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INDUSTRIAL AND ENGINEERING CHEMISTRY
good lubricating properties, and by this factor tend to desensitize ammonium nitrate (factor 2 ) . The sensitizing effect by factor 1 alone increases u p to zero oxygen balance, but the preponderance of the increase occurs from 0 to 1% hydrocarbon. This is probably because the sensitization occurs largely a t the interface between Dhe ammonium nitrate and the hydrocarbon. (Zero oxygen balance in ammonium nitrateparaffin mixtures corresponds to about 5.4% paraffin and the explosive reaction is then essentially as follows:
Q E 880 kg.-cal./kg. where Q is the heat of explosion. At lower percentages of paraffin, the oxygen balance is positive and at higher percentages it is negative. ) By factor 1alone the sensitiveness of ammonium nitrate-hydrocarbon mixtures will increase a t a decreasing rate as the hydrocarbon content is increased from 0 to 5.47& -4bove 5.4% no additional sensitization b y factor 1 will occur. Factor 2 behaves in just the opposite manner for hydrocarbons in ammonium nitrate. At first, the lubricating action of the hydrocarbon is negligible and the desensitizing effect is small, but becomes large with increasing percentages of hydrocarbon in ammonium nitrate. The sensitiveness of ammonium nitrate-hydrocarbon mixtures thus passes through a maximum experimentally a t somewhere between 0.75 and 1.570. AMMONIUM NITRATEHYDROCARBON MIXTURES IN PAPER BAGS
The authors desire to mention some pertinent previously known facts concerning the use of ammonium nitrate-hydrocarbon mixtures in paper bags with emphasis on the hazards involved, While it is known that even pure ammonium nitrate may be exploded under appropriate conditions (1, 3, 5 , 8, 9, 11, 13, 14), even the most sensitive ammonium nitrate-hydrocarbon mixtures are actually comparatively quite insensitive. This does not necessarily apply, however, to such mixtures used in paper bags. Actually, the minimum primer and propagation sensitivity studied experimentally in this investigation are not increased by the use of ammonium nitrate-hydrocarbon mixture in paper bags; however, the thermal stability of ammonium nitrate and ammonium nitrate-hydrocarbon mixtures, ordinarily quite high,
Vol. 43, No. 5
is lowered phenomenally in the presence of carbonaceous materials. This situation was described by Findlay and Rosebourne ( 4 ) , and was the subject of an extensive investigation by Kistiakowsky and Guinn ( 7 ) . While the “explosion temperature’’ of explosive ammonium nitrate-hydrocarbon mixtures as the authors are aware from experimental determinations, is in the range 270’ to 350” C., the results of the studies cited show that, in the presence of bagging paper or cellulose, the “explosion temperature” is lowered to around 150” C., with decomposition taking place a t an appreciable rate as low as 100’ C. Furthermore, the impregnation of paper by ammonium nitrate increases the ease of ignition of the paper because of the intimacy of the oxidationreduction mixture. ACKNOWLEDGMENT
This work was supported by the Texas City Committee of Lawyers representing plaintiffs in the recent litigation in connection with the explosions of “fertilizer grade ammonium nitrate” on the S. S. G r a d Camp and S. S. High Flyer, April 16 and 17, 1947. It is hoped, that the publication of this information, together with similar studies carried out by others in this connection, will be instrumental in our mutual efforts toward the prevention of such catastrophies. LITERATURE CITED
Aufschlauger, R., Chern. Met. Eng., 30, 619 (1924). Cook, R. M., Ibid., 31, 231 (1924). Davis, R. 0.E., U. S. Dept. Agriculture, Circ. 719 (March 1945).
Findlay, A., and Rosebourne, C., J . SOC.Chem. Ind., 41, 38 (1922).
