ISDUSTRIAL A S D ENGINEERING CHEXISTRY
June, 1926
also slightly higher in the springwood. Even here, however, the ratio of lignin to cellulose is higher in the springwood than in the summerwood. An explanation of why the lignin constitutes a larger percentage of the total wood substance in springwood than in summerwood is already available in a recent paper by Ritter,3 in which it was shown that the lignin is located partly in the cell wall mixed with the cellulose and partly in the middle lamella with very little, if any, other substance present. If the ratio of lignin to cellulose in the cell wall, exclusive of the middle lamella, is the same in springwood as in summerwood, then the lignin in the middle lamella, which constitutes a greater proportion of the total wood substance in the a TRIS J O U R N A L .
17, 1194 (1925).
609
springwood, would account for the higher proportion of lignin in springwood than in summerwood. The remaining determinations showed no uniform differences in chemical composition between springwood and summerwood, although a tendency was apparent toward higher percentages of (a) pentosans in the springwood, (b) pentosans in the isolated springwood cellulose, and (c) extractives in the springwood. Conclusions 1-A higher percentage of lignin exists in springwood than in summerwood. An explanation is offered for the different lignin yields in the two bands of growth. 2-Cellulose forms a larger percentage of the total wood substance in summerwood than in springwood.
Relation between Fuel Deposition Temperature and Equilibrium Boiling Point’ By W. A. Whatmough FRIERN W A T C H AvE., NORTH FINCHLEY, LONDON h-,12. ENGLAND
The determination of “fog points” of combustible mixtures in internal combustion engines under roadrunning conditions confirms the conclusion of Barnard and Wilson t h a t the equilibrium boiling point of a motor fuel is a measure of its volatility. I n t h e writer’s opinion the equilibrium boiling ranks equally with the first-drop and end-point temperature of a n Engler distillation in providing prime characteristics for t h e evaluation of a motor fuel. The first-drop temperature, or preferably the temperature range of the first 10 or 20 cc. of a n Engler distillate, indicates t h a t volatility which gives ease of “starting from cold.” The equilibrium boiling point provides information regarding volatility of t h e motor fuel as a whole, and fixes the induction pipe and mixture temperatures necessary to insure stability of its combustible mixture
under normal conditions. Along with t h e end-point temperature of a n Engler distillation, the equilibrium boiling point affords definite criteria in regard to prevention of crank-case dilution. However, it is t h e equilibrium boiling point t h a t indicates when t h e induction pipe temperature is dangerously low, irrespective of whether this is due to low volatility of t h e fuel available, or to prevailing climatic conditions. The results show t h a t t h e equilibrium boiling point test for mixture stability can be extended t o all types of motor fuels, whether hydrocarbons (gasoline and kerosenes), or mixed motor fuels containing aromatics, naphthenes, and alcohols. The writer has found i t t o apply also to fuels containing vaporizable coal-tar productsnaphthalenes, phenols, and cresols.
MERICAN chemists are already familiar with the investigations of Barnard and Wilson2 on the vapor pressures of equilibrium solutions prepared from motor fuels, from which data the dew point, or fuel-deposition temperature, of gasoline-air or kerosene-air mixtures can be calculated. Several years ago the writer3 determined the “fog points,” or fuel-deposition temperatures, in engine manifolds-these being temperatures a t which visible droplets of liquid form in a flowing fuel-air mixture made from gaseous components. Fuel is deposited as liquid a t the fog-point temperature when the velocity of the mixture is low and if the “induction” pipe is a t or below the fuel-deposition temperature. Figure 1 depicts graphically a somewhat surprising agreement between the results obtained by two researches utilizing methods differing radically in principle. Thus Barnard and Wilson measure, in the absence of air, the vapor pressure of a relatively stationary column of mixed saturated vapors of hydrocarbon gases, which is representative of their equilibrium solution. The author’s observations relate to a mix-
ture of fuel gases from an equilibrium distillate admixed with air and flowing as a pulsating stream through the induction pipe of an internal combustion engine.
