Susceptibility of Wood to Decay EFFECT OF UREA AND OTHER NITROGEN COMPOUNDS F. H. ICAUFERT'
AR'D
E. A. BEHR
University of Minnesota, St. Paul, Minn.
The rate of decay and susceptibility to decay of southern pine sapwood, Douglas fir heartwood, red oak heartwood, and cypress heartwood was not appreciably affected by t h e addition of small amounts of urea, ammonium sulfate, and ammonium phosphate. Stimulation of decay by these compounds was either absent or so small t h a t from a practical standpoint it is unimportant. Higher concentrations of these compounds caused marked reductions i n decay. This was more marked for urea and ammonium sulfate than for ammonium phosphate and nitrate. Concentrations approaching those used for chemical seasoning or fireproofing wood prevented growth of wood-rotting fungi on t h e test blocks of all woods. Small concentrations of the organic nitrogen compounds, asparagine and peptone, increased the rate of decay of southern pine sapwood and red oak heartwood but had little or no effect on t h e rate of decay of Douglas fir heartwood. Cy-
u
-REBor carbamide is finding increasing use as a chemical seasoning agent for lumber. Its use has greatly facilitated the rapid seasoning of timbers and heavy lumber items urgently needed in the present emergency. Its use in conjunction with air and kiln drying has made possible the seasoning of refractory or difficultly seasoned species with minimum losses due to checks, cracks, and other drying defects. Recommended concentrations, methods of application, results obtained, etc., with urea as a chemical seasoning agent for lumber, have been fully described in a number of recent publications (2, 6-9). Other nitrogen compounds, ammonium sulfate and ammonium phosphate, are also finding greater application in the treatment of wood, various mixtures being used to impart fire resistance to wood products. Mixtures of ammonium sulfate and ammonium phosphate are considered the most economical and practical fire-retardant or flameproofing chemicals for wood, and they are being used in increasing amounts due to the substitution of wood for other building materials. Most of the investigations on these compounds as woodtreating chemicals have been limited to determinations of their effectiveness as chemical seasoning agents and fireretardants. Their effect on other wood properties has received little or no attention. This lack of information on the possible effect of urea, ammonium sulfate, and ammonium phosphate on certain wood properties, resistance to wood-destroying organisms, strength, etc., has been the cause of some anxiety to users of lumber products treated with these chemicals. The question most often asked is: What is the effect of urea 1
Present address, Forest Products Laboratory, Madison, Wis.
press heartwood showed no signs of decay i n these tests. These nitrogen compounds appear to be more readily utilized by wood-rotting fungi than urea or the ammonia compounds. The practical significance of the decay increases observed with these compounds is questioned. The addition of bacteria to urea-treated wood did not appear to affect its susceptibility to decay by wood-rotting fungi. Since only a small number of soil bacteria, whose ability to decompose urea was not well established, were used, more work is required on this point. Heating urea-treated wood to 70-100' C. for 12-14 hours causes considerable decomposition and loss of urea, b u t such heat treatment appears to fix some of the urea i n t h e wood so t h a t it is difficult to remove by leaching. With t h e exception of t h e urea-treated wood heated to 70-100° C., all of the nitrogen compounds are easily leached from wood.
and the ammonia compounds on the decay resistance or durability of wood? It has been reported that small quantities of other nitrogen compounds, asparagine, peptone, and ammonium nitrate, may appreciably speed up the rate of decay of wood blocks and wood sawdust (4,10). Although the results of these investigations are far from conclusive and have not been checked by field observations or actual service records, they indicate that wood containing small quantities of certain nitrogen compounds, when used under conditions conducive to decay, may decay more rapidly than untreated wood. These reports have probably contributed to the expressed concern regarding the decay resistance of lumber treated with urea, ammonium sulfate, and ammonium phosphate. The laboratory studies here described were made to obtain a t least a partial ansver to questions regarding the durability of lumber treated with these nitrogen compounds. The principal objects of these studies were: 1. To determine the effects of urea, ammonium sulfate, and ammonium phosphate on the rate of decay of sapwoods, which deteriorate rapidly under conditions conducive t o decay. 2 . To determine whether these nitrogen compounds measurably affect the durability of durable heartwoods, such as cypress, or the resistance t o decay of the less durable heartwoods of Douglas fir or red oak. 3. T o compare these nitrogen compounds xith ammonium nitrate, asparagine, and peptone, which have been reported t o speed up the rate of decay. 4. To determine whether a combinat'ion of fungi and bacteria would cause more decay of nitrogen-treated wood than fungi alone. 5. To determine the ease with which these compounds can be removed by leaching and whether heating noticeably affects their leachability. 1510
December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
1511
U. S. Forest Service, Forest Produots Laboratory Photo Cross Sections through Douglas Fir Timbers Chemically Seasoned with Sodium Chloride Lighter margins, produced when freshly cut surfaces were painted with silver nitrate, indicate depth of penetration and conoentration gradient of t h e salt.
