588
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
by heat showed a rise in temperature of only 13” C. with acid under the same conditions. Since fuller’s earth is known to polymerize even simple olefins such as amylenes, and since heating such yellow gasolines with fuller’s earth evidently causes polymerization of these yellow hydrocarbons, it has been assumed that whatever hydrocarbons could be recovered from the fuller’s earth would very probably not be the original diolefins, but their polymers. Observation of the boiling points of the diolefins present
Vol. 16, No. 6
also makes it very uncertain whether the oils retained by the fuller’s earth and which can be recovered from it represent the original colored hydrocarbons. Two methods for the isolation of these colored hydrocarbons appear to give some promise of success-namely, fractional separation by means of solvents, and the use of mercuric acetate. It is intended to continue work in this direction along the lines just indicated, with the expectation that these colored hydrocarbons may be isolated in a sufficient state of purity to prove their identity.
T h e Sodium Plumbite or Doctor Test of Gasolines’ By B. T. Brooks THEMATHIESON ALKALIWORKS, INC.,N a w YORK, N. Y.
RACTICALLY all gasoline refined today is treated to be negative to this well-known test. Though the chemistry of it is not understood, positive doctor tests have become associated with more or less malodorous gasoline and most gasolines high in sulfur give heavy precipitates in this test. It is well known that gasolines that have been treated so that they are negative to this reaction may still contain substantial proportions of sulfur derivatives. The types of sulfur derivatives which react in this test are not known, but that in the great majority of cases, some sort of sulfur derivatives are responsible for a positive reaction seems practically certain, and this is the prevailing opinion. Inasmuch as a negative doctor test is a common commercial requirement and is also legally required in some states, the writer believes it advisable to call attention to a reaction with sodium plumbite solution which very closely resembles the positive results obtained with unrefined or “sour” gasoline. The resemblance is so close that when shown the test many experienced petroleum chemists have pronounced it a positive and characteristic doctor reaction. A positive. result in the test in question may be obtained with oils absolutely free from sulfur, and since the results are due to peroxides, it will be referred to as the “peroxide reaction.” I n a typical doctor test the oil is agitated with a solution of litharge in caustic soda; a yellow discoloration results, usually without the formation of any visible precipitate. A very small proportion of sulfur is then added and the mixture agitated again, when the color is much intensified and a flocculent precipitate begins to form, the color passing through a dull orange, rapidly becoming darker, to brown, and finally assuming a brownish black or black color. (When free hydrogen sulfide is present, black lead sulfide is immediately formed,) I n ‘rapid routine testing the initial orange tints are usually all that are noted, these being obtained in a few seconds. A sample of cracked gasoline that had been treated until entirely negative to the alkaline plumbite test showed a very positive test after standing several months; the usual color changes were noted, but the brownish black precipitate suggested that it might be lead peroxide. When the gasoline was tested for organic peroxides by shaking with a little starch-iodide solution, a very positive reaction was obtained. Another sample of cracked gasoline was then refluxed over metallic sodium for about 6 hours and then distilled over
P
1 Presented under the title ”Note on the Doctor Reaction for Sulfur” before the Division of Petroleum Chemistry at the 65th Meeting of the American Chemical Society, New Haven, Conn., April 2 to 7 , 1923. Received December 19, 1923.
this metal. The distillate was entirely negative to alkaline plumbite and the addition of sulfur caused no discoloration; any sulfur derivatives not reacted upon by the metallic sodium were certainly very stable and at any rate showed not the slightest reaction with alkaline plumbite and sulfur. After standing 3 weeks in a partially filled and loosely stoppered bottle, this gasoline showed the lead peroxide test with alkaline plumbite and the peroxide test with starchiodide solution. A sample of turpentine was then refluxed over sodium and then distilled, the distillate collected a t 156” to 158” C. and tested for sulfur by all known methods, with entirely negative results. It was also entirely negative to alkaline plumbite, but after standing in a partially filled bottle soon acquired a peroxide reaction and with alkaline plumbite showed the yellow-orange-brown color changes. After standing about 3 months, the reaction was so pronounced that to simulate a very sour gasoline it was necessary to dilute i t ten times with a doctor negative gasoline. When a few drops of aqueous hydrogen peroxide, about 0.5 per cent, are added to a mixture of sweet gasoline and alkaline plumbite, the dark brown precipitate of lead peroxide is produced almost immediately. When a trace of benzoyl peroxide is added to sweet gasoline and then agitated with alkaline plumbite, the yellow-orange-brown color changes are observed, indicating that organic peroxides are responsible for these color changes in this peroxide test, with the ultimate formation of lead peroxide. It was noted that the addition of sulfur did not intensify the color and its addition was not necessary to bring about the formation of the precipitate; in parallel tests the amount of precipitate was not visibly increased by the addition of sulfur. This difference helps to distinguish this peroxide test from the true doctor test, which is almost certainly due to sulfur ‘derivatives. Moreover, the precipitate in the latter case, if allowed to stand a few hours, becomes quite black, whereas the lead peroxide retains its distinct dark brownish shade. Another difference that may sometimes be noted is that cracked oils which have become oxidized by air during storage may show considerable discoloration when treated with alkali, due probably to the presence of aldehydes formed by the air oxidation, Oxidation of cracked gasoline by air is, like all such processes, much accelerated by sunlight, and such a peroxide test as described above is much more likely to be developed in glass sample bottles than in iron storage tanks, from which light is excluded and which have relatively little surface, compared with the volume, exposed to air.
June, 1924
INDUSTRIAL A N D ENGIhTEERING CHE-VISTRY
589
Thermal Reactions of Coal during Carbonization',' By J. D. Davis and Palmer B. Place PITTSBURGH
EXPERIMENT STATION, BUREAU O F MINES, PITTSBURGH, PA.
