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I X D USTRIAL A X D ENGINEERING CHEMISTRY
Vol. 15, No. 5
Transmission of Sound by Standard LPIasonryPartitions’ By Paul E. Sabine RIVERBAXK LABORATORIES GEXEVAILL
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NVESTIGATIONS have been carried on from time to time to determine the relative merits of various types of partition walls in reducing the transmission of sound between adjacent rooms. The results obtained by different investigators have often been conflicting and, in general, the methods employed have been so different as to make direct comparisons impossible. One of the main problems in applied acoustics a t the Riverbank Laboratories has been that of determining the factors that enter into the transmission of sound from room to room by intervening partitions, and the relative importance of these factors. The earlier investigations were on simple structural units of wood, glass, and steel, such as doors and windows. These investigations showed that the heavier, and consequently stiffer, units, are more effective in reducing the intensity of the transmitted sound, but it was not possible to tell which of these physical properties was the more important. The work was then extended to flexible, porous, and inelastically compressible materials usually employed as “deadening quilts.” The transmission by such materials was found to be surprisingly large, as compared with stiff, impervious wood or steel. The transmission by porous materials, such as felt, was found to be greatly reduced by the interposition of layers of impervious materials, such as building paper. It further appeared that the logarithm of the reduction of sound produced by any material of this general type increased linearly with the thickness employed. This means that each added unit of thickness reduces the transmitted energy in a constant ratio. For different materials of the same thickness, this reduction mas found to follow the order of their relative densities. The most recent work has been on masonry partitions constructed according to standard practice. These walls were built into a doorway, 8 X 6 ft., cut into an 18-in. brick wall between two adjoining rooms. These rooms were built upon separate foundations, so that transmission of sound from one to the other was necessarily by way of the partition being studied. Measurements were made at each stage in the construction of each wall, so that the effects of the separate constituents of the finished structure were known. The earlier experiments had shown that the pitch of the sound was an important factor. Accordingly, the tests were conducted using twenty-three different tones covering a total range of five octaves. The method of measuring the relative intensity of the sound on the two sides of the partition was that developed by Prof. Wallace C. Sabine.2 For experimental details, the reader is referred to earlier articles from this laboratory. The ratio of sound intensities in two rooms separated by a given partition has been called the “reduction factor” for that partition. The logarithm of this factor is a fair measure of the relative loudness as perceived by the ear, and may be used as a numerical measure of the sound-insulating merits of the partition in question. A logarithmic reduction of six would render loud conversation in an unfurnished office room inaudible in an adjoining room; one of four would render it faint and unintelligible, but still fairly audible. Received March 16, 1923. 2 “Collected Papers,” Harvard University Press, 1922. a American Architect, July 30, 1915; July 28, 1920; September 28, 1921; October 12, 1921, 1
The results of the tests are summarized in the accompanying table. The average logarithm of the reduction for all tones is given in the third column. I n Column 4, the figures are the hydrostatic pressures over one surface of the wall measured in hundredths of a pound per square inch necessary to produce a displacement of one hundredth of an inch a t the middle point. These were determined by raising the pressure in one room, which was sufficiently airtight for the purpose, above that in the other, and measuring the flexure in the wall by means of a delicate optical micrometer. The table indicates that mass rather than stiffness is the determining factor in the general reduction of sound intensity. Sound reduction and mass per square foot follow the same order, regardless of material. On the other hand, there is no obvious correspondence between stiffness and sound reduction. For example, Kos. 8 and 14, about equally stiff, differ widely in the reduction factors, and No. 11, the stiffest wall, does not produce the greatest reduction. The accompanying graph of the data of the table is instruc-
Average Log Mass Relaof Re- per Sq. tive TESTS duction Ft. Stiffness 1 2 in. gypsum unplastered 2.36 10.4 2 3 in. hollow gypsum unplastered 2.42 11.1 4 3 1.5 in. plaster on lath 2.53 13.5 4 3 in. solid gypsum unplastered 2.67 14.2 5 2 in. solid gypsum 0.5 in. plaster 2.72 15.0 6 4 in. hollow clay tile unplastered 2.83 17.0 7 2 in. solid gypsum 1 in. plaster 2.95 19.6 8 2 in. solid gypsum 1.28 in. 21.4 84 plaster 3.05 5 4 in. clay tile 0.5 in. plaster 22.0 , 3.07 10 2.5 in. plaster on lath 3.24 23.2 17 11 3 in. solid gypsum 1.25 in. plas3 28 25 4 130 t er --. 27.0 ,. 12 4 in. clay tile 4- 1 in. plaster 3.36 120 3.40 28.0 1 3 4 in. clay tile 1.25 in. plaster 32.5 77 14 3 . 5 in. plaster on lath 3.60 3.82 41.8 15 4 . 5 in. plaster on lath
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+ ++
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AverageReduction 230 260 340 468 52 5 677 892
1120 1180 1740 i_._. ~ i n
2300 2500 4000 6600
I N D U X T R I A L Ah'D ENGINEERIXG CHEMIXTRY
May, 1923
tive as showing the possible degree of sound insulation that may be expected from partitions of this type. The particular material employed is clearly unimportant. Furthermore, one notes that equal increments of weight do not yield equal increments in the logarithm of the reduction, as is the case with quilt-like materials. Extrapolating the curve,
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it appears that for a logarithmic reduction of four a masonry wall weighing 50 lbs. per sq. ft. would be required, a figure which for cost and structural loading would be excessive in ordinary practice. The investigation is now being extended to distinctly different types of construction.