Decay Tests on Woods
WOODBUSED. Southern pine sapwood and the heartwoods of cypress, Douglas fir, and red oak were used. Southern pine lumber usually has a high sapwood content, and it is fairly safe to assume that southern pine lumber treated with any of these nitrogen compounds (urea, ammonium sulfate, or ammonium phosphate) would contain a high percentage of sapwood. Also, since the sapwoods of all tree species are very susceptible to fungus attack, the results with southern pine should be applicable to the sapwoods of other species. The sapwood samples were cut from a log of green loblolly pine (Pinus caribaea). The Douglas fir heartwood samples were cut from a partly air-seasoned timber obtained from a local lumber yard and cut on the Pacific Coast. The red oak heartwood samples were cut from a green northern red oak log (Quercus borealis var. maxima) from southern Minnesota. The cypress heartwood samples were cut from a green plank obtained from a southern Louisiana sawmill. The heartwoods of red oak and Douglas fir have less natural durability than cypress heartwood. The selection of these species affords a comparison with the nitrogen compounds on woods of different durabilities. Furthermore, urea has found its greatest use as a chemical seasoning agent on oak, Douglas fir, and cypress. PREPARATION AND TREATMENT OF MATERIALS.Blocks 2 X 1X inch were used in all except one series of tests. In ~ '/,-inch this test the blocks were 1/1 inch thick. Since the a / or measurement was along the grain, the samples were thm cross sections that were easy to impregnate with water solutions of the nitro en compounds tested. The blocks were either airdried or tried at 70" C., and their oven-dry weights computed from data on control blocks dried a t 100" C . The samples were impregnated with water solutions of the various nitrogen compounds by placin them in suction flasks connected to water pumps. The dry bfocks were ven an hour under dry vacuum, the solutions added througi separatory funnels, and the vacuums held for 2 hours longer. After the vacuums were broken, the blocks were allowed to remain in the solutions for several more hours. By followin this procedure, complete and uniform saturation was obtaines even with the heartwoods of cypress and Douglas fir, generally considered among the most difficultly penetrated of all our woods. Absorptions or retentions were computed from concentrations and volumes of solutions absorbed. By varying.solution concentrations, a range of retentions was obtained. Because the test blocks were completely saturated in every case, computed
retentions were very uniform. It is recognized that this method of determining retention may involve some errors because of the possibility of selective adsorption from the solutions during the time blocks were immersed. The urea was an industrial grade widely used in chemical seasoning. The ammonium sulfate, ammonium phosphate (dibasic) ammonium nitrate, asparagine, and peptone were of c. P. grade. PREPARATION OF CULTURES AND DECAYTESTS. A number of the most important fungi attacking wood roducts, Lenzites trabea, Lentinus lepideus, Poria incrassata, a n 2 Trametes serialis were used. In addition, Daedalea quercina was used on oak and an unidentiiied wood rotter, designated by the letters RS, was used on Douglas fir. The fungi were grown on malt agar in square quart jars with metal caps. Two sterilized birch applicator sticks, 0.1 inch in diameter, were laid on the fungus mats in each jar and the test blocks placed on these. The blocks were dipped in boiling water for one second before lacing on the applicator sticks. Althou h there was considerabg variation in moisture content of blocfs at the end of the decay period, this was no greater than when Blass rods are used to support the test blocks above the agar. amples showing highest losses from decay usually had the highest moisture content. Sixt and ninety-day decay periods were used. The blocks were t i i n removed from the jars, dried at 100' C., and weighed. Losses in weight were computed as follows: original oven-dry oven-dry wt. wt. of absorbed chemical original oven-dry wt. (wt. of absorbed chemical)
+
% ' loss in wt.
