Jan., 1915
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
acid t o t h e ethereal solution of t h e unsaponifiedmatter in t h e separatory funnel before evaporation, stopper and shake vigorously. Draw off t h e aqueous layer and discard. Evaporate t h e ethereal solution, dry and weigh. Heat , t o boiling with 20 cc. alcohol, titrate with N / I Osodium hydroxide and phenolphthalein, running a blank on t h e alcohol. Multiply t h e corrected reading by 0.028. The result is grams f a t t y acids in t h e unsaponified matter. Subtract this from t h e unsaponified matter. The amount of f a t t y acids dissolved in t h e ethereal solution of unsaponified matter is, on a n average, 16 mg. for substances very low in unsaponified matter and this figure may be used if very accurate results are not desired. The amount of f a t t y acids in unsaponified fractions from samples containing 2 j per cent or more of unsaponified may be disregarded. It amounts t o about 2 mg. on a n average and is balanced by a corresponding amount of unsaponified matter in t h e soap solution. The results on a number of ether extracts from plant and animal products are given in Table I , together with results by the method of Fraps and Rather’ (Digestion Method). TABLEI-UNSAPONIBIEDMATTERIN ETHEREXTRACTS METHOD PRECIPITATION DIGESTION Percentage of Extract 1 Wheat shorts . . . . . . . . . . . . . . . . . . . . 6 2 Corn chops 3 Cottonseed
NO.
5 6
Milo maize chops.. . . . . . . . . Cold pressed cottonseed.. . .
9 Red rice ......................... 10 Wheat bran.. . . . 11 Wheat shorts.. . . 12 Rice polish.. . . . . 13 Tobasa grass. . . . . 14 Sheep excrement f 15 Prairie h a y . . . . . .
Mothbean h a y . . . . . . . . . . . . . . . . . . . Excrement from No. 20.... Excrement from No. 2 2 . . .. Average concentrates.. . . . . . . . . Average, hays and excrements.
0.23 0.16 0.47 0.60 0.21
0.29
9 6 6
0.5
17 Excrement from No. 15 . . . . . . . . . . . 59 18 Excrement from No. 16 . . . . . . . . . . . 74 19 Sudan straw.. . . . . . . . . . . 22 23 24
.
Sample .Extract Sample
0.26 0.29 0.15 0.25 0.17 0.51 0.56 0.70 0.84 0.55 1.68 1.41 0.55 0.49 1.09
43 61 66
5
53
0.66 1.08 1.99 0.30
0.97
6 6
2
2 4 2 17
0.23 0.29 0.28 0.18 0.13 0.16
..
9 4 3 0.5 36 47 46 36 63 69 30 32 69 47 45 58 5 50
0.07
0.19 0.33 0.50 1.05 0.53 1.78 1.32 0.43 0.58 1.18 0.73 0.80 1.76 0.22 0.92
The results are expressed in percentage of extract and in percentage of sample. The digestion method, as already reported12was devised because t h e ordinary methods for the removal of unsaponified material from ether extracts very rich in t h a t substance proved inadequate. The method is very long, b u t i t gave satisfactory results with hays and fodders. On applying i t t o extracts consisting almost entirely of fats, t h e method was found t o be very tedious. The precipitation method described herein was found t o be equally as applicable t o extracts rich in f a t as t o those poor in fat. It is a very rapid method and the process is not attended with any’difficulty. The results obtained by this method were, as a rule, about t h e same as by t h e digestion method. The ether extracts of the concentrated feed-stuffs examined contained an average of 5 per cent unsaponifiable matter in percentage of extract and 0.30 per cent i n percentage of sample. The error introduced by estimating this material as f a t amounts t o 0.50 per 1
Texas Exp. Sta., Bull. 160.
9 LOC.
Cil.
