1366
INDUSTRIAL AND ENG INEERING CHEMISTRY
spectrum. Owing to the high damping by the underwater gap, the duration of the spark was very short, probably less than 10+ second. It is not likely that appreciable reaction would take place as a result of this illumination between the time the spark started and the time it was extinguished. Before the exposure of the spectrum was continued by means of another spark, a fresh charge of gas was introduced into the engine. With the underwater spark source, the formaldehyde and continuous absorption were detected under knocking conditions. This source was not used for the present work because its spectrum was not sufficiently continuous to serve as a convenient background for the study of the formaldehyde bands. The results outlined in this paper are not in disagreement with certain theories of knock based upon studies of the slow oxidation of hydrocarbons outside of the engine. However, there is considerable uncertainty in applying the reeults of such studies to the engine. One reason for this difficulty is that all the conditions existing in the fuel-air mixture prior to knock are not known. Even such an essential factor as
Vol. 25, KO.12
the maximum temperature attained by the noninflamed gas has not yet been measured. Accordingly, speculations on the mechanism of the reactions preceding knock will be postponed until further experiments are completed. ACKNOWLEDGMENTS The authors take this opportunity to express their appreciation to C. F. Kettering, T. A. Boyd, and E. J. Martin for their continued interest in this work. The authors are also indebted to s. J. Owens of the University of Michigan for the preparation of the microphotometric records.
LITERATURE CITED (I) (2) (3) (4) (5) (6)
Henri and Schou, 2. Physik, 49, 774 (1928). Rassweiler and Withrow, IKD. ENG.CHEY.,24, 528 (1932). Rieche and Hitz, Be?., 62, 226 (1929). Withrow and Boyd, ISD. ENG.CHEST., 23,539 (1031). Withrow and Rassweiler, Ibid., 23, 769 (1931). Ibzd., 25, 923 (1933).
August 2 5 , 1933. RECEIVED
Large-Scale Experiments in Sulfuring Apricots 11. Effect of Dehydrating, Shade-Drying, and Blanching E. M. CHACE,C. G. CHURCH,AND D. G. SORBER Bureau of Chemistry and Soils, U. S. Department of Agriculture, Los Angeles, Calif. It was found t h a t , w i t h o u t H E results of e x p e r i Samples of apricots, part grown in a n inland doubt, there is some correlation ments in sulfuring aprivalley and part in a coastal valley of Cali,fornia, between the sulfur dioxide concots with various conare used in experiments carried out to ascertain tent of the dried fruit and its centrations of sulfur dioxide gas the effect o n the dried fruit when the fresh fruit q u a l i t y . This correlation is for different lengths of time and is blanched by steam either before or after it is most pronounced in dried apriat different temperatures were cots containing less than 2000 described in a former paper (1). sulfured. A comparison is made between samparts per million. It was shown that the concenples dried in a recirculating dehydrator and those tration of sulfur dioxide in the dried in the sun; this series includes samples exatmosphere in which the fruit EQUIPMENT BND PROCEDURE posed to the sun for 2 days before being dehydrated was treated and the length of the and some of the blanched samples. Tests are The w o r k r e p o r t e d h e r e treatment were the prime factors was carried out with the same governing the retention of sulfur made in which the fruit is dried in the shade, equipment used during previdioxide in the dried fruit. A others where the fruit is exposed to the s u n f o r ous seasons and under the condishort period of sulfuring or a low 2 days and the drying finished in the shade. tions which had been found to concentration of gas in the sulI n this work comparable samples are sulfured be most favorable for the profuring cabinets produced dried d u c t i o n of d r i e d apricots of and then dried in the sun in the usual commercial fruit containing small quantities good quality yet containing a of sulfur dioxide but also of poor way. A study is made of the penetration test m o d e r a t e a m o u n t of sulfur quality. On the other hand, exwhich is used by commercial driers to ascertain dioxide. posure to high concentrations of the eficiency of their sulfuring operations. I n a d d i t i o n to this equipgas or for long periods resulted in ment, a small portable dehydrafruit c o n t a i n i n e: excessive amounts of sulfur 'dioxide and of a quality no better than that tor (Figure l),a steam blanching cabinet, and racksfor drying produced where moderate amounts of gas with shorter ex- in the shade were used. The dehydrator held twelve trays of fruit, equivalent to the posures were used. Satisfactory results were obtained by exposing the fruit to an atmosphere containing 2 per cent of sul- capacity of three of the sulfuring cabinets used. It was fur dioxide for 3 hours, or to one containing 3 per cent of gas rarely operated, however, with more than eight trays. Heat for 2 hours. Temperature was found to have little effect on was supplied by space heaters of the nonglow type, wet toweleither the retention of the gas by the fruit or on its quality. ing being used to raise the humidity. The air was circulated However, when the temperature exceeded 120' F. (48.9' C.), over the trays by means of a motor-driven fan, dampers in the the dried apricots produced had an undesirable reddish color. air ducts providing means of recirculating the air, thus help-
T
INDUSTRIAL AND ENGINEERING CHEMISTRY
1368
were completed within 48 hours, and the samples were then placed in friction-top one-gallon cans. Sulfur dioxide and moisture were determined as previously described, and the grading system was also that formerly used (1). As many fruit driers and packers believe that the retention of sulfur dioxide is different in fruit grown in coastal valleys from that grown in inland valleys, the experimental work carried out in the San Joaquin Valley was continued in a coastal valley a t Hollister during the drying season there. No dehydration, however, was undertaken. The results on penetration, sulfur dioxide retention, and grade of all samples are given in Tables I and 11.