=
+
x
100
Chemical retentions are expressed in pounds per cubic foot of wood and as a percentage of the oven-dry weight. The average specific gravities of the woods used were as follows: red oak 0.62, Douglas fir 0.44, cypress 0.44, southern pine 0.46. Although ten blocks were used for each chemical concentration and fungus, and the majority of the values in Tables I through V are based on this number, some material had to be discarded because of contamination due to molds. All values in the tables that are based on less than ten blocks are noted. The minimum number of blocks considered was six, and unless this number was available, the entire series was discarded, This accounts for the blanks in some of the tables. As could be expected, molds caused most trouble in tests with southern pine eapwood.
Vol. 34, No. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
1512
All values for decay losses were rounded off to the nearest per cent. Some of the data were analyzed statistically to determine whether certain losses due to decay were significantly greater than the losses for the controls (Tables I and 111). Fisher’s analysis of variance and T-test were used in making these determinations.
Rate of Decay It should be pointed out that small weight losses occurred, as they do in most decay tests, for blocks showing no visible signsof fungus growth or decay. It is difficult to determine the exact cause of such losses, but probably they result from slight leaching of chemicals from the blocks during surface sterilization, while they are in the test jars, and from volatilization of compounds during oven drying. I n the case of urea-treated blocks, such losses may be due to a slow decomposition of urea during oven drying. Later in the paper it is shown that heating urea-treated wood a t 100’ C. causes a gradual decomposition and loss of urea. Since weight losses as great as 4.0 per cent were often obtained for blocks showing no visible signs of decay, losses of this magnitude may be attributed to causes other than decay. The results of tests to determine the effect of added nitrogen compounds on the rate of decay of southern pine sapwood,
T A B L11. ~ RESULTS ON REDOAKHEARTWOOD Absorption of Chemical Compound Urea
%Gf wood 0.06 0.23 0.85
Ammonium sulfate
0.05 0.19 0.89
Peptone
0.05 0.23 0.86
Control
...
% Loss in Wt. Due to Decay (in 90 Days)
Lb./cu. Et. wood 0.015 0.06 0.22 0.012
Fungus RS 18 10 3 12 21 2
Daedalea querczna
Lenzites trabea
22 19
7
13 16 3
24 24 3
13 13 1
0.015 0.06 0.22
17 27 23 16
25 28 27 20
17 18 21 16
0.05 0.23
....
Douglas fir heartwood, and red oak heartwood are shown in Tables I and 11. CYPRESS HEARTWOOD. The results on cypress heartwood are not given because little or no decay was present in any of the samples, whether controls or treated with nitrogen compounds. Trametes serialis, Lenzites trabea, and Poria incrassata were used on cypress heartwood but failed to produce measurable decay losses in 90 days. The only conclusion permissible from the tests on cypress heartwood is that none of the nitrogen compounds decreased the decay resistance of this TABLE I. RESULTS ON SOUTHERN PINESAPKOOD AND DOUGLAS very durable wood to a measurable extent. FIR HEARTWOOD SOUTHERN PINE SAPWOOD. None of the concentrations of urea or ammonium sulfate used stimulated decay, and concentrations greater than 1.0 per cent, based on oven-dry weight Compound of wood, markedly inhibited decay. With minor variations, Southern Pine Sapwood the wood rotters used exhibited about equal tolerance to these 0.02 43 40 45 Urea 0.07 compounds. Some stimulation of decay was obtained with 0.09 49 16 27a 0.31 0.37 7 1 6 1.29 0.07 per cent ammonium phosphate and 0.31 per cent ammo5.37 1.54 2 3 1 nium nitrate. The test fungi appeared to tolerate higher con0.07 0.02 56 .. 38 Ammonium 43 14 47 0.31 0.09 sulfate centrations of ammonium phosphate and nitrate than of urea 0.40 2 2 7 1.39 and ammonium sulfate. 