35
cent (on sample) or more in t h e cottonseed meal, rice bran and rice polish. With t h e hays and excrements t h e great need of a more reliable method for t h e estimation of fats is shown by the amount of unsaponifiable matter obtained. This varied, in t h e samples examined, from 2 7 t o 74 per cent of t h e extract and from 0.49 t o 1.99 per cent of t h e sample. These results confirm those previously reported from this laboratory. The precipitation method proposed in this article is believed t o be very rapid and accurate, and t o furnish a very complete separation of the unsaponified matter from the saponified material in ether extracts, fats, oils and waxes. SUMMARY
A method for t h e removal of unsaponifiable matter from ether extracts has been devised, which is applicable t o materials both rich and poor in unsaponifiable matter. The method is believed t o have several points of superiority over others which have been proposed. TEXASEXPERIMENT STATION TEXAS COLLEGE STATION,
DETERMINATION OF FORMIC ACID IN KETCHUP By C. A. PETERSAND I,. P. HOWARD Received October 24, 1914
This work was undertaken t o find out whether formic acid can be determined readily and quantitatively, if present in ordinary ketchup. The process in brief consisted in passing steam under pressure through a sample of ketchup in a flask, in allowing t h e material carried from t h e ketchup t o be i n contact with a suspension of calcium carbonate in a second flask, and in determining t h e soluble formate in t h e filtrate from the calcium carbonate suspension. The ketchup used was a sample of “Blue Label” purchased a t a local store, said t o contain 0.1per cent of sodium benzoate,‘ t o which formic acid was added as desired. The method for t h e estimation of t h e formic acid was t h e gravimetric method described by Fincke.2 To obtain steam for nearly all t h e work, a connection was made with a heating radiator. To assure intimate mixing of t h e distillate in t h e second flask with t h e suspension of calcium carbonate, the hydra-headed tube, described by S t o l ~ e n b e r g ,was ~ used except t h a t the tube had only six openings, whereas Stolzenberg specifies eight. The openings were of 0 . j to 1.0 mm. in diameter. For both flasks we used long neck joo cc. Kjeldahl’s, those with wide openings being selected t o admit t h e variously bent tubes. In a few distillations, where t h e steam supply was taken a t some distance from its source, the condensation of water in t h e flask containing ketchup was so great t h a t a third flask had t o be placed between the steam supply and t h e flask containing t h e ketchup t o catch t h e condensed water. Some preliminary experiments were necessary t o 1 Zeit. Nahr. Genussm., 22 (1911), 98. benzoic acid does not reduce mercuric chlorid. 2 Zeit.Nahr. Genussm, 21 (1911). 5. I Chem. Z t g . , 32 (1908). 770.
Fincke here states that
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
36
ascertain t h e conditions under which the determination could be carried out. T o see if t h e steam or reagents used contained substances t h a t would reduce mercuric chloride, steam was passed through the apparatus for one a n d one-half hours until 1000 cc. of distillate had collected. The filtrate from t h e calcium carbonate suspension was evaporated t o a small volume, a n d allowed t o act on mercuric chloride with t h e addition of a few grams of sodium chloride and sodium acetate (the latter t o neutralize the hydrochloric acid formed during t h e reaction). After eliminating several samples of acetate and acetic acid, which contained considerable amounts of reducing substances-Finckel states t h a t most acetic acid contains formic acid-the amounts of reduced mercurous chloride corresponded t o only 0 . 2 t o 0.4 mg. of formic acid, a n amount which was accepted as a constant error in the process with the reagents a t hand. Experimentation with various amounts of ketchup i n t h e first 500 cc. Kjeldahl flask established t h e fact t h a t 40 g. of ordinary ketchup in I O O cc. of water could be subjected t o a vigorous action of steam without serious danger of spattering. Inclining t h e flask a t a n angle of 4 5 O , keeping t h e outlet tube a t t h e top, reduced this danger. A piece of paraffin, as large as half a pea, also helped t o reduce the frothing. Larger amounts of ketchup t h a n 40 g. in IO? cc. of water made spattering a difficulty, some colored material being carried over i n t o t h e suspension of calcium carbonate. The time necessary t o volatilize formic acid in this apparatus was next subjected t o test. An amount of formic acid equal t o 0.0405 g. was placed in I O O cc. of water in t h e first Kjeldahl flask ultimately intended t o receive ketchup. One gram of precipitated calcium xarbonate in I O O cc. of water was placed in the second flask a n d steam passed through for various lengths of time, flames under each flask being adjusted so t h a t t h e volumes remained constant. After 50 minutes, 80 per cent of the formic acid in the first flask was held by t h e calcium carbonate in t h e second flask, a n d in one a n d one-half hours 91.6 per cent of the formic acid was held by t h e suspension. Steam was next passed through 41 g. samples of ketchup acidulated with 0.5 g. of tartaric acid t o determine if material capable of reducing mercuric chloride would be caught b y t h e suspension. The filtrates from t h e calcium carbonate gave a t first up t o 6 mg. of suspended matter after treatment with mercuric chloride. It was evident a t a glance t h a t the light brown flocculent precipitate was not calomel. Filtering t h e solutions through paper before adding the mercuric chloride reduced t h e amount of the precipit a t e subsequently appearing t o 0.3 t o 0.8 mg. calculated as formic acid. The character of this precipit a t e was not investigated, a n d i t was considered t h a t t h e amounts of reducing substances volatilized from ketchup by steam a n d acting upon calcium carbonate, other t h a n the 0 . 2 to 0.4 mg. introduced in the reagents, were negligible. If new rubber stoppers are used i n the flasks during t h e reduction of t h e mercuric chloride t h e stoppers 1 LOC.
