January, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
also contain D, using this letter to designate the antirachitic factor? Hess’s experiments with spinach led the writers to expect a negative result, and this expectation was confirmed by experiment. Two groups of 30-day rats were selected. For a period of 45 days (controls) Sherman and Pappenheimer’s diet 84 (a rickets-producing diet) mas fed to one group. The second group also received Diet 84, but in addition 3 grams of peas daily. At the end of 45 days Diet 84 was replaced in both groups with Pappenheimer and Zucker’s Diet D (containing butter and casein). At the end of 55 days all rats were chloroformed, the blood analyzed for inorganic phosphate, and the rib junctions sectioned for rachitic symptoms. The rachitic diets were improved as growth stimuli by addition of peas, but rickets on these diets was quite as severe as in the controls. There is then no evidence of the
89
presence of vitamin D in green peas a t the level of intake used. However, since rachitic tendencies are enhanced by an increased rate of growth it is still possible that peas contain a small amount of vitamin D which was not manifest because of the demand created by the increased growth rate. Table 11-Effect
of Feeding Peas on Inorganic Phosphorus in Blood Chin nn .~. Oiin on -.-
SEX
Male Female Female
Diet 84 in 45 days Grams
Diet D Inorganic in 55 days phosphorus Grams Per cent Grou9 I-3 grams Deas daily 25 45 1.5 21 34 2.15 32 35 2.53
Group II-No Male Female Female
5 2 8
AUTOPSY Rickets Rickets Rickets
p u s , controls 5 0
7
2.14 3.01 2.14
Rickets Rickets Rickets
Jelly Strength of Pectin Jells’.’ By George L. Baker ~ 7 N l V E R S I T YO F
DELAWARE EXPERIMENT STATION, NEWARK, DEL.
Jelly strength as determined by the device described is shown to be influenced by several factors. When quantity of acid is considered, optimum points of jelly strength for pectin jellies follow Tarr’s 1 :2: 3 ratio for sulfuric, tartaric, and citric acids. However, the relative strength of the optimum points varies for the various acids. Also the pH of the optimum points varies slightly. A 69.44 per cent concentration of sugar produces the maximum jelly strength for a pectin jelly with 1 gram of pectin. With an increase in the concentration of pectin to 2 grams the optimum jelly strength appears at a 66.66 per cent concentration of sugar. A definite pectin-sugar ratio must be maintained for a certain pH in order to obtain a jelly of optimum strength. *
Jelly strength increases with an increase in pectin concentration. An optimum concentration of pectin at 0.97 per cent of the weight of finished jelly is apparent, beyond which cloudiness and an undesirable texture appears. Concentration of pectin in presence of acids before adding sugar is detrimental to jelly strength, while boiling after the addition of sugar has a negligible effect. Thus an increase in invert sugar has no harmful effect upon jelly strength. Decreasing the temperature of a jelly increases the jelly strength. A pectin jelly increases slightly in strength while standing for a period of time at a temperature of 22O
c.
. .. . . . . , , ., . .
EW physical measurements have been recorded on jellies made from fruit juices or pectin solutions. Past
F
methods of measuring jelly strength have been approximate, especially when the comparison was made by the “finger test”-the resistance of the jelly to the finger. The observations recorded have been accordingly in inaccurate terms, such as tender, good, tough, etc. The object of this paper is to describe a n apparatus which is especially adapted for measuring the strength of pectin jellies and to present a discussion of some of the factors of jelly strength as determined by the device. Jelly Strength Tester
After several of the testers for glues and gelatins on the market were tried, none was found to be satisfactory for measuring the strength of pectin jellies, because they are much more tender than glues or gelatins. Consequently, an instrument was devised for measuring jelly strength which proved satisfactory in this work and which is easily adapted to stronger jellies by using a heavier liquid in the manometer. The principle of the apparatus is simple; 1 Presented as a part of the Pectin Symposium before the joint session of the Divisions of Agricultural and Food Chemistry and Biological Cnemistry with the Division of Sugar Chemistry at the 70th Meeting of the American Chemical Society, Los Angeles, Calif., August 3 to 8, 1925. a Based on experiments of jelly strength factors performed at the Delaware Agricultural Experiment Station by I,. W. Tarr and G . I,. Baker. A complete account will be published later in bulletin form.