5.12 1.47 3 2 1 Although the results were somewhat variable, statistically Ammonium 0.07 0.02 58 b 33 .. phosphate 0.28 0.08 .. 330 49 significant increases in decay were obtained with most of the 1.32 0.38 39 29 38 5.68 1.63 4 1 2 lower concentrations of peptone and asparagine. This checks Asparagine 0.07 0.02 51 33 57 b the results obtained on these compounds by earlier investi0.35 0.10 63 b 35 48 gators (4, IO). It is difficult to determine the practical sig1.46 0.42 61%b 42b 58 b 5.08 1.46 6 .. 14 nificance of these decay increases. The controls for Trame67 b .. .. 0.07 0.02 Peptone tes serialis lost 48.0 per cent, whereas the losses for asparagine0.31 0.09 60 b .. .. 1.29 0.37 59 b .. .. and peptone-treated blocks were from 9.0 to 19.0 per cent 4.87 1.40 16 .. .. greater. These increases were found to be statistically signifi0.02 60 .. 41 Ammonium 0.07 cant, but in appearance, texture, and brittleness the decayed 57%b .. 41 nitrate 0.31 0.09 0.33 18 1.15 12 blocks, whether controls or treated with asparagine or peptone, 4.74 1.36 3 ..* . 1 were similar. Such stimulation of decay appears to have .... 48 33 45 Controls little practical significance. Douglas Fir Heartwood DOUQLAS FIR HEARTWOOD. The decay losses with this 0.013 29 1 20 Urea 0.04 wood were much smaller than for southern pine sapwood. 0.07 0.025 26 3 15 0.14 0.052 27 3 12 Preliminary tests on Douglas fir heartwood had shown that 12 1 0 0.27 0.100 concentrations of 0.5,to 1.0 per cent of most of the nitrogen 0.012 23 10 20 Ammonium 0.03 0.025 21 5 20 0.07 sulfate compounds inhibited decay, so much lower concentrations 0.14 0.052 12 5 21 were used. 0.28 0.103 8 3 19a The results with”ammonium sulfate and urea are similar Ammonium 0.04 0.013 13 6 21 0.026 22 6 19 0.07 phosphate to those obtained with southern pine sapwood. The lower 0.14 0.051 19 5 19 0.105 27 3 22. 0.29 concentrations had no appreciable affect on decay, and the 0.03 0.012 30 11 26 Asparagine highest concentration, 0.27 per cent of the dry wood, de0.07 0.025 32 8 18 creased decay. 0.14 0.052 19a 6 26 0.105 26 15 25 0.29 Ammonium nitrate was not used, but ammonium phosPeptone 0.013 23 11 17 0.04 phate appeared to be tolerated far better than urea or ammo0.07 0.026 23 145 16 0.14 0.052 21 10 17 nium sulfate. 0.29 0.106 24 13 23 Peptone and asparagine did not seem to influence appreControl ... .... 26 9 19 ciably the rate of decay of Douglas fir heartwood. Although Values based on 6 to 9 blocks. the results were not treated statistically, differences between b These values show significant increases over the controls. controls and treated blocks are small.
...
0
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1942
RED OAK HEARTWOOD. Only urea, ammonium sulfate, and peptone were used on this wood. The results with urea and ammonium sulfate are similar to those obtained with these compounds on Douglas fir. The results with peptond appear to be similar to those obtained with peptone on south: ern pine sapwood, some stimulation of decay is indicated for fungus RS and Daedalea quercina.
Decay of Urea-Treated Douglas Fir Heartwood by Fungi and Fungi Plus Bacteria Urea is considered a much more favorable source of nitrogen for bacteria than for fungi, and it has been well established that many bacteria are able to decompose urea and transform it into other nitrogen compounds, some of which may be more readily utilized by other organisms than is urea (6, 11). It has been suggested that a similar action might occur when urea-treated wood was placed in contact with the soil and became saturated with soil water and soil bactbria. Since organic nitrogen compounds appear to be readily utilized by wood-rotting fungi and may even stimulate decay,
TABLE 111. DECAYOF UREA-TREATED DOUQLAS FIR HBARTWOOD BY FUNGIALOXEAND FUNGI IN COMBINATION WITH
BACTERIA
Urea Concn. % of dry wood Lb./cu. ft.
% LOSSin Wt. Due to Decay (in 90 Days) Fungus RS Trametes serialis Alone
...
15
..