C i l . , p. 2.
Vol. 7 , No.
I
should be boiled in caustic soda t o remove t h e loosely adhering sulfur, some of which might otherwise be weighed as mercuric chloride. The d a t a collected in these preliminary experiments just described enabled us t o a d a p t the method of Fincke t o t h e determination of formic acid in ketchup. The reagents used a n d details of t h e process follow. REAGENTS-Mercuric chloride solution : I O O g. per liter containing 30 g. sodium chloride.' Sodium acetate: 300 g. per liter. Acetic acid a n d acetate should be free from formic acid. Tartaric acid: I O O g. per liter. PRocEss-About 40 g. of ketchup were weighed out and washed into a 500 cc. wide mouth, long neck KjeIdahl flask t o which was added 0.5 g. of tartaric acid. This flask was supported a t a n angle of 45' and steam passed through it for one and one-half hours. Volatile matter from the flask was forced through a Stolzenberg tube, adjusted in the second Kjeldahl flask of 500 cc. capacity, containing 1.0 g. of precipitated calcium carbonate. Material distilling from the calcium carbonate suspension passed through a Liebig condenser. T h e volume in both flasks was kept a t I O O cc. by regulation of t h e flame underneath. When 1000 cc. of distillate had been collected (which took one and one-half hours with our apparatus) t h e steam was shut off-it was found desirable t o insert a T-tube, closed.with a pinch-cock, in t h e system t o quickly adjust t h e pressure. The contents of t h e flask containing the calcium carbonate were then filtered and well washed with hot water, a n d t h e filt r a t e was evaporated on a steam b a t h t o a volume of 2 0 t o 50 cc. If a n y precipitate appeared in t h e liquid i t was filtered; otherwise i t was transferred i n t o a 300 cc. Erlenmeyer flask t o which j t o 2 0 cc. of mercuric chloride2 a n d 5 t o I O cc. of sodium acetate2 solutions were added. The flask was stoppered with clean rubber stoppers, carrying 2 feet of glass tubing t o act as air condensers and was inserted in t h e hot water of a steam bath. The larger rings of t h e bath were p u t over the flask, so t h a t all t h e liquid was under water a n d some of the air space above was not exposed t o steam. After two hours' heating the precipitate was filtered on weighed Gooch crucibles previously dried a t IOOO, and washed with hot water, alcohol a n d ether in the order named, dried a t I O O O for three-quarters of a n hour, cooled and weighed. The weight of calomel multiplied by 0.0975 gave t h e weight of formic acid.s Results obtained by this method are given in t h e following table: DISTILLATION OF FORMIC ACID IN KETCHUP -N. O-.
.. . . . . . .. . ..
1
2
3
0.0405 Formic acid used-grams.. . . . . . . . . . . , . , . _, 0.0405 0.0405 120 90 Time of distillation-minutes. . . . , . . . . . 80 Formic acid recovered from calcium carbon91.9 91.6 ate suspension-per c e n t . . , . , . . . . 89.5 SUMMARY
It is evident t h a t by applying the Fincke process, 1 Fincke states that sodium chloride prevents the formation of insoluble compounds between mercuric chloride and salicylic acid. 2 The amount of mercuric chloride is 15 times the amount of formic acid present, while 3 g. of sodium acetate are necessary when the largest amounts (125 mg.) of formic acid are present. 8 Z. Nahr. Cenussm., 26, 386.
