UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 LABORATORY TESTS OF 
 ORCHARD HEATERS 
 
 A. H. HOFFMAN 
 
 BULLETIN 442 
 
 November, 1927 
 
 UNIVERSITY OF CALIFORNIA PRINTING OFFICE 
 
 BERKELEY, CALIFORNIA 
 
 1927 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of California, Davis Libraries 
 
 http://www.archive.org/details/laboratorytestso442hoff 
 
LABORATORY TESTS OF ORCHARD HEATERS* 
 
 A. H. HOFFMAN t 
 
 Field studies of the economic phases of orchard heating have been 
 made by Young/ 9 ' 10 ' ll > 12) Young and Cate, (13) Schoonover, Hodgson 
 and Young/ 6) West and Edlefsen/ 8) Webber et al./ 7) Garcia and 
 Fite, (1) and others. Tests to determine the effectiveness of different 
 orchard heaters to stay the fall of temperature have been made in 
 large number and variety by Young/ 9 ' 10 ' 11 > 12) West and Edlefsen/ 8) 
 (VGara/ 4) and others. Aside from some measurements of radiation 
 made by Kimball and Young/ 3) exact measurements of the perform- 
 ance of the individual heaters have in general been lacking and are 
 needed for the guidance of both the user and the manufacturer. At 
 the urgent request of the Citrus Growers ' Department of the Southern 
 California Farm Bureaus and others the work here reported was 
 undertaken. In general it has been found that the methods which 
 mechanical engineers commonly use in testing the performance char- 
 acteristics of steam-boiler furnaces and the like are inapplicable to 
 orchard heaters for the reason that the latter, burning in the open, 
 present an entirely different problem. Hence it has been found 
 necessary to devise new methods and apparatus. 
 
 THE IDEAL ORCHARD HEATER 
 
 Those who have made the most thorough study of the subject are 
 generally agreed that the following characteristics in an orchard 
 heater* are desirable for reasons obvious or specified. 
 
 1. It should be able to burn fuel (and hence to produce heat) at 
 rates that will enable the fruit grower to control the temperature of 
 his orchard within the necessary limits. The only practical method 
 yet found for preventing frost damage in orchards is by adding heat 
 to the air. 
 
 2. It should burn the fuel completely so that all the heat contained 
 may be liberated. 
 
 * The purpose of this bulletin is to make the results of these studies imme- 
 diately available to the user and to the manufacturer of orchard heaters. The 
 test methods will be explained in a later publication. 
 
 t Associate Agricultural Engineer in the Experiment Station. 
 
4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 3. Its radiation above the horizontal plane should not be excessive. 
 
 4. The gases rising from the stacks should be discharged at a level 
 close to the ground and should not have too great an upward velocity 
 or they may be shot so high that they may not effectively warm the 
 orchard. 
 
 5. The higher the temperature of the heater surfaces and of the 
 gases rising from the stacks the greater will be the rate of radiation 
 and the higher the upward velocity. It follows therefore that very 
 high temperatures are undesirable and that as much cold air as 
 possible should be mixed with the products of combustion before they 
 are discharged from a heater. 
 
 6. An orchard heater should not smoke, since smoke is a general 
 nuisance to all persons in the region. It damages ripe fruit by black- 
 ing it and rendering washing necessary, and wastes a small portion 
 of the heat content of the fuel. 
 
 7. All the foregoing desirable characteristics should be embodied 
 in a heater (a) that can be produced at a reasonable cost, (b) that 
 can be operated with a minimum of skill, labor and care, (c) that will 
 have a low up-keep expense and a satisfactory length of life, and (d) 
 that will burn available fuel. 
 
 THE PROBLEMS TO BE SOLVED 
 
 The following items are the principal objectives sought in this 
 study : 
 
 1. What are the characteristic burning or fuel consumption rates 
 of the different heaters? 
 
 2. How efficiently do they convert fuel into heat ? 
 
 3. What per cent of the heat is lost by radiation ? 
 
 4. How fast do the hot gases rise from the stacks of the heaters ? 
 
 5. What temperatures are attained by the gases and by the heater 
 surfaces ? 
 
 6. How much smoke is produced by each heater and how may a 
 visible record of the smokiness be obtained? 
 
 7. What characteristics are necessary in a satisfactory fuel for 
 orchard heating? 
 
Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
 THE HEATERS STUDIED 
 
 A total of nineteen heaters, figure 1, and table 1, were included. 
 Extra stacks and "spiders" for placing over lard-pail type to reduce 
 the burning rate (see Nos. 6s and 8s as typical spiders) brought the 
 actual number of heaters tested up to twenty-six. Six of these are of 
 the briquet or solid fuel burning type, two are non-distilling, and 
 
 Fig. 1. — Names of the heaters tested: 1. Pomona. 2. Kittle. 3. Scheu 
 Jumbo Cone Louvre. 4. Scheu Baby Cone Louvre. 5. Scheu Double Stack. 
 6. Bolton. 6s. Bolton (with spider). 7. Troutman. 8. Canco. 8s. Canco (with 
 spider). 9. Diamond. 10A. Dunn (10 in the illustration). IOC. Dunn (with 
 30-inch stack; not shown). 11A. Citrus, 9-gal. low stack. 11B. Citrus, 9-gal. 
 medium stack. 11C. Citrus, 9-gal. high stack. 12A. Citrus, 6-gal. low stack. 
 12B. Citrus, 6-gal. medium stack. 12C. Citrus, 6-gal. high stack. 13. Karr. 
 14. Jessen (large). 15. Jessen (medium). 16. Jessen (small). 17. Low Delivery. 
 18. Baby Double Stack. 19. Citrus Gas Flame. 
 
 eighteen distilling oil burners. Four additional heaters were received 
 too late for test. Three of these are Citrus heaters and similar to 
 Nos. 11B, 11C, and 19. They differ from those illustrated in that each 
 has a baffle plate inside the reservoir and a filler tube and filler cap 
 in the cover, and the one similar to 11B also has the stack height 
 reduced from 31 inches to 18 inches. The fourth is the new Scheu- 
 National Jumbo Cone Louvre heater and differs from heater No. 3 
 of the tests in the following particulars : weight 18.3 pounds ; over-all 
 height 44 inches; stack, height 22% inches, top diameter 7 inches, bot- 
 
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8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 torn diameter 9 inches. The cone is larger at the top than that of No. 3. 
 A self-contained lighting cup is placed at the top of the down-draft 
 tube. With the exception of the Dunn heater (no longer manufac- 
 tured but many still in use), all the heaters studied were supplied by 
 courtesy of the manufacturers. In each case the maker was asked to 
 supply any directions for use which he had found necessary to give the 
 buyers of his product. In the tests such instructions were followed 
 as closely as possible. 
 
 The heaters studied are of three types or classes, (1) those that 
 burn solid fuel, especially briquets, (2) those that burn oil in a burner 
 separate from the fuel reservoir, and (3) those that burn oil within 
 the reservoir itself. The names in common use for these three types, 
 briquet, non-distilling oil, and distilling oil, are used in reporting this 
 work, although the last two terms do not seem entirely fitting since 
 condensation is not a feature in the operation of either type. In the 
 so-called non-distilling heater the oil is metered through a suitable 
 device in flowing from the reservoir to the burner. The fuel left in 
 the reservoir after a night's burning of the heater is practically the 
 same in quality as before lighting. In the so-called distilling type 
 heater the fire inside the reservoir causes the more volatile portions of 
 the oil to be vaporized and burned first. Hence, after some hours of 
 burning, the oil remaining in the reservoir of such a heater may be 
 considerably denser (lower Baume number) than the original fresh oil. 
 
 Briquet heaters are not so easy to extinguish as the oil burners. 
 They are usually left until the complete charge of fuel has burned out. 
 Though some fuel might be saved by emptying the contents of the 
 heaters upon the ground, generally the labor cost would be too great. 
 