Gawthrop, D. B., A r m g Ordnance, 6, 47 (1925). Jost, ‘A’., “Explosion and Combustion Processes in Gases,” New York, hIoGraw-Hill Book Co., 1936. Kistiakowsky, G . B., and Guinn, V. P., unpublished data. Lorby de Bruyn, S. A,, Rec. trav. chim., 10, 127 (1891). Munroe, C. E., Chem. Met. Eng., 29, 535 (1922). Nuckolls, A. H., Underwriters Laboratory, Inc., BvlZ Reseaich 20 (1940); 3 9 (1947).
Saunders, H. L., J . Chem. SOC.,121, 698 (1922). Semenoff, N., “Chemical Kinetics and Chain Reaction,” London, Oxford University Press, 1835. Sherrick, J. L., A r m g Ordnance, 4, 329, 294 (1924). Torsuev, W. S., J . Chem. I d . ( M o s c o w ) , 13, 102 (1926). RECEIVED January 3 0 , 1950.
REED V. VAAR1\;ER AND ROBERT L. ICELAUSE Grasselli Chemicals Department, E . I . du Pont de ATemours& Go., Inc., K’ilrnington, Del. ESEARCH workers in the field of wood preservation have long recognized the need for a reliable and easily reproducible laboratory method for the evaluation of new chemicals, new formulations, and new treating procedures. The desirability of a generally approved standard test procedure is becoming increasingly acute because of the growing rate at which potentially effective compounds arc being made available through the rapid advances taking place in all phases of chemistry. It is no longer practical for each investigator to compare all promising chemicals by personal tests; he must be able to integrate his results with those of others and, to permit this, a readily dupli-
cated standard technique is required. The results of studies in which two laboratory test methods were critically compared are presented here as a contribution which may aid in bringing about greater standardization. The ultimate objective of laboratory preservative tests is to make possible, after only a few months of study, accurate prediction of the service life of wood treated in a given manner with a new chemical. It is not likely that this objective will be completely realized in the near future. There are many ways in which information obtained in laboratory preservative tests a t their present stage of development may be safely employed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1103
TEST PROCEDURES Most of the laboratory preservative testing techniques now in use will adequately separate ineffective compounds from those The simplest procedures for ascertaining the toxicity of chemicals to fungi are those involving the application of the test comthat may be of value, at least in specific applications (7,9,10,16). The approximate w e concentration and cost efficiency determinapounds to an agar, .or similar, medium which normally supports tions which should be made for new materials prior to the initiafungus growth. Rvlative efficiency is measured by the amount tion of extensive developmental research programs are possible of retardation in the rate of growth of pure cultures of selected following preliminary laborafungi. This type of test has tory evaluation. Accelerated been widely used in the As a contribution toward the establishment of an easilj United States ( 1 4 , ~ ~rt) has . field tests and service performance studies can be reproducible, standard laboratory technique for testing been shown (5, 6 , IS), howout most economically wood preservative candidates, three chemical compositions ever] that results o b t a i n e d when the range of concentrawere compared by the agar-block and soil-block Procedures with an agar-fungicide tions can be limited to those which are now most widely used. tem do not always agree with Similar relative ratings of equivalent statistical signifithose obtained with the srtme likely to be significant. The use, in such investigations, of cance and precision were obtained for the three materials chemicals when applied to preservative retentions which by each test method. wood. Notwithstanding, the Thus, the ultimate selection of one technique in prefvarious modifications of the are decidedly too great or too small obviously represents erence to the other depend upon the relative facility petri dish toxicity test remain with which the two tests can be run and upon the degree useful tools for preliminary WaSte. of standardization that may be attained* From these There are still other importesting when the results are tant applications for laborastandPoints, the agar-block method had advantages Over used with discretion. the method’ European scientists in the tory test data, short of the ultimate but more remote obmid 1920’s began to use methjective of predicting service life, for which establishment of reliods of laboratory testing in which the preservative candidate was impregnated into wood. Falck in 1927 ( 4 )and Liese in 1928 ability represents an important