INDI;STRISI; A S D E,YGISEERISG CHEJIISTRY
February, 1930
The tolerance of acetone in the outlet gas is: 10,000 X 0.06 X 0.02 = 12 cubic feet per hour, or 0.12 mol per cent. The intercept on the 2 axis of the operating line is therefore
P
zp
(W - 0)
+P
__
27.87
68.34 - 66.67
- = + 27.87
The operating line is now plotted, and the number of theoretical plates developed in the usual manner. The number of steps on the operating line is 6, and this is the theoretical number of plates.
Literature Cited
0.113
mol per Cent.
167
(1) McCabe and Thiele, IND. ENG.CHEM.,17, 605 (1923).
-
of Comparative Efficiencies of the Components Creosote Oil as Preservatives for Timber' F. I€.Rhodes and F. T. Gardner CORXELLUNIVERSITY, ITHACA,h-.1 ' .
A new method for the determination of the fungicidal T'arious methods have been H E value of c o a l - t a r powers of preservatives for timber is described. suggested for the accelerated creosote oil as a preThe fungicidal powers of various fractions from the testing of timber preservaservative for timber is dead oil, the tar acids, and the tar bases from creosote tives under controlled condiclue in part to its action in exoil, and of some of the pure components of creosote oil tions in the laboratory. Sevcluding moisture from the were measured. eral investigators h a v e dewood. The oil w e t s wood Phenolic compounds vaporize much less readily from termined the minimum conreadily, so that the surface of wood than do aromatic hydrocarbons, probably becentration of the preservative the treated timber is covered cause the phenolic compounds wet the wood more which is required to inhibit with a rather firmly adhering readily and are more strongly adsorbed by it. The the growth of a wood-rotting film of water-repellent matepossible action of tar acids as mordants for creosote fungus in an artificial culture rial. Since moisture is necesoil on wood is discussed. medium and have taken this sary to the growth of the fungi The vapor pressures of various fractions and mixtures minimum inhibiting concenw h i c h d e s t r o y wood, the of fractions of creosote oil were measured. tration as a direct measure formation of such a water-reThe percentages of certain hydrocarbons in the fracof preservative efficiency. pellent film aids in protecting tions from coal-tar creosote oil were determined. W o r k d o n e by this method the timber. I n addition t o Drior to 1915 has been sumthis general sealing a c t i o n , some-of the components of the oil have a specific toxicity for marized by Humphrey and Fleming (20). Kithin recent years fungi. It was formerly thought that the specific fungicidal the method has been employed by Dehnst ( I S ) , Falck (15), power of creosote oil was due largely or entirely to its content Makrinov and Shtrobinder (&3),and Schmitz (29), and by of phenolic compounds. At the present time it is rather Bateman and his co-workers (4 to 9) a t the U. S. Forest generally recognized that some of the other components, Products Laboratory. Bateman and his associates, working with cultures of Foines such as the hydrocarbons, may also be toxic l o fungi, although information as to the exact nature of the compounds annostis on agar-agar media, have modified this general principally responsible for the specific fungicidal properties method to render it suitable for measuring the inhibiting action of solutions which are so dilute or so ineffective that of creosote oil is still rather incomplete. Various methods have been suggested for comparing the growth of the fungus is merely retarded and not comthe efficiencies of different types of creosote oils and for de- pletely prevented. These investigators concluded that only termining quantitatively the preservative powers of the in- those compounds which are a t least slightly soluble in water dividual components of coal-tar creosote oil. Rather ex- have fungicidal properties and that, among similar comtensive service tests (3, 10, 11, 1.2, 14, 16, 18, 18, 22, SO, 32, pounds, the efficiency as a preservative is approximately 33,34,35, 36) have been conducted for many years, and from proportional to the solubility. Phenolic compounds with the data thus collected conclusions have been drawn as to the lower molecular weights than that of naphthol showed a t types of preservatives and the methods of impregnation which least partial inhibiting action; those with higher molecular may be expected to give satisfactory results under various weights were not fungicidal. Alpha-naphthol had no effect conditions of service. Our present specifications for creosote upon the growth of the organism, while beta-naphthol showed oils for various purposes are based partly upon the results of some inhibiting action. Aromatic hydrocarbons with