INDUSTRIAL A N D ENGIhTEERIMG CHEMISTRY
June, 1923
571
A Preliminary Study of a Plunger Type of Jelly-Strength Tester'j2 By S. E. Sheppard and S. S. Sweet EASTMAN KODAK Co., ROCHESTER, N. Y. (a) By using the principle K PREVIOUS papers3 A balanced-beam type of plunger tester with continuous chain of balanced moments, fricthe authors have deincrement loading and variable plunger heads has been devised. tion of the moving element is scribed a torsion dyIt is found that with plungers having a rounded base unsatismade a minimum. namometer for measuring ( b ) The rate of loading is factory load-defection curves are produced, because the area of concontinuous and uniform. By the jelly strength of glues tact varies with the load. A satisfactory plunger is a frustrum of the use of chains of different and gelatins. With this a cone, with the larger base applied to the jelly surface. gage, wide limits are possible apparatus they have inFor any diameter of plunger, the depth of the jelly must be great in this respect. vestigated the relation of The apparatus does not enough, or an interfering reactance from the base occurs. Similarly, differ in these respects from the jelly strength (elasticthe ratio of diameter of plunger to diameter of vessel must be less that of Schweizer,? who has ity) to gelatin concentrathan a certain value, or spurious rigidity-i. e . , spurious j e l l y previously used a balance for tion, hydrogen-ion concenstrength values-will be obtained. jelly-strength measurements. tration, ash constituents, The chain-loading principle Jelly strengihs may be determined as accurately as viscosities, is, however, a very conveniand certain other factor^.^ and can be expressed in absolute units. ent method of applying the The authors are satisfied I t is suggested that for relative measurements manufacturers load. Furthermore, it was that the method involving and colloid chemists agree on a standard plunger type of tester, arranged to have the plungtorsion of definite jellycyliner head removable, so that with elimination of systematic errors. plungers of various sizes, ders is accurate: it also shapes, etc., could be tried. ciives a method of exmessing relly strength in c. g. s. units, as will be noted later.5 On the OPERATIONOF JELLYTESTING other hand, the majority of manufacturers of gelatin and glue, The same technic for controlling the apparatus was used as also many investigators, have used and are using various in preparing all the jellies. Ash-free gelatin8 was swollen jelly-strength testers of the plunger type.6 Essentially, they are modifications of the "finger test," in which some form in water for 16 min., heated a t 65" to 70" C. for 30 min., of plunger replaces the finger and is loaded until a definite allowed to cool a t 20" C. for 30 min., then chilled a t 0" C. fixed displacement of the jelly is observed. The authors for 16 hrs. The temperature of the test jellies was 5" C. have felt it desirable to compare the performance of *thetor- Under these conditions good reproducibility of deflections sion instrument with that of the plunger types. Before in- for given loads was obtained. With regard to surface stituting direct comparisons with existing instruments, it "skin" formation, the writers find that if precautions are seemed necessary to determine the conditions of freedom from taken against surface drying, error from this cause is negsystematic instrumental errors.
I
CONSTRUCTION OF INSTRUMENT The instrument designed and used for the present work is illustrated in Fig. 1. It consists of a standard, A, carrying a pivoted beam, B. The plunger member C is pivoted so as to remain vertical, and is counterpoised by the jockey weight. Increasing load is applied to C by unwinding a calibrated chain from the wheel D. The vessel containing the jelly is placed on the turntable E, and adjustment for balance made by a rnicrometric screw. The depressions produced by the plunger are magnified about six times by the balance system, the actual relation between deflections and depressions being as follows: Deflection (Scale Reading) 1 2 4 6 10
Depression Cm. 0.09 0.18 0.37 0.55 0.91
The small platform above the plunger is used to carry a spirit level to enswe correct centering and leveling. It is not regarded as a final form, but it fulfils certain primary conditions, as follows: 1 Presented before the Division of Leather Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. 2 Communication No. 164 from the Research Laboratory of the Eastman Kodak Compafiy. 8 THIS JOURNAL, 12 (19201, 1007. 4 J . A m . Chem. Soc., 45 (1921), 539; 44 (1922), 1857. 5 I b i d . , 45 (1921), 539. e Bogue, THIS JOURNAL, 14 (1922), 439.