step forward. One of these is a precise relative rating of preservative effectiveness under various (11) described experimental procedures involving treated wood conditions of exposure; another is determining the comparative blocks that are similar to those still used by many investigators in margins of safety furnished by different wood preservative matethe United States. At Herman von Schrenk’s suggestion a conference of European workers was held in Berlin in 1930 a t which rials at given levels of concentration. Both of these objectives may be attained by determining for all promising compounds what laboratory methods of testing wood preservatives were disRichards and Addoms (16)have called “threshold concentration” cussed. An international committee organized a t that time or “threshold band.” These terms refer to the minimum concenstudied the problem and published a proposed standard wood block test (12). Breaszano ( 1 ) [as quoted by Cartwright and tration of a preservative which will entirely prevent decay under a carefully delineated set of test conditions. As preservatives Findlay (S)]agreed in principle with the proposal made by the differ in their resistance to dissipation by volatilization and leachcommittee but held that reliable results could be obtained more ing, any expression of the threshold concentration should be rapidly if thin transverse sections of wood were used. British Standards specification 838 ( 2 ) , published in 1939, described a accompanied by a description of the handling afforded the treated wood prior to exposure to fungus attack. A direct comparison method for determining the effectiveness of wood preservatives of threshold concentrations resolved under similar circumstances which is similar to that advocated by the Berlin committee. makes easy the relative rating of a number of compounds. An I n 1940 Hubert (8) described a test method that had been acexpression of the margin of safety provided by any preservative cepted by the National Door Manufacturers Association (now treatment may be computed by dividing the recommended use the National Woodwork Manufacturers Association) for the concentration by the threshold concentration of that preservative. evaluation of nonswelling, oil-soluble preservatives. T h L Both the relative rating and the determination of the safety method, hereafter referred to as the N.W.M.A. test method, factors provided by the generally recommended use concentrais also much like that proposed by the international committee, tions for two organic compounds used in wood preservation are but incorporates Breazzano’s (1) suggestion that transverse discussed below. Exemplary use is made of the data obtained sections be used. In addition, volatilization and leaching steps in comparative studies with two laboratory methods which are are embodied. The N.W.M.A. test method is one of the methods commonly employed. included in the studies reported here. I
*
*
TABLE I. COMPARATIVE PERFORMANCE AQAINST Lenzites trabea OF VARIOUSPHENYLMERCURY OLEATEAND PENTACHLOROPHENOL TREATMENTB AB EVALUATED BY N.W.M.A. TEST METHOD” Not Heated or Leached Heated Heated and Leached % Absorp- Visual Absorp- Visual Absorp- Visual Active in tion of eval. Av. tion of eval. Av. eval. Av. tion of Treating toxicant, of % wt. t toxicant of % wt. t toxicant of % wt. t Compound Solution lb./cu. ft. decayb change valuec lb./cu. fd. decayb change valueC lb./cu. fd. decay change value Phenylmercury 0.1 0 f 1.12 9.12 0.0091 0 0.0098 f 2.24 6 27 0 0.81 9.28 0.0099 oleate 0.05 0 4- 1.30 9.07 0.0045 0 0.0045 f 1.56 6.11 0 2.03 9.65 0.0043 0.025 0 1.56 9.19 0.0023 0.0021 0.2 0.75 5.96 0 0.0020 0 42 9.17 Pentachloro1.5 0.1619 0.3 C 0.65 9.06 0.1466 1.0 1.31 6.09 0.1541 0.0 1.44 8.62 phenol 0.75 0.0734 2.2 2.51 8.44 0,0690 2.5 6.96 3.95 0.0783 2.0 - 2.23 7.38 0.375 0.0371 3.3 -25.32 2.25 0.0330 2.5 9.05 3.67 0.0339 3.2 -22.48 1.08 Phenylmercury 0.1 0.0084 0.0084 ’ 0.0089 oleate 1.25 0.1056 0 4- 1.18 9.10 0.1060 0 f 1.69 6.14 0.1111 0 1.74 9.39 pentachloro0.05 0.0043 0.0036 0.0046 phenol 0.625 0.0545 0 1.88 9.30 0.0454 0.2 1.62 6.16 0.0579 0 2.67 10.00 0.026 0.0022 0.0021 0.0024 0.3125 0.0278 0.3 4- 0.68 9.,00 0.0262 0.6 1.44 6.10 0.0301 0.5 1.84 8.45 Control ... 0 4.0 -46.22 0 3.8 -33.61 0 4.0 -30 93 a Each figure represents an average of six test blocks. Amount of rot rated visually usin a scale of 0 to 4.0. 0 denoting no visible decay and 4.0 representing heavy rot throughout the test blocks. Value of t determined using “Stufent’s” unpaired d i t a technique with a set of treated blocks and the corresponding set of control blocks. The 1 value required for significance a t the 5% level IS 2.228; at the 2% level, 2.764; a t t h e 1% level, 3.169; a t the 0.1% level, 4.587.