Vol. 25, No. 12
TABLE111. SULFURDIOXIDERETENTIONS AND GRADES RESULTIXG FROM DIFFERENT METHODS OF BLAXCHING THENBLANCHED
-SULFURED,
SOa
-BLANCHED,THEN- -SULFUREDWITHOUTSULFURED BLANCHINQ
so2
penetrapenetration $01 Grade tion
% 43 48 41 67 66 78 Av. 57 a
P. p . m. 3166 2776 3438 2726 2395 2912 2902
85 76 79 72 71 73 76
so2
SOz
%
P.p . m.
46 48 54 43 43 52 48
2104 2015 2287 1991 1746 1998 2024
penetraGrade tion SOZ Grade % P . p . m. 76 72 66 63 54 55 64
46 47 46 57 67 66 55
2466 1994 1929 2188 1786 1984 2058
88 80 80 75 77 74 79
All figures on sulfur dioxide calculated to moisture-free basis.
At Merced seven sets consisting of sixteen samples of unDIOXIDERETENTIONoAI\'D GRADESRESULT- blanched sun-dried samples were prepared in such a way as to ING FROM DIFFERENT METHODS OF TREATMENT, HOLLISTER be comparable with the same number of sets consisting of 1930 SEASON SAMPLES, thirteen blanched samdes (Table I). These sets do not SULFUBING CONDITIONS F-SUN-DRIEDY-BHADE-DRIEdiffer greatly when the peneiration 0; the sulfur dioxide and SulSon SOa its retention are considered, the averages being 68 per cent SO1 furing penepeneconon. time tration SOs Grade tration SOa Grade penetration and 2514 p. p. m. of sulfur dioxide for the un% P.p . m. % P.p. m. % Houra blanched, and 62 per cent penetration and 2408 p. p. m. of sulSAMPLES NOT BLANCHED fur dioxide for the blanched. However, the average grade of 2 2 3 the blanched samples was seven points below that of the unblanched. This difference alone is large enough to be serious, and in each comparable set the tendency of the difference is always in the same direction. 5 While there are but three comparable sets of samples from 72 1039 73 64 874 79 3 1 1471 .. .. .. 66 77 Hollister (Table 11),the data as far as grade is concerned show 1225 . . .. .. 78 55 1464 .. .. 84 80 the same tendency. 1164 2 90 15% 78 86 71 It appears, therefore, that blanching has no advantage in .. .. .. 1697 78 82 1323 74 .. .. .... 82 reducing the sulfur dioxide retention and has the disadvantage 1237 .. .. 72 56 1424 .. .. *... 82 94 of lowering the grade. Moreover, although the blanching .. 1060 72 86 was never so severe as to cause the fruit to lose its shape, the lOi0 79 1336 76 3 99 98 .. . . 662 83 56 1036 86 halves always filled with juice. This fact alone would be an 5 0.5 78 63 883 1 68 obstacle of no small importance if blanching had been found 1460 81 .. . . .. 63 1318 80 .. .. * . 54 beneficial. I n moving the trays, the juice in the halves slops .. .. .. 1446 75 60 .. .. 1329 77 61 over and not only injures the appearance of the dried fruit 91 16184 75 1306 77 75 2 but causes it to stick t o the trays to such an extent that it is 83 1703 83 .. .. 10 0.5 88 3602 80 .. .. .. 2 often torn in scraping. 15 2 99 5056 75 .. .. .. 20 TABLE 11.
SULFUR
I .