FIG.I-PLUNGER TYPEJELLY-STRENGTHTESTER
ligible in measuring rigidity.9 For the temperature of test they prefer 5' C. when possible, since they have observed that up to 10' C. there is very little change of rigidity Oakes and Davis, THIS JOURNAL, 14 (1922), 706. J . A m . Chem. Soc., 44 (1922), 1858. 0 So far our results are in agreement on this point with those of Oakes and Davis (Loc. c i t , ) ; certain secondary phenomena are being reserved for future discussion. 7
8
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
572
with temperature, but above this it decreases very rapidly, approaching zero a t the melting point. The ash-free gelatin gave a pH of 4.8 in solutions from 1 to 5 per cent, and rigidity measurements were made at this p H unless otherwise stated. ROUNDED PLUNGER
M
M
P I % & R 2 q
EFFECTOF SHAPEOF PLUNGER
Vol. 15, No. 6
to produce this arbitrary deflection may be erroneous. This source of error may be avoided by simply using a plunger making a constant surface of contact from the start. For this, a frustrum of a cone, with the larger section in contact with the jelly surface, has appeared to us the most
As far as the writers have been able to ascertain, the majority of plunger-type instruments have plungers of rounded contour.1° If such a plunger, ing originally the fiatjust surface touchof a
jelly, is pressed down into it, it is obvious that the common surface of cont)act will FIG 2 increase steadily from the first application of the load up to a certain value, as illustrated in Fig. 2 . A result of this is a distortion of the load-displacement curve. From Ilooke’s law, which has been shown to apply to gelatin j e l l i e ~the , ~ load-displacement curve should be a straight line, passing through the origin, the slope of which is proportional to the elasticity. This will not be reached, however, until the surface of contacti. e., of application of load-is constant. Using a rounded plunger (Fig. 2) curves of the type in Fig. 3 were obtained.ll The initial induction corresponds to the period of increasing contact. If the later straight-line portions of the curves are produced, ’it is found that they meet a t a common point outside the reference coordinates originally taken. It is this point which t is the true origin of 24 USING ROUNDED P ~ U N G E R the coordinates, the load factor in the loaddeflection curve being really load p,er area of application. T h e s e curves are similar in shape to those given by Oakes and Davis7 using the Schweizer apparatus. In Fig. 4 is reproduced their figure illustrating this, and it should be noted that a convcrgence point for the straightline portions of all but ihe lowest curves can be obtained. The true jelly strengths a r e measured by the slopes of the lines passing through this point. Consequently, if the const ant-deflection line -e. g . , a t 6-cuts the observed curve before the straight-line portion for one jelly, but cuts the straight-line part of another, comparison of jelly strengths by comparing the loads required v
10 This is the case for the Forest Products Laboratory jelly tester (Forest Products Laboratory, Technical Notes F33), also for Schweizer’s tester as used b y Oakes and Davis. 11 Jelly strength was altered here by variation of hydrogen-ion concentration.
DEFLECTION ON SCALE FIG.4
suitable (Fig. 2 ) . The liability of the abrupt discontinuity a t the edge to produce a n early break in the surface-fear of which has possibly been the reason for the general adoption of rounded plungers-was found to, be negligible when using either wooden plungers rubbed smooth and impregnated with paraffin, or rubber corks.12 Accommodation of the edge discontinuity can either be met, as heretofore, by rounding off-which has been much overdone-or by using a material the absolute resilience of which, near the faced back edge, is approaching that of the material under test. Using plungers of t,liis form, and maintaining constant contact area, straight-line load-deflection curves are obtained, forming, 12 Actually, up to three times the maximum load in these experiments no sensible deformation was observed with rubber corks.
