August, 1930
ISDUSTRIAL AA'D ENGINEERIAVGCHE.ZIISTRY
contact between graphite and water is approximately 80 degrees, the value of adhesion tension is about 14 dynes per centimeter, and the value of K , the adhesion constant, is roughly 0.2. This difference in wettability of packed and loose pigment may offer some explanation of the efficiency of various paint mixers and paste mills. Any mixer with a tendency to pack the pigment particles more closely together-for example, a kneading action-will render the pigment more easily wet by the oil. The action of mixing equipment can be thought of as being effective in two ways: (1) tumbling the pigment particles about so that they ultimately come into contact with the oil; (2) compressing the pigment mass so that the oil easily penetrates and wets it. The mixers which give the kneading, compressing action are far more effective in forming pastes than a mixer that merely stirs pigment and oil together. The paint man is also interested in how the wettability of pigment by vehicle influences the plasticity of the resulting paint. Heretofore it has been customary to observe the plasticity of a pigment-liquid mixture and estimate wettability of the pigment by the liquid from the observed plasticity. It has been assumed that a liquid producing plasticity was a poor wetter for the pigment and one producing a fluid mixture was a good wetter for the pigment. This assumption was supported by the theory that poor wetting, with its high interfacial tension between liquid and solid, resulted in a definite tendency to diminish the free energy a t the liquid-solid interface by flocculation or grouping of the particles, such flocculation being thought to produce the structure giving rise to plasticity. No one thought to test the theory except by visual observations of wettability when pigment and oil were stirred together. The visual observation of wettability is influenced to a large extent by the viscosity of the liquid, and if structure viscosity results, with either a poor or good wetter, such structure slows down the process of wetting additional pigment and renders the visual observation of wettability a very inaccurate test. The advent of the adhesion-tension cell made possible the testing of this theory by enabling actual measurements of adhesion tension, adhesion constant, and work of adhesion to be compared with the experimentally observed plasticity of pigment-liquid mixtures. It was found (6) that plasticity was more pronounced the better the liquid wetted the pig-
893
ment. These data applied only to the range of wettability between contact angles of 90 and 0 degrees or adhesion constants of 0 to 1. More complete data, especially in the range of wettability where the adhesion constant is greater than unity, will be necessary before the complete relation between wettability and plasticity is known. These data indicate, however, that the cause of plasticity lies in the force of adhesion between liquid and solid. Adhesion between solid and liquid is thought to result in an adsorbed liquid layer upon the solid whose dimensions may greatly exceed that of the familiar mono-molecular layer. De Waele ( 7 ) believes that the source of plasticity lies in the adsorbed liquid layers about the solid particles. He believes that the greater the force of adhesion the more tenaciously the adsorbed layer is held; but that the adsorbed layer is thicker the weaker the force of adhesion between solid and liquid. He believes that plasticity or, more specifically, rigidity is proportional to the thickness of the adsorbed layer. Rigidity or yield value of pigment-liquid systems has in the past been attributed to flocculation of the pigment particles, by which is meant the bunching together of particles to form groups which link up together and impart structure to the system. Bartell and Greager (1) have shown that the liquidabsorption value of a pigment is less the greater the adhesion tension, indicating that strong forces of adhesion between solid and liquid tend t o pull the particles of the solid more closely together when they are wetted by the liquid. Undoubtedly wettability of the pigment by the vehicle is a major factor governing the consistency of pigmentvehicle mixtures. Whether plasticity observed in mixtures of pigment with good wetting liquids is to be explained upon the basis of adsorbed liquid layers or of flocculation remains to be seen. The Bartell-Osterhof cell is the weapon which will make possible the experimental correlation of wettability data with plasticity data. Literature Cited (1) (2) (3) (4) (5) (6) (7) (8)
Bartell and Greager, IND.ENG.CHEX.,21, 1248 (1929). Bartell and Osterhof, Ibid., 19, 1277 (1927). Davidson, Paint Oil Chem. Rev., 89, 12 (1930). Harkins and Feldman, J . A m . Chem. Soc., 44, 2666 (1922). Lipseet, Johnson, and Maass, Ibid., 49, 926 (1927). McMillen, I N D . ENG. CHRM.,21, 1237 (1929). Waele, de, and Lewis, Kolloid-Z., 48, 126 (1929). Young, Phil. Trans., 1806, 65.