Furfural from Corncobs' I-Factors
Influencing the Furfural Yield in the Steam-Digestion Process By F. B. LaForge BURFAUO F CHEMISTRY, WASHINGTON, D. C.
IKCE the publication ever, since these results are The reactions inoolved in the production of furfural from cornof the first prelimiused only for comparison cobs by the steam-digestion process occur i n three stages. The nary article2 on the and are those commonly conuersion of the pentosans into furfural does not take place guantiproduction of furfural by given in reporting detertatively; the yield depends upon the temperature, the time, and the the action of Superheated minations of furfural and ratio of the amount of cobs to the amount of water employed. The water on corncobs, the work pentosans, no correction optimum conditions of operation were determined in order to apply done by the Bureau of has been made. them to larger-scale inuestigations. These conditions are a temperChemistry on this subject The cobs employed were ature of about 180" C., a reaction period of about 2 hrs.. and a air-dried and contained has been extended until it ratio of cobs to water of not greater than I : 4. has now reached the stage from 8 to 10 per cent of where the process is being m o i s t u r e . Their theoput into operation on a semicominercial scale a t the Color retical furfural content (determined by the standard 12 per Laboratory at Arlington, Va. Before this stage was reached, cent hydrochloric acid digestion method) was about 20 per however, it was necessary to determine the optimum con- cent, based on the air-dried weight. All furfural-yield values ditions of operation by small-scale laboratory experiments. in this paper are based upon the air-dried weight, because Because of the lack of exact knowledge of the chemical that basis is the only one of importance in commercial work. nature of the corncob, the reactions involved are still imDETERMINATION OF OPTIMUMTEMPERATURE perfectly understood. It is apparent, however, that they proceed in three stages, as follows: In the experiments to determine the optimum temperature, conditions were chosen whereby practically all the furfural (1) Under the influence of superheated water the pentosans are partially hydrolyzed and changed to a condition in which formed would be obtained as a distillate. I n all cases 600 they pass into solution. g. of cobs mere heated with 5000 cc. of water for 45 min., (2) Hvdrolvsis then follows and the soluble colloidal Denafter which the outlet valve was opened and the vapors were tosans are transformed into the sugars, largely pentoses such allowed to pass through the condenser a t such a rate as to as xylose. permit about 3000 cc. of distillate to be collected in 2 hrs. (3) The pentoses are dehydrated, yielding furfural. There was a variation of from 3 to 4 min. in this time, owing to the difficulty of regulating the rate of blow-off. These These stages overlap somewhat, so that some furfural is relations were chosen arbitrarily. produced before complete solution of the pentosans has TABLEI-VARIATION IN FURFURAL YIELD WITH TEMPERATURE taken place. The conversion of pentoses into furfural does Time for Furfural not take place quantitatively. I n fact, there is a very great Collection Concentra- Yield on Airof 3000 Cc. Total Vol- tion in Dis- Dry Weight loss before or after the last stage of the process is complete, Temperature Distillate ume Distillate of Cobs NO. c. Min. tilled. Cc. % so that only a portion of the furfural, as indicated by the .- bv- Volume % .1 165 t o 157 119 3325 0.30 1.6 usual analytical method, is actually obtained. The maxi2 166 to 167 122 3350 1.00 5.6 3 168 to 170 108 3400 1.10 6.2 mum amount seems to be about 10 per cent, or 50 per cent 4 170 t o 172 118 3400 1.24 7.0 of the theoretically possible yield. 5 172 t o 175 118 3400 1.51 8.6 6 176 t o 177 117 3400 1.71 9.7 The yield of furfural is dependent upon the conditions of 7 180 t o 182 117 3440 . 1.75 10.0 S 185 to 187 113 3440 operation in which three factors are involved-the temper1.68 9.7 ature, the duration of the reaction, and the ratio of the amount The temperature was held constant to within 2 degrees of cobs employed to the quantity of water present. For the laboratory experiments a gas-heated autoclave, by regulating the source of heat in each case. After 3000 provided with thermometer and outlet tube and connected cc. had been collected the flames were removed and the rate with a large glass condenser, was used.z The distillate was of blow-off was increased. The amount of distillate obtained measured and the furfural was determined by precipitating after the heating had been discontinued was about 300 to an aliquot portion in 400 cc. of 12 per cent hydrochloric 400 cc., in addition to the 3000 cc. collected during the acid by phlor~glucin.~The results obtained were about heating period, making a total of from 3300 to 3400 cc. The 10 per cent too high, because of the presence in the distillate whole time involved, not including that necessary to reach of aldehydes other than furfural, fatty bodies, and other the temperature in question, was about 23/4 hrs. The dissubstances that give precipitates with phloroglucin. How- tillate was well mixed and the furfural was determined in small, duplicate samples by precipitation with phloroglucin 1 Received November 18, 1922. in hydrochloric acid. The results of eight experiments are 1 THIS JOURNAL, 13 (1921), 1024. a Assoc. Oficial Agr. Chem. Methods, 1920, p. 96. given in Table I, and are shown graphically in Fig. 1.
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