+
-
+
+ + +
+
+ +-
+ + + +
+ +
+ + +
-
-
1104
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Phenylmercury oleate
Figure 1.
Pentachlorophenol
Vol. 43, No. 5
Phenylmercury oleate plus gentaehlorophenol
Representative Treated Sugar Pine Blocks, Not Heated or Leached After 63 days of exposure to Lenzites trabea using N.W.M.A. method
I n 1933 Flerov and Popov (6) reported excellent results using soil covered with wafers of wood as a medium for the growth of test fungi. Pieces of treated wood were introduced into the test containers after the soil and the untreated wood had become overgrown with mycelium. It was found that fungus growth was vigorous and that the moisture content in the test samples was maintained near the optimum. il modification of this test method described by Leutritz (IO), and reported to be highly satisfactory, was compared with the N.W.M.A. method in the tests reported here. The technique in which soil is used as the medium is designated as the soil-block test method.
Phenylmercury oleate
Figure 2.
Pentachlorophenol
Richards and Addoms ( 1 6 ) , folloffing a preliminarg- coniparison of an agar-block technique similar t o the N.\.T;.M.A. method and the soil-block method, indicated that either procedure could be relied upon to give results sufficiently reliable to screen out useless candidates and to determine the approximate retentions at which the materials might be expected t o be effective in service tests. FUNGI USED. The selection of the fungi to be used in testing preservatives is just as important as the choice of technique. As fungus populations are relatively constant for a given microclimate, the proposed application of the preservative t o be tested
Phenylmercury oleate plus pentachlorophenol
Representative Treated Sugar Pine Blocks, Not Heated or Leached
After 63 days of exposure to Hormiscium gelatinosum using N.W.M.A. method. which were in contact with mycelial mat during test.
Surfaces shown are those
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
May 1951
1105
PERFORMANCE AGAINST Horrnzscium gelatinosum OF VARIOUSPHENYLMERCURY OLEATEAND ,TABLE11. COMPARATIVE PENTACHLOROPHENOL TREATMENTS AS EVALUATED BY N.W.M.A. TESTMETHOD^
%
Compound Phenylmercury oleate Pentaohlorophenol
Active in Treating Solution 0.1 0.05 0.025 1.5 0.75 0.375
Not Heated or Leached Absorption of % % % toxicant top interior bottom lb./cu. f t . stain stain stain 10 0.0091 0 0 47 0,0044 0 3 0 8 57 0.0020 0.1581 10 35 95 0.0820 73 60 100 0.0310 66 62 100
*
Heated Absorption of toxicant Ib./cu. ft. 0.0079 0.0041 0,0021 0.1684 0.0827 0.0349
%
top stain 0 0 1
30 17 12
%
%
interi r bottom stainS stain 0 8 3 48 8 62 45 98 38 100 36 92 I
' 1
...
Control 0 95 90 a Each figure represents an average of six test blocks. Average of two radial cuts per block.