Flash Points of Mixed Solvents' Foster D. Snell 130 CLINTONSr., BROOKLYN, N. Y
T
HE practice of adding non-inflammable solvents to inflammable ones to raise the flash point of the mixture or to render the mixture non-inflammable is in general use. The products so produced are marketed as fabric cleaners, volatile suspension media for abrasives, larvacides, and in many other ways. This class includes various mixtures, many of them complex, having as the inflammable ingredients naphthas, benzene, toluene, xylene, acetone, ethylene dichloride, and many others. The outstanding flameproofing agent is carbon tetrachloride, although some trichloroethylene is used for the purpose. Unless molecular compound formation occurs between the solvents mixed, as is sometimes indicated in mixtures of two or more solvents, it is to be expected that the solvent with 1
Received July 7, 1930.
the lower boiling point will evaporate more rapidly. If, in a non-inflammable mixture, the non-inflammable solvent has a boiling point higher than the other solvent or solvents, it is to be expected that the mixture will evaporate without giving an inflammable vapor a t any time. If the boiling points are approximately the same, a similar result is to be expected. If, however, the inflammable solvent has a boiling point higher than that of the non-inflammable solvent, it is to be expected that the mixture after partial evaporation will be inflammable. Mixtures Used To indicate the extent to which this occurs in practice, mixtures were prepared to represent cases where the inflammable solvent was less volatile and where it was more
894
I N D U S T R I A L A N D ENGIh'EERIiL'G CHEMISTRY
volatile. These were varying proportions of toluene and carbon tetrachloride in one case and of acetone and carbon tetrachloride in the other. The examples were selected as cases known to occur in commercial operations. The more common case of naphtha and carbon tetrachloride was not investigated because of the indefinite nature of naphthas. These mixtures were prepared to cover a range a t 10 per cent intervals which would include the points a t which each mixture passed the Interstate Commerce Commission regulationrminimum of 26.5" C. (80" F,). Experimental Method
The-flash"points of the original mixtures were obtained with a Tagliabue closed tester. A duplicate set was allowed to stand in 100-cc. graduated cylinders until the original volume of 100 cc. had been reduced to 50 cc. During this period the cylinders were loosely covered with filter papers to prevent dust contamination. The flash point of the mixture remaining after 50 per cent evaporation was then determined. Table I-Effect of Partial Evaporation o n Flash Points of Mixtures MIXTURE FLASHPOINT After 50% Of original evaporation (CHshCO CClr Per ccnf Per cent O c. e c. 30
5 12
> 30
Vol. 22, No. 8 Results
The data are given in Table I. The flash point of the acetone-carbon tetrachloride mixture has been raised over 15" C. during 50 per cent evaporation under these conditions. Similarly, the flash point of the toluene-carbon tetrachloride mixture has been lowered by IC-12'' C. The danger of the latter type of action is obvious. When such a solvent mixture, which is originally non-inflammable, stands in an imperfectly closed container, the mixture noninflammable according to I. C. C. regulations becomes inflammable. Qualitatively, it is readily observed that a fabric saturated with such a mixture is not originally inflammable, but after partial drying has taken place it becomes highly inflammable. Among the many factors to be considered, which cannot be readily, quantitatively evaluated, are possible molecular compound formation between the two solvents and relative rates of diffusion of the solvent vapors from the liquid vapor interface. Conclusion
The brief data shown indicate that, in some cases a t least, a mixture flameproofed with a non-inflammable solvent such as carbon tetrachloride will become inflammable on standing until partial evaporation has taken place. It is therefore necessary as a matter of safety to the user to be sure that not only the original solvent, but the solvent remaining when partial evaporation has taken place, shall be non-inflammable.
Culture of Indigo in the Provinces of South Carolina and Georgia' J. E. Copenhaver U N I V E R S I T Y OF S O U T H C A R O L I N A , C O L U M B I A ,
IKCE the manufacture of synthetic indigo has almost completely supplanted the culture of the indigo plant, very few American chemists are aware of the fact that it was cultivated and exported from this country immediately following permanent settlement. Although the dye was exported from what are now the states of South Carolina, Georgia, and Louisiana, this paper is confined t o its culture in the first two states. Ross (10) has discussed the subject in an earlier article but it was thought that a more detailed account might be of some historical interest. Indigo was known to the ancients, for we find in Sanskrit methods describing its preparation and from the Egyptian mummies there is obtained cloth colored with this dye. It is not definitely known by what route it came to the Western Hemisphere but most probably it came through Europe to the West Indies, where it was acclimated and afterwards introduced into the colonies. Culture in South Carolina
S
The first permanent settlement in South Carolina was made in 1670 a t Charles Town, forming a part of a grant from Charles I1 to eight of his supporters, known as "lord proprietors." Soon after the establishment of a permanent colony, experiments were made to determine what commodities would best be suited for the new country. Among 1 Received March 5, 1930. Presented before the Division of History of Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930.
