300
ANALYTICAL EDITION
in working with samples of leafy vegetables, dried milk, mixed cattle foods, tankage, fish scrap, and commercial ground meat. Ground beef containing some fat has been successfully ashed without being previously dried. Using an oxygen speed of 1 liter per minute, a good iodine recovery was made by a simplified collecting train consisting of one condensing tube containing glass wool moistened with sodium bisulfite solution immersed in an ice bath, a Cottrell precipitator 30 cm. in length, and a single Milligan wash bottle containing caustic solution. Operating a t the low rate, the average sample is consumed at approximately 25 grams per hour. Although designed to make possible the ashing of samples with a simplified collecting train, the ashing bulb will operate equally well with trains capable of handling the products from a more rapid combustion. I n comparing the apparatus with others previously described, its chief advantage is in its smooth and governable operation. The burning of the sample being complete and controllable, little difficulty is encountered from the development of back pressure from the ignition of accumulated combustibles. It is therefore unnecessary to handle the rapid stream of gas that is usually recommended. It is possible to obtain satisfactory combustion without the usual application of heat from supplementary burners or coils outside or inside the apparatus. Heat-flow direction, distribution, and dissipation make special cooling devices, such as water-circulating coils, unnecessary either in the apparatus or about the feed mechanism. The behavior of the apparatus in this respect also makes it capable of prolonged use when constructed almost entirely of glass. The above-mentioned features, whose simplicity is readily recognizable by the experienced operator, are difficult to evaluate quantitatively in a procedure which is laborious a t
Vol. 4, No. 3
best. However, analysts have developed satisfactory technic using the ashing bulb in four or five trial runs. Since the ashing device is used in the preparation of the sample, recovery is important only as the total procedure is influenced by the device in question. It suffices to say that using the ashing bulb with collecting trains described by McClendon and Remington, the recovery of iodine is equivalent to that obtained by them. When compared with the McClendon and Remington ashing tubes, it is more convenient to clean on account of its size, shape, and lack of internal coils, and on account of the fact that no ash can fuse into the bulb as it sometimes does with glass or silica tubes. The bulbs have been used for approximately one hundred runs without becoming noticeably affected in their hotter portions, a considerably longer life than that of the ashing tube made of Pyrex, which must be used at temperatures approaching its softening point. 'These, in the hands of operators of some experience, are often in bad condition after five or six runs. The bulb is better in this respect than the more expensive silica tubes, which often crack after alkaline ash fuses into them, even when special precautions are taken. Experience has demonstrated that the smooth operation of the ashing process in this apparatus makes available dependable types of collection hitherto unutilized in analyzing commodities for iodine. LITERATURE CITED (1) McClendon, J . Biol. Chem., 60, 289 (1924). (2) McClendon and Remington, J . Am. Chem. Soc., 51, 394-9 (1928).
RECEIVED December 30, 1931. Presented before the Division of Agricultural and Food Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y.,August 31 t o September 4, 1931.
Determination of Reducing Sugars in Food Products Proposed Colorimetric Method University of Colorado, Boulder, Colo, CHARLESF. POEAND FRANK G. EDSON, INCE Lewis and Benedict (4) first announced their colorimetric method for the determination of reducing sugars, several methods have been proposed for the estimation of these sugars in blood and urine. In the field of food chemistry these colorimetric methods have been applied but little. The authors ( 7 ) , in testing the effect of some reducing sugars on certain organic nitro compounds, found several compounds which might form a basis for a reagent for the quantitative estimation of reducing sugars in food products. Among these sodium 2,4-dinitrophenolate appeared to be very satisfactory. The purpose of the investigation reported in this paper was to develop a reagent using this compound for the estimation of reducing sugars in food products. While experimenting with sodium 2,4-dinitrophenolate: many different combinations of this substance with alkalies and alkali carbonates were tried. To the above combinations were added Rochelle salt, phenol, and sodium bisulfite separately and then in various combinations. All of these reagents were tested for the development of color with dextrose. As a result, two different reagents have been sug-
S
gested, the first to be used when small amounts (1 to 10 per cent) of reducing sugars are present, and the second for larger amounts. Two reagents are suggested in order that the dilution factor may be eliminated as far as possible with the foods containing a large percentage of reducing sugars: 1.