100
should be considered in deciding upon the fungus species to be used. Certain fungi are tolerant t o specific compounds; therefore, results will be more reliable if more than one fungus are employed. Since the primary utility of one of the chemicals used in these studies (phenylmercury oleate) is in connection with millwork and similar uses not involving soil contact, Lenzites trabea (Pers.) Fr. and Hormiscium gelatinosum Hedg. were chosen. Hubert ( 7 ) has reported Lenzites trabea t o be the most important of the rot fungi attacking millwork in the United States and Hormiscium gelatinosum as one of the stain organisms commonly found in sapwood in use. The N.W.M.A. test method as described by Hubert (@specifies Forest Products Laboratory strains 617 for L. trabea and 595 for H . gelatinosum. These strains were used in the tests described here. COMPOUNDS AND CONCENTRATIONS USED. The two compounds employed in these studies were phenylmercury oleate and pentachlorophenol. Phenylmercury oleate was tested a t 0.1, 0.05, and 0.025%; pentachlorophenol at 1.5, 0.75, and 0.375%; and a combination of phenylmercury oleate and pentachlorophenol ( 1 to 12.5 ratio) a t three concentration levels. The solvent and diluent used in all instances consisted of 4% acetone and 96% Stoddard solvent naphtha (Atlantic Refining Co. No. 52). Each treating solution was tested both b y the N.W.M.A. method and by the soil-block method. NATIONAL WOODWORK MANUFACTURERS ASSOCIATION METHOD
*
*
Hubert (8) has described the N.W.M.A. method in detail. Briefly, dry sugar pine sapwood with an avera e of 30 growth rings per inch was cut into blocks with a 0.64 cm.!ongitudinal dimension, a 3.5 om. radial dimension, and a 5.09 om. tangential surface, All blocks were conditioned to equilibrium in a constant humidity room, weighed, and then impregnated under a pressure differential of 125 2 mm. of mercury with the preservative solution. The wet blocks were weighed immediately after treatment so that the preservative absorptions could he determined. Following reconditioning, one third of the blocks from each treatment were heated a t 71" C. for a period of 24 hours and another one third was both heated as above and leached for a period of 5 days with distilled water. After a second reconditioning, all of the blocks were weighed and then placed in the culture containers. I n all L. trabea cultures a sterile U-shaped glass rod 0.32 cm. in diameter was placed on the mycelial mat so that one arm of the U was on each side of the central1 placed inoculum plug. The test block was then placed across U and gently pressed so that each end was supported by glass and the center was in intimate contact with the fungus mycelium a t the point of the inoculum plug. This arrangement prevents the test blocks from becoming too wet but at the same time assures uniform infection of equally susceptible wood. Where the test fmgus was H. gelatinosum, the block was allowed to rest directly upon the mycelium. At the termination of the test period, all blocks were taken from the containers and brushed light1 to remove the mycelial growth. Both the wet weight immeJately following removal
til
0
32
35
97
Heated and Leached Absorption of % % ' toxioant top interior Ib./cu. f t . stain stain 0,0087 0 0 0.0043 0 4 0.0021 0 11 0 1513 33 22 0.0726 9 20 0.0346 13 15 0.0088 0 0 0.1101 0.0038 0 2 0.0484 0.0023 0 7 0.0294 0 11 32
%
bottom stain 5 42 67 92 78 60 8 58 55 65
from the jar and the oven-dry weight were obtained and recorded for each block in the decay test. A visual evaluation of the amount of rot or stain in each block was also made.