s. c.
these were rice, indigo, silk, and cotton, each of which has played an important part in the export trade and development of the country. The first introduction of indigo into South Carolina is not actually known, but it was probably about 1690, the approximate date for the advent of rice in the colonies (11). Evidence to support the fact that indigo was one of the products of the young colony is that in 1690 there is on record a request of the people to be allowed to pay their rents in silk, cotton, rice, and indigo, and an act w ~ ratified s to that effect on March 16,1695-96, by the general assembly. However, very little attention was given to the culture of indigo until about 1741-44. I n 1741 or 1742 Miss Eliza Lucas wrote to her father, then Governor of the Island of Antiqua, for seeds to plant on his plantation near Charleston (9). Among these seeds was indigo. She was interested in finding some crop that would prove a valuable product to the comparatively new country and, with the encouragement of her father, she made a sort of an experimental station of their plantation. Her first crop of indigo, planted in March, was killed by the frost; her second, planted in April, was destroyed by "a worm," but her t h r d reached maturity. She reported her success to her father and the next year more seed was sent as well as a man who was experienced in the process for extracting the dye from the plant. This man, not wishing to jeopardize the French West Indies trade in indigo by showing the American colonists their method, attempted to make a mystery of the process of extraction
August, 1933
INDUST;I2ISL A-VD E.VGI.VEERISG CHEJIISTRY
and prepared an inferior product. However, Miss Lucas suspected his treachery, dismissed him, and with the assistance of a neighbor, hIr. Devereaux, carried out the process and obtained a very good dye. Indigo seeds were distributed among the neighboring colonists and they were induced to try its cultivation as a new economic possibility. ilt this time rice, which was grown in the low swampy land, was approaching its maxinium production in the colony. but the planters desired some crop that could be profitably grown on the higher lands. Indigo seemed to fulfil these qualifications and its cultivation spread so rapidly that during the season of 174748 it was being exported to England to the amount of 134,118 pounds weight, valued a t about 17,000 pounds sterling. As stated above, indigo was grown in the colony before the experiments of hfiss Lucas, for as early as 1723 the colonial legislature granted a bounty on each pound exported. After so extensive cultivation of the plant, this bounty was removed in 1746 as it placed a much too heavy burden on the other colonists. The indigo from the American colonies attracted considerable attention in England. At that time England was importing 600,000 pounds annually from France, her commercial rival, a t a cost of 150,000 pounds sterling. At the request of the colonists and England wishing to encourage the growth of indigo in her provinces, Parliament in 1848 passed an act allowing a bounty of 6 pence (about 12 cents) per pound on all indigo imported from British colonies. This was reduced to 4 pence in 1764. Indigo had already become a profitable commodity and with this added incentive the exportation from South Carolina and Georgia rapidly increased. By 1754 the export from Charleston amounted to 216,924 pounds and in 1761-62, 239,626 pounds. Just before the Revolution, in 1775, the exportation of indigo amounted to 1,150,662 pounds, valued a t $1.10 to $1.20 per pound in our present currency. From 1749 to 1773 the British goveriiment paid 145,022 pounds sterling in bounties on American indigo, practically all of which came from Charleston. Other ports in the South Carolina province, Georgiaton and Beaufort, exported indigo, but records of these ports were destroyed during the Civil War. The English colonies not only ran the French provincial indigo out of England but undersold them in the general European markets. Culture in Georgia Indigo was introduced into Georgia from South Carolina. Records concerning its culture are not so complete as those in South Carolina, but it is certain that it was not so extensively grown. I n 1743 we find the statement (1) that “indigo flourished in Georgia,,, and in 1750 that “many farmers were engaged in the cultivation of indigo” ( 5 ) . By 1756 there were exported 9375 pounds and in 1763, 9633 pounds (7). Another writer (14) states that in 1758 there were 25,000 pounds exported. iMany references in the colonial records can be found concerning its intermittent cultivation, but t h t’re are no available records showing the amount exported from this colony. It was grown for home consumption even up to and during the Civil War. Indigo Plant and Extraction of Dye There were two varieties of indigo cultivated in these colonies-that imported from the West Indies ( I . ani1 and I . tinctoria) which was an annual plant; and the native wild, or indigenous, variety, I . Carolinia and I . leptosepala. Although the imported type had to be planted yearly, it was preferred, because of its greater yield of dye, to the native plant, which was septennial and more hardy. The