27
These values show significant increases over the controls.
there may be danger from combined baoterial and fungus action when urea-treated wood is placed in contact with the soil. The bacteria used were isolated from soil decoctions, grown on bacto-peptone agar in Petri plates, and the colonies were washed off with distilled water. The ureatreated blocks, after a one-second surface sterilization in boiling water, were dipped in the bacterial suspensions and then placed on fungus mats. The results of this test with urea-treated Douglas fir heartwood are summarized in Table 111. The significance of the decay increases observed with several of the lower urea concentrations was determined statistically. Significant increases in decay were found for several of the lower urea concentrations. This was the only test in which such stimulation with urea was observed, so it is difficult to evaluate the practical significance of the differences. There was no observable difference in appearance of the control blocks and blocks containing small amounts of urea. The results with the higher urea concentrations checked with those reported in Tables I and 11, and a marked reduction in decay was obtained for all samples containing 0.30 per cent or more urea.
With bacteria 384
..2
3
.43
Control
Alone
.*
,zz
0
With. bacteria
..
1513
TABLEIV. EFFECTOF HEATING AND LEACHING ON UREA CONTENT OF DOUGLAS FIRHEARTWOOD Urea Concn.
i n Wnnrl
71 82 93 100
20.9 20.4 20.2 19.5
0.9 1.6 10.0 60.8
20.7 20.1 16.2 11.9
95.6 93.3 82.4 29.4
3.5 5.1 7.6 9.8
Heating and Leaching of Douglas Fir Treated with Nitrogen Compounds Wood impregnated with urea is reported t o be easily bent or molded when the dry urea-treated wood is heated to 100’ C. (8,8). It has also been shown that sawdust impregnated with urea can be molded into hard dark plastics by applying heat and pressure (8, 8). Although chemical proof is lacking, it has been suggested that this plasticizing action may be due to some reaction between the urea and lignin or other wood constituents a t elevated temperatures. If such a reaction does occur, it should be difficult to remove the urea from the wood by leaching. The tests reported in Tables IV and V were made to determine the ease with which urea and other nitrogen compounds could be leached from wood after heating and the effects of such treatment on the decay resistance of treated wood. The tests summarized in Table IV were made on thin cross sections of Douglas fir heartwood. The nitrogen content of the samples was determined by a modified Kjeldahl method ( I ) and duplicate samples that checked within 3 per cent were used in every case. This method for nitrogen content yielded accurate results on known samples of urea and was therefore
U. S. Forest Service, Forest Products Laboratory Photo
Large Wooden Tanks (in Background) for Applying Urea Solutions t o Douglas Fir Timbers a t a West Coast Sawmill The sections of Douglas fir timbers in the foreground were treated with urea in an experimental tank and then air-seasoned. Degrade. due to drying checks, can be greatly reduced in heavy timbers by chemical seasoning
1514
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 34, No. 12
decay fungi; and one set was heated for 12 hours at 100" c. leached for 3 days in tap water, air-dried, and then placed on the decay % Loss in Wt. Due to Decay (in 60 Days) fungi. Trametes sarialis Lenzites trabea The results on the blocks of group 1 agree Not Absorption of Chemical h z L d Heated heated Heated quite well with those reported for Douglas fir % of or and OP and in Table I. Decay losses are lower than those Compound dry wood Lb./cu. it. leached Heated leached leached Heated leached 20 given in Table I because the decay period was Urea 0.14 0.05 11 ' 17 20 3 13 0.30 0.11 7 10 11 1 7 17 only 60 days. There was no evidence of stimu0.55 0.20 4a 5 15 2 4 21 1.10 0.40 3 1 17 1 3 22 lation of decay by any of the nitrogen com2.17 0.79 2 0 12 1 1 18 4.65 1.69 3 1 11 2 1 16 pounds, and the higher concentrations caused Ammonium 0.77 0.28 0 2 23a 0 15 13 marked inhibition of decay. sulfate 1.48 0.54 0 1 0 0 22 The results on blocks heated for 12 hours are 3.06 1.11 1 1 21 1 1 19 21 similar to those onunheated blocks. The heated 7 10 21 2 3 0.77 0.28 Ammonium nitrate 1.51 0.55 6 4 20 0 2 17 urea-treated blocks lost somewhat more weight Asparagine 0.80 0.29 17 18 26 13. 10 21 due to decay than comparable unheated blocks. 0.58 11 10 23 5 7 1.80 20 24 This can probably be traced to the loss of urea 1 4 26 4 3 3.19 1.16 Control ... ... 21 23 25 18 18 19 during heating (Table IV), a Values baaed on 6 to 9 blocks. The most interesting results were obtained ___ on samples that were heated and then leached. Most of the material receiving this treatment decayed to about the same extent as the considered satisfactory for the analysis of urea-impregnated untreated or control samples. The only exceptions were the wood. Prior to the heating and leaching studies, preliminary samples treated with the higher urea concentrations. The runs were made to obtain the nitrogen content of untreated somewhat smaller decay losses for these samples indicates Douglas fir heartwood. The nitrogen content of Douglas that not all of the urea was removed by leaching and corrobfir heartwood was found to be very low, 0.024 to 0.03 per cent. orates the results reported in Table IV, that heating ureaThis nitrogen content was considered in all later determinatreated wood either changes the urea to some less soluble comtions and calculations. pound or causes it to combine in