BLANCHED SAMPLES
1 2 3
0.5
1 1 0.25 0.5 1
5
0.25
0.5 1
6
10
0.25
15 20
0.5 1 0.5
100 99 95 77 100 100 100 69 96 94 80 62 49 89 95 53 100 98 94 90
375 410 664 486 640 314 536 870 868 892 840 796 1428 1376 886 944 824 1190 2740 2424
61 70 74 64 72 63 62 74 73 72 70 75 73 78 74 74 74 86 75 77
.. .
I
.. ..
.. .. ..
.. .. .. .. .. .. ..
..
.. ....
.. .. ..
.. .. .. .. .. ..
.. ..
.. ..
.. .. .. .. ..
....
..
.. .. .... .. .. ..
.. .. ..
.. .. .. .. .. .. ..
..* .
Sulfur dioxide data are given on dry basis.
EFFECT OF BLANCHING Some years ago, blanching was suggested as a partial or complete substitute for sulfuring, and some experimental work was undertaken. So far as the writers know, the results of these experiments were never published, and no commercial application resulted from them. I n the present experiment with blanching, only steam was used, hot water having the disadvantage of dissolving the soluble solids from the fruit and having to be changed frequently, owing to other contamination. The fruit was blanched before it was sulfured in one set of experiments and after it was sulfured in another set (Table 111). The usual variations in sulfuring and drying were used.
BLANCHISG BFTER
SULFURING
Three sets of six samples each were run in order to test the effect of blanching the fruit after it was sulfured. Comparable samples of the same fruit were blanched before sulfuring, and others were dried in the usual way without blanching. The results (Table 111)indicate that fruit blanched after it was sulfured retained almost 50 per cent more sulfur dioxide than that blanched before sulfuring or than that dried unblanched. The grade of this fruit was superior to that of the fruit which had been sulfured after it was blanched but was somewhat lower than that of the comparable unblanched samples. There seemed to be no difference in the manner in which the half apricots filled with juice in either method of blanching, so that the same trouble of fruit sticking to the drying trays was encountered.
DEHYDRATION The dehydration of apricots is not an innovation ( 3 ) . Many advocates of dehydration claim that a product containing less sulfur dioxide and superior to that dried in the sun can be produced in this way. However, few data are available resulting from carefully controlled experiments in which, after all the fruit has been sulfured in one sulfur house, part of it has been dried in the sun and part in a dehydrator. The dehydrated apricot has a color unlike that of the product dried in the sun, and therefore encounters more or less sales resistance. I n order to overcome this difference in
Uecernber, 1953
I N 0 U S 'I it I A L A N 11 E li G I N I3 I< I< 1 ,Y (;
color, a method which is in part sun-drying, in part delrydration, lias been borrowed from the grape dehydrators wlio use it to produce amber-colored raisins. The apricots are exposed to the sun for a short period (not more than 2 days) and then dehydrated, the color of the dried fruit being mu& like that of the fruit which has been dried in the usual way. This method was tried in the experimental work. Owing to the superior color of the dried fruit produced by exposure to tl!c a n n before dehydration, only three sanrples of fruit wcre dehydrated without this previous exposure. Contrary t o expectation, these samples did not contain appreciably less sulfur dioxide tiran the comparable sun-dried samples and were lower in grade (Table IV). Two samples were hlanched before dehydration; one 'il'as loiver in grade than the comparable sun-dried samples and had 300 p. p. m. less sulfur dioxide. The other contained approximately the same amount of sulfur dioxide and -'as of the same grade as tlre normally dried fruit. The greater part of the dehydrated samples were exposed to the sun before they were dehydrated. Usually the exposure was from 40 to 44 hours, the fruit heing exposed for approximately two periods of daylight and two nights.
C I I i S 11 1 S T I $ Y
1369
Seven blanched samples w e ~ einferior in quality to their controls nod contained only a small amount less of sulfur dioxide. Inexplicably tlre fruit dried in tlic shade a t IIollister was superior in qualit,y to that diied in the sun, although the sulfur dioxide ret.cntion wa8 not greatly different. All of the seven samples but one showed tlre same tendency. It is not apparent why this should be the case, for the weather a t Hollister was much less favorable for drying than a t iMerced. The mornings were overcast and cold, and the afternoon temperatures rarely exceeded 90' F. (32.2' C.). The mind velocity, however, w,zs liiglrer than a t Merced.
F~CURE 2. APRICOT SLICESSHOWING ZONES OF PENETRATION OF SULFUR Droxro~ P. p . m.