AVAILABLE METHODS H E N coal is The thermal behavior of coals during carbonization is discussed heated, as in a and methods applicable to the determination of reaction heats are Methods that have been coke oven or gas compared. The heating rate method originally used by HoNings employed in the study of retort, the first effect of the and Cobb for investigating reaction heats of English coals has the reaction heat of coal are heat is to drive out occluded been applied with slight modification to seven typical American as follows: gases and moisture. At coals and a sample of pine sawdust, and an attempt has been made to 1-The indirect calorimethigher temperatures, over compare the results with those found by direct determination in a ric method, in which the the range 105' to 310' C.,3,4 constant volume calorimeter. reaction heat is taken as the water of composition, oxides difference between the comThe heating rate results show no oery close relation to the net reacbustion heat of the coal and of carbon, and gaseous hytion heat as determined calorimetrically; other thermal effects.such as that of its distillation proddrocarbons-both saturated sensible and latent heats of the carbonization products, are of much ucts. and unsaturated-are greater magnitude than the reaction heats, and they do not vary in the 2-The direct calorimetric evolved, Water of comsame way for different coals. The heating rate method may doubtless method, which involves the position continues to come use of the calorimetric apparabe used to advantage for comparing the actual coking rates of different tus adapted to the measureoff up l,o and beyond the coals, but the inflection points in the rate curves do not necessarily ment of the reaction heat point of tar formation (310" indicate heats of reaction comparatively although they seem to come at while the reactions are in C.), while the gaseous prodpoints where strong thermal reactions take place. progress. ucts increase in volume Approximate results are presented showing the relation of reaction 3-The heat balance over the same range. While method as applied to comheat determined calorimetrically to the maximum distillation temmercial-scale coke ovens, and most of the uncombined perature for coking coals. The results indicate that for high temperaalso to experimental carbonwater is driven off under tures prevailing in coke oven operations the reaction heats are izing apparatus. 105' C., according to Mack endothermic. 4-The h e a t i n g r a t e and Hulett,6it is not enmethod, wherein the heating tirelv rernovedunder230 "C. rate of coal indicates its Tiylor and Porter4 have shown that 66 to 75 per cent of reaction heat when compared with that of an inert substance such as coke. The same heating conditions are maintained the volatile matter of coal, as primary volatile products, is for coal and coke over the carboiiizing range, and variations removed under 500' C.; and that a t temperatures as low as in the temperature of the coal relative to that of the coke are 475' C. secondary decomposition of the tar into permanent ascribed to reaction heats developed a t the temperature in gases is appreciable. Beyond this point secondary reac- question; where the coal heats faster than the coke, positive tions increase rapidly with rising temperatures, depending reaction heats predominate, and vice versa. largely upon the time of exposure of the distillation products The indirect calorimetric method was used by Mahler,' to the heat. Thus, primary and secondary reactions doubt- who found the heat of reaction of a bituminous coal to be 264 less go on simultaneously over a fairly wide temperature calories per gram. This method, however, is exceedingly range during the carbonization of coal, and it is known that difficult to carry out. The results are rendered uncertain, they are subject to considerable variation with slight varia- because they include a summation of errors of all the combustions in the carbonization conditions. It would be expected, tion determinations, and the difference due to the reaction therefore, that for any given distillation range the heat of heat is small compared with the total heat of combustion of reaction,6 being a summation of all the heat effects included, the raw coal and that of its distillation products. A further would be constant for a particular coal only when all distillation point to be considered is that a t the time Mahler worked conditions are maintained constant within narrow limits. (1891) the methods of combustion calorimetry were not so This has been found to be particularly true within primary well developed as they are now, and the accuracy attainable distillation ranges; the total amount of heat involved is small, could hardly have been better than 0.5 per cent. not over 50 calories for a coking coal-and it is extremely Strache and Grau8 have recently determined the reaction difficult to maintain closely reproducible distillation condi- heats of gas coals, brown coal, lignite, and cellulose by the tions. For these reasons, experimental results obtained so direct calorimetric method. Their results show a heat far do not warrant an attempt to correlate closely the heat absorption of 8 and 9 calories per gram for gas coal carbonof reaction with the nature of reactions predominating; ized a t 720" C., and as high as 262 calories evolved for celluit does vary, however, with the temperature of carbonization lose. The reactions became more exothermic the higher the and this point will be discussed in this paper. oxygen content of the sample. On a later paper Strache and Frohng gave the relation of the lower reaction heat to the oxy1 Presented by J. D. Davis before the Section of Gas and Fuel gen content of the coal, arrived a t by determination of the Chemistry a t the 65th Meeting of the American Chemical Society, New amounts of the distillation products, and calculating the heat Haven, Conn., April 2 t o 7, 1923. Received March 10, 1924. 2 Published by permission of the Director, U. S. Bureau of Mines. carried off by them a t the carbonizing temperature. Strache's Burgess and Wheeler, J. Chem. SOC. (London), 97, 1917 (1910); results apply only to the one temperature-namely, 720" C.99, 650 (1911). that is, they represent the sum of all the reaction heats up t o 4 Taylor and Porter, Bur. Mines, Tech. Paper 140 (1916). that temperature, and give no information as to what the 5 A m . J. Sci., 43,89 (1917).
W
8
6 The term "heat of reaction" or "reaction heat" as used in this paper will mean the ~lgebraicsum of all heats of the decomposition reactions within the tempeiature range in question, not including any sensible or latent heat effects.
7 8
Compt rend., 113, 862 (1891). Brennstoff-Chem., 2 , 97 (1921).
* Ibzd.,
3, 337 (1922).
