416
T H E JOI;'R,VAL O F I - V D C S T R I A L AilrD E - V G I S E E R I X G C H E i M I S T R Y
precipitate was dried a t 95' and then at IO^'. The additional loss in weight a t the higher temperature was usually about 3 or 4 mg.. or 1.j per cent. The following results were obtained with 0 . 2 j - g . portions of gum: R E S C L T OBTAIKED S BY T H E A m r o m ~COPPERSULFATE METHOD SERIES A B C D Percentage of gum f o u n d . . 96.6 100. I 100.4 101.6 98.0 99.0 101.2 102.8 96.9 98.3 99.1 103.3 98.4 99.3 99.7 ... 96.7 100,i 98.8 ...
...........
Averages. ...................... 97.3 General a v e r a g e . . . . . . . . . . . . . . . . .9 9 . 5
99,s
99.9
102.6
I t is evident from a n inspection of the figures t h a t the method as finally modified is capable of giving results as accurate as could be expected. It is realized, ho\Tever. t h a t much work could yet be done upon mixtures of gum arabic with ghatti. dextrin. etc.. as well as upon mucilages of known composition. A few preliminary determinations, made while Fehling's solution was still being experimented with. indicate t h a t dextrin and ghatti tend t o be carried down with g u m arabic. At t h e same time a sample of mucilage mas prepared according t o the formula in the U. S. Pharmacopoeia; from this the gum vias precipitated with strong alcohol. dried and analyzed. The net gum found in four determinations was about 91 per cent. This low result may be due t o a fault of the method or t o partial hydrolysis of the gum. The publication of the results so far obtained has been so long delayed, and the opportunity t o complete the v o r k seems so remote, t h a t i t has been decided t o present this paper without furiher postponement. S T U 11A R Y
T h e most characteristic qualitative test for gum arabic is the precipitate formed with basic lead acetate. AIixtures of copper sulfate and sodium hydroxide, and of neutral ferric chloride and alcohol are of value as confirmatory tests. A summary of t h e more important methods t h a t have been proposed for the estimation of gum arabic is followed b y a description of the steps t h a t led the authors t o the use of alcoholic copper acetate-ammonia solution for this determination. BUREACOF STANDARDS, WASHINGTON
THE OCCURRENCE OF AZELAIC ACID AS A PRODUCT OF THE SPONTANEOUS OXIDATION OF FATS B y BEN H. P\-ICOLET
.ISD
LEONARD M. LIDDLE
Received October 13, 1915
I t is very well known t h a t azelaic acid, COOH(CH2)?COOH, is a normal product of the artificial oxidation of various unsaturated f a t t y acids. All of t h e common eighteen-carbon unsaturated f a t t y acids (oleic, linolic. linolenic) very probably have a double bond located between the ninth and tenth carbons, that is, in the center of the carbon chain. I t is further pretty well established that neither linolic nor linolenic acid has a double bond between this position and the carboxyl group. Consequently it was t o be expected, and it has been found, t h a t azelaic acid results from t h e oxidation of these acids with alkaline permanganate, from t h e decomposition of their ozonides, and from the breaking down of their nitrogen peroxide addition products.