A
Arrangement of Apparatus
Figure 2 shows the general arrangement of apparatus used for determining the fog points of motor fuel-air mixtures under road-running conditions. The liquid fuel is evaporated in a “flash”-type balanced pressure boiler under equilibrium conditions-i. e., a t the same rate as it is used. This boiler is shown in greater detail in Figure 3 and consists of an outer vessel, G, with an internal heater consisting of a metal block, E , intersected by vertical saw cuts. The block E is continuous with the plate P, bearing the staggered pins C for collecting heat from the exhaust gases entering a t A , which pass downwards and then upwards as shown by the direction of the arrow. Heat is transmitted from above downwards, and only the top layer of the liquid fuel is a t its boiling point, the liquid being pushed away if gas is generated faster than it is used. The level of the boiling liquid falls or rises to meet any variable demand for fuel gas. 1 Received August 15, 1925. Revised paper received April 5 , 1926. 2 J . Soc Aulomolzve E n g , 9, 313 (1921); 12, 287 (1923); THIS The boiler is part of the Keith-Whatmough system4 of JOURNAL. 17, 428 (1925). dry gas carburation for utilizing heavy or nonsprayable ‘Keith and Whatmough, Proc Inst. .4ulomolzoe Eng., 17, Pt. I 363 (1922).
4
English Patent, 184,266 (1922).
1-01. 18, KO.6
IA-DCSTRIAL A N D E-VGINEERISG CHEMISTRY
610
motor fuels. The fuel-gas capacity of the boiler, and quality control governor attached, is only a few cubic inches, or sufficient for a few revolutions of the engine. The conditions of gas production are accordingly precisely those used by the writer5 for determining equilibrium boiling points, inasmuch as fuel is boiled continuously as it is fed from a variable level feed with balance pipe, or pressure-equalizing tube, between the float chamber and boiler. The vaporized fuel from the 115,
narrow annulus (and not as drawn). The original paper3 should be consulted for details of the relationships of the varying flows of air, gas, and combustible mixture. Tests
Road tests with a Ford van (total weight with load 2800 pounds) was used as a check on fuel efficiency. The mixture strength used was that which gave good power with reasonable economy. The following mileages per British gallon were consistently obtainable on a known test route when using commercial motor fuels in the form of dry combustible mixtures: aviation petrol, 30; No. 1 petrol, 32; benzol, 38; paraffin, 35. The weakest possible running mixture (corresponding to 15 air to 1 fuel gas) gave about 20 per cent increase in mileage-e. g., benzol 44 miles per gallon. On this basis the running mixture for economy with power and comfort mas probably a close approximation to 12: 1 air-fuel ratio. Thermometers were used for checking the temperatures of the combustible mixture and its gaseous components. The readings available were: (I) temperature of in-going air, (2) fuel gas temperature, (3) mixture temperature before throttling, and (4)mixture temperature after throttling. Saturally the temperature of the air supply varied according to season and distance of intake from heated surfaces, advantage being taken thereof to vary conditions in order to obtain critical fuel deposition temperatures. Thus a mixture temperature of 40' C. would be made up as follows: c. Air temperature (atmospheric) Temperature rise due to hot fuel gas Temperature rise due to heating of air supply by surroundings
21 11
-8 40
€ququrlrbnum Temperature
Figure &-Equilibrium Boiling Point Temperatures of Motor Fuels 08. Their Fuel-Deposition Temperatures
boiler becomes superheated during its passage towards the governing device used to maintain the combustible mixture at a constant strength. The working temperature of the fuel gas (240" to 260" C.) is ordinarily well above the saturated vapor temperature of motor fuels a t pressures approximately atmospheric, the variation being * 1 pound per square inch from prevailing pressure of the atmosphere. For the heaviest fuels, kerosene, and Edeleanu (aromatic) extracts, with equilibrium boiling points above 240' C., an aluminum boiler was found to be advantageous as it enabled the attainment of gas temperatures of 280" to 320" C. The device for maintaining a definite ratio of fuel gas and air in the combustible mixture, independent of variation in engine speed or load, consists of a floating piston attached to a sliding valve, which takes charge of fluctuations of pressure in the boiler and at the same time regulates the pressure of the (governed) fuel gas. The pressure gradient in the fuel gas between that in the piston chamber and the mixing point is the same as that existing in the air flow between the end of the pressure loading pipe to the back of the piston chamber and the point of admixture of fuel gas and air. Accordingly, whatever variations occur in the air stream are reproduced in the gas flow. The quantity of mixture flowing to the engine is regulated by the throttle in the ordinary way. The quality can be set by varying the contracted passageway by the quality control valve between the governed gas pressure and the mixing point, this restricted gas passage being in practice a THISJOURNAL. 18, 43 (1926).
