide, t h e hiding power of t h e pigment decreases. I t is, therefore, between t h e limits of 28 per cent a n d 38 per cent zinc sulfide t h a t t h e greatest hiding powers are obtained, a n d t h e increased hiding power of lithopone containing 38 per cent is hardly greater t h a n t h a t shown b y those containing t h e theoretical equivalent of 30 per cent. Rapidity of precipitation, strength of solution. and temperature control are factors which also aid i n t h e production of fine grained particles t h a t give t h e pigment great opacity. T h e phenomenon of surface adsorption shown b y certain lake bases in t h e presence of organic coloring matters is also interesting, a n d explains why t h e highly colloidal pigments are often preferred for t h i s purpose. A measure of t h e degree of dispersion of pigments might be based on their color adsorption values. SUSPEKSOID PIGMENTS
T h e adhesive p r o p e r t i e s a n d c e m e n t i n g v a l u e s of p a i n t p i g m e n t s a p p a r e n t l y i n c r e a s e w i t h a p p r o a c h to colloidal f o r m . T h a t all paint pigments are t o some extent colloidal, is t h e assumption of t h e writer as t h e result of some recent tests. These were first suggested b y some previous experiments in which a number of white pigments were ground in clear linseed oil. After standing for a year, t h e oil upon t h e surface of t h e settled paints was examined and found t o be much higher in ash t h a n t h e original oil. This condition could easily be accounted for in t h e case of t h e lead a n d zinc paints b y t h e presence of dissolved metallic linoleates formed by reaction between t h e pigments a n d t h e free f a t t y acid of t h e oil. No explanation, however, was offered as t o t h e cause of t h e high ash in those paints made of silica, barium sulfate a n d other pigments which it was thought could exert no chemical effect upon t h e vehicle. A sample of t h e oil from one of t h e inert pigments (blanc fixC), after standing in a bottle for a further aging period, became viscous a n d thick, later on developing a peculiar cloudiness. Examination showed t h a t t h e pigment had probably been held i n colloidal suspension and previous t o its precipitation had effected a change i n t h e oil t h a t h a d caused t h e gelatinous condition. As a result of these observations, t h e writer prepared a series of paints b y grinding in a clear linseed oil
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T H E J O C R N A L OF IA’DCSTRIAL AiYD E S G I S E E R I S G C H E M I S T R I ;
a number of standard white pigments, including basic carbonate- and basic sulfate-white lead, zinc oxide, lithopone, and china clay. After settling for a period of two weeks, t h e clear oil was removed from each paint. T h e oils were examined under t h e ultramicroscope b y Dr. E. C. E. Lord, of the U.s. Office of Public Roads, a n d the writer. Particles were visible b u t apparently in a quiescent state. This condition was undoubtedly due t o t h e viscosity of the oil media which exerted a cohesive force upon t h e particles, binding t h e m together in aggregates a n d thus impeding their motion so t h a t the Brownian movement was not observable. These liquids, however, after dilution with 4 volumes of redistilled 90’ benzol (disperse free) were again examined. T h e viscosity of t h e media thus being reduced, great rapidity of motion of the particles was shown. This Brownian movement was observed in every liquid and indicated t h a t all of the above pigments may contain particles t h a t act as suspensoids in oil. A sample of the original oil used in making t h e paint was also examined and although Brownian movement was observed therein, t h e number of particles present was not comparable t o those shown b y the oils removed from t h e paints. The particles present in the original oil were probably due t o the i‘foots” present, regarding which reference is made below. For t h e sake of concenience, the writer has given the name of “Linosols’! t o pigment suspensoids, since paint pigments are almost universally used in conjunction with linseed oil. When a condition is produced by these pigments. whereby the oil assumes the state of a gel, as in the case of the blanc fix6 pigment mentioned above. the product of reaction might be called a “Linogel.” The precipitation of the blanc fix6 which was first visible as a cloudiness in t h e oil might possibly have been caused by absorption of oxygen by the oil, and would then be comparable t o the precipitation of silica when carbon dioxide is absorbed b y a sol of hydrated silicic acid. The term “Linoxygel” might, therefore, be more acceptable for such a product. Experiments were then made with t h e same series of pigments ground in various oils, including a heavy bodied linseed oil of very high viscosity. I n the latter, separation of the pigment from t h e oil, even after standing €or two months, was only partial. After the paints were diluted with 4 volumes of benzol, only the coarser particles subsided, the liquid above remaining cloudy and suggestive of a true colloidal condition-the subdivided particles no longer showing any tendency t o settle. Even after standing five weeks, the same cloudy condition was observed. It was apparently impossible t o clarify t h e turbid liquid by sedimentation, even with the aid of a high-speed centrifuge. Attempts were then made t o precipitate the Linosols. I t was found t h a t b y mixing two of the cloudy paints (zinc oxide and silica), a fairly clear liquid could be produced. The explanation of this phenomenon might be t h a t t h e pigments being oppositely charged had neutralized each other and thus disturbed the disperse phase, resulting in precipitation.