 THE LABORATORIES USED 
 
 In order that the conditions under which the heaters were placed 
 during test might be comparable with those in practice, the laboratory 
 chosen for the bulk of the tests was a tilled field about 50 yards wide 
 flanked on the east by a deciduous orchard and on the west by a vine- 
 yard. The only building near was a small shed built to shelter the 
 necessary instruments. Here the tests were run at night and only 
 when the wind speed, measured at a height of 18 feet 10 inches above 
 the ground was less than about 5.5 miles per hour. The speed at the 
 level of the heaters was much less. Higher wind speeds caused too 
 great variations in the burning rates and made it impossible to obtain 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 9 
 
 satisfactory measurements of the quantities under study. The air 
 temperatures during the testing were not so low as is desirable but 
 were the best available at Davis. However, it is believed that a 
 re-running of the tests at temperatures between 18° F and 28° F 
 would not change the relative positions of the heaters as to the 
 measurements. Since colder air is denser and therefore contains more 
 oxygen per cubic foot it would be expected that for a given adjust- 
 ment and kind of fuel a heater would burn faster at the colder air 
 temperature. A test indicated that this was true. An open lard-pail 
 heater was burned four times at night and thrice in the daytime using 
 17 pounds of No. 2 oil (see table 7) for each test. The wind speeds 
 were nearly the same for all tests. The average day burning time was 
 3 hours minutes and air temperature 48.7° F ; the average night time 
 2 hours 29 minutes and air temperature 36.3° F. See curves ' ' 8 (day) ' ' 
 and "8" in figure 2. 
 
 In general at least two tests in the field laboratory were made on 
 each heater, one at ''high adjustment" and one at ''low adjustment, 
 meaning, respectively, about as high as a grower would ordinarily 
 burn his heaters if he feared he might not be able to hold a safe air 
 temperature, and about as low as the heater could be made to burn 
 properly. In some cases it was found later that adjustments had been 
 somewhat too high or too low. It was not always possible to re-run 
 the test. 
 
 To make sure that the comparative records of smoke and of upward 
 velocities of the gases were correct it was decided to make a "normal 
 adjustment" run indoors so that wind effects might be entirely elimi- 
 nated. The indoor tests were made in daytime in a large room which 
 was ventilated after each test, the heaters being lighted and warmed 
 up outside and brought in on a small flat-car. 
 
 FUEL CONSUMPTION RATES 
 
 From the utility standpoint the burning or fuel consumption rates 
 are of the utmost importance since to produce heat in large quantities 
 is the prime object. The heat produced equals the number of pounds 
 of fuel burned times the heat content per pound, assuming complete 
 combustion. The heat content of a fuel is generally expressed in 
 British thermal units (abbreviated B.t.u.) per pound. Its value is 
 about 20,000 for oil, 16,000 for coke, and 13,000 for coal. A B.t.u. is 
 
10 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
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 Fig. 2. — Characteristic burning rates. Each curve, except "8" and "8 
 (day)," is the record of a single test on the heater of the corresponding num- 
 ber. The fuel reservoirs were full at lighting. The only draft adjustments, if 
 any, were made immediately after lighting. All briquet heaters were top 
 lighted. The deviations from smooth curves are due principally to wind 
 variations. Briquet type heaters vary more than the oil burners (curves 1, 9, 9', 
 and 13). Curve 9' shows a typical case of imperfect lighting (heater No. 9). 
 The dotted line curve "8 (day)" is the average of three tests run in daytime 
 and shows how higher air temperature slows the burning rate. Curve "8" 
 is the average of 4 tests all run at night. See figure 1 and table 1 for identi- 
 fication of heaters. 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 11 
 
 the heat required to warm one pound of pure water one degree Fahren- 
 heit. It is comparatively easy to measure burning rates. For the field 
 tests the scales used were sensitive to one-fourth ounce and were set 
 into the ground so that the bottom of each heater was on a level with 
 the ground surface. Readings of weights were taken at 30-minute 
 intervals in the field laboratory and at 10-minute intervals indoors. 
 It was found that the burning rates of distilling type oil burning, and 
 of briquet burning heaters were greatly affected by slight changes in 
 wind speed. The two non-distilling heaters tested were of course 
 unaffected, since in these heaters the fuel is metered into the burner; 
 however such heaters are sensitive to temperature effects, especially 
 when the oil used is of such nature that it thins rapidly on being 
 warmed, for example, oils A, B, C, and L in figure 11 (see also table 6). 
 The oil burning heaters have characteristic burning rate curves, a 
 few of which are shown in figure 2. 
 
 It should be emphasized that in the tests in which data for these 
 curves were obtained the only draft adjustments were made imme- 
 diately after lighting. Also no fuel was added during test. Frequent 
 regulation is essential in practice to secure the desired results. Gen- 
 erally the adjustment will be for a low burning rate at lighting when 
 only a little heat is needed. Towards morning when the temperature 
 may tend to go very low a much higher burning rate may be required ; 
 this would necessitate re-regulation and, in lard-pail and briquet 
 heaters, re-fueling, or lighting of reserve heaters. It should be noted 
 that all briquet type heaters tested were lighted at the top. Bottom 
 lighting causes the fuel to burn out in a shorter time. 
 
 The peaks that are found on curves 3 and 8 (fig. 2) at points about 
 one hour after lighting are evidently caused by the warming of the oil 
 and consequent more rapid vaporization. The later falling off of the 
 burning rates is no doubt due to the oil level becoming lower in the 
 reservoirs and to the fact that the more volatile portions of the fuel 
 burn first leaving the heavier, more slowly vaporizing portions. In 
 some heaters clogging with soot undoubtedly tends to slow the rate 
 of burning. 
 
 Most of the deviations from smooth curves are due to the effects 
 of variations in wind speed and air temperature; some may be the 
 result of errors in the readings. It will be noted (fig. 2) that the 
 burning rates of briquet type heaters are often much more erratic 
 than those of the oil burners. The method and skill used in kindling 
 and in lighting and also the character of the material used for kindling 
 
12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 have a considerable effect upon the promptness with which the heater 
 will come up to its maximum burning rate for a given adjustment. 
 Curves 9 and 9' show variations that may be expected. Curve 9' is 
 a typical case of slow starting which may be caused by using too little 
 or poor quality kindling, by improper placing of the kindling, or by 
 unskillful application of the oil from the lighting torch. For briquet 
 heaters two jute balls (fig. 3) filled with paraffin and placed under 
 the top layer of briquets proved to be very satisfactory kindling. No 
 deterioration of the kindling would occur even if the unlighted heater 
 were left standing several years. Pieces of old automobile casing were 
 found to serve well except for the smoke and odor. A quart of dried 
 peach pits similarly placed was also satisfactory. Short pieces of 
 seasoned wood thoroughly soaked with refuse crank-case oil served 
 the purpose though they were less pleasant to handle. 
 
 Balls of Jute Wait* 
 
 Sta**?t\s<m Mi\U- 
 
 Fig. 3. — A satisfactory kindling for briquets. Balls of jute waste 2y 2 inches 
 in diameter dipped into melted paraffin. Two are placed under the top layer 
 of briquets. They are unaffected by weather or time and start readily when 
 lighted with fuel from a lighting torch. 
 
 Another factor that influences greatly the burning rate of a given 
 heater under given conditions is the volatility of the fuel used. If 
 light oil is used the rate of burning will be more rapid. 
 
 In these tests the briquet heaters burned up to nearly 5 pounds of 
 fuel per hour (table 4), and the oil burning heaters up to nearly 15 
 pounds per hour (table 5). It is understood, of course, that the oil 
 burning heaters other than lard-pail type could have been adjusted so 
 as to consume at considerably more than the highest rates given in the 
 summaries, but in general it would have been at the penalty of higher 
 upward velocities and higher radiation rates. Also such excessively 
 high adjustment would have greatly increased the smoke nuisance. 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 13 
 
 FUEL-TO-HEAT CONVERSION EFFICIENCY 
 
 To find out how efficiently the several heaters converted fuel into 
 heat it was necessary to analyze the hot gases arising from them to 
 find the per cent of carbon monoxide gas and to determine the weight 
 of smoke (carbon) per unit volume of the hot gases. It was found 
 necessary to take the samples of the gases just above the tip of the 
 flame. If taken too low, considerable amounts of unburned oily vapors 
 and much larger amounts of carbon would be drawn. If taken too 
 high, there was greater danger of taking some fresh air. Hence good 
 results could be obtained only when the wind was nearly still. Espe- 
 cially sensitive apparatus was used to determine the per cent of 
 carbon monoxide. This was in no case found to be greater than five- 
 hundredths of one per cent even when the gas sample had been taken 
 a little too close to the flame. The heat loss represented by the 
 unburned carbon in the smoke of some of the smokiest heaters was 
 only about one-tenth of one per cent of the heat value of the fuel used. 
 We must conclude therefore that the fuel-to-heat conversion efficiency 
 of all the heaters tested was practically 100 per cent. That is to say, 
 the heaters tested got out of the fuel used practically all the heat there 
 was in it. This takes no account of fuel left unburned in the reservoirs, 
 or else assumes that the drafts in distilling type heaters are opened 
 sufficiently at the last to burn out completely the asphaltic residues. 
 In practice this latter would not usually be done on account of the 
 danger of warping and of burning holes in the bottoms of the 
 reservoirs. In the tests here reported only fresh oil was used. In 
 practice it is customary to add enough fresh oil to refill the partially 
 emptied reservoirs after each night's use. Thus the heavier residues 
 may accumulate. Cases have been reported where from this cause near 
 the close of a long period of freezing weather lighting became very 
 difficult and large quantities of tarry or asphaltic matter were left 
 when the fires would no longer burn with the ordinary draft regu- 
 lations. (For further discussion of smoke measurements see p. 17, 
 and of fuels, p. 27.) 
 