Fog points at temperatures below 40" C. were determined in winter. With petrol mixtures the Venturi mixing nozzle was unheated. A throat heated by exhaust gases was used for relatively heavy nonsprayable fuels with fog points above 60" C. Gain or loss of heat from the induction pipe was prevented as far as possible by lagging. It is necessary to stress two important points in connection with the determination of dew-point and fog-point temperatures. First, the temperature reading when fuel deposition occurs is due to a wet bulb effect as in hygrometry, and owing to condensation or evaporation the temperature registered by the thermometer may depart considerably from that of the surrounding mixture saturated with vapor, particularly if the latter is stagnant. Induction-pipe temperatures from wet mixtures are misleading owing to evaporation effects when the mixture is receiving external heat. The thermometer bulb is cooled by evaporation of liquid from its surface and frequently registers temperatures 10" C. below that of the mixture. Second, the production of dew or fog depends upon an actual flow of heat which is normally from combustible to mirror or induction pipe. With engine tests a heat balance can be attained between combustible mixture and external atmosphere (heated by engine), this occurring ordinarily in the induction manifold of a Ford engine between 40 " and 50" C. Above this temperature insulation by lagging prevents that extreme readiness of fuel deposition which is characteristic of heavy fuels and which increases with heat loss through induction pipe to external air. With very volatile fuels the opposite effect is evident. The great dBiculty with the lightest petrols is to exclude external heat because the latent heat of hydrocarbon fuels is so low that a small amount of heat transmission from external air through the induction pipe is sufficient to cause re-evaporation of condensed vapor and prevent fuel deposition. I n determining fog-point temperatures these effects are greatly minimized
I,VDVSTRIAL .4ND ENGl‘,VEERISG CHEUISTRY
June, 1926
by the large volume of combustible mixture flowing through a well-insulated induction pipe. It is obvious that the temperature registered by the thermometer as the fueldeposition temperature may deviate from the temperature at which the combustible mixture is fully saturated-i. e., with fuel vapor in equilibrium with liquid fuel-but any error is in the direction a t which fuel deposition occurs under roadrunning conditions.
minimized owing to the flowing mixture cleansing the bulb, as is evident in (6) below. ( 5 ) The critical temperature at which fog is formed (fog point) is readily determined with a motor fuel under running conditions, with an accuracy between 1’ and 2’ C. (6) Fog formation is accompanied by deposition of liquid when engine is running slowly. This layer of liquid fuel is snuffed up bodily upon speeding up. When this occurs the ennine shows the characteristic signs - of bad distribution-stangering or uneven running. I I
Thermometer h r Mixture Temperature after throttlina
n
n
Thermometer f o r Air Temperature
Thermometer fbr M i x t u r e Temperatun
ometer 6 r Gas Temperature
b Figure 2-Apparatus
tank
for Determining Fog P o i n t s
Results
The data in Table I are from actual determinations of both fog-point temperature and of equilibrium boiling point on the same fuel. The percentage position of the latter on the Engler distillation curves is included. between Fog Point a n d Equilibrium Boiling Point Approx. percentage position of equilibrium Temperature Equilibrium boiling point on of fog boiling Engler formation point distillation FUEL O c. O c. curve Petrol I 29 121 60 Petrol 111 127 70 33 Light kerosene (50%) 69 179 65 Benzol (50%) Heavy kerosene (50%) 77 196 65 Benzol (60%) Light kerosene (50%) 215 iJ 88 Light tar oil (50%) 98 226 SO Light kerosene 242 85 108 Heavy kerosene
Table I-Relation
611