molecuthese tests and partly upon general impressions gained by lar weights less than that of naphthalene completely preexperience in the use of treated timber. While the protection vented the growth of Fomes unnosus, those of higher molecular afforded under actual service conditions must always be the weights showed partial but not complete inhibiting action. final criterion of the value of a preservative, the service test I n mixtures of two or more hydrocarbons, none of which is not a satisfactory guide in the control and improvement of prevented growth entirely, the effects of the individual comthe quality of creosote oil. A very long time is required to ponents were geometrically additive. obtain the final data; tests made on a scale large enough to The use of Fomes annosus as a standardizing fungus was be significant are expensive; and the final results may be so criticized by Dehnst ( I S ) , who pointed out that this organism greatly influenced by unavoidable variations in the conditions is usually found as a parasite on living timber and only of service that direct comparison of the results of different rarely occurs on timber in service. Despite this fact, Fomes series of tests may not be possible. annosus does offer several advantages as a test organism in the comparison of the efficiencies of preservatives. It is rather Received h'ovembt*r 21, 1929. T h e nork described in this article easily obtained in pure cultures and can be propagated in the % a s done under a fellowship maintained a t Cornell University by the American Creosoting Company. laboratory readily and without loss of virility. It appears
T
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
168
to be as resistant to fungicides as any of the true wood-rotting fungi, so that a concentration of preservative which will inhibit growth of this organism may reasonably be expected to preserve timber effectively in service (27). There can be no doubt that laboratory tests made with cultures on agar-agar have afforded much valuable information as to the relative fungicidal powers of the various components of creosote oil. It does not follow, however, that deductions drawn from experiments with such cultures can be used directly in predicting the protective efficiencies of the various preservatives as applied to the timber. There is a possibility that the fungicide may show different chemical or physical (colloidal) reactions with the agar-agar than with the wood, and that these differences may render the results not directly comparable. The protection afforded by creosote oil is apparently due, in part, to its sealing and waterproofing action-a factor which does not affect the results of tests made with ordinary aqueous cultures. Components Soda Lime
G l a a Wool
Vol. 22, No. 2
in diameter). The pad was compacted by pressing and was then dried at room temperature for 24 hours. The paperlike disk of dry pulp was uniformly saturated with 10 cc. of a solution containing a known amount of the preservative dissolved in ether, dried in the air for 30 minutes, and finally placed under vacuum (under a bell jar) for 5 minutes. The circle of impregnated pulp was placed in a Petri dish on top of a malt-agar culture of Fomes annosus2 which had been allowed to develop until the entire surface of the culture was covered with the fungus, a large watch glass was inverted over the dish, and dish and cover were set in a shallow basin of water and incubated at 25" C. The water in the outer basin was of such height that it covered the lower edge of the watch glass and thus prevented loss of the preservative by volatilization. The first evidence of the growth of fungus in the pulp was the appearance of white threads or mycelia on the surface of the disk. On further incubation, stains of brown rot appeared. In the absence of a preservative, the white mycelia appeared in a few days, quickly followed by brown stain covering all or almost all of the surface. The addition of a preservative increased the time required for growth until, with an amount of fungicide barely insufficient to prevent growth entirely, the white threads appeared only after several weeks and then only in small amounts and over limited areas. Complete inhibition was indicated when no growth occurred after incubating for one month. By progressively varying the concentration of the preservative it was possible to establish two limiting concentrations, the higher of which wm just sufficient and the lower just insufficient to prevent growth. These were taken as the "toxic limits" of the preservative. Preliminary experiments showed that disks of pulp which had been treated with ether alone and dried and incubated in the usual way gave as rapid growth of fungus as did untreated disks.