 RADIATION FROM HEATERS 
 
 Heat that passes out in straight lines from a hot object as a center 
 does not appreciably warm the air or other medium through which 
 it passes. It is only when the heat ray strikes some opaque object 
 and is absorbed that it is able to warm the air in the neighborhood. 
 For these reasons that portion of the heat that is radiated upwards 
 
14 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 from an orchard heater is largely lost to the sky. Whatever heat is 
 radiated along lines that fall below the horizontal will of course be 
 absorbed by the soil and be effective in warming the air. Also any 
 rays that strike leaves, twigs, branches, and stems of trees would be 
 saved. Hence more of the radiant heat would be lost in a deciduous 
 orchard than in a citrus grove. 
 
 Fig. 4. — Apparatus for measuring radiation from orchard heaters. Four 
 heaters placed on scales set in an arc of a circle were tested in succession by 
 swinging the radiometer from one to another. Readings were taken at seven 
 positions from 0° angle (horizontal) up to 90° angle (vertical). The radiometer 
 was connected electrically to a sensitive galvanometer in the instrument shelter. 
 
 The higher the temperature of the hot gases and of the heater 
 surfaces the greater will be the radiation loss. Evidently the radiation 
 rate will vary as gas and surface temperatures change. A flaming 
 heater radiates more than one that is too cool to emit light. 
 
 Apparatus was devised for measuring the heat radiated above the 
 horizontal plane through the effective radiation centers of the several 
 heaters (fig. 4). The total heat radiated upward was in some cases 
 nearly 5 per cent of the total heat in the fuel burned (see summaries 
 of night tests, tables 4 and 5 ) . 
 
Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
 15 
 
 A number of attempts were made to reduce the radiation loss by 
 the use of screens of various shapes. All of these proved effective in 
 some degree. The most practicable form of radiation screen found 
 (though far from being the most effective) was a simple flat baffle 
 plate placed a few inches above the stack. Figure 5 shows graphically 
 the effect. 
 
 Fig. 5. — How a deflector affects radiation to the sky. Distances out from 
 center are proportional to the intensity of radiation. The space between the 
 two curves indicates roughly the heat saved by the use of an 18-inch square 
 deflector placed on a Scheu Jumbo Cone Louvre heater burning 10.63 pounds of 
 No. 1 oil per hour. 
 
 UPWARD VELOCITY OF THE WARM GASES 
 
 The warm gases rising from an orchard heater should not rise too 
 rapidly or they may not spread out horizontally and come to rest at 
 a sufficiently low level. If shot out at high velocity and high tem- 
 perature they may instead "penetrate the temperature-equilibrium 
 ceiling" above the orchard and in some degree become ineffective as 
 far as warming the orchard is concerned. Measurement of the upward 
 velocity of the hot gases was accomplished by use of a high-temperature 
 anemometer especially designed and built for the purpose. Calibra- 
 tion was made to enable interpretation of its readings in terms of 
 feet per second. A further study is to be made to find out how high 
 gases starting at 14 feet per second will normally rise in an orchard. 
 
16 
 
 UNIVERSITY OF CALIFORNIA. EXPERIMENT STATION 
 
 Fig. 6. — High-temperature anemometer as set ready for use in out-of-doors 
 tests. This measures the upward velocity of the hot gases. The revolutions 
 are recorded electrically on the chronograph roll seen on the right. 
 
 Figure 6 shows the high-temperature anemometer in position for 
 use in a field laboratory test. In the field tests the anemometer was 
 placed in line with the center line of the stack and partly within the 
 top to lessen wind effects. In the indoor tests it was placed as in 
 figure 7, in the region of highest velocity of the gases. In a few cases, 
 
 Fig. 7. — Anemometer placing in indoors tests. The region of highest velocity 
 generally found at about two diameters distance above the stack in still air. 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 17 
 
 especially of low or medium stack heaters, slightly higher velocities 
 (and sometimes higher gas temperatures also) were found at low 
 burning rate adjustment than at higher adjustment in the same heater. 
 These apparent discrepancies were in general due to the fact that the 
 column of rising gases in some cases did not fill the whole area of the 
 stack but was concentrated in a portion of the space. As will be seen 
 in the summaries, tables 2, 3, 4, and 5, the velocities range from less 
 than 2.5 feet per second (below which the anemometer would not run 
 satisfactorily) to about 5 feet per second for briquet burning heaters, 
 and from the same low limit up to about 14 feet per second for oil 
 burners. 
 
 The same flat baffle plate that was found practicable to reduce 
 radiation to the sky may be used satisfactorily above many of the 
 heaters now in use. Its use will stop the rapid rise of a concentrated 
 stream of high temperature gases and send them out horizontally at 
 greatly reduced speed, at the same time mixing them more effectively 
 with the cold air. It was found that the upward velocity of the gases 
 from heaters Nos. 2 and 17 was less than 2.5 feet per second when the 
 regular baffles were in place but about 8 and 6 feet per second, 
 respectively, when the baffles were removed. 
 
 TEMPERATURE OF GASES AND HEATER SURFACES 
 
 It was found very simple and easy to measure these temperatures 
 by use of electrical pyrometers designed to work at the temperatures 
 involved. Measurement was made just at the top of the stacks. 
 Luminous flames were found very hot, in some cases running about 
 1400° F. The temperatures of the heater surfaces were found to vary 
 considerably, depending upon the distribution of the fires inside. 
 In briquet burning heaters lighted at the top large and very irregular 
 variations were found. Hot spots develop and move as the fire spreads 
 through the fuel. As before indicated, excessively high surface tem- 
 peratures are undesirable because they tend to increase radiation 
 losses. They also tend to cause rapid destruction of the heaters. 
 
 SMOKE FROM ORCHARD HEATERS 
 
 While, as before indicated (under "Efficiency," p. 13), the smoke 
 from orchard heaters does not represent an appreciable heat loss, it is 
 nevertheless a great nuisance to the fruit grower and his helpers and 
 to everybody else within its range, and does not itself appreciably 
 lessen the danger of frost damage. (8) 
 
18 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 In the study of smoke two things were sought: (1) to weigh the 
 smoke in a given volume of the gases and, (2) to secure a visible record 
 by which relative smokiness might be compared. Some difficulties 
 were encountered, but satisfactory methods and apparatus were finally 
 evolved. The weights of smoke were found to be exceedingly small 
 (summaries, tables 2, 3, 4 and 5). 
 
 TABLE 2 
 
 Summary of Daytime Tests Briquet Burning Heaters* 
 
 No. 
 
 Heater 
 
 Fuel 
 charge, 
 pounds 
 
 Fuel, 
 pounds 
 per hr. 
 
 Time since 
 lighting, 
 
 Heat 
 in fuel a , 
 
 B.t.u. 
 per hr. 
 
 Maximum 
 upward 
 
 velocity 15 , 
 feet per 
 second 
 
 Temper- 
 ature of 
 gases t, 
 degrees 
 F. 
 
 Smoke, 
 pound 
 per 1000 
 
 
 Hr. 
 
 Min. 
 
 cu. ft. 
 gas 
 
 1 
 
 
 24 
 20 
 17 
 
 2.94 
 2.81 
 1.41 
 
 1 
 2 
 5 
 
 00 
 00 
 20 
 
 39,590 
 37,839 
 18,987 
 
 4.7 
 4 4 
 
 2.7 
 
 690 
 305 
 485 
 
 .0085 
 .0062 
 
 
 
 Clear 
 
 9 
 
 
 19 
 13 
 
 3.44 
 2.06 
 
 1 
 4 
 
 55 
 17 
 
 35,281 
 27,740 
 
 2.6 
 3.0 
 
 600 
 415 
 
 Trace 
 
 
 
 Clear 
 
 13 
 
 
 22 
 
 4.31 
 
 2 
 
 00 
 
 58,038 
 
 5.1 
 
 460 
 
 .0145 
 
 
 
 
 14 
 
 Jessen, large 
 
 
 
 No 
 
 day 
 
 run 
 
 
 
 
 15 
 
 Jessen, medium 
 
 
 
 No 
 
 day 
 
 run 
 
 
 
 
 16 
 
 Jessen, small... 
 