895
plant grew well in dry loose soil and was cultivated much like cotton but did not demand such careful attention. In outline it resembled cotton somewhat, but its branches were more smooth, straight, and slender. The dye occurred principally in the pinnate leaves, which were bluish green. The flower was purplish yellow and bell-shaped, giving upon maturity a bean-shaped pod. It took from two to three months after seeding for the plant to mature. The seeds were planted about the middle of April and harvesting began the latter part of June or first of July. This was usually done when the plant was in full bloom, a t which time the leaves became thicker, more juicy, and would break when doubled together. Harvesting was done, if possible, during the early morning or late afternoon, to prevent undue withering. The plant was cut close to the ground and the roots were disturbed as little as possible so that a second, and sometimes a third, crop might develop. It was bound into bundles and hauled to the indigo vats, where it was subjected t o a simple process for extracting the dye (13). The weed was placed in the steeper, which was made of a cypress or pine tank about 16 feet square and from 3l/2 t o 5 feet deep, weighted down, and covered with water. The dye, which occurs in the plant in the form of the glucoside indican, was broken down by a ferment or enzyme into glucose and the soluble indoxyl. The fermentation process usually required from 10 to 14 hours, depending upon the temperature. Upon giving certain tests to indicate the end point, for the best dye, the liquor mas drawn into the beater. The beating vat was about 15 feet long, 8 feet wide, and 5 feet deep, and was usually made of the same material as the steeper. I n this vat the dark green bluetinged solution of indoxyl was oxidized by atmospheric oxygen. The beater derived its name from the fact that in the early days negroes were employed to whip the solution with bushes or paddles, but this process was later accomplished by securing paddles or perforated wooden buckets on an axle shaft placed lengthwise of the vat and turned by the negroes. After precipitation had begun, limewater mas added from the lime vat to aid the coagulation of the dye. Agitation could not be continued too long after precipitation, as fermentation set in again and formed what was known as “burnt dye.” Precipitation was complete after about an hour of agitation and the blue precipitate was allowed to settle. The supernatant liquid was drawn off by a series of holes in the side of the beater and the dye was strained through a woolen cloth. It was carried to the indigo shed, pressed to remove as much water as possible, cut into cubes about 2 inches square, and dried on trays. The drying had to be done in the shade as the sun injured the wet dye, and during this process the cubes were turned periodically. After drying it was placed in an open-headed barrel, covered with damp moss, and allowed to mold, which required several days. The mold was brushed from the cakes, dusted with some dry indigo, and then graded. The best grade was termed “fine blue,” the next “ordinary blue,” then “fine purple,” and the most inferior “ordinary copper” (15).
During the process of fermentation there arose disagreeable odors from the vats and the extracted plant attracted flies, the latter probably being due to the sugars present from the decomposition of the indigo glucoside. It was thought that these odors were very unhealthy as well as offensive and among the early statutes of Georgia (13) is found the following law: (‘An act to oblige the planters of indigo after steeping the weed to bury or destroy it within a limited time.” The estimated average yield was from 30 to 40 pounds per acre, although some state that good land would produce
I,VDUSTRIAL A N D E-VGINEERISG CHEMISTRY
896
as high as 80 pounds. The usual calculation (4) was that eight good slaves could cultivate, harvest, extract, and prepare for the market the dye from 40 acres, “raise provisions besides and have the winter months to saw lumber.” The return for the crop depended upon the quality of the dye and the price varied from 30 cents to $2.25 per pound. It was said that a planter could double his capital in three to four years. One Georgia writer in 1751 (2) stated that the planters had brought the commodity somewhat into disrepute by attempting to produce quantity instead of quality. Cultivation after the Revolution
The cultivation of indigo grew rapidly once the planters realized the profits that i t yielded. There was a gradual increase in the production from the time of Miss Lucas’ experiments until just prior to the American Revolution, when the exportation reached the maximum. During the war it could not be classed as a “necessity,” and its culture was overshadowed by that of rice. After the war, with the market shattered and many of the plantations destroyed by the British, its cultivation was limited. One historian (8) states that “in 1783 indigo began to be cultivated again and 2051 casks were exported and continued to be a valuable export for several years.” George Washington, upon his visit to Georgia, entered in his diary on May 15, 1791, that “lumber and indigo are also exported but the latter is on the decline” (6). I n 1828-29 planters were encouraged to diversify their farming and plant indigo instead of cotton ( l a ) . It was cultivated to a comparatively small extent up to and during the Civil War, but most of it was consumed locally or “vended in the neighboring states.” I n 1848 there was published an account of the amount grown in one of the central districts (Orangeburg) of South Carolina ( 1 4 ) : YEAR 1831 1841 1842