Gruse6 has determined by a direct method the dew points of gasolines identical with those investigated by Barnard and Wilson, and thereby comparable with the writer’s fog points. There is a difference of 20’ C. or more betn-een Gruse’s “dew-point temperatures and the writer’s fog points,” and the discrepancy is so great that it is advisable to retain the earlier name “fog point” to indicate formation of visible vapor in the induction manifold of an internal combustion engine. The difference is inexplicable unless metastable conditions of supersaturated vapor are present with Gruse’s method, owing to slow heat transmission in a relatively stagnant mixture (see notes on wet bulb effects above). It is agreed that poor admixture and wet (evaporating) fuel gas would tend to give low dew points but these defects are decidedly absent in the experimental procedure used by the writer. Conclusions
The linear relationship between observed fog points and equilibrium boiling points of the author on the whole agree with those calculated by Barnard and Wilson for light fuels (petrols, gasoline, benzol mixtures, etc.) but diverge steadily on progressing towards heavy fuels, the observed fog point for kerosene being some 10’ C. lower than the calculated dew point. This is understandable if it is remembered that fog formation is consequent upon loss of latent heat of vaporiaation and that this heat loss increases directly according to
--
-C
The actuality of the relationship between equilibrium boiling points and fuel-deposition or fog-point temperatures in an engine manifold is obvious from Figure 1, and from the following considerations: (1) Fuel was boiled under equilibrium conditions in a balanced pressure boiler. (2) Mixture of constant quality was maintained automatically. (3) Fuel gas, air, and mixture temperatures were available as check. Temperatures were not affected by heat changes due t o evaporation or condensation until actual fog point was attained. (4) “Fog” or visible drops of fuel were formed in a moving column of combustible mixture made from gaseous components. Irregularities of temperature readings due to evaporation from the thermometer bulb or condensation of liquid thereon are
r-=pbv _ >
Figure 3-Equilibrium
Boiler Emplo e d for Producing Dry Gas f r o m Motor &el*
temperature difference between the fuel mixture and external air. Thus a t higher temperature more rapid loss of heat by radiation will result in quicker fog formation. This is in accord with actual conditions during carburation of internal combustion engines. 8
TAISJ O U R N A L , 15, 798 (1923).
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IXDUSTRIAL A N D ENGINEERING CHEMISTRY
Table I and the writer's previous article show that the 85 per cent point of an Engler distillation does not represent with sufficient accuracy the equilibrium boiling point of all types of mixed motor fuels. Accordingly, it is desirable to make a direct determination of the equilibrium boiling point. With this exception, the writer's results confirm Barnard and Wilson's conclusions, their corrected 1 2 3 line on
Vol. 18, No. 6
Figure 1 undoubtedly corresponding to ideal mixtures and conditions. The foregoing data prove that equilibrium boiling point is a real measure of the volatility of a motor fuel under running conditions. Furthermore, the equilibrium boiling point of a motor fuel is an accurate guide to the induction-pipe temperature necessary to maintain a combustible mixture in a stable condition and thereby prevent fuel deposition.
The Chemical Composition of Rosin' By Dexter N. Shaw and L. B. Sebrell THE GOODYEAR TIRE& RVBBERCO.. A K R O S ,
OHIO
T
HE exact composition of rosin is still open to question. That it is of an acid nature has long been recognized but whether this is due to the presence of free acids or of acid anhydrides is still disputed. The work described in this paper was carried out in an endeavor to obtain first-hand information as to which of these theories was most plausible.