2.
Sodium 2,44initrophenolate 8 grams Sodium hydroxide] 5 per cent 200 cc. 100 Phenol 2.5 grams Rochelle salt Distilled water, q. s. 1000 cc. Sodium 2,4dinitrophenolate 8 grams Sodium hydroxide] 5 per cent 200 cc. 100 grams Rochelle salt Distilled water, q. a. 1000 cc.
I n the above formulas the sodium 2,4-dinitrophenolate and phenol are dissolved in the sodium hydroxide solution. The Rochelle salt is dissolved in about 700 cc. of water. The solutions are mixed and diluted to 1 liter. The procedure used for the estimation of the reducing sugars may be stated as follows: A given amount of the food product containing the reducing sugars is weighed and the necessary dilution made. One cubic centimeter of this dilution
JuIy 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
is placed in a Folin-Wu sugar tube, and 3 cc. of the proper reagent (depending upon the amount of reducing sugar present) are added. The tube is heated in a beaker of boiling water for 6 minutes, then cooled in running water for 3 minutes, and finally diluted to the 25-cc. mark with cold distilled water. Then this solution is compared in a colorimeter with a standard made by treating a given amount of pure glucose in the same manner as the unknown. The side of the colorimeter containing the unknown is set a t 20, and the standard varied until the colors match. An average of five readings is taken and the percentage of the reducing sugars calculated.
301
Since reducing sugars in food products usually contain levulose, the reducing equivalent was determined for this sugar. With the proposed method, it was found to have exactly the same reducing power as dextrose. Frequently, when colors are developed by reducing sugars in alkaline solutions of organic nitro compounds, their intensities are either changed according to the length of the time of heating, or fade upon standing. Eight tubes, each containing the same amount of glucose, were heated with the reagents for varying lengths of time-namely, 5, 7, 10, 12, 15, 20, and 25 minutes. The results indicated that the time of heating up to 25 minutes caused no difference in the color produced. Subsequent work has shown in every case TABLEI. READINGS FOR 1 PER CENTGLUCOSE IN SOLUTIONthat 6 minutes is ample time for complete reduction to take WITH DIFFERENT AMOUNTS OF SUCROSE place. Similar experiments were conducted differing only in (Per cent sucrose) that the various tubes, after having been heated for 6 minutes, ATO AT5 A T ~ O A T 2 0 A ~ 3 0A ~ 4 0 A ~ 5 0A ~ 6 0 A ~ 7 0 were allowed to stand from 5 to 20 minutes immediately 19.8 2 0 . 0 20.0 20.0 20.0 2 0 . 2 20.0 1 9 . 8 20.0 after the dilution of their contents. No change in the color 20.2 19.8 2 0 . 2 19.8 2 0 . 2 19.8 19.8 19.8 2 0 . 2 2 0 . 3 19.9 20.0 20.1 2 0 . 1 2 0 . 2 2 0 . 0 20.0 20.0 was noted up to 20 minutes' standing. 19.8 20.0 20.0 19.8 19.8 20.0 20.0 2 0 . 0 2 0 . 0 19.8 2 0 . 0 19.9 2 0 . 2 20.0 2 0 . 0 1 9 . 9 20.1 20.2 The proposed colorimetric method was used to determine Av. 20.04 20.00 20.04 19.94 20.06 19.94 20.00 19.92 20.00 the reducing sugar in a number of food products. Table I1 gives the results for pure maple sirups, cane and maple With the ordinary sirups, jellies, jams, and fruit juices, sirups, and maple sugars. Table I11 includes the results the color present did not interfere with the accuracy of the when fruit juices, jams, and jellies were analyzed. Table method. I n products very high in coloring matter, such as IV gives the results of the analysis of milk for lactose. I n molasses, preliminary clarification was necessary. The use all of the food products, the reducing sugar was also estiof neutral lead acetate as directed in the Methods of Analysis mated by the official Munson and Walker method (6). of the Association of Official Agricultural Chemists (6) was satisfactory. This clarification could also be accomplished TABLE11. ANALYSISOF SIRUPS AND MAPLESUGAR