P. P. m.
MSRCED s*MPl.P:S
3 3
Sun Dehydrntion StLn Sun
Bun
+ dehydra1,iun
Shade
S"" Sun
+ shade
11 11
8
8 4
4
2293 2449 2494 2299 2470 2440 2878 250s
79 734 79 77
78 76 80 80
2 2 I1 11
2204 2027 2445 2435 a490
71 67 73 74 75
7
2203
:z
.. ..
.. ..
.. ..
0?
AOLL18TER I*h%PLns
S"" Shsde 0
7 7
I088 950
74 80
sulfur dioxide data are aiven o n dry basis.
There are eleven comparable sets of saniples (Table IV), half treated in tlris way and half sun-dried in the usual manner. The forrner failed to show appreciably lower amounts of sulfur dioxide, having 200 p. p. in. less than the sun-dried. These sundried samples were 2 grade points higher. The significance of these differences is not apparent, however, as four of the dehydrated samples contained more sulfur dioxide than their cornparable sun-dried samples, and five were slightly higher in grade points. Again tho blanched samples were lower in quality without appreciable difference in retention of sulfur dioxide. Thcve results seem to cast doubt on the statements often made that sulfured dehydrated fruit contains less sulfur dioxide than the sun-dried. There are other advantages in dehydration not, within the scope of these experiments.
SHADE-DKYINQ os. GUN-DKYING The system of drying apricots in the shade reported from Australia ( 2 ) does not differ greatly from that used in the interior valleys of California. In both cases the fruit is exposed to the sun for 2 days or more, and then placed in stacks until the drying is completed. I n coastal valleys where good drying weather is not as prevalent as in the interior, the method is used less frequently. Some of the material used in these experiments was dried completely in the shade, the samples being transferred directly from the sulfuring or blanching cabinet to the shade-drier. The results (Table IV) did not present anything unusual, the eight samples which were not blanched containing approximately the same amount of sulfur dioxide and being 3 grade points lower than the eight control samples. The
Another set of four sanrplcs (Table IV) WAS placed in the sin, for 48 hours before bcing placed in the shade-driers, the comparable set being left in the sun somewhat longer and then stacked as in tlre commercial methods. As was to be expccted, the sample a t Merced shoived no difference in quality and only a slight one in sulfur dioxide retention. The blanched samples showed no difference in sulfur dioxide rercntion, but the sliade-dried fruit W ~ L Ssomewhat inferior in quality. I'~sr:.rii~r~o.u OF Smruii DIOXIDE
In curninercial practice, samples of the sulfured fruit are cut after tlre sulfuring is thought to be completed, and the penetration of the gds is noted. Penetration is shown by the \vater-logged zone (Figure 2 ) which is largely adjacent to the pit side of the half, but a180 occurs to a lesser extent next to the skin. The region hetween these sones retains the original texture of tile fruit and is called tlre "uncooked" part. If the nncooked part is too large, the fruit is returned to the sulfuring liouse for further treatment. Operators have noted that the nncooked zone disappears entirely witliin 12 hours after the fruit has been placed on the dry yard. As previously stated, in order to ascertain the value of this test, each tray of fruit which made up the samples was tested as it came from the sulfuring cabinet. The selected halves were out with a sharp knife, and the thickness of the fruit a t the center (halfway between the stem and blossom ends) and the uncooked zone were carefully measured with a metric scale. The figure in the tables was calculated from these measurements. It is therefore the percentage of penetration at the thickest part of the fruit. A study of the data on penetration does not reveal any instification for the confidence usually placed in the test by sulfur house operators. Of the forty-five unhlanched samples dried at Merced, ten showing a high penetration (91 to 100 per cent) retained an average of 2642 p. p. m. of sulfur dioxide and had a grade of 76. Five samples originally showed a penetration of 81 to 90 per cent, retained 2735 p. p. rn. of SUIfur dioxide, and were graded at an average of 78. The nine samples showing a penetration of 71 to 80 per cent in the freshly sulfured fruit retained 2663 p. p. m. of sulfur dioxide and were graded a t an average of 78. There were twenty-
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INDUSTRIAI. AVI>
ISUG I N
one sarnples having penetration below 71 per cent; these retained 2202 p. p. m. of sulfur dioxide aud had a grade of 78. The unblanched samples a t flollister, thirty-six in number, likewise showed no general trend. Those having a pnetration ovcr 90 per ceut (nine samples) coutaiiied after drying an average of 1618 p. $1. 111. sulfur dioxide, with an average grade of 78; tliose having a penetration of 81 to 90 per cent (ten samples) oontaincd 1323 11. p. in. sulfur dioxide and were graded a t T6. The 71 to 80 per cent lot (tlirec samples only) had 1170 p. p. ni. sulfur dioxide and graded 77. The samples below 71 per ccnt penetration (fourteen) carried I186 11. p. in. sulfur dioxide and gradcd 79. The data given in Table V are riot couchisivc evideuce of correlation between penetration and tlie length of the sulfur period, or betwein penetration and the concentration of tlie gas i n t,lic sulfuring calbinetn. While it is true that tire greatest yeuetrations in the utiblanched saurples resulted from a 5-110nr sulfuring period arid a 20 per cent concentration, it is evident that where the number of samples was large enough to overcome inequalities in the fruit, no great difference is shown. In the esse of the thirty samples sulfurcd for 2 hours and the twenty-eight sulfured For 3 hours, the average penetration was about the same. Likewise little differenceis apparent between samples subjected to concentrations of 2, 3, and 5 per cent sulfur dioxide in the sulfuring cabinets. Tho same lack of correlation exists in tlie samples which were blanched. It would seem t.herefore that long exposure to sulfur dioxide or exposure to high concentrations probably resulted in a thorough penetration, but, where the exposure was normal as to time and concentration, the penetration does not vary greatly.