 18 
 12 
 
 3.28 
 1.78 
 
 1 
 3 
 
 30 
 55 
 
 44,169 
 17,477 
 
 Less than 2 . 5J 
 Less than 2.5 
 
 645 
 335 
 
 .0044 
 Trace 
 
 * All tests made indoors with No. 3 briquets (see table 7). 
 
 a Product of pounds fuel per hour by heat content per pound as obtained by bomb calorimeter. 
 ' Measured at region of maximum velocity, 
 t Measured at top of stack. 
 X Regular lid in place. Without lid, 4.8. 
 
 For making a visible record of relative smokiness of all the heaters 
 the same volume of gases for each, taken from just above the tip of 
 the flame, was passed at the same rate through a circle 3 inches in 
 diameter in the center of a 5-inch square of white felt. For the speed 
 at which the gases passed through, the felt used made a practically 
 perfect filter. Because of its long bill or tube (for cooling the gases 
 before they reached the felt) the device in which the square of felt was 
 clamped was termed the 'smoke mosquito." Figure 8 shows it in use 
 in an indoor test. The record of smoke in the out-of-doors tests is 
 shown in figure 9 and in tables 4 and 5. Series of records were taken 
 on two briquet heaters (Nos. 1 and 14, fig. 9) to show the behavior with 
 the passage of time. Where in the summaries (tables 2, 3, 4 and 5) the 
 
Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
 19 
 
 TABLE 3 
 
 Summary of Daytime Tests, Oil Burning Heaters* 
 
 No. 
 
 Name and type 
 
 Fuel 
 charge, 
 pounds, 
 approx. 
 
 Fuel, 
 
 pounds 
 
 per 
 
 hour 
 
 Heat 
 
 in fuel a , 
 
 B.t.u. 
 
 per hr. 
 
 Maximum 
 
 upward 
 
 velocity, 
 
 ft. per sec. 
 
 Tempera 
 
 ture of 
 
 gases, 
 
 °F. 
 
 Smoke, 
 
 pound 
 
 per 1000 
 
 cu. ft. gas 
 
 2 
 
 Kittle, non-distilling 
 
 36 
 
 44 
 
 41 
 
 ) 32 
 
 > 31 
 i 30 
 
 i 35 
 
 i 34 
 
 12 
 
 11 
 
 8 
 
 12 
 10 
 9 
 13 
 
 24 
 
 1 22 
 
 > 31 
 
 1 29 
 
 1 25 
 
 >" 
 
 !" 
 
 1 28 
 13 
 12 
 
 22 
 
 3.38 
 
 1.97 
 
 3.72 
 
 6.67 
 
 5.44 
 
 3.00 
 
 3.56 
 
 2.91 
 
 3.94 
 
 0.85 
 
 1.56 
 
 5.63 
 5.83 
 6.04 
 1.03 
 
 4.25 
 
 4.50 
 
 3.09 
 
 4.98 
 
 10.78 
 
 2.69 
 
 5.0 
 10.0 
 3.00 
 1.60 
 3.94 
 
 66,748 
 
 38,904 
 
 73,463 
 
 131,719 
 
 107,429 
 
 59,244 
 
 70,303 
 
 57,467 
 
 77,807 
 
 16,786 
 
 30,807 
 
 109,838 
 115,131 
 192,779 
 20,340 
 
 83,929 
 
 88,866 
 
 61,021 
 
 98,345 
 
 212,883 
 
 53,122 
 
 98,740 
 197,480 
 59,244 
 31,597 
 77,807 
 
 Less than 2.5 
 
 Less than 2.5 
 
 Less than 2.5 
 
 10.9 
 
 11.8 
 
 9.7 
 
 8.0 
 
 6.9 
 
 4.7 
 Less than 2 . 5 
 
 3.5 
 
 4.8 
 5.7 
 
 665 \ 
 
 460 j 
 715 j 
 955 J 
 865 f 
 645 j 
 1,060 j 
 655 j 
 670 f 
 286 f 
 
 Tracef 
 .0053f 
 
 17 
 17 
 
 3 / 
 
 Low delivery, non-distilling . 
 
 Low delivery, non-distilling.. 
 
 Scheu Jumbo Cone Louvre, 
 distilling 
 
 .0053f 
 
 .0053 
 
 .0107 
 
 Trace 
 
 Trace 
 
 .0044 
 
 Clear 
 
 Clear 
 
 4 < 
 
 Scheu Baby Cone Louvre, 
 distilling 
 
 .0124 
 .0329 
 
 4 \ 
 
 Scheu Baby Cone Louvre, 
 distilling 
 
 .0062 
 Trace 
 
 5 { 
 
 Scheu Double Stack, dis- 
 tilling 
 
 .0062 
 .0071 
 
 'I 
 
 Scheu Double Stack, dis- 
 tilling 
 
 Trace 
 Trace 
 
 6 
 
 Bolton, distilling 
 
 .0338 
 
 6s 
 
 7 
 
 Bolton, spider on, distilling... 
 Troutman, distilling 
 
 .0373 
 .0115 
 .0115 
 .0364 
 
 8 
 
 Canco, distilling -1 
 
 Canco (spider on) distilling... 
 Dunn, distilling 
 
 1,020 
 940 
 
 .0409 
 .0364 
 .0267 
 .0249 
 
 8s 
 10A 
 
 Less than 2 . 5 
 8.0 
 8.8 
 7.7 
 8.1 
 14.1 
 
 6.0 
 
 9.8 
 
 310 f 
 1,420 f 
 
 830 \ 
 1,160 f 
 1,125 | 
 1,140 f 
 
 885 1 
 
 1,160 f 
 
 1,115 f 
 
 1,010 f 
 
 1,070 f 
 
 850 / 
 I 
 
 .0178 
 .0187 
 .0275 
 
 lOCf 
 
 Dunn, with 30' x 6' stack, 
 distilling 
 
 .0249 
 .0364 
 .0382 
 
 11AJ 
 
 Citrus, 9-gal., low stack, dis- 
 tilling 
 
 .0151 
 .0124 
 
 HBf 
 
 Citrus, 9-gal., medium stack, 
 distilling 
 
 .0187 
 .0222 
 
 ncj 
 
 Citrus, 9-gal., high stack, dis- 
 tilling 
 
 .0293 
 .0213 
 
 12Af 
 
 Citrus, 6-gal., low stack, dis- 
 tilling 
 
 .0231 
 .0258 
 .0258 
 
 12B( 
 
 Citrus, 6-gal., medium stack, 
 distilling 
 
 .0258 
 .0187 
 .0240 
 
 12C( 
 
 Citrus, 6-gal., high stack, dis- 
 tilling 
 
 .0115 
 
 
 4.3 
 6.3 
 4.0 
 
 .0142 
 
 18 
 18 
 19 
 
 Baby Double Stack, distilling 
 Baby Double Stack, distilling 
 Citrus Gas Flame, distilling . 
 
 Trace 
 .0178 
 Clear 
 Clear 
 Trace 
 Trace 
 
 * All tests made indoors with No. 2 oil (see table 7). 
 
 a Product of pounds fuel per hour by heat content per pound of fuel as obtained 
 
 t Determinations of smoke density were sometimes made in duplicate or in tri 
 
 by bomb calorimeter, 
 plicate. 
 
20 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
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Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
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Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
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24 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 "smoke, pound per 1000 cu. ft. of gas" is given as "clear," no sign 
 of smoke was visible on the felt. Where "trace" is recorded a faint 
 circle was visible but the quantity caught was too small to be weighed. 
 In the indoors tests a pair of smoke records were taken in the test 
 of each heater. Figure 10 shows these pairs and indicates how closely 
 the smoke records check. The conditions of burning rates, etc., when 
 the indoors smoke records were taken, may be found in tables 2 and 3. 
 
 Fig. 8. — The "smoke mosquito" in use. A measured volume of the gases 
 is drawn from just above the tip of the flame through a square of white felt. 
 Note pyrometer (left) measuring the temperature of the gases. 
 