pressure is developed by the displacement of air by water in a bottle and transferred to a syringe chamber and manometer, forcing the syringe plunger into the jelly and recording the energy required on the manometer. This device is shown in Figure 1. A is the inlet for water to the 2-liter Woulfe bottle, B. Cis the outlet for air pressure developed. D is a 3-way stopcock, outlet E bringing the system to equilibrium, outlet F transferring the pressure to manometer G (30-cc. bulb) and to the plunger chamber above the plunger H . I is a heavy rubber connection. J is the manometer scale. K is a stopcock controlling the overflow of water from B through L. The plunger H and container is an ordinary 10-ml. Luer syringe, the thumb-piece being used to penetrate the jelly. No lubricant is used between plunger and container, as it is a groundglass joint and air-tight. The manometer G contains water colored by a red dye. The scale is in centimeters, 0 to 150. The glass tubing used in the connections to the Woulfe bottle is 5 mm. in outside diameter, that for the manometer scale tube is 4 mm. in outside diameter. The area of the thumb piece of the syringe coming in contact with the jelly is 2.836 sq. cm. There are two ways of regulating the pressure availableby changing the height of the water in B or by regulating the flow from A . The flow of water is slow, about a hundred drops per minute. The pressure is always regulated so that the manometer registers 30 at the end of one minute
90
I N D U S T R I A L AND ENGINEERING CHEMISTRY
when the plunger is held against an unyielding substance. Only with a constant, even pressure can equivalent results be obtained. Operation of Jelly Testing The pressure is brought to the standard requirements of 30 cm. water pressure per minute. The jelly is placed under the plunger H , and the plunger allowed to rest gently on the surface. Then the stopcock is turned from E to F and the pressure allowed to increase at a steady, even rate until the plunger just breaks through the surface of the jelly. At this point the manometer is read and the reading recorded as the relative breaking strength in centimeters of water pressure. Before another reading can be taken the water level in B must be readjusted to insure the same pressure. To avoid criticism concerning “skin effect,” the jelly is turned from the glass and the operation repeated upon the bottom surface. This second reading, where the jelly is free from containing walls, gives a higher relative reading in the case of a desirable jelly but a reading which is analogous in relationship when two or more jellies are being compared. Preparation of Pectin
T h e pectin used in this work was from a concentrated -commercial stock pectin solution, similar to that used by Tam3 and Tarr and Baker,4 specially purified in the following way: The pectin was precipitated from the stock solution by 95 per cent alcohol, filtered through cheesecloth, thoroughly washed with more alcohol, and pressed
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plate. The desired amount of sugar was then added and the boiling continued until a definite weight of the contents of the dish was reached. The hot plate, dish, and a protecting sheet of asbestos were previously weighed on 100
f YSO 9
e
g60
$0 m
c
p 0
f 0 Figure 2
a solution balance. I n this way an accurate control could be exercised over the weight of the final product. The final product was poured into a jelly glass, covered quickly, and allowed to stand for a t least 12 hours.
Factors of Jelly Strength Effect of Acidity
Tenth normal solutions of three acids-sulfuric, tartaric, and citric-were used to determine the effect of acidity on jelly strength. These three acids were used because “‘ they showed up so interestingly in comparison with each other in Tarr’s3 studies. Jellies were made according to the directions given in the preceding section, using 100 cc. of 1 per cent pectin solution, adding varying amounts of 0.1 N acid, and making the volume up to 120 cc. As soon as the solution came to a boil 100 grams of sugar were added, and this mixture was boiled to a constant weight. The jelly strength measurkments were taken on like quantities of jelly in identical jelly glasses. The final weight of the jelly was taken as 144 grams, because the preliminary work on varying the end point showed that to be the most favorI I able weight. In order ACIDS COMPARED to compare the measurements of the jelly 1 W J strength upon the surJELLY STRENGTH T E S T E R .face and upon the botFigure 1 tom of the jelly, the dry. The shreddy, fibrous mass was redissolved in water, jelly was turned carethen subjected to a second precipitation with 95 per cent fully from the glass and alcohol, drained off, worked over with more alcohol, washed another measurement thoroughly, and then pressed as dry as possible in a cider taken. T h e measurements press. It was put in an oven and allowed to dry a t 60” C. When thoroughly dried the pectin was ground to a fine are plotted in Figure 2. The ordinates on the powder. left give the relative The dried pectin had an ash of 4.03 per cent. I n order to simplify the use of this pectin for making jel- b r e a k i n g strength of Figure 3 lies it was put into solution by weighing out the desired the jelly in centimeters ,quantity and dissolving a t room temperature. Forcing the of water pressure, those on the right give the actual breaking pectin into solution by using warm water or allowing it strength in grams per square centimeter of plunger surface. t o stand on the water bath resulted in distinct loss in strength It will be noted that at the optimum jelly strength in each jelly the top and bottom determinations are both at a ,of the jelly. The dissolved pectin and acid were measured into an agate maximum. This relationship of the two values will disprove dish and the contents brought to a boilon an electric hot any opinions that place stress on “skin effect.” The three sets of curves obtained were of a similar char8 Delaware Agr. Expt. Sta., Bull. l S 4 , Tech. No. 2. acter; therefore, in the following discussion reference is 4 Ibid., Bull. 136, Tech. No. 3.
