December, 1931
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
peratures, some of the results being shown graphically in Figure 2. It is seen that for various combinations of fuel, temperature, and humidity, the difference in gross and net heating values per kilogram of water formed may be anything from 0 to 595 Gal. per kg. (0 to 1070 B. t. u. per pound). Thermodynamic Proof of Difference
In making the foregoing computations it was observed that the difference between gross and net heating values, at constant pressure, per pound of water vapor condensed was equal to the latent heat of water a t the final temperature. The proof that this is true is as follows: It has already been shown that the difference b e t w e e n HYPOTK f TICA gross and net heating values is equal to the difference between the decrease in thermodynamic potential, i, for the actual path and the decrease for the hypothetical path. In the actual I 1 cooling piocess the water vapor EKrQnpv becomes saturated a t A (FigFigure 3-T-E Diagram for Water Vapor ure 3). An infinitesimal drop in temperature will cause an infinitesimal mass of vapor to condense and in so doing move across the diagram to D. Further cooling will cause more vapor to condense and cause the liquid already a t D to be cooled. The f i s t particle cooling will follow the path A-D-C; the last particle will follow the path B-C. However, since i is a point function di = i n A- i’, regardless of the path. For the purely hypothetical process of cooling the vapor from t, to tl without condensing, which is a constant-pressure process, any path may be drawn. However, the specific
1421
heat of saturated vapor at constant pressure for this range is about constant, and the decrease in i will be equal to dQ = di = cP ( t c
- ti)
since dQ = d i for a constant-pressure process. It remains to be proved that the end of the hypothetical path is a t B. The water vapor a t B is at a low pressure corresponding to the temperature t l , whereas at the end of the hypothetical path the pressure corresponds to that at t,. However, the product of PV for both cases is practically the same, owing to the low pressures involved, which makes the value of i the same and fixes the end of the hypothetical path a t B. Then since the d i , following any path between two points, must be the same,
- j’,
=
cp
(tc
- tl)
+
TI
when r is the latent heat a t tl, and also represents di from B to C. Rearranging the expression, we have (;‘A
- i’c) -
c p (tc
-
tl)
=
11
the left side being by definition the difference between the gross and net heating values. This has been checked and found true for various conditions, so that the following general rule can be accepted: The difference between the gross and net heating values of a fuel burned a t constant atmospheric pressure is equal to the weight of water vapor actually condensed multiplied by the latent heat of steam a t the initial temperature of the mixture, which is also the temperature to which the products are cooled. Literature Cited (1) Goodenough, ’‘Principles of Thermodynamics,” pp. 294-1, Henry Holt 1927. (2) Goodenough and Felbeck, Univ. of Ill. Eng. Expt. Sta., 138 (1924).
BuU. 180,
Chemical Composition of Avocado Seed’ LeRoy S. Weatherby and D. Glenn Sorber CHEMICAL LABORATORY, UNIVERSITY OF SOUTHERN CALIFORNIA, Los ANGELES.CALIF.