FIG.&-INFLUENCE
OB DEPTH OF JELLY UPON APPARENT JELLYSTRENGTH
B
INDUSTRIAL A N D ENGINEERIhTG CHEMISTRY
June, 1923
with the same gelatin jelly and a series of plungers of different diamet,ers, a common family of lines passing through the origin (Fig. 5 ) . The plunger diameters-i. e., base of the cone-correspond to the numbers as follows: Sumbcr Diameter in cm.
0 0 0
1
2
1.4 1 . 6 1 . 8 2 . 0
3 2.3
4 2.5
5 2.7
6 3.1
7 3.6
TABLE I-INFLUENCE OF DEPTXOF 5 Per cent Load
G . Depth = 1 cm. 0 0 4.6 0.05 9.2 0.1 13.8 0.2 18.4 0.3 23.0 0.4 27.6 0.5 32.2 0.6
Load G.
CENT
2cm. 0
0.2 0.4 0.6
Deflection3.5cm. 0 0.35 0.6 0.85 1.1
0.8 1.0 1.4 1.2 1.6 1.4 1.8 3 Per cent .------Deflection-------. Depth = 2 cm. .3 cm.
0 4.6 9.2 13.8 18.4 23.0 27.6 32.2
FIG.6--1 PER
573 JELLY
--___9 c m .
4.5cm. 0 0.35 0.65 0.9 1.2 1.45 1.65 1.95
4.5 cm.
0
n
n
0.5 1.0
6 5 1.0 1.6 2.0 2.7 3.3 3.8
0.6 1.2 1.9 2.5 3.2 3.7 4.1
1.4 1.8 2.2 2.6 3.0
0 0.35 0.65 0.95 1.2 1.5 1.7 1.9
9.5 cm. n i.0 1.85 2.65 3.5 4.4 5.0 5.6
JELLY-STRENGTH CURVES F O R DIFFERENTDEPTHS
EFFECT OF DEPTHOF JELLY The theoretical condition for the plunger test under investigation is that of a cyIinder of definite diameter or cross section resting on a flat jelly of infinite area and infinite depth.'a It seemed necessary to determine the conditions under which the effect of supporting and containing walls become negligible, and the depth (or height) of the jelly will be first noticed. Using 5.0 and 3.0 per cent jellies, the following values were obtained with a Xo. 1plunger (1.8-cm. diameter) : 'a Sheppard, "Viscosity Determination with Falling Spheres, and Stokes' Law," THIS JOURNAL, 9 11917), 523.
TABLE 11-INFLUENCE OF DEPTH ON APPARENTJELLY STRENGTH Depth SLOPE--Cm. 3% 5% 5.3 1 2.3 2 1.0 ... 3 0.94 .... 1.8 3.5 0.76 1.6 4.5 0.73 1.6 6 .... 1.6 9 0.70 1.6 9.5
_--_ ....
----
TABLE 111-INFLUENCE OF DEPTH ON APPARENTJELLY STRENGTH" Depth SLOPE-------^ Cm. 1% 3% 57 010% .. , 6 120 120 120 24 3 58 120 15 1.8 75 42 13 1.5 36 70 12 70 1.5 30 11.5 1. 60 29 11.5 1 58 28 1 11.5 58 27.5 a See Figs. 6, 7, 8, 9, and 10. I"
FIG
7-3
PER
CENT
JELLY-STRENGTH CURVES FOR DIBRERENT DEPTHS
0
IATDUSTRIALA N D ENGINEERING CHEiMIXTRY
574
Vol. 15, No. 6
From these results, it does not appear that the absoldte rigidity (or the concentration) has any definite effect upon the limiting depth, which may be taken as approximately 5 cm. For the subsequent experiments a depth of 10 cm. was used-later, of 7 cm. RATIOOF DIAMETERS OF VESSELAXD PLUNGER Keeping the depth a t 7 cm., the next factor studied was the ratio of the inner diameter of the vessel to that of the plunger. The results of these experiments are given in Table I V and Figs. 11 to 14. The apparent rigidity, or jelly strength, is again given by the slope of the load-deflection curve,14 and when this is plotted against the ratio of the diameters of the vessel and the plungers, it will be. seen again that the apparent j e 1 1y strength decreases rapidly at first, and only reaches a constant value when the ratio is greater than 5 (Fig. 15). For a ratio 5 1.0-i. e., when the plunger is of equal or greater diameter than the vessel, the apparent jelly strength approaches ‘‘infinity”-i. e., approaches the rigidity of the container walls-but below this asymptote falls off rapidly till a practiFIG. 9-10 PER CENT JELLY-STRENGTR cally constant value is CURVES FOR DIFFERENT DEPTHS obtained. This limit again appears to be comparatively independent of the absolute rigidity or concentration of the jelly. TABLE IV-INFLUENCE Plunger No. 7