Figure 1-Apparatus for Determining Vapor Pressures of Fractions of Creosote Oil
which affect the manner and extent to which the oil wets the wood may conceivably have a marked influence upon the degree of protection afforded by creosote oil in actual service, although they might not of themselves be strongly fungicidal or noticeably affect the fungicidal power of the oil in artificial culture media. Several investigators have suggested laboratory methods by which the protective action may be measured under conditions which simulate those existing in actual service. I n some of these tests (20) the rate of growth of wood-rotting fungi in chips or blocks of wood impregnated with preservative has been measured. Such tests require a very long time; and usually the concentration of preservative differs among different test pieces and varies within the same piece so that any quantitative comparison of the results is difficult. Schmitz and Zeller (B),Sowder @ I ) , and Reeves (25) have suggested tests in which the nutrient medium is sawdust or wood flour treated with the preservative to be tested. These methods represent a marked improvement over the older methods, but are still not free from objection.
80
1 and 2
Materials Used
The creosote oil used as a source of material was from a 50gallon shipment of typical coal-tar creosote from the American Tar Products Company, at Utica, N. Y. It showed the following analysis: BULB DISTILLATIOW' Tempernture
Distilled Per cent by weigh; Start-210 1.2 210-235 14.3 235-270 20.8 270-315 20.5 315-355 20.2 Residue 21.0 Limpid point.. . . . . . . . . . . .27' C. Specific gravity (spindle) . . . 1.065 3So/15.5O C.. . . Tar acids (contraction method), , , . . . . . . . . . . .11.6per cent. Tar bases (contraction . . . . . . . . 5 . 9 per cent method). . . American Society for Testing Materials, Method D 246-27" (2).
c.
.. . . .. . . . . . . .. . . . .. . .
Method for Determining Fungicidal Power
The method used by the writers to measure preservative efficiency was a modification of that suggested by Reeves (25). Three grams of mechanical wood pulp (Norway spruce) were disintegrated and suspended in water and the suspension was filtered through a muslin disk on a Biichner funnel (9 cm.
100
PFR CkN% FRACTION I Figure 2-Vapor Pressures of Mixtures of Fractions
0
2 Obtained through the courtesy of C. Audrey Richards of the U. S . Forest Products Laboratory, Madison, Wis.
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1930
Thirty gallons (113.5 liters) of the oil were extracted with two successive portions, of 12 gallons (45.4 liters) each, of a 10 per cent solution of sodium hydroxide. The extraction was made a t 60" C. The resulting carbolate was reserved for recovery of tar acids. The treated oil was then agitated with two successive portions, of 3 gallons (11.3 liters) each, of 30 per cent sulfuric acid, the separated acid solution being set aside for recovery of the tar bases. The final extracted oil was washed exhaustively with several portions of a 10 per cent solution of sodium hydroxide and with 30 per cent sulfuric acid in order to insure complete removal of acidic and basic materials, and was then separated into ten fractions by distillation through a 10-inch (25.4-cm.) Hempel column. i
PLR CCNT: FRACTION I
.
The combined carbolate extract was washed twice with benzene (1.5-gallon or 3.7-liter portions), steamed to remove any residual benzene, blown with carbon dioxide until almost neutral, and finally acidified with hydrochloric acid. The liberated tar acid was separated, dried, and fractionally distilled, The solution obtained by extracting the oil with sulfuric acid was washed with benzene and made strongly alkaline with sodium hydroxide. The separated tar bases were dried and fractionally distilled. The various fractions of dead oil, tar acids, and tar bases were collected between the following distillation temperatures: DEADOIL
c.
TARACIDS a
c.
Start-193 193-196 196-199 199-201 201-209 209-219 219-286 286-331 331-341 Above 341
T A UBASES O
BOILING POINT
c.