E
1:. I1 I N G
c I1 E M I S T I1 Y
Vol. 25,
No. 12
for the seasuns at Merced and llollister do not overlap sufficiently.
C"WN. "Y 80s
70
.. I
2 1 5 10 16
20
2 15 80 28
7
..
as
33 17 I 1
1
84
io
64
75 76
96
is
76 75
xa
26
24 8 3 2 16 24 12 3
88 9'1
85 69 69 90 100 62 73 71 s4
".
Ob
90
CoxcLusro.vs
SU far as the results of this investigation show, blaucliing
as a pretrcatmont for apricots intended for drying does not give satisfactory results. It does not improve the quality of the dried Fruit or affect the quantity of sulfur dioxide that is retained. While dehydration has some advantage over sun-drying, results did not show that the fruit retained less sulEur dioxide or was of better grade. Exposing the fruit to tlie sun belore dehydrating gave it a color more like that of sun-dried fruit and would probably overcome the objections on the part of the trade to the unusual color of the dehydrated fruit. The results do not show any material advantage in drying in the shnde, and the process requires more time and therefore more drying trays. Exposure to the sun for 2 days and EFFECT OB Exvinoxnim-r ON SULWUR DIaxxm I~E'PEENTION then drying in the shade did not result in material advautage. Axn GIIADI'I This method is not greatly different from that used in the inTables I aud II show that there is a great difference in t.erior valleys of California, but it is not practical in the coastal the sulfur dioxide retention between fruit dried at Merced areas where the sky is often overcast and the temperature and at IIollistcr. The dried product from the former district moderate. The extent of the penetration of sulfur dioxide shown hy retains much liiglier quantit.ies of sulfur dioxide. Tlie onblanched, sun-dried Merced fruit (nineteen samplcs) average freshly sulfured fruit is not a satisfactory guide for estimating 2533 p. p. m. of sulfur dioxide, and tliose from Hollister either tlie arnoirrit of sulfur dioxide which will be retained in the dried fruit or its grade. (tventy-nine samples) 1492 p. p. m. of sulfur dioxide. Just why this difference exists is hasd to say. It may be ~ J I T B J I A T I J ICITED ~~ inherent in the fruit; it may be the result of the markedly (1) Ciiaco, E. M.,Churah, 0. G., and Sorber, U . G., IN". Eso. different drying conditions. Unfortunately it is not satisC ~ E M 22, . , 1317-20 (1930). factory to transport the fruit from one district to the other (2) Lyon, A. V.. J . Cozincil Sci. Ind. Rcsaarch, 3, No. 3 , 161-6 (l'i30) and dry it. In order to stand transportation, the fruit would have to he picked before it is at tho uptimum stage for drying. ( 3 ) Nichols, P. F., snrl Christie, '4. W . , Cdif. Agr. Eayt. Sta., B i d . 485 (IRaO). Further, it would he irnpossible to obtain strictly comparable samples sulfured in the same house and dried a t the same time,
Ponariro CELOMNECELLWSE PUNT AT SANTIAGO DE CHILE From left t a right: water settling plant, paver house. cell room. brine T O O I ~ .salt atorage, ~ellulasechemical se~tion.and oellulosa meohanma1 motion