FOR with alumina cream, fuller's earth, decolorizing carbons, REDUCING SUGARS and dry basic lead acetate without interfering with the acAUTHORS' MUNSON-WALKER FOODPRODUCT METHOD METHOD curacy of the method. % % Because of the fact that the percentage of reducing sugars Pure maple sirup 6.23 6.08 3.40 3.24 Pure maple sirup in the original food product is not known, readings are often Pure maple sirup 1.83 1.94 obtained which are not very close to the standard reading Pure maple sirup 6.62 6.58 2.56 Pure maple sirup 2.48 of 20. This brought up the question as to whether or not 2.29 2.22 Pure ma le airup Cane a n i maple sirup 2.22 2.03 the colorimetric method was accurate when these readings Cane and maple sirup 1.66 1.61 were rather far apart. Solutions were prepared containing Cane and maple sirup 2.20 2.12 Cane and maple sirup 4.82 4.65 glucose in varying amounts from 0.5 to 3 per cent. The 2.29 Cane and maple sjrup 2.22 Cane and maple sirup 1.16 1.05 color developed by these amounts was compared to a soluBeet molasses sirup 0.52 0.61 tion containing 1 per cent glucose. In each case, the corCane sugar sirup 1.42 1.31 1.22 1.21 Beet sugar sirup rect theoretical readings were obtained. These experiments 6.50 Maple sugar 6.49 Maple sugar 5.68 5.60 showed that with the proposed reagents, the intensity of the Maple sugar 5.72 5.66 color is directly proportional to the amount of glucose present. Cane and maple sugar 0.95 0.83 This is a distinct advantage, because it is difficult to have the standard and unknown always read exactly the same. TABLE111. ANALYSISOF FRUITPRODUCTS FOR REDUCING SUGARS According to Rothberg and Evans (8), this is not true for AUTHORS' MUNEON-WALKER t h e Folin and Wu method; and Folin and Denis (3) and FOODPRODUCT METHOD METHOD Bierman and Doan (2) state this is also the case with the % % picric acid method. Sumner (9), however, found with his Apple juice 9:60 9.-54 White grape juice 13.45 13.39 method that 1 mg. of glucose compared to 0.5 to 2 mg. of 9.00 Pineapp!e, juice 8.91 Orange juice 5.03 5.10 glucose without error. Benedict ( I ) made the same obser9.05 Loganberry juice 8.92 vations with his method, Grapefruit juice 30.87 30.92 Apple ielly 16.49 16.61 Many food products contain a large amount of sucrose Grape jelly 23.81 23.92 Raspberry jelly 17.12 16.96 and a small amount of reducing sugars. Therefore, a series Currant jelly 48.92 48.78 of experiments was conducted to determine whether or not Plum jam 48.90 48.80 Strawberry jam 48.88 48.81 a large amount of sucrose had any effect on the accurate estimation of the reducing sugars by the proposed method. TABLEIV. ANALYHS OF MILK FOR LACTOSE Solutions were prepared containing 1 per cent of glucose AUTHORS' MUNSON-WALKXIR with varying amounts of pure sucrose-namely, 10, 20, 30, MILK METHOD METHOD 40, 50, 60, and 70 per cent. A determination was made of % % each of these solutions by comparing the color developed Raw 4.63 4.60 4.80 4.74 Raw with a 1 per cent solution of pure glucose as the standard. Pasteurized 4.35 4.29 Pasteurized 4.73 4.68 'Table I gives the reading found in these determinations when the standard was set a t 20.0. As may be seen from the average reading given in Table From Tables 11, 111, and IV, we see that the proposed I, the different amounts of sucrose had no effect on the ac- method checks very closely with the Munson and Walker curacy of the determination of glucose by the proposed method. The latter, however, in some cases gives slightly method. lower results, but the proposed method has the advantage
ANALYTICAL EDITION
302
over the Munson and Walker method in that it is much more rapid. LITERATURE CITED (1) (2) (3) (4j
Vol. 4, No. 3
(5) Munson and Walker, “General Method,” Assoc. Official Agr. Chem., Methods of Analysis, p. 78 (1920,). (6) Munson and Walker, Ibid., p. 379 (1930). (7) Poe, C. F., and Edson, F. G., Univ. Colorado, Studies 18, 201 ii a m ~&”””,.