 In practically all the heaters clearer burning was obtained at low 
 burning rates than at high. Nearly all oil burning heaters smoked 
 badly when burned at maximum capacity. A comparative study of all 
 the heaters tested indicated that in some cases a very slight difference 
 in design apparently caused a large difference in smokiness. While 
 absolute smokelessness under all conditions seems not feasible under 
 present conditions of available fuel and equipment, still a great 
 improvements could be made by the elimination, especially in the 
 citrus growing districts, of the lard-pail and all other open type 
 heaters ; by redesign of some of the other heaters ; by more care in the 
 production of the fuels used ; and especially by more care on the part 
 of the user to regulate more frequently and to avoid burning at too 
 high rates. In justice to the user it should be added that poorly 
 designed or constructed heater covers sometimes make it impossible to 
 regulate the burning rate. 
 
Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
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26 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 EFFECT OF ORCHARD HEATING ON THE PUBLIC HEALTH 
 
 Considerable complaint has been heard that gaseous products 
 injurious to the health of residents in the citrus growing districts 
 are given off by the heaters. Bronchial and pulmonary affections 
 apparently caused by the smoke or by the gases have been mentioned 
 repeatedly. No exhaustive study of this matter was made but the 
 following facts are determined. Comparison with data given by 
 Henderson, Haggard, Teague, Prince and Wunderlich (2) and by 
 Sayers, Meriwether and Yant (5) of the U. S. Bureau of Mines shows 
 
 Fig. 10. — Smoke records, indoor tests. At least 2 daytime tests were made on 
 each heater ; note the close agreement between the records in each pair. The same 
 fuels (No. 2 oil and No. 3 briquets) were used for all the indoor tests. Wind 
 effects were eliminated in this portion of the test by running indoors. See tables 
 2 and 3 for rates of fuel consumption, etc. 
 
 that the per cent of carbon monoxide given off by orchard heaters is 
 too small to produce any appreciable effect. In fact very much higher 
 concentrations of carbon monoxide are found where automobile traffic 
 is heavy in some of the streets of our cities than would ever be present 
 under the worst conditions in a heated orchard. Some of the fuels 
 sold for orchard heating in this state are rather high in sulphur 
 content (table 7). This sulphur is almost completely . ' anged to 
 sulphur dioxide, a gas which, while not dangerous to the same degree 
 as carbon monoxide, is very disagreeable and irritating to the nasal 
 passages, throat and lungs. No method was found to determine 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 27 
 
 whether smoke of itself had any effect upon the health. Removal of 
 sulphur from the fuels sold for orchard heating would certainly be 
 highly desirable. Along with this, of course, should go reduction of 
 smoke to a minimum. 
 
 FUELS USED IN ORCHARD HEATERS 
 
 Various complaints have been made concerning the oils sold for 
 orchard heating purposes in this state. Several samples of orchard 
 heater oils were secured and subjected to such tests as seemed likely 
 to indicate how satisfactory they might prove in use. Since usually 
 in non-distilling heaters the rate at which the oil will run through a 
 small opening determines the burning rate, tests of viscosity were 
 made on eleven oils (table 6). The California residue test (later 
 
 TABLE 6 
 
 Oils Tested for Viscosity and Per Cent of Eesidue* 
 
 No. 
 
 Source 
 
 Residue, by 
 
 California test, 
 
 per cent 
 
 1 
 
 
 6.83 
 
 2 
 
 
 0.201 
 
 3 
 
 
 0.206 
 
 A 
 
 
 0.924 
 
 B 
 
 
 0.935 
 
 c 
 
 
 1.206 
 
 D 
 
 
 0.277 
 
 E 
 
 
 0.639 
 
 K 
 
 
 0.741 
 
 L 
 
 
 2.586 
 
 M 
 
 
 
 
 
 small) 
 
 * All from 1925-26 season supply. The viscosities are given in figure 11. 
 
 described) was also made and the results for some of the oils compared 
 with results obtained for the same oils by use of the regular Conradson 
 carbon test .and Holde hard asphalt test. Figure 11 shows graphically 
 the results of the viscosity tests. Evidently the samples that show 
 nearly straight vertical lines (that is, that maintain their free flowing 
 character almost constant from 100° F down to well below the freezing 
 temperature of water) would run satisfactorily in a non-distilling type 
 heater. On the other hand an oil like C, B, or L, if lighted and the 
 burning rate properly adjusted at 25° F, would flow very much faster 
 after the fuel in the reservoir came up to 35° F or 40° F. Oil A was 
 solid at 12° F and oil L at 16° F. Oil L would hardly flow at all 
 below 25° F. 
 
28 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 To study the effect of settling, two samples of oil No. 1 were taken, 
 one from the top and the other from the bottom of a 50-gallon drum 
 after it had stood undisturbed for three weeks. The bottom oil was 
 found to be 0.5° Beaume heavier than the top, but both showed the 
 same viscosity curve as that of the composite sample of oil No. 1. 
 Possibly longer settling might have made a noticeable difference. Also 
 other oils might have behaved differently. Oil No. 1 was chosen 
 principally because it was very dark in color and on being burned left 
 much asphaltic residue. 
 
 \//scos/ties or 
 
 O&chard Heater O/ls 
 
 J 925 '-'26 Reason 
 
 SO 120 160 
 
 Viscosity, Seconds Soybolt 
 
 Fig. 11. — As the oils thicken on becoming colder, longer times are required 
 for a standard unit quantity of oil to flow through the standard opening in the 
 Saybolt test apparatus. The straighter lines show oils that thicken less rapidly 
 on cooling. See table 6. 
 
 The accumulation of heavy residues in the reservoirs of distilling 
 type heaters and in the burners of the non-distilling type has been a 
 frequent cause of trouble. In extreme cases the heaters would operate 
 very unsatisfactorily or could scarcely be made to burn at all. It 
 seems that these asphaltic residues are not necessarily merely so much 
 asphalt that was present in the original oil, but are probably produced 
 by what the oil chemist calls ' ' cracking of the molecules ' ' of oil when 
 heated. In the "cracking" process a molecule of the oil may be 
 regarded as breaking up and then reassembling it component parts to 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 29 
 
 make two new molecules different from each other and from the 
 original molecule. Thus the heat to which the oil in the reservoir is 
 subjected may change some of the oil into two new kinds of oil, one 
 that vaporizes easily and therefore burns readily, and one that is very 
 heavy and hard to vaporize and hence is liable to fail to mix with the 
 oxygen of the air and so be left unburned. Some oils will "crack" 
 much more readily than others. 
 
 An attempt was made to find a simple test that would show 
 whether a given oil would "crack" badly or not. The apparatus used 
 consists of a sheet copper burner bowl A (fig. 12), a pedestal B on 
 
 Fig. 12. — California residue test for orchard heater oils. Ten grams of the 
 oil to be tested is placed in bowl A. Bowl is placed on pedestal B and draft 
 pipe C placed over as in figure 13. Lighting is by an alcohol swab burned 
 under one edge of the bowl. The residue remaining when the fire dies is 
 weighed. See data in tables 6 and 7. 
 
 which to support it, and a draft pipe, C. A 10-gram sample of oil is 
 weighed in the burner bowl, the bowl placed level on the pedestal and 
 the draft pipe placed over it (fig. 13) . Lighting is accomplished by the 
 use of a swab soaked in alcohol burned under one edge of the bowl 
 until the fuel ignites. A pasteboard screen to prevent air currents is 
 placed around the apparatus. When the fire dies out the residue is 
 found by weighing the bowl on a sensitive analytical balance. Table 7 
 gives the results obtained on the oils used in the heater tests and a few 
 other oils, together with results of other standardized tests for oils. 
 It will be noted that there is a rather close parallel between the new 
 California residue test and the Conradson carbon and Holde hard 
 asphalt tests. Since the per cents of residue are considerably larger 
 in the new test than in the Conradson, higher accuracy should be 
 obtained by the California test, with the same degree of care and 
 sensitiveness of instruments. The Conradson test results given were 
 obtained from two companies engaged in commercial oil testing. It 
 will be noted that the results differ somewhat. The Holde tests were 
 made by the Chemistry Division staff at Davis. 
 
30 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 A very simple test with inexpensive apparatus (fig-. 14) may be 
 made by the rancher himself to try orchard heater oils for residue. 
 This is a modification of the California test but is less accurate and 
 gives only a visual instead of a numerical comparison. However, the 
 results obtained are sufficiently definite for all ordinary purposes. 
 
 Fig. 13 Fig. 14 
 
 Fig. 13. — California residue test apparatus (assembled). When in use, a 
 pasteboard screen (not shown) surrounds the apparatus to reduce the effects 
 of air currents. The balance shown is used to weigh the 10 grams of oil. A 
 delicate analytical balance is used for the bowl and residue. 
 