Naphthalene a-Methyl naphthalene @-Methylnaphthalene Diphenyl Acenaphthene
TOXICLIXXTS W l . of 9uE9 0 5-1 0 0 5-1 0 0 5-1 0 0 5-1 0 1 0-2 0
% by
128 243 245 256 277.5
The toxic limits of the individual hydrocarbons are in agreement with those of the fractions containing them. Within each group of compounds the fungicidal power d e creases as the boiling point increases. The neutral hydrocarbons are fully as effective as the phenolic compounds of similar distillation ranges, while the tar bases have comparatively slight fungicidal power. Any desirable effects of the presence of tar acids in creosote oil are not due to the high specific fungicidal power of the tar acids themselves. Volatilities of Various Components of Creosote Oil
Figure 3-VapOr Pressure8 of Mixtures of Fractions 1 and 3
FRACTION
MATERIAL
169
c.
Start-233 233-249 249-256 256-267 267-286 286-308 308-333 333-343 343-361 Above 361
I n some of the preliminary experiments which were made to determine the fungicidal powers of the various fractions of creosote oil, the Petri dishes were not water-sealed but were simply covered with loosely fitting covers in the usual way. It was found that under these conditions the more volatile preservatives vaporized from the test specimen, so that at the end of one month only a relatively small portion of the fungicide remained in the pulp. Experiments made to determine the amount of the original preservative which r e mained in the test disk after standing for one month a t 25" C. in a covered Petri dish gave the following results: FRACTIONORIGINAL PRESERVATIVE REMAINING ON PULP Dead oil Tar acid Tar base
8 9
%
%
%
13.4 15.0 34.8 43.8 67.4 89.8 100 100 100
43.7 45.0 46.7 49.2 52.0 54.4 100 100 100
30.6 43.8 48.5 61.0 86.5 100 100 100 100
A blend of the first eight fractions of the dead oil gave 68.8 per cent remaining on the pulp a t the end of the test period, although the average for the individual fractions of which the blend was composed was only 58 per cent. It appears that the presence of the high-boiling components markedly reduces the rate a t which the low-boiling materials vaporize from the test sample.
Fungicidal Powers of Various Fractions
Each of the fractions of dead oil, tar acid, and tar base was tested for fungicidal power, using the method described above. The results were as follows: DEADOIL TARACIDS TARBASES Fraction Toxic limits Fraction Toxic limits Fraction Toxic limits % bs wl. of Pulp 70 bs wl. of PULP 5% b y w l . of PULP Entire 0.5-1.0 Entire 1.5-2.0 Entire 3.5-4.0 1 0.5-0.75 1 0.65-0.9 1 1.2-1.5 2 0.5-0.75 2 0.65-0.9 2 2.0-2.1 3 0.5-1.0 3 0 . 7 -0.95 3 2.2-2.3 4 0.5-1.0 4 0.75-1.0 4 2.7-3.0 n 5-1 n 5 0 . 8 -1.05 5 2.8-3.0 6 1.0-1.5 6 1 . 1 -1.2 6 4.0-4.25 7 1.5-2.0 7 3.25-3.5 7 4.0-4.5 8 4.5-5.0 8 Above 6 8 4.7-5.0 9 Above 6 . 0 Blend of 9 4.2-5.0 Blend of first 7 Blend of first 8 fractions 0 . 7 5 - 1 . 0 first 9 fractions 0 . 5 - 0 . 7 5 fractions 3 . 5 - 4 . 0
The toxic limits of a few of the pure hydrocarbons which are present in creosot,e oil and which constitute the major portion of the dead oil were also determined. The results were fbs follows:
0
20 40 60 80 P f R CENT FRACTION 2
Figure 4-Vapor
100
Pressures of Mixtures of Fractions 2 and 3
The rate a t which vaporization occurs from the treated timber is an important factor in determining the suitability of a preservative for industrial use. The results indicate that the presence of a t least a small amount of high-boiling mBterial in creosote oil may be of advantage in retarding the vaporization of the low-boiling components, which are highly fungicidal, although the high-boiling material itself has comparatively little fungicidal power.