but were unable to obtain any product by vacuum distillation which corresponded to the anhydridc formula. Their analyses gave figures which checked the C20H3002 formula and the distillate on cooling and recrystallization from alcohol gave crystals whose melting point was nearly the same as that usually accorded abietic acid and much higher than that recorded by Bischoff and Nastvogel. Historical Knecht and his co-workers'o have more recently advanced The work on the chemistry of rosin dates back to 1826, the idea that rosin consists essentially of an acid anhydride. when Baupe2 first showed that it contained crystallizable Their experiments showed that samples of abietic acid preacids. A large amount of pared by recrystallization from glacial acetjic acid or work has since been pubalcohol would easily split off lished on the rosin acids Samples of abietic acid were prepared from rosin by almost exactly one mol of and on their relation to the five different methods. All are isomeric compounds water per each two C20H3002 original c o m p o s i t i o n of having the same analysis but different physical propermolecules when heated in rosin. Acids of different ties. Abietic acid readily oxidizes to a monoxy derivaan atmosphere of dry carp h y si c a 1 properties have tive, which on heating readily evolves water forming bon dioxide. The residue been isolated by different monoxyabietic anhydride. In the absence of oxygen remaining after the evoluinvestigators and variously abietic acid does not evolve water and the correspondof the water gave on tion named abietic, pinic, sylvic, ing anhydride is not formed. analysis results in accordsapinic, etc. The empiriRosin must, therefore, be composed of free acids ance with the formula cal formula of these acids rather than acid anhydrides. was first d e t e r m i n e d as (C20H290)2 0 . Stockll concluded that C20H3002 by T r a m m ~ d o r f , ~ rosin consisted of three free who analyzed the copper salt, which formula has now been generally accepted. The isomeric acids, which he designated as CY, b, and y abietic acids. physical properties of the acids, such as the melting point These he isolated according to the method of Tschirch by and optical rotation, vary according to the method of prep- means of their metallic salts. Ruzicka and Meyer12 and Ruzicka and SchinzI3 were unaration, such as crystallization from alcohol or acetic acid, or precipitation from an alcoholic solution by hydrogen able to verify the work of Knecht that abietic acid was dechloride,4 but they do not change the chemical behavior.5 hydrated by heating to 190' C. in carbon dioxide for 8 hours. Malye first expressed the opinion that the rosin consisted They claimed that in their experiments not. a trace of water essentially of anhydrides which on crystallization from was liberated under these conditions. Knecht later offered alcohol were transformed into acids. This conclusion was the objection that the acids which Ruzicka investigated were further strengthened by Bischoff and N a ~ t v o g e l ,who ~ re- not the same as those which he used for the following reasons: ported that rosin, if distilled in a high vacuum, gave a dis- (1) they were prepared by different methods, (2) they were not tillate which corresponded t o the anhydride C40H~803,and identical in melting point, and (3) that heat distillation forms this distillate on recrystallization gave an acid having the for- a new acid by pyrogenic action which is not present in apmula C20H3002. This assumption was questioned by Hen- preciable amounts in commercial rosin. H e offered further rique* and also by Esterfield and Bag1ey.Q The latter in- experimental evidence of the correctness of his results. vestigators repeated the work of Bischoff and Nastvogel, Steele,l4 assuming that rosin was composed of the anhydride, developed a method for the preparation of abietic acid by 1 Presented before the Division of Organic Chemistry at the 69th supposedly hydrolyzing the anhydride with glacial acetic Meeting of the American Chemical Society, Raltlmore, Md., April 6 to 10, 1925. Received October 28, 1925. acid. On the other hand, SchorgerI5 crystallized some vacAnn. chim. phys., 1826, 108. Ann. Phavm., 18, 169 (1835). 4 Fluckinger, J . firakl. Chem., 101, 235 (1867). 6 Aschsn, Chem. Z l g . , 84, 149 (1924). I Ann., 182, 249 (1864). Ber., 28, 1921 (1890). 8 Chem. Rev., 1899, 106. 0 J . Chem. SOC.( L o n d o n ) , 86, 1238 (1904). I
10 Knecht and Hibbert, J . Soc. Dyers Colourisls, 86, 148 (lQlQ); 89, 338 (1923). 11 Fnrben-Zlg., 27, 156, 221, 287, 353, 416 (1921). I* Heluelica Chim. A d a , 6 , 315 (1922). I* I b i d . , 6,833 (1923). 1 4 J . A m . Chem. Soc., 44B 1333 (1922). 16 Ibid , 46, 1339 (1923).