1-01. 8, S o . 5
I t seemed probable t o us t h a t the difference between artificial and natural oxidation would be one of d e gree. or perhaps only one of time, rather t h a n a coniplete difference in kind. In this case azelaic acid should be a product, and perhaps an important p r o d uct, in t h e development of rancidity, and particularly in its more advanced stages. Griigerl exposed some oils t o air on filter paper and examined them after four years. One of the products isolated was an impure azelaic acid, supposed t o he mixed with some suberic acid. Scala2 isolated from rancid material a number of f a t t y acids ranging from formic t o pelargonic, and also most of the corresponding aldehydes. He obtained one fraction of nonvolatile, water-soluble acids, which yielded crystals t h a t he suspected of being azelaic acid. Here apparently the matter rests to-day. I t is the purpose of the present note t o call attention to the occurrence in very highly rancid cottonseed oils of amounts as high as I O per cent of azelaic acid or a glyceride of this acid. The glyceride, whose presence is indicated, would belong t o a type heretofore unknown. Certain grades of fuller's earth are largely used in The oil rethe bleaching of refined cottonseed oil. maining absorbed in t h e earth after filtering and pressing! is in a n ideal condition for oxidation by air. I n fact the oil-soaked clay, in large scale work, frequently becomes heated t o the ignition point b y simply standing in contact with air. The oil from a specimen of earth t h a t had been used t o bleach cottonseed oil. and had since been kept for a year and a half without any effort t o protect it from t h e air, was extracted for examination. From IOO g. of clay, low-boiling petroleum ether extracted only 4 g; of oil. H o t alcohol extracted z j g. The characteristics of the oils from these two extracts are given below. EXTRACT Ether Amount of Extract (grams). . . . . . . . . . . . . . . . . . . . . . . . . 4.0 Acid No. (mg. KOH per g . oil), . . . . . . . . . . . . . . . . . . . . . . 145.4 Saponification N o . (mg. KOH per g . oil saponified). . . . . 282 . O Volatile Acids ( m g . KOW t o t i t r a t e steam-volatile acids f r o m 1 n.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46.0 Azelaic Acid (after saponification). . . . . . . . . . . . . . . . . . . 3%
Alcohol 25 . 0 144 8 260.0 35.0 10%
I n spite of its high acid number, the fraction extracted b y alcohol gave very little azelaic acid when extracted with hot water. I t was accordingly saponified, and the liberated f a t t y acids extracted with hot water. The water solution thus obtained was concentrated and g a r e in various fractions crystals of crude azelaic acid amounting t o about I O per cent of t h e fat saponified. This crude acid,' after two or three recrystallizations from water, showed the constants of pure azelaic acid. Found Melting p o i n t . . . . . . . . . . . . . . . . . . . . . . . . . . . 105' Equivalent weight (by t i t r a t i o n ) . . . . . . . . . . . 9 3 , 9
Pure azelaic acid 106O 94.0
Another sample of clay was extracted wholly with alcohol, and azelaic acid determined in the hot water extract both from the original material and from t h e acids obtained on saponification. Z . angew. Chem., 1889, 62; J . SOC.Chem. I n d . , 1889, 202. Slue. s f i e v . U E Y . i t a l . , 30 (1897). 613; Goza. chim. ital., 38, I (1908). 307; abstract Chem. Zenlr.. 1908, I. 2085. 1 2
M a y , 1916
T H E J O L;R N A L O F I S D U S T RI A L A X D E S G I S E E RI A-G C H E M I ST R Y
AZELAICACIDFOUND Before saponification After saponification 0 . 6 per cent 9 8 per cent
TOTAL 10 4 per cent
T h e crude acid had a n equivalent weight of 1 1 2 (calc. 94). A “shredded” (laundry) soap, which had developed 2 per cent of free acid on storage, was also worked u p for azelaic acid. A4bout 0 . j per cent ‘was found. T h e most remarkable thing about t h e oxidized cottonseed oil described is, however, not so much its abnormally high content of azelaic acid, as t h e form in which it was evidently present. Only about oneeighteenth of t h e total amount was present as free acid. T h e rest was in a form t h a t was insoluble in hot water, and became soluble only after saponification. T h e simplest assumption t o explain this behavior is t h a t the oxidation proceeded practically independently of hydrolysis, and thus gave rise t o the formation of glycerides of a hitherto unknown type, t h e semiglycerides of dibasic acids. T h e simplest one t h a t might be present here may be called trisemiazelain, C H P O C O(CHz);COOH C H O C O ( CH2) i C O O H
I CHzOCO ( C Hz) ;COOH T h e formation of mixed glycerides is of course not excluded. For instance, a-palmito diolein might be expected t o give a-palmito disemiazelain, CH20COCijH3i C H O C O (CH2)i C 0 0 H 1
C Hz0 C 0 ( C H2) ;.COO H . These results t e n d also t o justify t h e modern tendency t o regard rancidity of fats and oils as due not simply t o hydroiysis of t h e glycerides present, b u t a t least equally t o oxidation phenomena which are not necessarily dependent on such hydrolysis. I n the case described, it is evident t h a t the oxidation and hydrolysis were entirely independent processes. MELLOS INSTITUTE OF INDUSTRIAL RESEARCH UNIVERSITYOF PITTSBURGH ~
~~~~~~~~
JELLY INVESTIGATIONS By W.V. CRUESS
AND
J. B. MCNAIR
Received F e b r u a r y 14, 1916
A great deal of work has been done upon the chemistry of pectin and related bodies from both t h e purely scientific and practical standpoints. One of t h e best pieces of work has been done b y Th. von Fellenberg,‘ who seems t o have obtained more definite information upon t h e derivation of pectin from more complex compounds and upon its composition and chemical behavior t h a n any of t h e other investigators. Bigelow and Gore in Bull. 94 of the U. S. Dept. of -4gric., Bureau of Chemistry, gave a very good summary of the literature a t t h a t date. Miss N. E. Goldthwaite* studied jelly making largely from the practical side and dealt with such factors as effect of acid concen1
T h . von Fellenberg, M i l l . Lebensm. H y g . , 1914, 2 2 6 - 2 5 6 . X. E. Goldthwaite, THISJOURXAL,1 (1909) 333; 2 (19101, 457.