 Fig. 14. — Modified form of California residue test apparatus. This enables 
 making a residue test without expensive or delicate apparatus. Half-pint 
 samples of the oils are burned in small tin pans and the residues compared. 
 
 Equal volumes (% pint) or equal weights (% lb.) are taken of 
 the several oils to be tested. Instead of the small copper burner A of 
 figure 12, an ordinary tin pan 5% inches inside diameter at the top, 
 4^/2 inches at the bottom and 1% inches deep is used. It is well to 
 have as many pans as there are oils to be tested, so that the results 
 may be kept for comparison. An empty tomato can placed bottom 
 end up may be used as a pedestal. The draft tube is not necessary. 
 The oil may be lighted by placing a 2-inch diameter asbestos swab 
 soaked in torch oil (gasoline and kerosene equal parts) under an edge 
 of the pan. If preferred the pan of oil may be heated on top of a 
 stove until it will ignite readily when a lighted match is applied. 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 
 
 31 
 
 Fig. 15. — Residues from orchard heater oils obtained by use of the apparatus 
 shown in figure 14. Upper, oil No. 1 unsatisfactory; lower, oil No. 2 more 
 satisfactory. 
 
32 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 After lighting, a screen to keep off air draughts should be placed 
 around if the test is made out-of-doors. A carton about 2 feet square 
 and 3 feet high from which the top and bottom have been removed 
 makes a satisfactory screen. 
 
 An unsatisfactory oil will leave a residue that is very noticeable 
 though it may weigh less than half an ounce. Usually such a residue 
 will consist of two parts, a thin layer of black, shiny, asphaltic 
 material on the bottom of the pan, and above it a hard, flaky crust 
 consisting mostly of carbon. A satisfactory oil will have no noticeable 
 asphaltic residue and very little of the crusted carbon. 
 
 Since the temperature of the pan and contents during the burning 
 determines in a large measure how much residue will be left, it is 
 essential that all the conditions that might affect this temperature 
 should be alike in all tests, if the results are to be compared. This 
 refers especially to the method of lighting and the level placing on the 
 pedestal. Using an asbestos pad between the burner pan and the 
 pedestal in some of the tests and not in the rest, would make the results 
 of doubtful value. Differences of 5° F or 10° F in the air tempera- 
 tures when the tests are run will not appreciably affect the results. 
 Figure 15 shows the residues obtained by this test on oils Nos. 1 and 2 
 (for other data of these oils see table 7). Oil No. 1 produced quite a 
 drip of asphaltic material from the burners of the non-distilling type 
 heaters tested. At intervals the crusted carbon left in the burners by 
 this oil had to be removed. Oil No. 2 burned much more satisfactorily. 
 The briquets used were in general satisfactory. The sulphur fumes 
 were noticeably worse from the coal dust briquets as would be expected 
 from the high sulphur content (table 7). The relatively large ash 
 residues from the coal dust briquets sometimes partially clogged the 
 grates and so reduced the burning rates. The coke and carbon 
 briquets used had less sulphur and left no noticeable ash. They were 
 however less satisfactory to handle because of their tendency to 
 blacken anything they touched and to break into pieces. 
 
 Comparison of California residue test results with specific gravities 
 (table 7) shows that the latter do not give any indication of the 
 probable behavior of an oil with respect to asphaltic residue. 
 
 It was found that the asphaltic residues from some oils collected in 
 and under the burners of the non-distilling heaters tested. Sometimes 
 these residues spread over the ground around the heater. "With some 
 oils at certain adjustments the residues burned out automatically at 
 intervals or could be made to burn out without apparent harm to the 
 heater by applying a little fuel from the lighting torch to the base of 
 the burner. The residues resulting from "cracking" of the fuel and 
 
Bul. 442] 
 
 LABORATORY TESTS OF ORCHARD HEATERS 
 
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34 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 from droppings of soot that accumulated in the reservoirs of the dis- 
 tilling heaters tested could be burned out in many cases by opening 
 the drafts wide. Very high temperatures in the reservoirs would 
 result. Whether this would rapidly destroy the heaters by burning 
 out the bottoms was not determined by these tests. Growers report 
 that reservoirs frequently burn through at the bottom of the down- 
 draft tubes. No intensive study of orchard heater troubles was made 
 in connection with the laboratory tests here reported. In general the 
 test runs were of too short duration for characteristic troubles to 
 develop fully. It is believed that these can be studied more satisfac- 
 torily in field tests such as are reported by Schoonover, Hodgson, 
 and Young. (6) 
 
 It was found that refuse oil drained from crankcases of auto- 
 mobiles and tractors could be burned satisfactorily in several distilling 
 type heaters. 
 
 CAUTION NECESSARY IN USE OF DATA 
 
 It is inadvisable to draw hard and fast conclusions as to the 
 relative merits and demerits of the several heaters tested, using as a 
 basis of comparison the data given in the summaries. This is particu- 
 larly the case where the quantities measured were themselves very 
 small. It should be remembered that the smaller the quantity, the 
 less, in general, will be the degree of accuracy to which it can be 
 measured. Also it should be borne in mind that the quantities 
 measured were often changing appreciably from moment to moment. 
 It was not in every case possible to take and to average a large number 
 of readings for the reason that limited time was available when 
 weather conditions were fit for making the tests. Nevertheless the data 
 presented enable the making of a fair general comparison. 
 
 SUMMARY 
 
 New methods of testing were necessary because those used by 
 mechanical engineers for testing furnaces were found inapplicable. 
 Full description of methods is to be made in a later publication. 
 
 Nineteen heaters were studied and each was given a high and a 
 low test in the open and a " normal" test indoors. 
 
 The burning rate was found important since it governs the rate 
 of heat production. Each type of heater, if left without readjust- 
 ment, was found to have a characteristic burning rate curve the shape 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 35 
 
 of which was altered by changes in wind speed and air temperature 
 and in temperature and volatility of the fuel. The burning rate is 
 adjustable in most heaters. Too high a rate was found undesirable 
 since it tends to increase smoke and losses by radiation and by gases 
 rising too high. It also tends to cause rapid scaling off and destruc- 
 tion of the stacks. Frequent and careful regulation is highly desirable 
 as a means of overcoming the smoke nuisance as well as of securing 
 the desired heat production. 
 
 It is customary in many orchards to light only a portion of the 
 heaters at first and light others as the night grows colder. From the 
 standpoint of heat distribution and reduction in the amount of smoke 
 it is better to light all of the heaters and burn them at a low rate with 
 frequent regulation. This frequent regulation will control the burn- 
 ing rates of the heaters in such a way as to save considerable fuel. 
 With briquet heaters the most practical way of controlling the burning 
 rate is to start with a relatively small fuel charge and refuel at about 
 two-hour intervals throughout the night, 
 
 All the heaters were found practically 100 per cent efficient from 
 the standpoint of converting fuel into heat, there being almost no 
 carbon monoxide in the gases and the heat lost in the unconsumed 
 carbon of the smoke being in every case less than one-tenth of one 
 per cent of the total heat in the fuel used. 
 
 The heat radiated above the horizontal plane ranged from about 
 one to nearly five per cent of the total heat in the fuel. Not all of this 
 radiated heat is lost. The portion that strikes leaves, twigs, or other 
 opaque objects and is absorbed serves to warm the air. Baffles for 
 decreasing the radiation loss were found practicable. 
 
 High upward velocities and high temperatures tend to waste fuel 
 by sending the hot gases to high levels above the orchard. The 
 velocities found were satisfactorily low except in high stack heaters not 
 equipped with a horizontal baffle plate. In some of these velocities 
 as high as 14 feet per second were found. 
 
 Smoke is always a nuisance and of little or no benefit as a blanket 
 to prevent radiation. The lard-paid heaters were the worst offenders. 
 A number of the later oil burners were practically smokeless when 
 burned at normal and low rates, but all smoked some when burning at 
 very high rates. Satisfactory control of the burning rate was in some 
 cases made difficult if not quite impossible by ill-fitting reservoir 
 covers in distilling type heaters. Briquet heaters smoke considerably 
 at lighting and for a time afterward but become clearer as burning 
 progresses. Photographic smoke records were made. 
 
36 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 No exhaustive study was made of orchard heater gases and smoke 
 as affecting the public health. The concentrations of carbon monoxide 
 are evidently too small to cause appreciable effects. Sulphur dioxide 
 apparently caused annoyance to some of the workers. What part the 
 smoke itself played was not determined. 
 
 Oils, being higher in heat content per pound, are more effective 
 than solid fuels. The oils sold for orchard heating differ considerably 
 in characteristics that affect their suitability. Oils that leave large 
 asphaltic residues on burning are less desirable both for distilling 
 and for non-distilling type heaters. A new method for determining 
 per cent of residue is described. High sulphur content is objectionable. 
 High viscosity and rapid increase in viscosity when temperature 
 decrease make an oil unsuitable for non-distilling type heaters. 
 
 ACKNOWLEDGMENTS 
 
 The author wishes to express his grateful appreciation of advice 
 and assistance received from his colleagues and from many others. 
 Especial mention should be made of E. Ower, A. C. G. I., of the British 
 National Physical Laboratory who furnished unpublished data that 
 enabled the calibration of the high-temperature anemometer ; Professor 
 L. B. Spinney of the Iowa State College and Dr. W. W. Coblentz and 
 others of the U. S. Bureau of Standards who made valuable sugges- 
 tions concerning the measurement of radiation ; Dr. C. S. Bisson of the 
 University of California who directed the chemical work; Dr. W. L. 
 Howard, Professors R. W. Hodgson and A. H. Hendrickson of the 
 University of California, Mr. Floyd D. Young of the U. S. D. A. 
 Weather Bureau, and the members of the Research Committee of the 
 American Society of Agricultural Engineers, who criticized the 
 original plan of the work and read the manuscript. I am especially 
 indebted to Mr. W. R. Schoonover of the University of California for 
 a large number of practical suggestions for the orchardist which are 
 made a part of this bulletin. 
 
BUL. 442] LABORATORY TESTS OF ORCHARD HEATERS 37 
 
 BIBLIOGRAPHY 
 
 i Garcia, F., and A. B. Fite 
 
 1922. Preliminary smudging experiments. New Mexico Agr. Exp. Sta. 
 Bui. 134:1-26. 
 2 Henderson, Y., H. W. Haggard, M. C. Teague, A. L. Prince and 
 
 R. WUNDERLICH 
 
 1921. Reports of tunnel gas investigations, problem No. 2. Physiological 
 
 effects of exhaust gases. N. Y. Bridge & Tunnel Commission 
 
 Report: Appendix 4, p. 166-168. 
 s Kimball, H. H., and F. D. Young 
 
 1920. Smudging as protection from frost. Monthly Weather Review, 
 
 48:461-462. 
 4 0'Gara, P. J. 
 
 1910. The protection of orchards in the Pacific northwest from spring 
 
 frosts by means of fires and smudges. U. S. Dept. Agr. Farmers' 
 
 Bui. 401:1-24. 
 s Sayers, R. R., F. V. Meriwether and W. P. Yant 
 
 1922. Physiological effects of exposure to low concentrations of carbon 
 
 monoxide. U. S. Public Health Reports, May 12, 1922, Rept. 
 748:1. 
 
 6 Schoonover, W. R., R. W. Hodgson and F. D. Young 
 
 1925. Orchard heating in California. California Agr. Expt. Sta. Bui. 
 398:1-69. 
 
 7 Webber, H. J., and Others 
 
 1919. A study of the effects of freezes on citrus in California. California 
 
 Agr. Exp. Sta. Bui. 304:247-321. 
 s West, F. L., and N. E. Edlefsen 
 
 1917. Orchard heating. Utah Agr. Exp. Sta. Bui. 161:1-48. 
 a Young, F. D. 
 
 1922. Frost and the prevention of damage by it. U. S. Dept. Agr. 
 
 Farmers' Bui. 1096:1-48. 
 
 io 1922. Frost studies in southern California citrus orchards. The Cali- 
 fornia Citrograph (Los Angeles) 7:82-83. 
 
 ii 1922. Notes on 1922 low temperatures. The California Citrograph 7: 
 196-197, 208-209. 
 
 i 2 1923. Frost investigation in southern California proves citrus groves can 
 be protected. Citrus Leaves (Redlands, Calif.) 312:1-3, 19. 
 
 is Young, F. D., and C. C. Cate 
 
 1923. Damaging temperatures and orchard heating in the Rogue River 
 
 Valley, Oregon. Monthly Weather Review 51:617-639. 
 
STATION PUBLICATIONS AVAILABLE FOE FREE DISTRIBUTION 
 
 No. 
 
 253. Irrigation and Soil Conditions in the 
 Sierra Nevada Foothills, California. 
 
 262. Citrus Diseases of Florida and Cuba 
 
 Compared with those of California. 
 
 263. Size Grades for Ripe Olives. 
 
 268. Growing and Grafting Olive Seedlings. 
 
 273. Preliminary Report on Kearney Vine- 
 yard Experimental Drain, Fresno 
 County, California. 
 
 276. The Pomegranate. 
 
 277. Sudan Grass. 
 
 278. Grain Sorghums. 
 
 279. Irrigation of Rice in California. 
 283. The Olive Insects of California. 
 294. Bean Culture in California. 
 
 304. A Study of the Effects of Freezes on 
 
 Citrus in California. 
 310. Plum Pollination. 
 312. Mariout Barley. 
 813. Pruning Young Deciduous Fruit 
 
 Trees. 
 819. Caprifigs and Caprification. 
 824. Storage of Perishable Fruit at Freez- 
 ing Temperatures. 
 325. Rice Irrigation Measurements and 
 
 Experiments in Sacramento Valley, 
 
 1914-1919. 
 328. Prune Growing in California. 
 331. Phylloxera-Resistant Stocks. 
 835. Cocoanut Meal as a Feed for Dairy 
 
 Cows and Other Livestock. 
 339. The Relative Cost of Making Logs 
 
 from Small and Large Timber. 
 840. Control of the Pocket Gopher in 
 
 California. 
 
 343. Cheese Pests and Their Control. 
 
 344. Cold Storage as an Aid to the Mar- 
 
 keting of Plums. 
 
 346. Almond Pollination. 
 
 347. The Control of Red Spiders in Decid- 
 
 uous Orchards. 
 
 348. Pruning Young Olive Trees. 
 
 349. A Study of Sidedraft and Tractor 
 
 Hitches. 
 
 350. Agriculture in Cut-over Redwood 
 
 Lands. 
 
 353. Bovine Infectious Abortion. 
 
 354. Results of Rice Experiments in 1922. 
 
 357. A Self-mixing Dusting Machine for 
 
 Applying Dry Insecticides and 
 Fungicides. 
 
 358. Black Measles, Water Berries, and 
 
 Related Vine Troubles. 
 861. Preliminary Yield Tables for Second 
 Growth Redwood. 
 
 362. Dust and the Tractor Engine. 
 
 363. The Pruning of Citrus Trees in Cali- 
 
 fornia. 
 
 364. Fungicidal Dusts for the Control of 
 
 Bunt. 
 
 365. Avocado Culture in California. 
 
 366. Turkish Tobacco Culture, Curing and 
 
 Marketing. 
 
 367. Methods of Harvesting and Irrigation 
 
 in Relation of Mouldy Walnuts. 
 
 368. Bacterial Decomposition of Olives dur- 
 
 ing Pickling. • 
 
 369. Comparison of Woods for Butter 
 
 Boxes. 
 
 370. Browning of Yellow Newtown Apples. 
 
 371. The Relative Cost of Yarding Small 
 
 and Large Timber. 
 
 373. Pear Pollination. 
 
 374. A Survey of Orchard Practices in the 
 
 Citrus Industry of Southern Cali- 
 fornia. 
 
 375. Results of Rice Experiments at Cor- 
 
 tena, 1923. 
 
 376. Sun-Drying and Dehydration of Wal- 
 
 nuts. 
 
 377. The Cold Storage of Pears. 
 379. Walnut Culture in California. 
 
 BULLETINS 
 No. 
 
 380. 
 382. 
 
 385. 
 386. 
 
 387. 
 388. 
 
 389. 
 390. 
 
 391. 
 392. 
 
 394. 
 
 395. 
 396. 
 
 397. 
 
 398. 
 399. 
 
 400. 
 401. 
 
 402. 
 404. 
 405. 
 406. 
 407. 
 
 408. 
 409. 
 
 410. 
 411. 
 
 412. 
 
 415. 
 416. 
 
 417. 
 418. 
 
 419. 
 420. 
 
 421. 
 422. 
 
 423. 
 424. 
 
 425. 
 426. 
 
 427. 
 
 428. 
 
 429. 
 
 Growth of Eucalyptus in California 
 Plantations. 
 