ft
INDUSTRIAL ALVDENGINEERING CHEMISTRY
January, 1926
91
made to the curves from measurements on tartaric acid. Practically, the minimum amount of acid needed to form a jelly is 3 cc. of 0.1 N tartaric acid. With every 1 cc. addition of acid more than 3 cc. increase in jelly strength was noted, but the increase became less as the optimum was approached. As soon as the optimum was reached any increase in the active acidity caused a decrease in jelly strength due to syneresis or “weeping” of the jelly. Increase in acidity beyond a certain point yielded the sticky sirup which resembled that obtained with too little or no
In studying this factor no consideration was taken of the inversion of the sugar which takes place during the cooking operation. The percentages given are based on the weight of sugar used in the original batch in relation t o the weight of the finished product. Tarr and Baker4 present data on inversion of sugar during the cooking operation. The concentration of the sugar in the finished jelly was varied by varying the final weight of the jelly, All jel-
I n order to correlate this work with the work 1,.6 done by Tarr, jelly strength curves with pH values as abscissas were made for these same three acids (FigFigure 4 u r e 3 ) . I t will be noted that the minimum point of jelly formation Seems to vary from a pH around 3.70 for the organic acids to about pH 3.55 for the inorganic sulfuric acid. Tarr reports a minimum point of 3.46 for his dried pectin. The optimum point varied from a p H of 3.3 for citric acid and 3.2 for tartaric acid, to about 3.1 for sulfuric acid. The curves approach the optimum with about the same slope and drop correspondingly. As before, where the optimum point was reached, syneresis took place corresponding to the amount the pH, or active acidity, \vas c h a n g e d . Therefore, 77** from theminimumand points found, to see the imof control of -ion concen-
Figure 6
23.79
2
2
17.6y
Figure 5
e acids common s, tartaric acid d the stronger, sirable jelly. This observation has been repeatedly made in the past and was confirmed by the present jelly strength measurements.
Effect of Varying Concentration of Sugar in Finished Jelly
There must be some concentration of sugar in a finished pectin jelly which is most favorable from the viewpoint of jelly strength. It is quite common to get a test for the jelly point (two drop test-two drops of the concentrated solution falling from spoon simultaneously) a t a concentration a good bit less than is desirable for the best strength of jelly.
lies were made from 1 gram of pectin and 10 cc. of 0.1 N tartaric acid, diluted to a volume of 120 cc., brought to a boil, and 100 grams of sugar added. The jellies were taken from the electric hot plate when they reached the desired weights and poured to equal volumes in jelly glasses. Weights of the jelly were varied from 120 grams to 165 grams; the former was impossible to remove from a jelly glass, and the latter collapsed Soon after it was removed. The jelly taken to 120 grams, or 83.33 per cent of sugar, did not resemble a jelly in any respect; it was a caramelized, gummy, sticky mass. Until a weight of 144 grams, or 69-44 per cent sugar, was reached the jellies were sticky and dull in appearance; at that point the characteristics of a good jelly appeared. The corresponding jelly strengths appeared most favorable at this point. A jelly strength determination made on the bottom of the jelly, the jelly free from containing walls, showed the jellies below 144 grams final weight to be inferior; they seemed to be sticky, yet a clear cut break was obtained. The effect of sugar concentration on the strength of the finished jelly is shown in Figure 4. Two points on the 6 curves are especially : to be noted: first, the 0 rapid increase in jelly > s t r e n g t h while the 65.85F 0 weight of the finished 2$0 jelly %‘as being deE 2 53 * 8L c r e a s e d f r o m 165 $80 M grams; and second, 2 the strength &own 41.7: by the jelly in both top and b d t o m sur4 f f a c e determinations 24p 29.7% at 144 grams. Time utee Figure 7 ~ ~ p o1i n t1s (twodrop test) may be obtained a t any point from 165 down, so unless a definite final weight was taken for comparison, fallacies would exist in the other factors studied. Hence, a final weight of 144 grams was taken for jellies in the study of the other factors in this work. The question may arise-what would happen if the pectin concentration were changed while studying the effect of
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
92
varying the concentration of sugar in the finished jelly? To answer such a question the former experiments were repeated using 2 grams of pectin and 20 cc. of 0.1 N tartaric acid, but the solution previous to boiling was otherwise the same. The chief difference was the increase in jelly strength which accompanied . the increase in pectin concentration. For instance, a t a final weight of 160 grams, with 1 gram of pectin the jelly strengths were, top 28.5, bottom 19, whereas with 2 grams they were, top 103.5, bottom 117.5.