Quantitative determinations have been made of the Very early in the history of R E C E N T years the composition of the seed of the avocado (both Mexican organic chemistry, Avequin large increase of avocado production and the rapid and Fuerte varieties), including moisture, ash, acidity, (9)in 1831 and Melsens (8)in growth of the industry have nitrogen, protein, reducing sugars, sucrose, starch, 1839 found avocado seed to pentosans, crude fiber, and ether extract. s t i m u l a t e d search for bybe the source of d - p e r s e i t . a-d-Mannoheptite was prepared from the seed and products to utilize the culls. So far as is known, no mention Avocado dehydration, presidentified. was made of any of the other A flour consisting largely of starch was prepared and ervation in freezing storage, constituents until 1920 when identified as amylum. c a n n i n g , use in ice cream, a report (9) of various oilcocktail, m a y o n n a i s e , and yielding seeds was made by sandwich spreads have been investigated (4). Methods of ex- the food-testing laboratory of the Surinam. This report traction and refining, and possible uses of the oil are being states that the seed of Persea gratissima contains only 8 per studied.2 All of these, however, have to do with the pulp, cent fat and 2 per cent saponin, to which the poisonous charwhile the seed, comprising from 8 to 25 per cent of the fruit, acter is ascribed. Jamieson et al, (7) found but 2.2 per cent apparently has never been considered. I n attacking the oil in an air-dried crushed sample. problem of preparing by-products from the seed, it was conQuantitative Determinations sidered that a knowledge of the chemical composition would properly serve as a basis. The seeds available for the work here reported were from 1 Received JUIY16, 1931. Presented before the Intersectional Meetvarieties Of Persea drymifolia Of the Mexican race of horticuling of the American Chemical Society, in conjunction with the National ture, and the Fuerte was classed as a hybrid of p. drymifolia Meeting of the American Association for the Advancement of Science, and p. americana of the ~ ~race (11). ~The varie- t Pasadena, Calif., June 19, 1931. ties Of these two races are not separated into two 2 W o r k on the oil is being carried on in the laboratories of the University of Southern California. species, as some authorities list them all as belonging to P
I
~
INDUSTIZIAL AiVD E N @'NEERING CHEMISTRY
1422
omerieana,also known by some horticulturists as P. grutissiniu GIirtn (10). After removing tlie outer hard brown coats, which were discarded, the large white seeds were passed through a Russwin food chopper three times, using a nut butter cutter. The material was then thoroughly mixed, and portions for the various determinations weighed out in duplicate. The methods of analysis of the Association of Official Agricultural Chemists ( 1 ) were used for all quantitative work. Most of the methods selectcd were from those giveii for the analysis of feeding stuffs, as the ground material seemed to resemble this group more than any other. Ether extract was determined by niearis of tho ofiicial direct method, extractiiigin a Sorhlet for 113hours. c
Val. 23, No. 12
referred to Avequin (2). This was not verified, as only the determination of total acid soluble in cold water, as directed in thetentativemethod{Z),wasfollowed. Tho acidity,calculated as the number of cubic centimeters of 1 N sodium hydroxide required to neutralize the water extract from 1 gram of seed, gave, for the Mexican varieties, an average of 0.30 cc. or 0.64 cc. reduced to moisture-free basis, and 0.32 ec. and 0.65 cc. (moisture-Freebasis) for the Fuerte. Table I is a summary of results that can be classed as purely quantitative composition data. Moirtuir. %
Tabie I-Composlrion of Avocado Seed MexienN VhRIBTIBS FUSRTB 53.61 52.14 51.36 50.56 1 24 2.98
... ...
1.34 2.70
0.33 0.92
... ...
0.39 0.79
2.38 5.72
... ...
2.43 4.95
..,
1.60 3.24
2.21 4.47
..
2.58 5.40
..
0.92 1.91
... ... ...
3.50 7.31
...
..
27.54 57.21
2 9 . 00 50.87 1.64 3.33
..
2.04 4.12
..
... ...
3.66 7.28
1.10 2.21
.. ..
2.15 4.50
Figure I-&Perself 01 Ir-d-MannOheptlfe from Avoeado Seed. 250 x
3.78 9.08
4.14 8.66
The results of the first weighing of the ether extract from the seeds of the Mexican varieties, calciilated to percentage, gave an average of 0.80. This decreased with successive drying periods until it reached 0.70 per cent. The second set of Mexicans showed irregular losses at first, as indicated by three weighings during the first 3.5 hours, whereas the loss was slight and uniform during the second drying period of 3.5 hours. The results, after drying for 7 hours, checked at 1.00 per cent. An addit.ional 20 hours in the oven a t 100' C . brought the percentage down to 0.82. The extract from the Fuerte seeds was esdimated a t 1.10 per cent, which an additiopal drying of 20 hours lowered to 1.00 per cent. This continued loss on drying seems to indicate that either the ether extract is somewhat volatile, or decomposition takes place a t this temperature. The extract was a light-brown sticky gummy mass not easily soluble in anhydrous ether, even though extract4 witti it. An attempt was made to secure its refractive index at different temperatures, but the results were far from satisfactory. No reading of any kind could be secured of the extract much below 35" C., whereas tlie oil from tlie piilp was liquid at ordinary temperature, and readings could he taken at 20" C. So far as t.hey have been compared, the ext,ract of the seed has none of the characteristics of tlie oil from the pulp. Others have assumed i t to he an oil or fat; as the report on the oil-yielding seeds of Dutch Guiana (ii), previously mentioned, says, the seeds contain 8 per cent fat and the fiesh of the fruit only 5 per cent fat. Jamieson et al. ( 7 ) ,who were working with Fuerte avocados, found that "the large seed of the frnit contains very little oil; an air-dried crushed sample of the seed contained only 2.2 per cent of oil." This checks very closely with the 2 and 2.21 per cent of extract obtained from the Fuerte seed, as will be noted in the summary of analytical data. No evidence is given, however, to support the assumption that the substance is an oil. Wehmer (12) listed malic acid as occurring in tile seed and
0.70 1.70
0.91 1.90
1.00 2.07
0.99 2.w
... ...