some way with the lignin or The thin cross sections of Douglas fir heartwood were imother wood constituents so that it cannot be readily leached. pregnated with a 10.0 per cent solution of urea in distilled Conclusions water. The original urea concentrations in the wood are shown in the second column of Table IV. These blocks were The results of these laboratory studies are not intended to divided into four groups, one for each of the four temperasupply the final answer to questions regarding the relative tures, 71", 82", 93", and 100" C. After heating for 24 hours durability of wood treated with urea and the ammonia compounds. Such information must come from field or service a t these temperatures, nitrogen determinations were made to establish the amount of urea lost. The leaching was carried tests under actual use conditions. The results do indicate that, under laboratory conditions favorable for decay, there out by evacuating the blocks under water for 6 hours and subis no appreciable stimulation of decay by low concentrations jecting them to a current of running water (2.2 liters per minute) for 24 hours. The blocks were then air-dried and of urea and the ammonia compounds. The results also suggest that the reported stimulation of decay by organic nianalyzed to find the amount of nitrogen remaining. trogen compounds, asparagine and peptone, which was conIt is evident (Table IV) that there is considerable loss of firmed in our studies, is probably of little significance. urea from urea-treated Douglas fir heartwood when such maSince concentrations of urea and ammonium sulfate greater terial is heated for 24 hours a t 90" to 100" C. Although these than 0.30 per cent of the dry wood reduced the rate of decay, conditions were no doubt much more severe than those preand concentrations greater than 1.0 per cent prevented all vailing when wood is kiln-dried, the results suggest that there growth of the wood-rotting fungi on the surface of the blocks, may be some loss of urea during kiln-drying cycles. Despite eome wood-preserving action is suggested for these chemicals. the loss of urea during heating, the blocks heated to 100" C. However, when all the factors governing the use of wood precontained about three times as much urea after leaching as servatives and those which prevailed in these studies are caredid blocks heated to 71" C. It should be pointed out that the fully considered, it is clear that our results do not indicate any analyses were on total nitrogen, and the urea equivalents were appreciable wood-preserving value for these compounds. It found by calculation. It is possible that the nitrogen in the is true that when urea is used in chemical seasoning, and wood after heating and leaching was not in the form of urea ammonium sulfate and ammonium phosphate are used as fire but in some less soluble form or possibly combined with wood retardants for wood, the concentrations are usually greater constituents. Although these results are far from conclusive, than those required to check decay completely in these they lend support to the suggestion that urea may react with studies. The use of a minimum of 40 pounds of urea per certain of the wood constituents a t high temperatures and thousand board feet of lumber is recommended for chemical that this action may account for the plastic properties of seasoning. This is equivalent to concentrations of between 1.1 urea-treated wood when heated. and 1.5 per cent for the woods used in these experiments. A number of leaching studies were made on unheated, Also, in the case of wood chemically seasoned with urea, the urea-treated, Douglas fir heartwood blocks and sawdust, and chemical is not uniformly distributed. The effectiveness it was found that similar leaching schedules removed over of chemical seasoning depends upon the maintenance of a 99.0 per cent of the urea. considerable concentration gradient between the surface and To check on the effects of heat and leaching on the rate of interior. It is reported that urea concentrations for the outer decay of Douglas fir heartwood treated with various concen1/8 inch may be between 10.0 and 15.0 per cent, based on trations of urea and other nitrogen compounds, the tests weight of dry wood, and a t inch from the surface it may be summarized in Table V were made. One set of treated blocks less than0.3 per cent. In case of wood treated with ammonium was placed on the decay fungi without further treatment; one sulfate and ammonium phosphate to render it fire resistant, the set was heated for 12 hours a t 100" C., then placed on the TABLEv. EFFECTO F HEATING AND LEACHING ON DECAY RESISTANCE OF DOUGLAS FIR HEARTWOOD TREATED WITH NITROGEN COMPOUNDS
December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
chemical rarely makes up less than 5.0 per cent and usually is over 10.0 per cent of the dry weight. If such concentrations could be maintained under conditions conducive to decay, they would undoubtedly exert considerable preserving action. But leaching is usually a factor under such conditions, and all of the nitrogen compounds appear to be easily and completely removed from wood under conditions favoring leaching. By heat treatment it might be possible to fix a part of the urea so it would resist leaching, but i t has not been established that such action takes place under present kiln-drying practices. It is logical to conclude from these considerations that, when wood treated with these nitrogen compounds is used under conditions decay hazards, it be given a standard preservative treatment.