VARIATION OF STRENGTH W I T H TEMPERATURE
I 20
I
50
I
I
40 50 Temperature-"C.
I
60
I
70
8
Figure 8
The final weight of jelly was also increased with the increase in pectin. With 2 grams of pectin a jelly was obtained at 185 grams, which was as strong as the one with 1 gram obtained a t 160 grams. Surely an increase of 25 grams in final weight is important. One other difference noted was in the maximum jelly strength point obtained. With 1 gram of pectin the maximum was obtained a t about 144 grams, or 69.44 per cent sugar, but with 2 grams, considering both top and bottom measurements, the maximum was obtained a t 150 grams, or 66.66 per cent sugar. However, the general appearance should be considered. With a n increase to 2 grams of pectin all jellies appeared a bit cloudy and the texture was more crisp.
Vol. 18, No. 1
adding the sugar was considered first. A series of jellies was made up in which the only variable was the time of boiling the pectin-acid solution before the addition of sugar. The solution employed for making each jelly contained 1 gram of pectin and 10 cc. of 0.1 N tartaric acid in a volume of 120 cc. The period of boiling was varied from 0 to 12 minutes. I n each case 100 grams of sugar were added at the end of this time and the boiling was continued to a final weight of 144 grams, after which i t was poured into R jelly glass and covered. After the jellies had stood for 12 hours the jelly strengths were measured. The curves (Figure 6) plotted from these measurements show a marked decrease in jelly strength with the time of boiling the pectin solution. The time of boiling could not be lengthened beyond 12 minutes, because the final weight of 144 grams would be reached before the sugar was all dissolved. The variation in jelly strength between the jellies of the maximum and minimum boiling periods (0 and 12 minutes) was 25 cm. on the top and 30 cm. on the bottom of the jelly; the strength of the jelly decreased 40 per cent in this time. It has been noticed before that pectin deteriorates upon standing with acids, especially a t temperatures above 22" C. Mention of this was made by Sucharipa,s who made jelly strength measurements in its support. The data herein presented confirm his results and present the change in a more definite form. I n order to determine the effect of boiling the mix after sugar had been added, the volume of the solution was increased to make the time of boiling longer. This series of jellies was made exactly as above, with these exceptions: (1) in each case the 100 grams of sugar were added immediately after the pectin-acid solution began to boil; (2) the volume of the pectin-acid solution was varied in order to increase the boiling period necessary to arrive at the
Effect of Varying Concentration of Pectin
Jellies were made with amounts of pectin varying from 0.5 gram to 2.0 grams, the hydrogen-ion concentration being kept constant at a pH of 3.19, the measured value for 10 cc. of 0.1 N tartaric acid plus 1 gram of pectin. The usual 100 grams of sugar were added and the jelly poured a t a final weight of 144 grams. The curves (Figure 5) show a gradual increase in jelly strength with increased pectin concentration. However, it is apparent that a t a concentration of about 1.4 grams, or 0.97 per cent pectin, in the final jelly the optimum point is reached. Above this concentration the measurements on the bottom of the jelly fell below those on the top, which was the case when a tough or undesirable jelly was obtained. Moreover, above this concentration the jellies were cloudy, which showed that the optimum of pectin concentration had been passed. Effect of Time of Boiling
Two periods of boiling are considered-(1) the concentration of the juice, and (2) after the addition of sugar and ending a t the jelly point. The effect of boiling the pectin and acid previous to
Figure 9
final weight of 144 grams. The variation in the time of boiling is directly proportional to the volume of solution. It would appear from the results (Figure 7) that a longer time of boiling is favorable, a t least, the measurements on the bottom of the jellies so indicate, while those on the top vary but little. These results show no detrimental effects from increased boiling after the sugar is present; in other words, a decided increase in invert sugar has no harmful effect on jelly strength. Effect of Temperature