AMOUNT PLANTED 953 1091 1337
POUNDS MADE 27,700 34,150 38.935
Vol. 22, KO.8
The price ranged from 40 to 80 cents per pound. Causes for Decline of Indigo Culture
The principal causes for the decline of indigo culture are as follows: (1) England, upon the loss of the colonies, naturally discontinued paying the bounty on American indigo. (2) Soon after the Revolution, sea island cotton was introduced, 1786 in Georgia, and the planters turned their attention to its cultivation. Also, in 1792 the cotton gin was invented which stimulated the culture of that commodity. The preparation of cotton for the market did not demand any technical or skilled labor, and the plantations were free from the offensive odors associated with the indigo vats. (3) During the Revolution indigo was imported into Europe from the West Indies, as well as other countries, until it could be no longer profitably cultivated in the colonies. It is said that “indigo was more profitable to South Carolina than the mines of Mexico and Peru were to Spain.” Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
Colonial Records of Georgia, S, 696. Ibid., 26, 235. Ibid., Statutes, Colonial and Revolutionary, 1774-1805, 19, Pt 11, 33. “Description of South Carolina,” by order of Governor Glenn in 1761. Evans, “History of Georgia,” p. 44 (1900). Knight, “Georgia’s Landmarks, Memorials, and Legends,” Vol. 11, p. 103. McCall, “History of Georgia,” pp. 174, 209 (1811). McGrady, “History of South Carolina under the Proprietary Government,” p. 187. Ravenel, “Eliza Lucas Pinckney,” Scribner, 1896; Southern Agriculturist, 7, 514 (1834). Ross, IND. E m . CHEM.,14, 1153 (1922). Salley, “IntroduFtion of Rice into South Carolina,” Bulletin of H i s torical Commzssmn, 6 (1919), Columbia, S. C. Southern Agriculturist, 1, 484 (1828). I b i d , 2, 154 (1S29), gives description of dye extraction. Stevens, “History of Georgia,” 1,457. Tuomey, “Geology of South Carolina,” Appendix 23 (1848). Wallace, “South in Building of the Nation,” Vol. V. p. 178, Southern Historical Publication Society, Richmond, Va.
Explosion of Gasoline and Oxygen’ C. K. Francis SKELLYOIL COMPANY, TULSA,OKLA.
HE note of an explosion of cracked gasoline and oxygen in good condition, the oxygen valve was opened and the AND ENGINEERINQ published on page 473, INDUSTRIAL gas admitted until the gage registered 90 pounds, when it CHEMISTRY, May, 1930, suggests that notice of a similar explosion in our laboratories may be of interest and of value to others who are investigating the accelerated test for gum. We had a disastrous explosion of a bomb into which there had been placed 50 ml. of gasoline in a 4-ounce bottle. The gasoline was an experimental blend of straight run and cracked distillates, which had been caustic-washed and sweetened. The general quality of this product is shown by these tests: gravity, 55.1”A. P. I.; initial 100” F. (37.8” (2,); 10 per cent at 154” F. (67.8” C.); 20 per cent a t 188” F. (86.7” C.); end point, 420” F. (215.6” C.); gum, copper dish, 58 mg.; gum, steam oven, 2.8 mg.; doctor sweet. The bomb consisted of two parts, the bomb proper and a top, all of 3/&ch steel. The top was secured in place by means of six lag screws l / 2 inch in diameter and 11/4 inches long. A gage was connected directly to the top and there was an inlet opening which was connected with l14-inch pipe to the oxygen tank by means of a union. After the connections were made and everything appeared IBeceived June 20, 1930.
was discovered that the union was leaking. Then this first charge of oxygen was permitted to escape and the union made tight. Next the oxygen and inlet valves were slowly opened, but for some reason no pressure was indicated on the gage. After slightly jarring the gage by tapping, the oxygen and inlet valves were opened a little more, still without any pressure being registered. After again tapping the gage, the valves were opened further, when there was a terrific explosion with a ball of fire shooting up from the bomb. All the lag screws were broken and tbe top of the bomb with connections thrown some distance. The valve was shattered and the piping was torn open. The chemist working with the bomb was severely injured and burned, an operation of a serious nature being required. This explosion occurred in a small brick building, approximately 25 by 40 feet, with eight large windows, all of which were destroyed. We have decided that the oxygen-bomb test for potential gum formation offers too much hazard, and have consequently discontinued all investigations of this sort.
I