Yo1 5, No. 9
C 0 I. L O I D A L C 0 L 0 R PI G U E .UT S
In order t o study the condition of finely divided colored pigments, several were selected. including Prussian Blue, Chrome Green, Chrome Yellow, Cltramarine Blue, Lampblack. and Paranitraniline Red. These were ground in the same type oC oil t h a t was used with the white pigments, and treated in the same fashion. The clear liquid shown after settling n diluted with 4 volumes of benzol (disperse free) and examined. I t is of interest t o record the fact t h a t t h e oil obtained from the settled Para Red pigment was only sLghtly colored, but when benzol was added, i t became a bright. clear red. I t is probable t h a t part of the pigment present as a suspensoid was brought into actual solution by the solvent pom-er of the benzol upon the organic coloring matter present in t h e pigment. thus accounting for the increase in color. When the liquids were examined under the ultramicroscope, Brownian movement was exhibited by each, the green and blue being most active and apparently containing many times the number of particles present in the others. Comparing the blue roughly with a counted solution of colloidal asphalt, it is probable t h a t I cc. of t h e liquid contained 0~7era hundred million particles. Many of the particles or aggregates in the oil from the Chrome Green were colored crimson, orange, green, and blue. The colors were apparently permanent and did not change as would be the case if due t o refraction. Since i t is supposed t h a t ultramicroscopic particles simply reflect light and therefore do not show colors, t h e above result is interesting and should marrant some extended work on the subject. PREFERENTIAL ADSORPTION
EFFECTS
The effect shown b y carbon black is worthy of study. This pigment is supposed t o be one of t h e most inert t o linseed oil. I t is probable, however. t h a t i t is really h e of the most active in some ways. The great surface which its particles present, on account of their extreme fineness of division, probably gives t o it very high adsorptive properties. The purest pigment obtainable b y burning oil may be free of other solids and yet, according t o F. P. Ingalls,l contain only from 80 t o 9 0 per cent of carbon. t h e balance consisting of carbon monoxide, carbon dioxide, hydrocarbon compounds, nitrogen, oxygen, and water, all of which have been adsorbed b y the carbon particles during the process of manufacture, That these substances are firmly locked t o the particles is apparent. since vacuum treatment of the pigment fails t o remove them. When ground in oil, however, the mrirer believes t h a t the gas is removed from t h e pigment and the oil is adsorbed in place thereof b y a preferential adsorption a;tion of t h e pigment. Clifford Richardson has shown, for instance, t h a t asphalt particles hai-e the power of adsorbing some of t h e heavier constituents of a 1iqui.d b y preferential adsorption. The present writer has similarly noticed t h a t some finely dix-ided pigments may adsorb the heavier constituents of an oil medium. This may be shown b y dissolving a very heavy bodied linseed oil in benzine and grincl1
Private communication.
Sept., 1916
T H E JOURNAL OF INDUSTRIAL A N D ENGIJEERING CHEMISTRY
ing it with lithopone. After a period of time, a reaction will be effected, whereby t h e oil is adsorbed b y the settled pigment, leaving a clear, oil-free benzine floating on top. Very strongly oxidized and bodied oils may even show precipitation upon standing after being mixed simply with benzine. I t is a question, therefore, whether a n y t r u e solution of t h e oil has originally taken place. I t is very likely t h a t t h e apparent miscibility of t h e benzine is due in this instance t o a sponge-like process of imbibition which might be compared t o t h e absorption of benzol by rubber, or t h e swelling of gelatin in water (these effects, however, are illustrative of emulsoids). The preference shown by pigment particles for various liquids is aptly illustrated in t h e manufacture of pulp lead. T h e white lead, which contains a large amount of moisture, if agitated with linseed oil will immediately unite with t h e oil, and t h e water will be thrown out, floating on the surface of the paste paint. Other pigments and liquids may shorn a similar reaction. When zinc oxide or lithopone. for instance, are ground in alcohol and subsequently agitated with linseed oil! t h e oil will immediately unite with t h e pigments and t h e alcohol will be found floating on t h e surface of t h e paste. It is probable t h a t these reactions have been made possible by a lowering of surface tension by the introduction of the oil. SUSPENSOIDS I N OIL AND VARNISH