INDCSTRIAL A N D ENGINEERING CHEMISTRY
170
It will be observed that the rate of volatilization of taracid fractions from the pulp is very much less than that of dead-oil fractions of similar or even somewhat higher boiling points. Apparently the phenolic compounds wet the wood much more readily than do the neutral hydrocarbons and are much more strongly adsorbed. To demonstrate this difference in the retention of phenolic compounds and of hydrocarbons, similar samples of air-dried pulp were impregnated with equal quantities of solutions of naphthalene and phenol, respectively, in ether, dried for 12 hours a t room temperature or for 6 hours at 60" C., and finally analyzed to determine how much of the impregnating material was retained. The amount of impregnating substance was, in each case, 2 per cent by weight of the pulp. The sample containing naphthalene was analyzed by extracting the naphthalene with
Vol. 22, No. 2
If this is true, the presence of a t least a certain minimum amount of phenolic compounds in creosote oil may have a very important influence upon the suitability of the oil for use as a preservative, entirely apart from any value that the phenols themselves may have as fungicides. The presence in the oil of compounds which wet the wood readily, and which are rather strongly adsorbed by the wood fiber, should aid materially in attaining rapid and uniform penetration of the preservative oil and should tend to mordant the oil to the wood. The effect of phenols in aiding the wetting of wood by creosote oil should be somewhat analogous to that of free fatty acids in aiding the wetting of metal by lubricating oil. It does not follow, of course, that the preservative effect of creosote oil or its ability to wet the timber is directly proportional to the amount of tar acid present, any more than it is true that the lubricating power of a compounded oil and the ability of the oil to wet metal is directly proportional to the amount of oleic acid present. It is possible, and even probable, that the full wetting effect may be exerted by even a small amount of phenol and that further increase above this limiting concentration may have relatively little effect. The influence of the various components of creosote oil upon its ability to wet wood is being further studied in this laboratory. Vapor Pressures of Fractions from Creosote Oil
Figure 5-Vapor
Pressures-Ternary Mixtures (mm. Hg a t 2 5 O C.)
alcohol and determining the naphthalene in the extract by means of picric acid. The impregnated pulp was completely extracted with 50 cc. of 95 per cent alcohol in a Soxhlet extractor and the extract was poured into 300 cc. of a saturated aqueous solution of picric acid. The solution was made up to exactly 500 cc., allowed to stand for 4 hours, and filtered. The first portion of the filtrate was rejected. Subsequent portions of 50 cc. each were titrated with 0.1 N sodium hydroxide. A blank determination was made to find the titer of the solution of picric acid. From the amount of picric acid precipitated by the naphthalene the quantity of naphthalene retained by the pulp was calculated. The samples of pulp which were treated with phenol were extracted completely with benzene. The extract was shaken with a 10 per cent solution of sodium hydroxide, any benzene remaining in the carbolate layer was removed by distillation with steam, and the phenol in the alkaline solution was determined by precipitation as tribromophenol and titration with standard alkali (I). The results of these experiments are as follows: COMPOUND
Naphthalene Naphthalene Phenol Phenol
DRYING VAPOR TEMPERATURE PRESSURE c. M m . Hg 20 0 06 60 1.5 20 60
1 0 4 0
REMAINING ON P U L P
%
22.0
8.3
79.9
46.6
Phenol is much less readily volatilized from the pulp than naphthalene, although the vapor pressure of phenol is much higher than that of naphthalene a t the same temperature. Phenol appears to wet the pulp much more readily and to be much more readily adsorbed than the neutral hydrocarbon.