1515
Literature Cited pp. 20-21 (1) Aasoc. of 0 5 c i d Agr. Chem.. Methods of Analysis. . ._ (1930). (2) Berliner, J. F. T., Mech. Eng., 64 (3),181-6 (1942). (3) Champion, F.J., Am. Foreats, 42, 178-9 (1942). (4) Findlay, W. P.K., Ann. Botany, 48, 109-17 (1934). (5) Hart, E.B., Am. Miller, 70 (l),151-2 (1942). (6) Hill, D.F., and Mottet, A., Progress Rept., West Coast Lumbeman's Assoc., 1941. (7) Loughborough, W.K., Forest Products Lab. Ciro., 1938. Loughborough, W. K., Timberman, Feb., 1938. @) (9) Nelson, L. A., Zbid., July, 1938. (10) Schmitz, H., and Kaufert, F., Am. J. Botany, 23, 635-8 (1936). (11) Sinden, J. W., Penna. Agr. Expt. Strt., Bull. 365 (1938).
PAP^ 1998, Soientifio Journal Series, Minnesota Agrioultural Experiment Station.
Shattering and Cracking of Ice ROLE OF CARBON DIOXIDE PHILIP W. WEST Louisiana State University, Baton Rouge, La.
Waters having low total dissolved solids are capable of causing cracking problems when used for the manufacture of ice. In such cases the usual methods of eliminating cracking often fail. The effect of free carbon dioxide has been studied in these cases, and it has been found that carbonation of the waters being frozen will often eliminate cracking difficulties. In view of the present findings it is possible to reinterpret the results of earlier investigations. Where treated waters were alkaline and cracking resulted, it was probably caused by removal of the free carbon PROBLEM which has long confronted the ice industry is the tendency for certain manufactured ices to crack and shatter when frozen at low temperatures. Since
A
the capacity of any given plant is greatly increased by maintaining the lowest freezing temperatures practicable, it is of considerable economic interest that good ice be frozen at low temperatures. The production of manufactured ice is usually carried out by submerging cans, containing 300 pounds of water, in brines held a t 12' to 20" E'. The ultimate aim of each manufacturer is to use the lowest brine temperature consistent with the production of marketable ice. The desirability of low freezing temperatures is obvious from the relation between freezing time and temperature. Burks (4) gives this relation aa
dioxide. Where cracking tendencies were reduced by treatment with sulfuric acid or alum, the effect may be attributed to the resulting release of free carbon dioxide from the naturally occurring bicarbonates and carbonates in the water. No special equipment is needed for this new treatment. The cost per week for an average size ice plant will run about three dollars, using liquid carbonic as the source of carbon dioxide. Such treatment makes possible up to 30 per cent increases in production of ice by making feasible lower freezing temperatures. where F. T.
=
freeeing time, hours
6.25 = constant determined by experience 11 = can width at top, inoches
T = brine temperature, F.
Consequently, lowering the freezing time greatly increases the capacity of a plant of any given size. Typical plant data showing the effect of temperature on freezing time is shown in Figure 1. Unfortunately the use of low brine temperature leads to the formation of opaque ice, white butts, and other operational difficulties when the more highly mineralized waters are frozen. I n addition to the formation of opaque ice, decrease in brine temperatures increases the tendency of the frozen blocks of ice to crack or shatter upon their removal from the brine tank. I n general, the experienced chemist or engineer can predict from analyses of the water concerned whether or not transparent ice can be expected under normal operating conditions. When slight opacities are encountered,