A series of jellies was made up in the usual way-namely, by bringing 120 cc. of a solution containing 1 gram of pectin and 10 cc. of 0.1N tartaric acid to a boil, adding 100 grams of sugar, and boiling down the resulting mixture to 148 grams. (This weight was taken because this factor was studied before 144 grams was found to be the optimum final weight ... under conditions of mix like the above.) The a J . Assoc. Oficial Agr. Chem., 7, 57 (1923).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1926
pectin used was freshly prepared, and had an ash of 3.80 per cent. These jellies were then brought to the desired temperatures, ranging from 2" to SO" C., and their jelly strengths measured. (Figure 8) The curve is very regular below 60" C. -4n increase in temperature causes a decided decrease in jelly strength. The effect of temperature serves to correlate some of the previous measurements of jelly strength, which were made over a range from 22" to 28" c.
93
Effect of Aging
A set of jellies was made up and allowed to stand at room temperature. On various days from the first to the thirtysecond a jelly was taken and its strength measured. These jellies were made up as usual for the other tests and a final weight of 144 grams was taken. The days that each was allowed to stand with its measurements of jelly strength appear in Figure 9. It appears from these results that there is a definite increase in jelly strength with a certain time of standing.
Determination of Water Content of Liquid Glue' By William A. Kingman 29 ARCHST.,FRAMINGHAM, MASS.
EVERAL years ago a study was made of the existing methods for estimating the water content of liquid glue. None of the methods involving drying the glue, even under reduced pressure, were sufficiently rapid for factory control, and the methods using distillation and subsequent measurement of the distillate were not entirely satisfactory. A distillation method involving a special measuring tube was therefore developed which, after more than ten years of constant use has proved satisfactory both as regards speed of operation and accuracy of results. The two essential features of this method are the distillation and measuring tube, shown in the accompanying sketch, and the use of tetrachloroethane as a diluent, with which to mix the sample to be analyzed. The use of tetrachloroethane in place of benzene, kerosene, or naphtha is a distinct advantage for several reasons. Tetrachloroethane is noninflammable. Its boiling point is considerably above that of water so that the moisture will be entirely driven over as the tetrachloroethane distils. It is immiscible with water and the two liquids separate with a distinct line of demarcation. It is heavier than water, so that on condensing it sinks to the bottom of the measuring tube and can be drawn off as the tube becomes filled, leaving the supernatant water in the graduated portion of the tube. I n the distilling flask containing tetrachloroethane and the sample, the sample forms a layer above the tetrachloroethane and thus is heated uniformly and the moisture distils off quietly and without violent bumping.
S
the flask with the arm of buret as shown in diagram, turn on the electric current, and observe the course of distillation. The water from the sample together with a small amount of tetrachloroethane will distil over and condense in the buret. When the water has evaporated from sample, the inside wall of the buret side arm will become dry and clear. DisconE 7
Apparatus and Materials Special buret and condenser 150-cc. flat-bottom flask Oil bath
Electric hot plate Tetrachloroethane
lOc c M Gra
r.m
Procedure
Add approximately 3 cc. of tetrachloroethane to the cleaned and dried buret up to an approximate level as indicated by C in the drawing. Turn cold water on the condenser and the buret is ready for the test. Add 50 cc. of tetrachloroethane to the 150-cc. flask, D. Weigh the flask and contents and then add approximately 15 grams of the liquid glue and weigh the whole again. nect the flask and pour a few drops of naphtha into the buret The difference in weights represents the amount of material at E to wash down any drops of water adhering to wall of the buret. to be tested. We now have a column of liquid in the buret composed of Place the oil bath on an electric hot plate, immerse the tetrachloroethane a t the bottom, water, and naphtha a t top. flask and its contents into the oil bath, connect the neck of Allow the liquid to cool to room temperature and draw off the 1 Received.July 30. 1925. tetrachloroethane from the bottom, when the volume of water