417
tration, character of acid, sugar concentration, character of sugar, temperature, pectin concentration a n d source of pectin, on quality of jelly. The experiments discussed in the following paper were undertaken t o throw light upon some of the practical phases of jelly making, rather than t o add anything t o t h e knowledge of t h e chemical composition of pectin. The main points investigated were: ( I ) Suitability of rarious fruits and vegetables for jelly making; ( 2 ) yields of jelly from various fruits; ( 3 ) clarification of jelly stock;’ (4) loss of fresh fruit flavor in jelly making by hydrolysis and evaporation and production of jellies without application of h e a t ; and ( j ) effect of sugar and acid concentrations on jelly. These topics will be discussed in t h e order given. S C I T A B I L I T Y O F \ - A R I O U S F R U I T S A X D V E G E T A B L E S FOR
1ELLY MAKISG
T o produce a jelly of the proper consistency when t h e liquid, obtained from the fruit by cooking with or without addition of water. is mixed with sugar in t h e proper proportion and cooked, the fruit must contain a good supply of both pectin and acid, or if not a large supply of pectin, a large amount of compounds t h a t break down into pectin at the temperature of boiling water. Some fruits were found t o contain sufficient acid and pectin while others lacked one or the ot,her of these necessary constituents. Where t h e fruits were low in acid, attempts were made t o produce jelly without additLon of acid and also with addition of citric acid or lemon juice. I n most cases the pectin was extracted in the usual way b y cutting the fruit into small pieces, adding water t o cover, boiling slowly until tender and expressing the hot juice b y pressing in a small fruit press or b y straining through a coarse cloth with gentle pressure. The solution so obtained was analyzed for Balling or Brix degree (per cent dissolved solids) and acidity, and if much more dilute t h a n the juice of the fresh fruit itself, was concentrated before being made into jelly. In making jelly, sugar was added in most cases a t t h e rate of I ’ / ~volumes of sugar t o I of solution. The mixture was then heated t o boiling and boiled down t o a boiling point of 1 0 4 - 1 0 j ~ C. or t o a concentration of 65-70 per cent dissolved solids. A t these concentrations, a jelly will form if the fruit is suited t o the purpose. The tests enumerated in Table I show t h a t cull blackberries, loganberries. Isabella grapes, Tokay grapes, oranges, lemons. and pomelos can be used as jelly stock without addition of acid. These fruits are produced in from moderate t o very large quantities in California. The culls resulting during picking and packing are in many instances a total loss. Of those noted, only t h e loganberry is used t o any great extent as jelly stock. Commercially, this fruit is boiled with a small amount of water, pressed and the juice is sterilized in j-gal. cans. I t is stored in these cans until needed. The liquid settles in t h e cans so t h a t when
’
By “jelly stock” is m e a n t t h e pectin-containing solution obtained from f r u i t or vegetables b y heating t h e material with or without addition of water, a n d pressing or straining t o separate liquid from pulp.