Jan., 191j
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G G H E M I S T R Y
with t h e apparatusdescribed above, 9 1 t o 9 2 per cent of the total formic acid added t o ketchup can be collected in an hour and a half, when t h e amount of distillate t h a t has passed through the apparatus is about 1000 cc. Thanks are due Mr. H. C. Lythgoe, chemist of t h e State Board of Health Laboratory of Massachusetts, for the suggestion which led t o this work. DEPARTMENT OB GENERAL A N D AGRICULTURAL CHEMISTRY MASSACHUSETTS AGRICULTURAL COLLEGE,AMHERST
THE VOLUMETRIC FEHLING METHOD USING A NEW INDICATOR By A. M. BRECKLER Received October 21, 1914
The volumetric Fehling method has been looked on very unjustly as inaccurate and unreliable. An inspection of t h e work of A. W. Peters’ shows t h a t under t h e most carefully controlled conditions of t h e gravimetric method, the ability t o duplicate reducing sugar determinations is limited t o a n accuracy of about one part in 2 0 0 . His dextrose copper ratios fluctuate about a mean value of 0 . 5 2 2 in t h e range of 2 5 t o I O O mg. of dextrose. The highest value is 5 2 5 and t h e lowest is 5 2 0 , the value in each case being a mean of 4 t o 6 determinations. The work of Munson and Walker2 a t times shows departures from t h e average which are fully as great. I n seeking a method of reducing sugar estimation, therefore, an accuracy of one part in 2 0 0 is as great as can be expected. The method here described is dependent on a cons t a n t volume a t t h e close of t h e titration, a constant time of boiling, and the use of sodium monosulfide solution as indicator. DESCRIPTION OF METHOD
The Fehling solution used is made up as follows: A. FEHLING’S COPPER s o L U T I O N 3 - 3 4 . 6 3 g g. Of carefully selected crystals of pure copper sulfate dissolved i n water and diluted t o exactly 500 cc. B . FEHLING’S ALKALINE TARTRATE SOLUTIOK-I 73 g. of Rochelle salts and 50 g. of sodium hydroxide are dissolved in water and diluted t o exactly j o o cc. The solution of sodium monosulfide is made up by dissolving 4 g. of crystalline sodium: monosulfide in I O O cc. of water. It should be made fresh every day. The test is conducted in a test tube X 3 / 4 in. A wooden clamp for holding this tube should be provided. A spot tile with six or more cavities, a I O cc. pipette, some straight pipettes, and a burette for the sugar solution completes the outfit. To make a determination, I O cc. of the mixed Fehling solution are pipetted into the test tube. The sugar solution, which should contain between zoo and 400 mg. of dextrose or an amount of other sugar equivalent in reducing value t o these amounts, is then run in, starting with 8.5 cc. The solution is then boiled one minute, counting from the time a bubble of steam first traverses t h e entire length of liquid. After the addition of 8. j cc. and boiling, t h e color is noted. If = J .A . c. s.. 34, 928. Ibid., 38, 663. 3 Leach, “Food Inspection and Analysis,” p. 591. 2
37
t h e solution is very blue, t h e sugar solution may be added 2 cc. a t a time, boiling 1 5 seconds after each addition. When t h e solution in the tube is only a faint blue, a drop of it is added t o two drops of sulfide solution on t h e tile. The tile is given a slight rotary shake and the color of t h e spot noted. It will be seen t h a t the suspended cuprous oxide turns black and settles a t once, while the supernatant llquid turns a more or less intense yellow. The sugar solution is now added t o t h e test tube in smaller portions, depending on t h e intensity of t h e yellow coloration, boiling 1 5 seconds after each addition. It is usual in this laboratory t o use 0.4 cc. a t this point. As the color becomes fainter, less is added each time, until finally successive additions are only 0 . 1 cc. each. As soon as no color is perceived immediately upon t h e settling of the cuprous compound, t h e result is read from the burette and t h e mean of this reading and the previous one taken as t h e number of cubic centimeters required t o reduce the ten cc. taken. The experiment is then repeated, adding enough water t o make t h e final volume up t o 3 0 cc., and 97 t o 98 per cent of t h e sugar solution required in t h e previous trial. This is then boiled 1l/2 minutes and t h e exact amount adjusted, which can usually be done in two additions. This final determination should require from four t o six minutes from t h e time t h e solutions are mixed until the estimation is finished. It will rarely be found t h a t these t w o determinations differ more than I per cent in value from each other. The second determination is the one t o be used. When t h e approximate amount of sugar is known, as it is in most cases, t h e first approximation can be made much closer and the two titrations given equal weight.
.
NOTES O N T H E METHOD
The time of boiling after ‘/z minute seems t o play a comparatively unimportant part. I n a series of experiments 99 per cent of t h e sugar (dextrose) required t o reduce a solution was added and the mixture boiled different lengths of time. The amount required for complete reduction was the same whether the first portion was boiled ‘/2 minute or I ~ / Zminutes. Too protracted boiling, however, is undesirable on account of evaporation and exposure t o air. Hence the total time of boiling should be kept within 1 3 / ~ t o 2’/4 minutes. The desirability of a constant volume in the gravimetric method during the reduction is well known; preliminary experiments showed this plainly. Under the conditions of this method I O cc. of Fehling solution with a final volume of 5 0 cc. required as a mean of several determinations 4 9 . 3 mg. of dextrose for reduction; I O cc. with a final volume of 3 0 cc. required 47.6 mg. for reduction. By making a preliminary titration, bringing the volume up t o a constant amount, and adding most of the sugar a t once, its reducing values become constant. Even if the reducing values of the 2 or 3 per cent subsequently added vary 2 0 per cent, the results are still within the limits of the method. AS can be seen from t h e difference shown above, a variation of z or 3 cc. in t h e final volume may be con-
*