RESULTS.A summary of the results of the N.W.M.A. test is presented in Tables I and 11. The blocks shown in Figures 1 and 2 depict the average condition within each treatment following exposure to fungus attack. Only blocks from the sets not heated or leached were included in the photographs aa these generally showed the greatest amount of stain and decay. All solutions of phenylmercury oleate, including the lowest concentration of 0.025%, were effective in preventing decay by L. trabea. Pentachlorophenol, on the other hand, did not prevent rot a t concentrations below 1.570. Treating solutions containing both phenylmercury oleate and pentachlorophenol in a 1 to 12.5 ratio were no more eqective in preventing decay and stain than similar solutions containing the same amount of phenylmercury oleate alone. Phenylmercury oleate at 0.025% was more efl'ective against the stain fungus H. gelatinosum than pentachlorophenol at 1.570'0. The minimum effective concentrations as determined by this method of evaluation indicate that phenylmercury oleate is a t least GO times as effective as pentachlorophenol in preventing rot by L. trabea and relatively more effective in inhibiting the development of stain by H. gelatinosum. These results suggest that a use concentration of 0.2% phenylmercury oleate provides a margin of safety, against, these two fungi, which is more than twice as broad as that furnished by pentachlorophenol a t 5%. I n both the rot and the stain tests the untreated blocks were rendered less subject to fungus attack by both the heating and the leaching operations. This was also true, with but minor variation, for the treated blocks. A reduction in soluble carbohydrates due to leaching and an iDcrease in resin concentration at the surhce as a consequence of heating were probably the major factors involved. I n tests involving materials which are more volatile and less resistant to leaching than the two compounds used here, results with treated blocks do not adhere to this pattern (8). Consistently lower absorption readings were obtained when the treating solution contained phenylmercury oleate than when pentachlorophenol was used. Blocks treated with phenylmercury oleate solutions retained an average of 1170less material by weight than blocks similarly treated with pentachlorophenol solutions. This situation is only partly explained by the somewhat greater specific gravity of the pentachlorophenol solutions. SOILBLOCK METHOD
The test blocks in this portion of the studies consisted of 1.4 cm. cubes of the same wood that was used in the N.W.M.A. method. Ten blocks were prepared for each treatment and a
INDUSTRIAL AND ENGINEERING CHEMISTRY
1106
Phenylmercury oleate
Figure 3.
Pentachlorophenol
Phenylmercury oleate plus pentachlorophenol
Sugar Pine Blocks after 63 Days of Exposure to Lenaites trabea Using Soil-Block Method
control; four to be exposed to each fungus and two t o be used as reference blocks. Heating and leaching were omitted but, otherwise, conditioning and treatment were the same as in the previous test. Square 16-ounce bottles, 6-cm. wide and 16-cm. tall, with plastic screw caps were employed as test containers. Sandy loam soil with 4.270 organic matter and a p H of 5.0 was used. When the soil was at equilibrium with the laboratory air, the moisture content was determined, Sufficient soil was laced in each jar t o provide 300 grams on an oven-dry basis. Ffnough distilled water was added to bring the total water content of each jar to 75 grams. Two sugar pine feeder blocks (3.5 X 2 X 0.2 cm.) were aced side by side upon the surface of the soil in each container. he jars were then loosely cap ed, autoclaved, and inoculated. L. trabea was introduced by pfacing a 1 square cm. inoculum
G
Phenylmereury oleate
Figure 4.
Vol. 43, No. 5
Pentachlorophenol
block on the surface of the soil between the feeder blocks. The H. gelatinosum jars were inoculated by adding approximately 2 cc. of a. spore and fragmented mycelial suspension to the feeder blocks. All cultures were incubated at 27" C. in a relative humidity of 80% for one month prior to the addition of the test blocks. One test block was placed upon each of the two feeder blocks in a jar. I n each instance, the two blocks put into a jar represented the same treatment, thus obviating the possible unequal effect of toxic vapors. The test period used was 63 days so that direct comparison between the N. W.M.A. method and soil-block niethod might be obtained. The soil-block method as used here involved larger containers, greater volumes of soil, and a shorter test period than the procedure described by Leutritz (IO).
Phenylmercury oleate plus pentachlorophenol
Sugar Pine Blocks after 63 Days of Exposure to Hormiscium gelatinosum
Using Soil-Block Alethod
Surfaces shown are those which were in contact with feeder block during test.