The statement was made above that the presence of a reasonable amount of high-boiling material in creosote oil may be of advantage in reducing the vapor pressure of the preservative, even if the high-boiling material of itself is not a very efficient fungicide. To demonstrate this effect of the high-boiling materials and to measure it quantitatively, vapor pressures of various mixtures of fractions from the dead oil from coal-tar creosote oil were measured. The method used involved the determination of the amount of the oil vaporized when a known volume of inert gas was passed through the liquid a t a known temperature. The apparatus is shown in Figure 1. Air, purified by passing through concentrated sulfuric acid and through soda lime and brought to exactly 25" C., was passed through a series of bulbs containing the liquid of which the vapor tension was to be determined. The outgoing mixture of air and vapor was freed from any entrained mist by passing through a pad of glass wool. From the purified mixture the vapor was removed by adsorption in concentrated sulfuric acid, followed by soda lime to retain any carbon dioxide or sulfur dioxide which may have been formed by the interaction of the hydrocarbons with the acid, The combined increase in weight of the tube containing the sulfuric acid and the tube containing the soda lime represented the weight of oil vaporized by the measured amount of air a t the known temperature. From the data thus obtained the vapor pressure of the oil was calculated from the formula:
P
=
760 gRT/Mv
in which P is the vapor pressure of the oil in millimeters at 25" C., g is the weight of the oil vaporized, R is the gas constant in liter-atmospheres (0.082), T is the absolute temperature (298" A.), M is the molecular weight of the material (as determined by cryoscopic method, using benzene as a solvent), and u is the volume of air aspirated through the apparatus, corrected to dry air a t 0" C. and 760 mm. pressure. The fractions of which the vapor pressures were measured were prepared by the distillation of dead oil, using an apparatus similar to that described in the A. S. T. M. Method D 246-27T ( 2 ) . Three fractions were collected and the apparent molecular weight of each fraction was determined by the cryoscopic method, using benzene as a solvent. The
I X D LTSTRIALA S D ENGINEERIATGCHEJIISTRY
February, 1930
fungicidal value of each fraction was measured in the usual way. The results were as follows: FRACTION
nf0LECCLAR
\VEIGHI
VAPOR PRESSURE (250 C.)
TOXIC LIMITS
c. Start-270 270-316 Above 315
147.0 164.8 206,3
0.5--1.0 0.5--1.0 Above 5
0,3186 0.1251 0.0643
The results obtained in the determination of the vapor pressures of the various mixtures of these fractions are shown by the curves in Figures 2 to 5 . I n each case the addition of a relatively small amount of a high-boiling fraction to a low-boiling oil depresses the vapor pressure of the more volatile material to a marked extent, while further additions have relatively less effect. Oil of a desired average vapor pressure can be obtained by using either a properly proportioned mixture of light and heavy oils or a comparatively close-boiling fraction which, of itself, has a vapor pressure of the desired magnitude. The writers’ results indicate that the optimum combination of low volatility and high fungicidal power can best be secured by the use of a close-boiling fraction. For example, the fraction of oil which distilled between 270” and 315’ C. had a vapor pressure almost identical with that of a mixture of equal parts of the fraction distilling below 270” C. and that boiling above 315” C., whereas the close-boiling middle fraction had a fungicidal power considerably higher than that of the mixture. On the other hand, the amount of close-boiling material of the proper vapor pressure and fungicidal power to render it suitable for use as a wood preservative is limited. so that economic consider‘A t’ions render it necessary to include in the creosote oil fraction at least some material of higher and some material of lower than the optimum distillation range. Determination of Principal Components of Dead Oil In connection with the work on the fungicidal powers of the various fractions of the dead oil from creosote oil, each of the individual fractions was analyzed to determine the percentage of the principal components. The method of analysis used was the differential cryoscopic method for the analysis of mixtures of organic compounds, described by Rhodes, Gardner, and Lewis (26). The individual components determined were naphthalene, fluorene, diphenyl, acenaphthene, and phenanthrene. The benzene used as a solvent in determining the apparent average molecular weight of each fraction was purchased as “chemically pure.” The results of the analyses were as follows: NAPHTHA-
FRACTIONL E N E 1 2 3
4
5
6 7
8 9
DIPHENYL
ACENAPHTHEGE
PHENAN.
FLUORENE THREGE
(la
79
(la
5
50.2 53.3 38.1 26.1 17.1 1.8 h-one None None
:
