UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA WALNUT DEHYDRATERS: CHARACTERISTICS, HEAT SOURCES, AND RELATIVE COSTS P. F. NICHOLS, B. D. MOSES, AND D. S. GLENN BULLETIN 531 June, 1932 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA CONTENTS Page Introduction 3 Investigations of 1930 6 Types of plants studied 7 Conditions observed in tests 14 Basis for calculation of costs 14 Presentation and discussion of data, 1930 16 Equipment and investment 16 Load 17 "Dry-away" 22 Drying time 22 Thermal efficiency 22 Airflow 23 Temperatures observed 23 Moisture content 24 Labor required 30 Heat efficiency, power requirements, and costs 30 Operating costs, 1922-1930 31 Summary and conclusions 32 Acknowledgments 33 Literature cited 34 WALNUT DEHYDRATERS: CHARACTERISTICS, HEAT SOURCES, AND RELATIVE COSTS 1 2 P. F. NICHOLS,3 B. D. MOSES,* and D. S. GLENNs INTRODUCTION The use of artificial heat in the drying of walnuts apparently was first reported in California by Heath in 1889. 6 The Corona del Mar Ranch at Goleta has used a natural-draft wood-fired prune evaporator for drying walnuts since 1910 or earlier. Not until about ten years later were walnuts dried by dehydration ; this method may be defined as drying by artificially produced heat and forced drafts of air. Driers similar to some in common use at the present time were built by C. I. Crane, of Santa Paula, in 1918 and by F. T. Mahoney, of Saticoy, in 1920. It was not until 1922, however, that interest in the subject became at all general, stimulated largely by an address made by C. V. Newman before the Fourth Annual Walnut Institute at Santa Ana, in January, 1922. As a result of this new interest, investigations were undertaken by the University of California and the California Walnut Growers Association. (1)7 These investigations included both laboratory experi- ments and field observations during 1922 and 1923. From the laboratory experiments perhaps the most important conclusion was that the temperature used in dehydration should not exceed 110° Fahrenheit; this is still the accepted maximum in commercial prac- tice. From the field study it was concluded that, in spite of greater investment necessary for equipment, the cost of dehydrating walnuts did not exceed that of sun-drying. Dehydration permitted more 1 Eeceived for publication April 15, 1932. 2 This bulletin is the sixth contribution of a series planned to report the results of investigations conducted by the California Agricultural Experiment Station in cooperation with the California Committee on the Relation of Electricity to Agri- culture. s Associate in Fruit Products. 4 Associate Professor of Agricultural Engineering, and Associate Agricultural Engineer in the Experiment Station. 5 Formerly Graduate Assistant in Fruit Products. « Essay read by Hon. Russel Heath before the Eleventh State Fruit Growers ' Convention, 1889. 7 Superscript numbers in parentheses refer to Literature Cited, p. 34. 4 University of California — Experiment Station uniform and thorough drying of the nuts, reduced splitting, and required less labor, the saving being sufficient to compensate for added costs for fuel, power, and fixed charges. It was apparent that dehydraters provided weather protection and theft protection for the nuts. It permitted greater packing-house efficiency by stabilizing the rate of delivery from growers. It aided marketing by making it possible to place the nnts on the market ahead of imports and in time for the peak of the holiday demand. The number of walnut dehydraters built and operated since 1922 has been compiled from various sources and is given in table 1. During this period the building of plants has been rapid. It reached the peak in 1927 and since that time has steadily declined. From table 1 it will be seen that the present number of plants is more than sufficient to dehydrate in 30 days a normal California crop which for 1930 is calculated at 33,460 tons by the California Walnut Growers Association. The distribution of plants, however, is not such as to make this actually feasible. TABLE 1 Growth of Walnut Dehydration in California Year New plants built Total plants operating* Total dehydration capacityf Crop* 1922 13 18 64 41 128 90 72 46 9 22 40 104 145 273 363 435 481 tons 675 1,650 3,000 7,800 10,875 20,475 27,225 32,640 36,075 tons 27,000 1923 25,000 1924 22,500 1925 36,000 1926 .. 15,000 1927 1928 .. 51,000 25,000 1929 .. 39 , 000 1930 .... 29,000 * According to data compiled from a number of references (1-9) listed in Literature Cited, p. 34. t Based on a normal operating season of 30 days and an average daily capacity of 2* tons. J 1922-1929: California Cooperative Crop Reporting Service, Sacramento. 1930: Compiled from California Walnut Growers Association. By 1925 the interest in the dehydration of walnuts was so wide- spread that it led the California Committee on the Relation of Electricity to Agriculture to provide funds for a further field investi- gation. At that time the number of dehydraters in use was safficient to require a considerable amount of power for driving fans, drums, and conveyors. In addition, several dehydraters had been built using electricity as a source of heat as well as power. Bul. 531 Walnut Dehydraters K . . Q C3 • ft c8 M ! -<-2 ft > o t« O °T3 §8-3 3 u a> o£| a E 5 o >> 3 T3 a -C s 3^ a f< > M £i >> •n a 3 IH V o c a o 3 O >> u -3 c 03 -1 s ft 3 o J3 >. 0> a Q I cj ft Si? $1,900 1,400 1,250 1,250 1,375 951 951 567 IDON © O CO NO)U5 ci N m en ■* to o w oscoTfosuooor^t^ "5 CM IM mo>N OS000Ot^0O»O»OCO t-- OS CO cMCOCO^ifOOcMOO CM COOO OS I— CO OO^-rt-H-HCOCOlO 00 — 'UO cooooocococoeM « lO N N 1C CO CO ■* NON 00 t- if CO 00 00 00 00 "^ ^* ^ COOO if O3»Ocor^00>OOSCO CO "O O «5 lO CO tJI N O CO CO —I OlM HNtocqw-HrtH CM CO -H •*fOOOSCO-lOOCOiO CO CO OS DC COOS^iOOOOOifCO 30N CM CO ©lOOO-il^cOTfcO m oo io ■* ro co oc o> COCM-OlON ti. OSU5 •»t<(Moo — aco^ai -HCM-H NOSiOffliHOiO'* CO «0 ^ -< O ^ ■* OKO rt 00 co ^ 00 -*f •— i C8.S ©00© io co © CO © if CO ©00 CO © CO CM if © CM ©CM 00 if © t^ COOO •HMO 1--00 CO © if CO CO CO CO OSOO 00 OS © CO 00 CO CO coif oo co r^ co t^ CO CO CM COOO OS CO CO CO t^ CO I-. o "0 if r-^© CO -h OS COo-< CO "0 il 00 if if CM CM CO -h OSOO 1^ CD CM 0>0>0 COOO OS 8UOJ|BQ © CO CM CM CO CM CM i-i CM CO CM CO OS CM CO UNI »o©© CM if © rt i-i CM »n © >c WON H CM -H X5INQ0 CO if oi CO OS IO IO CM CM 00 »rt 00 (NION CO CO io CO »0 CM ©©© ©©© CM ^ 1 OPjJ i-lrt CM >• la coco © © © ooosooo o©©o© coco © if if CM if CO t^ OS ^1 CM -1 OOl^-OOt^t^ CO Tt< CO 00 t~ rt t--00 t~ r— t— no i^ co OS ^H OS © OS ©©t^r^co CMt-~co CO OS OS 00 © CO 6.92 6.92 4.16 4.16 4.16 CO CM CO CM OS rt lO CO if 4.05 3 25 3.79 2 91 2.80 CD >0 © CO ©00 CO if o © CO CO CO n CO ejnoq-'j^'BAVoii^i h- OS CD 00 l~» CO COCO if CO H n «0 >C "0 uo co r^ O0 CO CO CO »o ^H XOOt^OI OS OS CO 00 t~- t^ OS ^1 CO OS t^ 321 2 284.9 222.81 122 0% 96.3? if CM CO os -i co © CM OS CM CO ©"©©©© CO coi^-t^ t~- if ©O m t^ CO tftf >ls 6 University of California— Experiment Station Table 2 gives the results from tests made on 11 plants which were studied, during the 1925 investigations. The 1925 data exhibit a some- what greater regularity than the 1930 data because of the greater uniformity of seasonal conditions and moisture contents of the nuts. The performance data on electrically heated plants in 1925 were greatly influenced by the performance of the tray dehydrater, type 4. The nuts dried in this dehydrater were all washed before drying and much of the moisture was on the surface, and hence evaporated easily; on the other hand, the fact that this dehydrater employed trays greatly increased the labor cost, and as a result, this type of plant is now obsolete. However, the methods of making these studies, the data obtained, and the conclusions to be drawn therefrom are, on the whole, very similar to those in the more extensive investigations of 1930. The results of the former will, therefore, not be discussed here. INVESTIGATIONS OF 1 930 Numerous inquiries are received by the Division of Viticulture and Fruit Products regarding the costs of installation and operation of walnut dehydraters. Many are also received regarding the economy and efficiency of the various sources of heat, and requesting corrobo- ration or denial of the statements as to cost and efficiency made by the several manufacturers of plants. Much of the interest centers upon the feasibility of using electricity as a source of heat. The extent of the development of walnut dehydration and the vari- ety of sources of heat used are shown by the following data : By 1929 a total of 435 plants had been built, (9) in which from 50 to 60 per cent of the state crop was dehydrated. Only 2% per cent of the dehy- draters were homemade, and 96 per cent were built by the leading four manufacturers. The average capacity is 2y 2 dry tons per day. Of all plants, 45 per cent are gas heated, 40 per cent oil heated, and 15 per cent heated by electricity. Because of the extent of walnut dehydration and the interest in the subject, the writers undertook another field investigation, sup- ported in part by the funds supplied by the California. Committee on the Kelation of Electricity to Agriculture. In this investigation it was planned particularly to compare the efficiency and costs of the different sources of heat, Obviously such comparisons can best be made when the sources of heat are used under as similar operating Buu 531] Walnut Dehydraters conditions as possible. Not only was the thermal efficiency 8 to be studied, but also the costs involved, since the type of heat used may be expected to influence to some extent the investment and overhead costs or fixed charges, the labor, and the supervision required. Of the total number of plants, 133 are located in Ventura County, 120 in Los Angeles County, and 85 in Orange County. Practically all of the remaining 97 plants are in Santa Barbara, Santa Clara, Contra Costa, Lake, San Bernardino, San Joaquin, and Riverside counties. Since the greatest number and variety of walnut dehydraters are located in southern California where the bulk of the walnut crop is grown, and the operating conditions are most nearly uniform there, the 1930 investigation was planned for and restricted to that part of the state. Three areas were selected for the investigations, namely, Lcs Angeles County near Puente, Orange County near Santa Ana, and the Ventura district, including Santa Paula, Saticoy, Oxnard, and Owensmouth. The season is progressively later in each of these areas. Wherever possible the tests were conducted in groups in which the operating conditions were similar and the plants were of the same type and size, differing only in the source of heat used. However, these ideal conditions for comparison are rare and difficult to find because of the number of types and sizes used, and the tendency for different types or heat sources to predominate in different districts. Only about one plant a day could be studied because of the num- ber of observations to be made, the distance between the plants studied, and because usually only one investigator was in the field. A total of 42 tests were made on plants heated by gas, oil, or electricitv. The distribution of these tests was as follows : District Gas heated Oil heated Electricity Total 5 13 2 2 2 2 6 4 6 13 19 10 Types of Plants Studied. — Five makes of plants were studied. They are described in table 3 and shown in figures 1 to 10. Type Nos. 5 and 6 have been developed by manufacturers not in this business in 1925. Type 4, the tray type, was not included in the 1930 study. For definition of thermal efficiency, see p. 15. University of California — Experiment Station Zf.OvS/ef Fig. 1. — Diagram of plant type No. 1. Fig. 2. — Plant type 1-K; air flow from top to bottom or bottom to top. Bul. 531 Walnut Dehydraters Fig. 3.— Plant type 1-C. | lj ui | m g g 2. S?o/&''/>7 ? /Tut 0*-ru Cer>/> 0) CJ o o S 0) a> 0) 13 i> S 4> M O CD o3 u o o — - >> '8 |8 "3 >> '3 0) '° | ° "3 o ° '3 ^ o 5 »- >- 00 E in CD 'C w CD o 03 -^ 03 *i 03 03 +J 03 o a o O W W 6 t* a « (h a o >i a © 4> a> o> 01 t3 13 4) 1 T3 T3 T3 3 ,2 ai "o3 03 03 03 o3 3 3 3 :S -2 £ J2 ;fl (i, a> s 3 a> 3 a 3 3 3 § § O) § § § § t*H o . rs P to o> CD 4> o o O O O >.3 f* >" % fc fc fc ^ O o3 tf 03 || 2 OD o o 00 CD 45 8 K- 1 ?* £ £ >< tH k- 1 0) ti If o ,Q 5 3 >- o 0) t-, a r~ T3 4) js o a £ 'Id a 3 a o *• o ° a 13 o 3 o o o S o o +» J2 o o t! O o £ 75 00 O 3 o> T3 o ■** £ a> o o T3 S a o c -^ 4) o 4) -a 3 o o3 5 H o ffl ba O pq d s s 3* 3 a> $ £ a 4) 4> 4) 4) (H 1- H H tH o w « to S s ■a CO CO 4> co o> 1 fi CD 01 CO 4) <-, 1h u o is is P 0) O a; 0) ^ » is "5 o> oo ^2 s a "3 15 -° 0) 00 3 S o i 6^ 3 a IS | s o ? T3 3 03 45 6 T3 -O o 3 O 0J "O ■+o o 3 -a o> a> Xi a) 0) -3 O o 4) O % m m DO Ul m 13 ^ "5 M .3 ^_r A o a ja bp N 'ft ■j • _M 'u o a a O 'm 00 a 03 s J3 3 3 .3 b IB 03 "o3 13 03 1 -a"! <& 3 3 s _o 3 ,S J2 3 m M "u M h< 'E ^-c M i ~0 "O 3 o3 CD T3 <^ 3 03 a s .2 a >> S g .S 3 03 o o S >> >> Oi o -^ >> «-i 09 tf O O « O o P, aj a >> tf o ^ *■* ■ — z^— — = thermal efficiency, per cent. B.t.u. supplied The data on plant investment were obtained in most instances directly from the owners. In some instances these data are supple- mented by information supplied by manufacturers, particularly with regard to accessories and heating equipment. Some additional data were also obtained from contractors who made the installations. 16 University of California — Experiment Station The overhead cost per dry ton is calculated by dividing the total annual fixed charge by the seasonal tonnage. Since the 1930 crop was generally small and varied greatly in different districts, a fair method of comparison is to base the tonnage on the capacity of the plant and a normal period of 30 days of operation. The annual total fixed charge against the plant was calculated as follows : Per cent on total investment Depreciation, 5 per cent on total investment 5.0 Interest, 6 per cent on one-half total investment 3.0 Upkeep, 2 per cent on total investment 2.0 Taxes, 3 per cent on one-half total investment 1.5 Insurance, y 2 per cent on total investment 0.5 Total per cent on total investment 12.0 Since the dehydration of walnuts has become well established and no marked improvements have been made in either design or efficiency during the last few years, no charge has been made for obsolescence other than those implied in depreciation and upkeep. Such a charge should be made against some of the oldest plants, particularly those built largely of wood. PRESENTATION AND DISCUSSION OF DATA, 1930 The principal efficiency and cost data for the individual tests made in 1930 are given in table 4, grouping the plants according to source of heat used and according to type. Equipment and Investment. — The bin displacement of the plants varied from 52 to 842 cubic feet. Since a cubic foot of dry walnuts weighs 20 pounds, multiplying the bin displacement in cubic feet by 20 (1) gives figures very close to the actual holding capacity of dried nuts, in pounds; this did not always correspond with the rated capacity. Of the plants tested, the use of conveyors was fairly general in types 1, 2, and 3, but not in types 5 and 6. The cost of conveyor systems ranged from $200 to $500. Thermostats and automatic valves or switches for controlling the temperature were installed in all but two of the plants studied. The plants in tests 15 and 41 were controlled manually. Bul. 531] Walnut Dehydraters 17 Nearly all of the fans were of the multiblade type. The fan motors ranged in size from % to 10 horsepower. The investment in dehydraters, exclusive of buildings, hullers, and washers, ranged from $750 to $7,700 per plant. No great differences were found in the investment required for gas and electrically heated plants of similar type and size. The investment for oil-heated plants averaged higher than the others. One manufacturer regularly quotes prices $150 higher for oil-heated plants than for those using the other sources of heat. Apparently this is about as good a generalization as can be made. Since the difference in price does not increase in pro- portion to the capacity of the plant, the increased investment for oil-heated plants per dry-ton capacity decreases as the capacity increases. On the basis of dry-ton capacity, the investment in all types of plants varied from $750 to $2,000. Load. — The load varied in different plants from 0.516 to 6.174 tons of dried walnuts. As will be seen from table 4, tests 3, 7, 8, 16, 19, 20, 22, 30, 35, 36, 40, and 42 were made when the plants were not fully loaded, and may, therefore, show efficiencies slightly lower than the normal for the plant and operation. The tonnage of nuts dehydrated in the 1930 season was ascertained in 35 of the 38 plants tested. The average was 21.4 tons or about one- third of the normal plant output which, based on 30 days of operation at capacity, averaged 61.7 tons. The crop was very irregular; some plants turned out nearly a normal amount. Under these circumstances the normal seasonal tonnages are believed to give a better basis than the actual tonnages for estimating overhead costs and for comparing the overhead and total costs for the different plants studied. In recent years many dehydrater owners, especially in northern California, have installed inexpensive wood-slat bins directly above the dehydraters. Such bins were installed in the plant reported in tests 41 and 42. The freshly harvested nuts, particularly in plants employing machine hullers and washers, are elevated into these sup- plementary bins where they remain for a few hours to a day, during which time a considerable part of the easily evaporated moisture in the shells is evaporated by heat from the dehydrater below. This waste heat also serves to warm the cold nuts and increases the maxi- mum capacity of the plant. The bins add supplementary storage and convenience in loading. No tests or observations, however, were made to determine the additional cost involved or the saving in heat that resulted. 18 University of California — Experiment Station H ag^ !"i' a o^ 3 > ■S^ S c 03 03 bC-^ iS *^ S"5 c * &■« o g U >>.2 H* tO to tO O I-- co © co o cn CM oo tO CO CM ba CM CO CM OO © oo -- © CO CM 00 © -* to © © o t « tO © © © © o io m ■o to CO CO CO co l> © i^ >o 00 t* CO 00 ^ CO t-~ lO T* HOOH — c CO « >* 1^ <* r ^ © oo © © 00 OO © © OS O -H CM © CO CO rt N O 1-1 © © CO CO co co co co ec co i*< •»*l T*< CO CO © CO ^ CO ti ^ ec CM OO o to CO 00 OS tO CO © CO © © 0> CO CM CO © 00 CO CO r< CM *" N M H CO »H N W H US O CO tO CO N H oo CO >* 1* OS CM I* © £ -H CO © 1* 0O -H CO © 1^ CM © CO © to l^ CM © o o o o © © © © © © © o © © © © © © © o ^ lO OS •»r> © © oo ■* lO •"*! 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CM o © CM US IO CM CO fi tf tf tE o just- over- ead t per ried on O fc « g Eh ft— 8 o .,_ ctj O C o 0> o H 03 >>*■£ T3 S° a w s Is CI ffi ej a O h o i a ea a> o §■3 h-1 m> M ' M c c c t3 3; 5 0|"O o3 .J ea- The male cienc pei cen J&*^sS Q & ajj^ o : 5 j* » litiil : * & >ad iry uts, und ^ fl ft >. 11 03 O Is Ph* 5 K 6 H rn' I $11 14 11.64 11 39 11 64 11.14 as CO 7.61 11.64 5.20 $8 00 3.85 5.92 8.00 3 85 * O r~- ■* •*»< CO 1-1 ~H © »-i © $0.90 5 25 3 08 5 25 90 o OS d -h in oo CO IM CO »H tO O $0 26 4 23 2 24 4 23 26 o> o (M CO OS OS (M tH © ■* © - $0 64 1 02 83 1 02 64 00 o OO IM 00 CO © ■«*< © -H © j t^ co co co r-- b- CO © CO b- 00 20 5 55.8 2.8 & 00 OO OO OO OO h IO CO «0 »-c o >o NOW OO OO .-i 140 .8 407.0 273.9 407 140.8 o co 256.8 553.5 30 1 1,947 7,822 4,884 7,822 1,947 00 3,856 7,822 1,198 l-H OO - (M (M IM CM CM CO co s g — a 3 * • g a S 5 < s i 1C co ifl n w * oo O co co t~- o . 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Bul. 531] Walnut Dehydraters 21 j3"3 T3 I I §2 1 ^ alli- es « c 0.2 03 gj {J ihhc 3^ S-S* 3 ^ g butr H a*"* o o .,_ o3 O e o 0> is H Fan (and cylinder when rotating) CP >n M Jo a W CO O 03 CD tn o3 a 'el o O o 03 t-1 60 L bC c£a -9 J;ti 03T) o3 9 C O ,>><- Js a ? <~ «8 S ' o3 * Q is a is «2 o - ej m a "Dry- away' per dry ton, pound Tfb« >. 1! 03 o is — >> a,~ to O z; >* io a O s oi ^ •>*< in m m oo « s oo ic m n ") w eo ^ ^ ■* * * « 7.06 6.63 4 50 6 05 7 06 4 50 8 33 18.05 3 35 $1.96 2 00 2 00 2 00 2 00 2.72 2 11 2 72 1.96 ooo ooo ■* If ■* If If "*l CO CO CO CO CO CO r^ © to •^t CM OS B N H OOiOOiOr^t^ M oo m lO M 00 OO N H Tf m CO to CO O to to o tO N H tO tO h 4.86 14 32 1 10 » H rt N N N N W rt CO CO i-l CM CO i-l f 11 W N N C8 CM O lO if (^ CN 00 w m -hOOO^h^h O rt © 81 84 0.48 71 84 48 87 2.63 37 in O O CN if ,-c m os — m © © m oo © m © m ■* I-- in m t- 192.8 483 8 2 a o •* ^ h 1 in oi ■* oo 4 to OI 1 O OO if if m © co if o in i-M to if m to CM rt rt CM co rt oo a> rt in i^- co oo m co CO CM O oo CO o C O >0 tO lO kr) lO -— «-- —• a > s .a n * oi » to a J* *e ^ CN CN CN CO CO CO ** i .s CO CO ■* "* C<1 o CO ■1 CO CM If o m o Oj >. cq §5 8 o if o rt C a CN o 00 CD CO o C-i o < OO t^ co -f oo co GO t^ _4 fM o " -*l m CN s co 00 CI 1Q on oa co co 8 CO CN| y. < s s o J 22 University of California — Experiment Station "Dry-Away." — The "dry-away" ranged from 0.0 to 553.5 pounds of water per ton of dried nuts. The lowest appreciable "dry-away" observed was 8.2 pounds per dry ton. Many of the losses of heat through which the thermal efficiency of a dehydrater is lowered are practically constant during the operation period. Consequently the thermal efficiency of the plant may be expected to be highest when the latter is fully loaded and when the amount of water to be evaporated is highest. Because of differences in details of operation by different operators, it was not possible to show a direct and regular correlation between thermal efficiency and either load or "dry-away." It is believed, however, that this relation is at least partly responsible for the fact that such low thermal effi- ciencies were found in some of the tests. While the average "dry- awafy" was not greatly different from that found in the studies of 1925, there were numerous tests in which the "dry-away" was less than that in any of the 1925 tests. Drying Time. — During a few tests artificial heat was used only part of the time or not at all. The drying time varied from 5.00 to 38.25 hours, including the time when the plant was operated with the fan running, but without using artificial heat. The relation between drying time and "dry-away" in the different plant types is shown in table 5. TABLE 5 Drying Time and " Dry- Away, ' ' 1930 Plant Drying time Total "dry-away" "Dry-away" per hour type Average Maximum Minimum Average Maximum Minimum Average hours hours hours pounds pounds pounds pounds 1 16 22 30.92 5 00 438 6 2,061.0 5 27.1 2 23.35 38 25 9.83 531.0 1,594.0 137.0 22.7 3 19.56 23.08 14.67 213.7 539.0 18.0 10.9 5 15.79 27.92 6.00 218.4 700.0 52.0 13.8 6 23.96 24.17 23.75 215.6 300.0 131.3 9.0 Ther-nial Efficiency. — The thermal efficiencies varied widely in different tests, ranging from 0.0 to 84.8 per cent. The efficiency was, of course, calculated as zero when the "dry-away" was zero. In gen- eral, high thermal efficiencies may be expected when air is recirculated to the maximum extent compatible with rapid drying, when the mois- ture is present on the surface rather than within the kernel of the nut, and when the "dry-away" is high. The tendency toward high thermal efficiency when "dry-away" is high is evident from a study of table 4. The exceptions to this rule are probably due chiefly to operating prae- Bul. 531] Walnut Dehydraters 23 tices. The table also shows that plant type and heat source affect thermal efficiency. Air Flow. — Because of the arrangement and construction of the dehydraters studied, it was not found possible to secure satisfactory determinations of the total volume of air used, nor of the amount and humidity of the air discharged. Since heat is lost in the discharged air when recirculation is not employed, it is to be expected that the thermal efficiency of type 2 and type 3 plants which use no recirculation will be lower than that of the other types. However, the plants of types 2 and 3 that were studied were housed in buildings so that considerable accidental recir- culation undoubtedly took place. On the other hand, the amount of recirculation employed in plants equipped for it was noted to vary considerably with the judgment of the individual operators. These reasons are believed to explain why greater differences were not found between the average thermal efficiencies of the recirculating and nonrecirculating plants (see table 3). Much greater differences were found between the maximum thermal efficiencies of the recircu- lating and nonrecirculating plants, as shown in table 4. It seems probable that a considerably larger portion of the air could and should be recirculated in many of the plants equipped for it, particularly those of type 1. Plants of type 5 are so designed as to require no building over them for their protection ; all the others require at least a roof. It is probable that the thermal efficiency of any plant is increased by housing it in a closed building. This is particularly true of plants of types 2 and 3 which are not equipped for recirculation of any of the air. Temperatures Observed. — In a few tests thermocouples were buried at different points in the bins and readings of the temperature were taken at intervals. When this was first attempted, frequent and irregular variations of temperature were shown by all the individual thermocouples. This was attributed to shifting of the thermocouples with respect to the position of adjacent nuts and the air streams among them. An attempt was made to avoid this by fastening a wire cage, slightly larger than a walnut, over the tips of the thermocouples. Even after this change was made, the readings remained almost as irregular. Nevertheless, the thermocouples did serve to show that there is considerable variation of temperature at different points within the bins. These differences decreased as drying progressed. Some idea of this may be gained by a study of table 6, in which the range of 24 University of California — Experiment Station temperatures observed at several stages of drying are shown in a few tests. In a somewhat larger number of tests, recording thermometers were set at different points. Typical charts are reproduced in figures 11, 12, and 13. The thermometers, placed in the air stream at points just before the air reached the nuts and just after it left the nuts, showed more readily than the thermocouples that the temperatures of the air leaving the nuts approached the entering temperature as drying proceeded. Typical cases are shown in figure 14, tests 1, 2, and 3. This is, of course, to be expected from a consideration of the principles of drying, since a portion of the sensible heat of the air is given up to accomplish evaporation of the water, and some is lost in other ways. Figure 14 also shows that the temperature of the air entering the nuts is more uniform in plants heated h\y gas or electricity than in those heated by oil. TABLE 6 Range of Temperatures Observed by Means of Thermocouples in the: Drying Nuts Test 1 Test 2 Test 7 Hours dried Av. Max. Min. Diff. Hours dried Av. Max. Min. Diff. Hours dried Av. Max. Min. Diff. 1 2 3 16 17 °F 69.0 82.3 93.9 97.6 98 6 100 3 95.2 92.6 101 op 69.0 92.0 100.5 104.0 104.0 105.0 101 96.0 104.0 °F 69 .0 72 82.0 87.0 88 5 92.0 90.0 90.0 98.0 °F 20.0 18.5 17.0 15 5 13 11.0 6 6.0 H l m 2 17,4 18 18H 19 19H 20 21 24 25 26^ °F 69 76.4 87.9 92.7 92.6 98.0 99.3 91.9 94.7 99.6 96.4 95.6 99.3 93 4 101.6 °F 69.0 83.0 96.0 102.0 102.0 101.0 103.5 94 98.0 104 5 100.5 100 103.0 104.5 104.0 °F 69.0 72.5 79 85 84 93.0 92.5 88.0 90.0 91.0 89.0 87 97.0 95.0 98.0 °F 10 5 17.0 17 18 8.0 11.0 6 8.0 13.5 11.5 13.0 6.0 9.5 6.0 1 m 13 H 14H 15 °F 70 86.9 92.4 95.4 103 3 107.5 109.9 °F 70 98.0 103 104.0 108.5 112 113 °F 70 78.0 79.0 83 93 96 107 °F 20 24 21 15 5 16.0 6.0 * Dashes denote that a change in the direction of the air draft has been made. Moisture Content. — The moisture content of the wet nuts ranged from 28.3 to 4.7 per cent, generally decreasing as the season pro- gressed. The average moisture content of the nuts before drying was found to be already sufficiently low in several of the plant tests. The beneficial effect of drying in such cases is merely to reduce the moisture content of a few individual wet nuts Bul, 531] Walnut Dehydraters 25 Fig. 11. — Typical temperature record of air leaving the fan in a gas-heated dehydrater. Fig. 12. — Typical temperature record of air leaving the fan in an oil-heated dehydrater. 26 University of California — Experiment Station It is important to obtain the proper moisture content in the finished nuts. The moisture content of the finished nuts was too high in 7 of the tests made, reaching as high as 12.1 per cent; in 14 of the tests the nuts were drier than necessary, reaching as low as 3.1 per cent. The moisture content recommended by the California Walnut Growers Association is from 6.0 to 8.0 per cent, in order that the weight of the packed nuts shall be stable and that they shall bleach well. Overdrying should be avoided, both because it tends to make the nuts crack or come unsealed, and because it results in loss of Fig. 13. — Typical temperature record of air leaving the fan in an electrically heated dehydrater. valuable weight. For example, if a ton of nuts containing 8.0 per cent moisture were dried to a moisture content of 3.0 per cent, there would result a weight loss of 103 pounds. If walnuts were worth $0.15 a pound, this would amount to $15.45 unnecessarily lost by the grower, which is more than twice the average total cost of dehydrating, as shown in table 4. Therefore, the grower can well afford to spend time and money to prevent a loss of this kind. Gn the other hand, underdrying must be avoided because nuts of moisture content above 8.0 per cent do not bleach well and do not remain sufficiently constant in weight after packing. Also, if the nuts contain over 10.0 per cent moisture, they are likely to be rejected at the Bitl, 531] Walnut Dehydraters 27 packing house, and the grower will be put to the trouble and expense of extra hauling, handling, and redrying. It has often been suggested that the final moisture content of dehydrated walnuts or other products might be controlled by regulating the relative humidity of the drying air at a value that would prevent the drying of the product beyond the desired point. However, there are certain obstacles in the way of the success of this method. As yet there is insufficient information on the relation existing between the relative humidity of the air and the per cent moisture of the nut. Most of the available information on this relation is the result of work done by Christie and Guthier. 9 They found that the eating quality of the nuts is not impaired by using air with a relative humidity as high as 50 per cent. Such humidity has little retarding effect when the nuts are comparatively wet but during the later stages when the moisture content has been reduced to 10 or 12 per cent the drying time is noticeably increased. However, nuts can be dried to 5 per cent moisture content satisfactorily by using air with a relative humidity of 20 per cent during the late stages of drying. Christie and Guthier recommended this humidity for recirculating dehydraters. A device intended to control the final moisture content of the nuts by automatic operation of the damper through which exhaust air is discharged was under experimentation at one drier in 1930. A test (No. 33) was made on the plant in which the automatic humidity control apparatus had been installed and was in operation. The final moisture content of the nuts, 11.8 per cent, was too high to be satis- factory. The efficiency of the plant during this trial, though fair, was exceeded in another test on the same plant (No. 36) when the ap- paratus was not in operation. During the latter test, the " dry-away" was about twice as great and the drying time was less, indicating that the automatic device markedly retarded drying. Our observations would seem to indicate that the apparatus has not yet been brought to a practical stage of development. As a means of indicating to a dehydrater operator the stage at which the moisture content of the nuts has been reduced to the desired point, namely, 6.0 to 8.0 per cent, it occurred to the authors that the temperature changes of the air passing through the nuts may be of service. Therefore, these temperature changes were observed in a number of the tests made. Typical results are shown graphi- cally in figure 14. Because of differences in design of the plants, especially the depth of nuts through which the air passes, a given 9 Unpublished results of A. W. Christie and E. H. Guthier, 1925. 28 University of California — Experiment Station temperature difference cannot be said to represent any exact moisture content for all plants. In all plants, however, the temperature differ- ence decreases as drying progresses, and it seems entirely probable that in any given plant a temperature difference could be found to correspond to the desired moisture content. F e E F 3 . jP*~ E Y ' E ' Tn: 5 J 1 t L cl 9o / f v/ DIAGR AM 8 r ■) 1 < i t I \ / 9 1 B /1 f A s )a iino F - I „ v — F F ^ L Is— L fr E L 1 — lb — - 1 — -i / D/AGA •AM C 7CV id 20 ZS 24 MOCI/fS DEHYD/WT£D Fig. 14. — Temperature changes in the air entering and leaving the nuts during drying, for 3 plants of the same type. Diagram A, dehydrater heated with oil; diagram B, heated with gas; diagram C, heated with electricity and all thermostatically controlled. Crossing of the curves indicates reversal of direction of air flow. F, Temperature of air leaving fan; E, temperature of air entering nuts; and L, temperature of air leaving nuts. In view of the importance of correct moisture content in the finished product, it would probably be worth while for many growers or groups of growers to make use of a rapid method for the determina- tion of moisture content. Such a method, combining simplicity, speed, sufficient accuracy, and requiring* relatively simple apparatus has been described for dried fruits. (10) With slight modifications it also gives satisfactory results with walnuts. This apparatus is shown in figure 15. By this means the moisture content may be determined in about 20 minutes. One grower uses this test on every lot of nuts he dehydrates. It seems likely that the use of this method, com- bined with the installation of thermometers indicating the tempera- Bul. 531] Walnut Dehydraters 29 ture of the air entering and that leaving the bin, would, after a few trials, enable a dehydrater operator to estimate very closely the moisture content of nuts in his dehydrater without actually testing them. Frequent use of the method would permit a much more a Fig. 15. — Moisture-testing apparatus for walnuts. One hundred grams of nuts taken from a representative sample are used for the test. The nuts are to be well cracked and include both shells and kernels. This amount is put into a 1,000 cc Pyrex round-bottom boiling flask attached to a perfectly dry measuring tube and condenser, as shown above. Enough xylene to cover the sample is added. With cold water running through the condenser the flask is heated by an electric hot plate for 20 minutes after boiling begins. The amount of water then in the measuring tube represents the percentage of moisture in the nuts. 30 University of California — Experiment Station uniform adjustment of moisture content than now seems common, and would do much to prevent rejection of deliveries on account of insufficient drying-, as well as to prevent unnecessary and expensive loss of weight. Labor Required. — The number of man hours of labor required for all purposes varied from 0.88 to 10.55 hours per dried ton, averaging 1.96 hours in all plants. The cost of labor for loading and unloading in all plants averaged $0.82, that for supervision, $0.27, and the average total was $0.96 per dried ton. Whether or not' mechanical elevators or conveyors were used, the requirement of labor for loading only was almost exactly the same, both in average and in range. The average labor cost was $0.34 when conveyors were used and $0.31 when they were not. The cost of power to operate conveyors averaged only $0,009 per dry ton, ranging from $0,001 to $0,028. The overhead cost of the conveyors averaged twice as much as the labor cost, or $0.66 per dried ton, ranging from $0.16 $1.58. Thus the provision of conveyors did not appear to reduce the labor cost. While the power cost was inconsiderable, the overhead cost of conveyor equipment increased the total cost of loading by conveyors to three times that of loading where no conveyor was required. It should be pointed out that in plants where they were installed the conveyors probably reduced the loading labor costs below what they would have been in the absence of conveyors. The additional cost of loading in such plants should be charged not to the conveyors as such but to the plant design that makes conveyors necessary. Heat Efficiency, Power Requirements, and Costs. — The amount of gas used for heat varied from 94 to 3,505 cubic feet per dried ton; that of oil from 2.83 to 22.80 gallons; and that of electricity from 26.7 to 601.0 kilowatt-hours. The total mechanical power used ranged from 2.5 to 78.0 kilowatt- hours per dried ton. "Dry-away" per kilowatt-hour for fans varied from 0.7 to 62.8 pounds. The average thermal efficiency of all gas-heated plants regardless of type was 14.3 per cent; that for oil-heated plants was 20.5 per cent; while that for electricity was 37.5 per cent. The range of efficiencies found in gas-heated plants was least, while that in electrically heated plants was greatest as shown in table 4. At the thermal efficiencies found, the costs of electric heating are several times as large as those for gas and oil when the rates for each source of heat are in harmony with our assumptions. Even with Bui,. 531] Walnut Dehydraters 31 electricity at $0.01 per kilowatt-hour, the average cost of electricity for heat would be two and three times as great as for gas and oil respectively. The average costs for heat were $0.87, $0.67, and $3.58 for plants heated by gas, oil, and electricity, respectively. The average cost of labor for supervision was only $0.15 and $0.20 for gas and elec- trically heated plants respectively, while that for oil-heated plants was $0.92. The sum of the average costs of supervision and heat was $1.02 for gas-heated plants, $1.59 for oil-heated plants, and $3.78 for those using electricity. Thus the average costs for these two items was lowest for gas-heated plants, 50 per cent greater in oil -heated plants, and 250 per cent greater for electrically heated plants. A study of table 4 shows that the average operating costs were lowest in gas-heated and highest in electrically heated plants. The adjusted overhead costs were about the same in gas and electrically heated plants, and about 30 per cent higher in oil-heated plants. Considering all types of dehydraters, the average total costs were lowest in gas-heated plants at $5.89 per dried ton, about 25 per cent higher in oil-heated plants at $7.61, and about 35 per cent higher in electrically heated plants at $8.33. Thus the greater thermal effi- ciency and the absence of supervisional requirements for electrically heated plants failed to keep the costs as low as they were in the other types. As will be seen in table 4, the total operating cost varied from $1.10 to $14.32 per dried ton, averaging $3.43 for all plants of all types. The adjusted overhead costs ranged from $1.80 to $8.00 per dried ton, averaging $3.61 for all plants. The total costs, arrived at by adding total operating costs and adjusted overhead costs, varied from $3.06 to $18.05 per dried ton, averaging $7.15 for all plants, or about $1.70 more than for sun-drying. (1) OPERATING COSTS, 1 922-1 930 In addition to the tests made in 1925 and 1930 that are summarized herein, 30 additional determinations of operating costs were made by Christie and Guthier 10 during the years 1922 to 1925. These have never been published in detail, although they have been summar- ized. (1_9) The operating costs in all known tests conducted by mem- bers of the Fruit Products Laboratory of the University of California 10 Both were formerly of the Fruit Products Laboratory, University of California. 32 University op California — Experiment Station have been summarized in table 7. In this table it will be seen that the average labor cost in all tests is $1.12, heat cost $1.63, power cost $0.50, and total operating cost $3.30. The average total operating cost for oil-heated plants was almost exactly the same as the average for all tests, while that for gas-heated plants was about one-third lower and that for electrically heated plants about one-third higher. TABLE 7 Operating Costs per Dried Ton, 1922 to 1930 Cost Heat source Average Maximum Minimum Gas $0 66 1.59 1 32 1 12 $1.52 5.25 3.50 5 25 $0.31 Oil 55 Electricity 43 31 Heat Gas 88 1 08 3 00 1.63 2 10 4 36 12.03 12 03 06 Oil 14 53 0.14 Gas Oil 0.45 67 43 50 1 02 2 42 1 51 2 42 0.10 12 Electricity 05 05 Gas 2 20 3 34 4 62 3 30 3 56 9.44 14 32 ■ 14.32 85 Oil 1.33 1 10 85 SUMMARY AND CONCLUSIONS Two studies of thermal efficiency and comparative cost factors in walnut dehydraters are reported. The principal findings may be summarized as follows : 1. The total operating costs for all tests averaged $3.43 per dried ton. They averaged $2.23 in gas-heated plants, $3.04 in oil-heated plants, and $4.86 in electrically heated plants. 2. The overhead costs for all tests adjusted to normal operating capacity averaged $3.61 per dried ton. They averaged $3.44 in gas-heated plants, $3.47 in electrically heated plants, and $4.57 in oil-heated plants. 3. The total costs for all tests averaged $7.15 per dried ton. They averaged $5.89, $7.61, and $8.33 in gas, oil, and electrically heated plants, respectively. Bul. 531] Walnut Dehydraters 33 4. The thermal efficiencies averaged lowest in gas-heated and highest in electrically heated plants. They also averaged highest in plants using recirculation of air. 5. Electric heat, in spite of its high efficiency, proved the most costly, although not so expensive as to be prohibitive in walnut dehydration where low energy rates may be obtained. 6. The moisture content of the dried nuts varied excessively. No satisfactory means for controlling this automatically have been developed, but possible means of control have been suggested. 7. The investment in dehydraters, exclusive of buildings, mechan- ical hullers, washers, and other accessory equipment, was found to vary from $750 to $2,000 per dry ton average daily capacity. ACKNOWLEDGMENTS Acknowledgment is due to the California Committee on the Rela- tion of Electricity to Agriculture, which supported in part the investigations of 1925 and 1930. Special acknowledgment is also due to the Southern California Edison Company for assistance in deter- mining energy consumption, and to the California Walnut Growers Association for seasonal tonnage records and arrangements with growers for tests to be made. A. W. Christie and E. H. Guthier sup- plied much useful information, assisted in planning the work, and the former made helpful comments upon the manuscript, Our thanks are also due to the many growers who cooperated in the tests and to the manufacturers of dehydraters, some of whom provided necessary information. 34 University of California — Experiment Station LITERATURE CITED i Batchelor, L. D., A. W. Christie, E. H. Gtjthier, and R. G. Larue. 1924. Sun drying and dehydration of walnuts. California, Agr. Exp. Sta. Bui. 376:1-26. 9 figs. 2 Christie, A. W. 1923. Dehydration of walnuts. California Cult. 9:306. Also in Diamond Walnut News 5(2) :9, 11. s Christie, A. W. 1924. Dehydraters for walnuts. Diamond Walnut News 6(3) :37. * Christie, A. W. 1924. Walnut dehydration. Calif. Cult. 62:595. 5 Christie, A. W. 1925. Progress in walnut dehydration. Diamond Walnut News 7(2): 11-14. o Christie, A. W. 1926. Walnut dehydration developments. Diamond Walnut News 8(l):4-5. i Christie, A. W. 1927. Electric dehydration of walnuts. Electrical West 58:445-457. s Christie, A. W. 1928. Great growth in dehydration. Diamond Walnut News 10(1) :3. 9 Christie, A. W. 1930. Dehydration keeps on growing. Diamond Walnut News 12(3) :13. io Nichols, P. F., C. D. Fisher, and W. J. Parks. 1931. Finding moisture content. Western Canner and Packer 25:11-13. 4 figs. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. No. 253. Irrigation and Soil Conditions in the 433. Sierra Nevada Foothills, California. 263. Size Grades for Ripe Olives. 279. Irrigation of Rice in California. 435. 283. The Olive Insects of California. 310. Plum Pollination. 331. Phylloxera-Resistant Stocks. 439. 343. Cheese Pests and Their Control. 348. Pruning Young Olive Trees. 349. A Study of Sidedraft and Tractor Hitches. 357. A Self -Mixing Dusting Machine for 440. Applying Dry Insecticides and Fun- gicides. 361. Preliminary Yield Tables for Second- 445. Growth Redwood. 364. Fungicidal Dusts for the Control of 446. Bunt. 447. 369. Comparison of Woods for Butter Boxes. 370. Factors Influencing the Development 448. of Internal Browning of the Yellow Newtown Apple. 449. 371. The Relative Cost of Yarding Small and Large Timber. 450. 373. Pear Pollination. 374. A Survey of Orchard Practices in the Citrus Industry of Southern Cali- 452. fornia. 454. 379. Walnut Culture in California. 386. Pruning Bearing Deciduous Fruit 455. Trees. 389. Berseem or Egyptian Clover. 456. 392. Fruit Juice Concentrates. 393. Crop Sequences at Davis. 458. 394. I. Cereal Hay Production in California. II. Feeding Trials with Cereal Hays. 459. 395. Bark Diseases of Citrus Trees in Cali- fornia. 462. 396. The Mat Bean, Phaseolus Aconitifolius. 464. 404. The Dehydration of Prunes. 406. Stationary Spray Plants in California. 465. 407. Yield. Stand, and Volume Tables for 466. White Fir in the California Pine Region. 467. 408. Alternaria Rot of Lemons. 468. 409. The Digestibility of Certain Fruit By- products as Determined for Rumi- 469. nants. Part I. Dried Orange Pulp 470. and Raisin Pulp. 410. Factors Influencing the Quality of Fresh 471. Asparagus After It is Harvested. 