 Pumping for Drainage in the San 
 Joaquin Valley, California. 
 
 Pollination of the Sweet Cherry. 
 
 Pruning Bearing Deciduous Fruit 
 Trees. 
 
 Fig Smut. 
 
 The Principles and Practice of Sun- 
 drying Fruit. 
 
 Berseem or Egyptian Clover. 
 
 Harvesting and Packing Grapes in 
 California. 
 
 Machines for Coating Seed Wheat with 
 Copper Carbonate Dust. 
 
 Fruit Juice Concentrates. 
 
 Crop Sequences at Davis. 
 
 Cereal Hay Production in California. 
 Feeding Trials with Cereal Hay. 
 
 Bark Diseases of Citrus Trees. 
 
 The Mat Bean (Phaseolus aconitifo- 
 lius). 
 
 Manufacture of Roquefort Type Cheese 
 from Goat's Milk. 
 
 Orchard Heating in California. 
 
 The Blackberry Mite, the Cause of 
 Redberry Disease of the Himalaya 
 Blackberry, and its Control. 
 
 The Utilization of Surplus Plums. 
 
 Cost of Work Horses on California 
 Farms. 
 
 The Codling Moth in Walnuts. 
 
 The Dehydration of Prunes. 
 
 Citrus Culture in Central California. 
 
 Stationary Spray Plants in California. 
 
 Yield, Stand and Volume Tables for 
 White Fir in the California Pine 
 Region. 
 
 Alternaria Rot of Lemons. 
 
 The Digestibility of Certain Fruit By- 
 products as Determined for Rumi- 
 nants. 
 
 Factors Affecting the Quality of Fresh 
 Asparagus after it is Harvested. 
 
 Paradichlorobenzene as a Soil Fumi- 
 gant. 
 
 A Study of the Relative Values of Cer- 
 tain Root Crops and Salmon Oil as 
 Sources of Vitamin A for Poultry. 
 
 Planting and Thinning Distances for 
 Deciduous Fruit Trees. 
 
 The Tractor on California Farms. 
 
 Culture of the Oriental Persimmon 
 in California. 
 
 Poultry Feeding: Principles and 
 Practice. 
 
 A Study of Various Rations for 
 Finishing Range Calves as Baby 
 Beeves. 
 
 Economic Aspects of the Cantaloupe 
 Industry. 
 
 Rice and Rice By-products as Feeds 
 for Fattening Swine. 
 
 Beef Cattle Feeding Trials, 1921-24. 
 
 Cost of Producing Almonds in Cali- 
 fornia; a Progress Report. 
 
 Apricots (Series on California Crops 
 and Prices). 
 
 The Relation of Rate of Maturity to 
 Egg Production. 
 
 Apple Growing in California. 
 
 Apple Pollination Studies in Cali- 
 fornia. 
 
 The Value of Orange Pulp for Milk 
 Production. 
 
 The Relation of Maturity of Cali- 
 fornia Plums to Shipping and 
 Dessert Quality. 
 
 Economic Status of the Grape Industry. 
 
No. 
 
 87. Alfalfa. 
 117. The Selection and Cost of a Small 
 
 Pumping Plant. 
 127. House Fumigation. 
 129. The Control of Citrus Insects. 
 136. Melilotua indica as a Green-Manure 
 
 Crop for California. 
 144. Oidium or Powdery Mildew of the 
 
 Vine. 
 157. Control of the Pear Scah. 
 164. Small Fruit Culture in California. 
 166. The County Farm Bureau. 
 170. Fertilizing California Soils for the 
 
 1918 Crop. 
 173. The Construction of the Wood-Hoop 
 
 Silo. 
 
 178. The Packing of Apples in California. 
 
 179. Factors of Importance in Producing 
 
 Milk of Low Bacterial Count. 
 
 202. County Organizations for Rural Fire 
 
 Control. 
 
 203. Peat as a Manure Substitute. 
 209. The Function of the Farm Bureau. 
 212. Salvaging Rain-Damaged Prunes. 
 215. Feeding Dairy Cows in California. 
 217. Methods for Marketing Vegetables in 
 
 California. 
 
 230. Testing Milk, Cream, and Skim Milk 
 
 for Butterfat. 
 
 231. The Home Vineyard. 
 
 232. Harvesting and Handling California 
 
 Cherries for Eastern Shipment. 
 234. Winter Injury to Young Walnut Trees 
 during 1921-22. 
 
 238. The Apricot in California. 
 
 239. Harvesting and Handling Apricots 
 
 and Plums for Eastern Shipment. 
 
 240. Harvesting and Handling Pears for 
 
 Eastern Shipment. 
 
 241. Harvesting and Handling Peaches for 
 
 Eastern Shipment. 
 
 243. Marmalade Juice and Jelly Juice from 
 
 Citrus Fruits. 
 
 244. Central Wire Bracing for Fruit Trees. 
 
 245. Vine Pruning Systems. 
 
 248. Some Common Errors in Vine Prun- 
 
 ing and Their Remedies. 
 
 249. Replacing Missing Vines. 
 
 250. Measurement of Irrigation Water on 
 
 the Farm. 
 
 252. Supports for Vines. 
 
 253. Vineyard Plans. 
 
 254. The Use of Artificial Light to Increase 
 
 Winter Egg Production. 
 
 255. Leguminous Plants as Organic Fertil- 
 
 izer in California Agriculture. 
 
 256. The Control of Wild Morning Glory. 
 
 257. The Small-Seeded Horse Bean. 
 
 258. Thinning Deciduous Fruits. 
 
 CIRCULARS 
 No. 
 
 259. 
 261. 
 262. 
 263. 
 264. 
 
 265. 
 266. 
 
 267. 
 
 269. 
 270. 
 272. 
 
 273. 
 276. 
 277. 
 
 278. 
 
 279. 
 
 281. 
 
 282. 
 
 283. 
 284. 
 285. 
 286. 
 287. 
 288. 
 289. 
 290. 
 291. 
 
 292. 
 293. 
 294. 
 295. 
 
 296. 
 
 298. 
 
 300. 
 301. 
 302. 
 303. 
 
 304. 
 305. 
 306. 
 
 307. 
 308. 
 309. 
 
 Pear By-products. 
 
 Sewing Grain Sacks. 
 
 Cabbage Growing in California. 
 
 Tomato Production in California. 
 
 Preliminary Essentials to Bovine 
 
 Tuberculosis Control. 
 Plant Disease and Pest Control. 
 Analyzing the Citrus Orchard by 
 
 Means of Simple Tree Records. 
 The Tendency of Tractors to Rise in 
 
 Front; Causes and Remedies. 
 An Orchard Brush Burner. 
 A Farm Septic Tank. 
 California Farm Tenancy and Methods 
 
 of Leasing. 
 Saving the Gophered Citrus Tree. 
 Home Canning. 
 Head, Cane, and Cordon Pruning of 
 
 Vines. 
 Olive Pickling in Mediterranean Coun- 
 tries. 
 The Preparation and Refining of Olive 
 
 Oil in Southern Europe. 
 The Results of a Survey to Determine 
 
 the Cost of Producing Beef in Cali- 
 fornia. 
 Prevention of Insect Attack on Stored 
 
 Grain. 
 Fertilizing Citrus Trees in California. 
 The Almond in California. 
 Sweet Potato Production in California. 
 Milk Houses for California Dairies. 
 Potato Production in California. 
 Phylloxera Resistant Vineyards. 
 Oak Fungus in Orchard Trees. 
 The Tangier Pea. 
 Blackhead and Other Causes of Loss 
 
 of Turkeys in California. 
 Alkali Soils. 
 
 The Basis of Grape Standardization. 
 Propagation of Deciduous Fruits. 
 The Growing and Handling of Head 
 
 Lettuce in California. 
 Control of the California Ground 
 
 Squirrel. 
 The Possibilities and Limitations of 
 
 Cooperative Marketing. 
 Coccidiosis of Chickens. 
 Buckeye Poisoning of the Honey Bee. 
 The Sugar Beet in California. 
 A Promising Remedy for Black Measles 
 
 of the Vine. 
 Drainage on the Farm. 
 Liming the Soil. 
 A General Purpose Soil Auger and its 
 
 Use on the Farm. 
 American Foulbrood and its Control. 
 Cantaloupe Production in California. 
 Fruit Tree and Orchard Judging. 
 
 The publications listed above may be had by addressing 
 
 College of Agriculture, 
 
 University of California, 
 
 Berkeley, California. 
 
 19m-ll,'27