(8) Rothberg, V. E., and Evans, F. 9., J. B i d Chem., 58, 4 3 5 Benedict, S. R., J. Biol. Chem., 76, 457 (1928). (1923-24). Bierman, H. R., and Doan, F. J., J. Dairy Sci., 7, 381 (1924). (9) Sumner, J. B., Ibid., 62, 287 (1924). Folin. O., and Denis, W., J. Biol. Chem., 33, 521 (1918). Lewis, R. C., and Benediot, S. R., Ibid., 20, 61 (1915); Proc. SOC. RECEIVED Janurtry 22, 1932. Ezptl. Bid. Med., 11, 67 (1913-14).
Measurement of Surface Hardness of Cellulose Derivatives S. E. SHEPPARD AND J. J. SCHMITT, Eastman Kodak Company, Rochester, N. Y.
F
OR many purposes the surface hardness, including resistance to abrasion and indentation, of films and plastics formed from cellulose derivatives is of equal importance with the mechanical strength of the material in the mass. Various methods of measuring the hardness and resistance to abrasion have been suggested at one time or another. In this laboratory there has been developed and used for some time a method of measuring the resistance to scratching which gives quantitative results and which seems of interest as furnishing another criterion of the physical properties of cellulose derivatives. I A- POINT S-SLIDING WEIGHT L-LEVER ARM C- COUNTERPOISE P- PIVOT D-DRIVINO CAOLE
1-
R- RELEASE &STAGE
I
moving point starting from zero load, the load increasing steadily up to the desired limit. In the operation of the s c r a t c h dynamometer, t h e sample is placed in t h e holder a t A so that the face is parallel to the base and turned downward. The material is best used in the form of thin, uniform films coated on glass although, w h e r e desired, coatings may be on metals or other r i g i d s u p p o r t s , or skived plaques of sufficient rigidity may be taken. Point A is fitted on a slide weight, X,which is drawn from its initial p o s i t i o n of zero l o a d (in I’ counterpoise) by the weight C back toward pivot, P . Traction is effected by the cable D running over a pulley F~~~~~ 2. sHAPE d r i v e n by a constant-speed motor. OF POINTS Movement is started by tKe release R, and a scratch is produced by the point operated under d.W a load increasing according to the equation: L = b-d
a
*.Graduated Arc B P llluminafinp Telescope C mtarner D *Platform E.EyepiQ~e F-Clamps G = T r a c k f a r C ’a r r i w
1
.
FIGURE 1. DIAGRAM OF SCRATCH DYNAMOMETER
The comparison of the findings obtained by this apparatus with the results of direct abrasion tests comes properly under the subject of testing materials, particularly the testing of paints, lacquers, and varnishes, and this phase of the work will be discussed in another place. APPARATUS AND METHODS OF MEASUREMENT The apparatus used consists essentially of two instruments. One of these is a scratch dynamometer and the other a scratchobserving instrument. Scratch dynamometers may be divided into two types: (1) a series of scratches is produced, each made with a constant load, the load increasing from one scratch to another; (2) a single scratch is made under a load increasing at a definite rate. Instruments have been designed for both purposes, but most of the work described here was carried out with an instrument of the second type, whose construction is shown in,Figure 1. The apparatus is devised to produce a scratch by a
H Rack k Pinion I -Shaft
-
J -Lens L = Lamphouse R Reflector 5-Scale tn Centimeters M = A x I S of Microscope for Reading: Scratch Wtdlh TOP VIOW
U
U From View
Side View
FIGURE 3. DIAGRAM OF ILLUMINATOR FOR SCRATCH TESTER,