416. Culture of the Oriental Persimmon in 472. California. 473. 417. Poultry Feeding: Principles and Prac- tice. 474. 418. A_ Study of Various Rations for Fin- ishing Range Calves as Baby Beeves. 419. Economic Aspects of the Cantaloupe 475, Industry. 476. 420. Rice and Rice By-Products as Feeds 477. for Fattening Swine. 421. Beef Cattle Feeding Trials, 1921-24. 479. 423. Apricots (Series on California Crops and Prices). 425. Apple Growing in California. 480. 426. Apple Pollination Studies in California. 427. The Value of Orange Pulp for Milk 481. Production. 428. The Relation of Maturity of California 482. Plums to Shipping and Dessert 483. Quality. 484. 431. Raisin By-Products and Bean Screen- ings as Feeds for Fattening Lambs. 485. 432. Some Economic Problems Involved in 487. the Pooling of Fruit. Power Requirements of Electrically Driven Dairy Manufacturing Equip- ment. The Problem of Securing Closer Rela- tionship between Agricultural Devel- opment and Irrigation Construction. The Digestibility of Certain Fruit By- Products as Determined for Rumi- nants. Part II. Dried Pineapple Pulp, Dried Lemon Pulp, and Dried Olive Pulp. The Feeding Value of Raisins and Dairy By-Products for Growing and Fattening Swine. Economic Aspects of the Apple In- dustry. The Asparagus Industry in California. A Method of Determining the Clean Weights of Individual Fleeces of Wool. Farmers' Purchase Agreement for Deep Well Pumps. Economic Aspects of the Watermelon Industry. Irrigation Investigations with Field Crops at Davis, and at Delhi, Cali- fornia, 1909-1925. Economic Aspects of the Pear Industry. Rice Experiments in Sacramento Val- ley, 1922-1927. Reclamation of the Fresno Type of Black-Alkali Soil. Yield, Stand and Volume Tables for Red Fir in California. Factors Influencing Percentage Calf Crop in Range Herds. Economic Aspects of the Fresh Plum Industry. Prune Supply and Price Situation. Drainage in the Sacramento Valley Rice Fields. Curlv Top Symptoms of the Sugar Beet. The Continuous Can Washer for Dairy Plants. Oat Varieties in California. Sterilization of Dairy Utensils with Humidified Hot Air. The Solar Heater. Maturitv Standards for Harvesting Bartlett Pears for Eastern Shipment. The Use of Sulfur Dioxide in Shipping Grapes. Adobe Construction. Economic Aspects of the Sheep In- dustry. Factors Affecting the Cost of Tractor Logging in the California Pine Region. Walnut Supply and Price Situation. Poultry Houses and Equipment. Improved Methods of Harvesting Grain Sorghum. I. Irrigation Experiments with Peaches in California. II. Canning Quality of Irrigated Peaches. The Use. Value, and Cost of Credit in Agriculture. Utilization of Wild Oat Hay for Fat- tening Yearling- Steers. Substitutes for Wooden Breakpins. Utilization of Surplus Prunes. The Effects of Desiccating Winds on Citrus Trees. Drying Cut Fruits. Asparagus (Series on California Crops and Prices). BULLETINS— (Continued) No. 488. Cherries (Series on California Crops and Prices). 489. Irrigation Water Requirement Studies of Citrus and Avocado Trees in San Diego County, California, 1926 and 1927. 490. Olive Thinning and Other Means of Increasing Size of Olives. 491. Yield, Stand, and Volume Tables for Douglas Fir in California. 492. Berry Thinning of Grapes. 493. Fruit Markets in Eastern Asia. 494. Infectious Bronchitis in Fowls. 495. Milk Cooling on California Dairy Farms. 496. Precooling of Fresh Fruits and Tem- peratures of Refrigerator Cars and Warehouse Rooms. 497. A Study of the Shipment of Fresh Fruits and Vegetables to the Far East. 498. Pickling Green Olives. 499. Air Cleaners for Motor Vehicles. 500. Dehydration of Grapes. 501. Marketing California Apples. 502. Wheat (Series on California Crops and Prices). 503. St. Johnswort on Range Lands of California. 504. Economic Problems of California Agri- culture. (A Report to the Governor of California.) No. 505. The Snowy Tree Cricket and Other Insects Injurious to Raspberries. 506. Fruit Spoilage Disease of Figs. 507. Cantaloupe Powdery Mildew in the Imperial Valley. 508. The Swelling of Canned Prunes. 509. The Biological Control of Mealybugs Attacking Citrus. 510. Olives (Series on California Crops and Prices). 511. Diseases of Grain and Their Control. 512. Barley (Series on California Crops and Prices). 513. An Economic Survey of the Los Angeles Milk Market. 514. Dairy Products (Series on California Crops and Prices). 515. The European Brown Snail in Cali- fornia. 516. Operations of the Poultry Producers of Southern California, Inc. 517. Nectar and Pollen Plants of California. 518. The Garden Centipede. 519. Pruning and Thinning Experiments with Grapes. 520. A Survey of Infectious Laryngotrache- itis of Fowls. 521. Alfalfa (Series on California Crops and Prices). CIRCULARS No. 115. Grafting Vinifera Vineyards. 178. The Packing of Apples in California. 212. Salvaging Rain-Damaged Prunes. 230. Testing Milk, Cream, and Skim Milk for Butterfat. 232. Harvesting and Handling California Cherries for Eastern Shipment. 239. Harvesting and Handling Apricots and Plums for Eastern Shipment. 240. Harvesting and Handling California Pears for Eastern Shipment. 241. Harvesting and Handling California Peaches for Eastern Shipment. 244. Central Wire Bracing for Fruit Trees. 245. Vine Pruning Systems. 248. Some Common Errors in Vine Pruning and Their Remedies. 249. Replacing Missing Vines. 253. Vineyard Plans. 257. The Small-Seeded Horse Bean (Vicia faba var. minor). 258. Thinning Deciduous Fruits. 259. Pear By-Products. 261. Sewing Grain Sacks. 262. Cabbage Production in California. 265. Plant Disease and Pest Control. 269. An Orchard Brush Burner. 270. A Farm Septic Tank. No. 279. The Preparation and Refining of Olive Oil in Southern Europe. 282. Prevention of Insect Attack on Stored Grain. 288. Phylloxera Resistant Vineyards. 290. The Tangier Pea. 292. Alkali Soils. 294. Propagation of Deciduous Fruits. 296. Control of the California Ground Squirrel. 301. Buckeye Poisoning of the Honey Bee. 304. Drainage on the Farm. 305. Liming the Soil. 307. American Foulbrood and Its Control. 308. Cantaloupe Production in California. 310. The Operation of the Bacteriological Laboratory for Dairy Plants. 316. Electrical Statistics for California Farms. 317. Fertilizer Problems and Analysis of Soils in California. 318. Termites and Termite Damage. 319. Pasteurizing Milk for Calf Feeding. 320. Preservation of Fruits and Vegetables by Freezing Storage. 321. Treatment of Lime-induced Chlorosis with Iron Salts. 322. An Infectious Brain Disease of Horses and Mules (Encephalomyelitis). lOw-6,'35