The “foots” present in linseed oil offers another example of what might be termed a “Linosol.” When freshly crushed from t h e flaxseed, t h e oil will be apparently clear. If heated t o 100’ C., it will become cloudy and a large precipitate will form. This is referred t o as “foots” a n d consists of mineral matter -lime, silica, phosphoric acid, etc.-admixed with albuminous matter. The mineral matter is present in t h e raiy oil as a suspensoid1 and is agglomerated and precipitated when t h e albumen is coagulated by t h e heat. The aging of oil may accomplish a somewhat similar effect, b u t sufficient tankage space is not always available t o t h e crusher, a n d , therefore t h e raw oil is often marketed immediately after it has been produced. I n t h e writer’s opinion, such oil is not fit for use in high-grade paints, and t h e grinder should demand a better product. If t h e crusher should heat t h e raw oil t o 100’ C. and then centrifuge i t , this method might t a k e t h e place of tanking a n d would, at t h e same time, accomplish t h e destruction of fatsplitting enzymes2 which might be present in t h e oil. S’arnish constitutes another organic product t h a t may contain mineral suspensoids. Tanking of clear, newly made varnish always results in a slow precipitation of “foots.” Centrifugal force will bring about t h e result more rapidly. I t is gratifying t o note t h a t t h e centrifuge has become a part of t h e equipment of every modern varnish plant, and its use in this industry is bound t o be more extended in the future. E. E. AyresS “Refining Vegetable and Animal Oils,’’ Chas. Baskerville, J. Franklin
Ins!., June, 1916.
* “Changes
Occurring in 0i:s and Paste Paints, Due to Autohydrolysis of the Glycerides,” H. 4.Gardner, J. Franklin I n s f . , May, 1914. ”The Application of Centrifugal Force to Suspensions and Emulsions,” E. E. .4yres, J . SOC.Chem. I n d . . June, 1916, p. 676.
’
797
has recently commented upon the clarification of pyroxylin varnishes b y centrifugal action, and has mentioned t h e remarkable effect of a predpitant such as tricalcium phosphate. Similarly it is probable t h a t t h e addition of certain mineral matter t o freshly made varnishes, just previous t o centrifuging. may effect more rapid and permanent clarification. IXSTITCTE OF I N D U S T R I A L
RESEARCH, \vXSHISGTON
COUMARONE RESIN AND ITS USES By CARLETON ELLIS A N D Lours RABINOVITZ Received May 9, 1916
Resinous bodies obtained b y the polymerizing action of sulfuric acid on indene (C9Hs) and coumarone ( C s H 6 0 ) occurring in t h e fraction of coal-tar naphtha boiling between 160 and 180’ C., are found in t h e market under t h e name of coumarone resin. Various attempts have been made, with some measure of SUCcess, t o substitute these polymerization products for certain of t h e natural resins. This paper aims t o give a brief review of t h e subject and a rCsumC of some experimental work carried out b y us on coumarone resin. Coumarone (or cumarone) resin was obtained b y Kraemer and Spilker, during their investigation on indene and coumarone in coal-tar naphtha,‘ b y the action of strong acids, particularly sulfuric, on coumarone; they called the product p a r a coumavone. Somewhat later2 they subjected this resin t o a more thorough investigation and found t h a t when pure coumarone which has been diluted with benzol is treated with a moderate amount of sulfuric acid, t h e greater p a r t of the coumarone is converted into a resin soluble in benzol, while a lesser portion is transformed into a body insoluble in benzol and is carried down b y t h e sulfuric acid, from which it may be removed b y treatment with water T h e investigations of these chemists show t h a t polymerization begins with a n acid strength of 80 per cent (monohydrate). With this strength of acid t h e soluble resin is obtained almost exclusively. Ahthe concentration of t h e acid is increased more and more of t h e insoluble resin forms. Increase in t h e proportion of t h e acid acts in a similar manner. With acid of 9; per cent strength applied in sufficient amount t o a 2 per cent solution of coumarone in benzol t h e insoluble resin is formed almost quantitatively. When using jo per cent of acid, calculated on the coumarone taken, about 2 j per cent of soluble resin is formed while with four times t h e amount of acid no insoluble resin is formed. Indene behaved very much like coumarone, only in t h a t case t h e resinification was accompanied b y a rise in temperature. T h e coumarone resin was found t o melt between 1 0 7 and 108’ C. By the treatment of coumarone with a relatively large proportion of sulfuric acid,3 a t first a soft pasty mass was obtained which soon hardened t o a brittle and infusible body, insoluble in all solvents. Kraemer 1 2
3
Ber.. 23 (1890). 78, 3276. Ibid., 33 (1900). 2257. I b i d . . 23 (1890). 81.