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1107
SUMMARY AND CONCLUSIONS
TABLE111. COMPARATIVEPERFORMANCE AGAINST Lenzites Similar ratios of effectiveness were established by the N.W. trabea OF VARIOUSPHENYLMERCURY OLEATEAND PENTACHLOROM.A. and the soil-block metbods in comparing phenylmercury PHENOL TREATMIINTS AS EVALUATED BY SOIL-BLOCKMETHODO Absorp- Visual tion of Evalua- Average i n Treating Toxicant, tion of 5% Wt. t Compound Solution Lb./Cu. Ft. Decayb Change ValueC 0.31 13.42 Phenylmercury 0.1 0.0065 0.0 oleate 0.06 0.0029 0.5 0.42 13.37 0.025 0.0015 1.5 2.45 12.81 9.33 10.32 Pentaohloro1.5 0.1024 2.2 4.78 0.75 0,0540 4.0 -40.02 phenol -48.91 2.82 0.375 0.0218 4.0 Phenylmercury 0.1 1.25 0,0057 0.0 - 0.42 13.40 oleate 0.0713 pentaohloro0.05 0.625 0,0028 0.8 0 . 3 1 13.40 phenol 0.0351 0.025 -I-0.3125 0,0014 2.6 -10.36 9.63 0.0186 Control 0 4.0 -63.81 a Each fig-ure represents a n average of four test blocks. Amount of rot rated visually using a scale of 0 to 4.0: 0 denoting no visible decay and 4.0 denoting heavy rot throughout the test block. C Value of 1 determined using “Student’s” unpaired data technique with a set of treated blocks and the corresponding set of cont,rol blocks. The f value required for significance &t the 5 % level is 2.447; a t 2% level, 3.143; a t 1% level, 3.707; a t 0.1% level, 5.959.
70Active
-
+ +
+
-
...
*
...
RESULTS. A summary of the results of this test are shown in Tables 111 and IV. The lower surface of each of the test blocks may be observed in Figures 3 and 4. The soil-block method resulted in a more severe test than the X.W.M.A. method. The untreated control specimens lost more weight due to decay, and rot developed in blocks treated with higher concentrations of both preservatives. A treating solution containing 0.025% phenylmercury oleate permitted some rot here. A pentachlorophenol solution containing 1.50/0 active ingredient allowed an appreciably greater amount of decay. Bloclis treated with a 0.025% phenylmercury oleate solution were less stained than those treated with 1.5% pentachlorophenol. Solutions containing both phenylmercury oleate and pentachlorophenol were no more effective than solutions containing the same concentration of phenylmercury oleate alone. As in the N.W.M.A. method test, a comparison of concentrations of borderline effectiveness shows phenylmercury oleate to be a t least 60 times more effective than pentachlorophenol in preventing rot by L. trabea and stain by H. gelatinosum. Preservative absorptions in the soil-block method averaged 30% less than in the N.W.M.A. method. This was due primarily to the smaller proportion of end grain area in the cubes than in the waferlike transverse sections. Absorptions of phenylmercury oleate solutions were again lower than for those containing pentachlorophenol, but the difference was only 5.7% compared to 11% in the N.W.M.A. test.
TABLEIv. COMPARATIVE PERFORMANCE AGAINST Hormiscium gelatinosum OF VARIOUSPHENYLMERCURY OLEATEAND PENTACHLOROPHENOL TREATMENTS AS EVALUATED BY SOIL-BLOCK METHOD@ .
Compound Phenylmercury oleate Pentachlorophenol Phenylmercury oleate pentschlorophenol
+
YoActive in Treating Solution 0.1 0.05 0.025 1.5 0.75 0,375 0.1 1.25 0.05
+ + 0.625
0.025+0.3125
Absorption of Toxicant Upper Lb./Cu Fk. surface 0.0070 0 0.0030 0 0.0017 0 0.1105 0 0.0477 20 0.0228 50 0.0069 0 0.0873 0.0032 0 0.0400 0,0015 0 0.0188
...
Control .., 75 Each figure represents s n average of four test blocks. Average of one radial cut per block.