9.25 18.71
7.76 16.22 By the direct acid-hydrolysis method.
49.01
0.61 1.23
... ... ... ... ... ...
1.78 3.62
VAPIBTIB8
Tannin is present, as indicated by qualitative tests which Haas and Hill (G) have taken from Trimble. The water extract (washings from the starch determination of the Mexican varieties) gave, with ferric chloride, green color and precipitate; lime water, light pink precipitate, becoming red
Figwe 2-Avocado-Seed Granuies. 250
x
Starch
and brown; bromine water, yellow precipitate, becoming brown. Theae reactions, according to Trimhle, are characteristic of tannins containing 5Cb60 per cent carbon. This group includes tanning of osk hark, kino, canaigre ratanhia, and catechu. Investigations Relative to Composition and By-Products
Other kinds of investigations relative to cornpsition and by-products were carried on; while none of these solve the
... .., .
December. 1931
.. . ...... .
INDUSTRIAL A N D ENGINE8EING CHBiWIS'TR1'
problem of finding uses for the seed, they do give further insight into the nature of the material studied. In tho first set of determinations, ten seeds of the Mexican race (varieties of about average size) were selected. Thcy weighed 276.95 grams and their coats 6.12 grams or 2.22 per cent. The seeds have about the same consistency as chestnuts and can be chewed quite as easily. They have a very bitter astringent taste which roasting fails to destroy and which persists to some extent even after grinding aiid boiling. It is entirely removed, however, by extracting with 80 per cent alcohol. Within a few minutes after the seeds were ground, they turned a reddish bronn (very likely due to an oxidase) and retained this color when dry. In trying to secure a ground sample without this color, a portion of it was allowed to drop direc.tly from the chopper into a saturated salt solution. This remained white as long as it was below the surface of the solution, but as soon as it was exposed to the air to dry, the color appeared even after having been in the solution for days.
Fiewe 3-Avollado-Seed Starch Grant81 with Crosaed Nichols Prisms. 250 x
1423
The precipitate examined under the rnicroscope wits found to be made up of fine needle-like crystals, some of them arranging themselves in fan-shaped masses. When crystallized on a microscopic slide, they proved to be rhombic crystals, crystallizing in tufts usually at 90" to each other. Thefirst melting point obtained was 184" C. and, after one recrystallieation, was increased to 187" C. The crystals proved to be rl-perseit or ad-mannoheptite, a heptahydroxy alcohol first found by Avequin (Z) in 1831 in avocado seed (Figure 1). The optical rotation of 0.8 gram of the material of the first crystallization in 10 cc. of saturated borax solution in a I-dm. tube gave, as an average of six readings, +1.18" Ventzke sugar scale (corrected), or +0.41° angular rotation D. I n discussing the identity of d-manno1:eptit.e and perseit, R r o m e (3) says that Fischer and Passmore found the rotation of syntlietic d-mannoheptite to be +0.3S0 (0.4 gram of the substance in 5 cc. saturated borax solution in a 1-dm. tube), and natural perseit 0.39'. The brown extract remaining after the perseit crystals vere filtered out was coneentrated by distilling off the alcohol to a low point and continuing evaporation in an evaporation dish on the steam bath. When nearly a11 the alcohol had been removed, a thick sticky gummy dark-brown mass floated on the remaining water. This was collected and found to be difficultly soluble in water. I t possessed a very bitter astringent taste and formed a gummy coating on the tongne and teeth, which persisted for some time. Some of the ground-seed material, prepared in the same way as for analysis, was spread out on large sheets of paper and dricd. It contained a considerable portion of very fine lightbrown powder. This Aour was separated by sifting through a sieve of 100 mesh. The flour was found by examination under a microscope to consist largely of pcar-shaped starch grains, whicii gave the characteristic cross with polarized light and was turned blue by iodine, thus identifying it as common starch, amylum (Figures 2 and 3). Couclusions
During grinding and until dry, the seed material uf the Mexicans gave off a strong anise-like odor. I n the Fuerte this was much fainter. The leaves and bark of the trees possess the same odor. According to Popeiioe (11) this odor in the leaves is a distinguishing characteristic between P.dry9nijdiu (Mexican) and P. ammicana (Guatemalan). It occurs in the former but not the latter. Gildemeister and Hoffmann ( 5 ) describe this anise-like odor and the oil obtained from both the leaves and b a r k "In addition to small amounts of anethole, methglchicol =%Is found as its principle constituent, the first known natural occurrence of this substance. The presence of methylchavicol was established by its conversion into anethole and oxidation to homoanisic acid."
Avocado seed is made up largely of water, starch, sugar, protein, with but a small amount of crude fiber. There is a possibility of its use as a food product or feeding stuff,though the small amount of bitter-astringcnt principle present might have to be rcmoved. Perseit might figure as a by-product if a use for it could be found. There remains in the neighborhood of 16 to 18 per cent material (moisture-free basis) to be determined quantitatively. This includes perseit, tanning, pectic substances, gums, and possibly glucosides, a bitter principle, and other unidentified compounds.
Two hundred grams of the ground seeds were steam-distilled with water. The distillate, caught in an oil bottle, possessed
Literature Cited (1) Asrodation
give rise to the anise-like odor of the &ds, since they ha-& been found in both the bark and leaves, and since the same odor is common to all three. Nearly 2 kg. of seeds were ground in the same manner as for analysis, air-dried. and placed into two cloth bags that fitted into l.&liter beakers. Eighty per cent alcohol was poured over each and heated to boiling on a steam bath. The solution was then filtered into a Miter Erlenmeyer Bask which w a s placed on an electric hat date. and the alcohol was distilled back onto the bags in the beaker;. After this process was repeated once or twice, the flask full of the clear dark reddish brown extract was allowed to stand overnight, and in some cases several days, after which, small round whjte masses of crystals precipitated out. The precipitate was collected on a filter paper. washed two or three times with 80 per cent alcohol, and put aside to dry.
Official Agri~ultural Chemistts, Methods of Analydn,
. . (3) Brownr."A Handbook ofS,rgar Analysls,('Chapmao and Hall, London,
1913. (4) Cruen~and Harrold. Calif. Avocado Aasoc., Ann. ReDI., 1911, 34. ( 5 ) Gildemdsfei a d HoBmano, "The volatile oils." p. 478, Wlley, 1916. I B i Haas and Hill. "Introduction to the Chemistry of Plant Product%" p. 206, Longmirnr, 1913. (7) Jarnierun, Baughman.and Hann. Oil ond Pat Ind., 6, 202-7 (1928). ( 8 ) Melsm~,Ann. chim. oh%. IBS% 109. (9) O l i r n Veflen, No. 30. 387 (1820). (IO) Pope, Hawaii Agr. Expt. Sa., Bull. 61, 3 (1821). (11) Popenoe, "Maniial of Tropical sod Subtropical Fz'ruit~.1(Maemillan.
..
1920. (12) Wehmer, "Die PRanrenstto(fe;' Gustao-Fircher. Jena. 1911