% Stain Interiorb 1 5 23 48 78 90 1
Bottom surface 6 38 80 100 98
100 B
3
33
18
88
91
100
oleate and pentachlorophenol as woodwork preservatives. Although the range of concentrations used was not broad enough to permit a precise determination of threshold concentrations by both techniques, the results from both tests show that phenylmercury oleate was a t least 60 times as effective as pentachlorophenol in preventing the deterioration of wood by L. trabea and H . gelatinosum under the experimental conditions employed. A larger amount of rot developed in the control pieces and in the blocks treated with the lower concentrations of the toxic solutions when the soil-block method was employed than when the N.W.M.A. method was used. Variations in weight losses among blocks that had received the same treatment were greater with the N.W.M.A. method than with the soil-block method. Nevertheless, a determination of the standard error of the differences of the means and an application of “StudentJs” 1 test demonstrated that six replicates with the N.W.M.A. method gave results as significant as four replicates with the soil-block method. For the most part, the probability that the observed results were due to chance sampling was less than 0.1% with both test methods. As similar relative ratings of wood preservative materials were obtained with the N.W.M.A. and the soil-block methods as described herein, the ultimate decision as to which method is the more satisfactory for general use depends upon the comparative ease with which the tests may be carried out and upon the degree of standardization that may be attained. I n these studies, the N.W.M.A. test with six replications could be run with considerably less time and effort than the soil-block test with only fouy replicates. Also there is little evidence to indicate that standardization can be assured for the soil-block method if it permits the use of soils that may vary widely in chemical composition-vb., “, . a sandy loam type which contains 4 to 6% organic matter and a p H originally between 5 to 7” (10). Leutritz (10) and others (17, 18) have demonstrated the importance of various nutrients and nutrilites in wood decay and it seems likely that differences in the proportions of such materials occurring in test soils from scattered sources may alter results.
.
ACKNOWLEDGMENT
The authors are indebted to T. C. Scheffer, Division of Forest Pathology, U. S.Department of Agriculture, and Frank Kaufert, Division of Forestry, University of Minnesota, for the helpful comments which they offered following a manuscript review, LITERATURE CITED
(1) Breaziano, A., Boll. stat. patrol. vegetale, 14,185-201 (1934). (2) British Standards Institution, Brit. Standards, 838 (1939). (3) Cartwright, K.St. G., and Findlay, W. P. K., “Decay of Timber
and Its Prevention,” London, His Majesty’s Stationery Office, 1946. (4) Falck, R.,Hausschwammfwsch., 8,18-20 (1927). (5) Findlay, W.P. K., Ann. Applied Biol., 19,271-80(1932). (6) Flerov, B. C., and Popov, C. A.,Angew. Botan., 15, 386-406
(1933). (7) Hubert, E. E.,IND. ENG.CmM., 30,1241-50 (1938). (8) Hubert, E. E., IND. ENG.CHEM.,ANAL.ED., 12,139-41 (1940). (9) Kaufert, F. H., Am. Wood-Preservers’ Assoc., Reports of Preservatives Committee, pp. 38-42,1949. (10) Leutritz, John, Jr., Bell System Tech. J., 25, 102-35 (1946). (11) Liese, J., Angau. Botan., 10,156-70 (19’28). (12) Liese, J., Nowak, A., Peters, F., and Rabanus, A., 2. Ber. deut. Chem., 11,l-18 (1035). (13) Rabanus, A,, Angew, Botan., 13,352-71 (1931). (14) Richards, C.A,, Proc. Am. Wood-Preservers’ Assoc., p. 127 (1923). (16) Richards, C.A,, and Addoms, R. M., Ibid., p. 8 (1947). (16) Schmitz, Henry, et al., Ibid., pp. 81-6 (1931). (17) Sohmitz, H., and Kaufert, F., Am. J . Botany, 25,443-8 (1938). (18) Zycha, H., Holz., 3,50-1 (1940). RECEIVED September 6,1950.