6
5 4 3
2 1 0 00
-------
OF DIAMETER RATIOON APPARSNTJELLY STRENGTH Diameter SLOPE-----Ratio 1% 3% 5% 10% 2.2 3.5 29 58 60 60 2.6 2.5 19 42 58 2.95 2.3 13 34 3.2 2.2 12 32 50 50 3.5 1.85 11 27 45 4.2 1.4 9.5 20 4.45 1.3 9 I9 45 40 5.0 1.8 8 17 5.7 1.3 7.6 15 40
FIG.10-INFLWBNCE
O F DEPTH OB JELLY ON APPARENT JELLY
STRENGTH
strength testing may be vitiated, since comparisons of apparent jelly strengths before the limit value of the jelly mass is reached are by no means satisfactory. From these results, taken in conjunction with previous work using the torsion dynamometer, the following provisional conclusions as to comparative jelly-strength determinations have been reached : 1-Definite technic of preparation, thermal pretreatment, and temperature a t test should be adhered to. 2-A plunger type of apparatus may be used under certain conditions. The balance type, as used by Schweizer, Oakes and Davis, and the authors, is recommended. 3-To avoid systematic errors, the conditions for shape of plunger, depth, and size of contained jelly mass, as reported in this paper, should be observed.
REPRESENTATION OF JELLY STRENGTH Under these conditions, using instruments of standard dimensions and specifications, the measurement of accurate
The reason for these container effects, and for the region of “spurious rigidity,” as the values above the limits may be termed, is not yet certain.16 They are not affected by keeping the jellies for periods prolonged beyond the 16 hrs. It is possible that they represent a state of stress adjacent to the container walls, and annealing experiments are planned to test this. It is apparent, however, that without due attention to these factors even purely comparative jellytotal displacement , and for cylindrical plungers total load this gives applied load X area depression X area 15 A preliminary mathematical investigation of the elasticity problem inxolved, by L. Silberstein, does not indicate such P condition. I,
The rigidity =
FIG. 11-1
P E R CENT JELLY-STRENGTH
TESTSFOR DIFFERENTDIAMETER
RATIOS
June, 1923
FIG 12--3
P E R CENT
IlVDUSTRIAL A N D ENGINEERING CHEMISTRY
JELLY-STRENGTH TESTSFOR DIFFERENT DIAMETER FIG.13-5 RATIOS
relative jelly strengths is possible. From previous work of the authors on the elasticity of gelatin jellies2 they must express disagreement with the recent statement of Oakes and Davis.’ Referring to the grading of gelatins by viscosity, and j elly-strength measurements, they say: “Viscgsity measurements may be expressed in absolute units and may be very accurately determined; this is not true of jellstrength measurements.” This statement appears incorrect on both counts. Firstly, jelly strength, if expressed as it should be, either as (a) modulus of rigidity N ( b ) Young’s modulus of elasticity E (modulus of stretch or compression) or ( c ) Proof resilience per unit volume-i. e., f” the greatest strain 0.5 energy which can (f=load be stored without at elastic permanent strain limit)
can and should be expressed in absolute units. Thus, in (a) N can be measured in grams per square millimeter, or dynes R .i 1:2 ik 2!0 I _t per square centimeter; in ( b ) , E = 2 N (1 p) where p FIG. 14-10 P E R CENT JELLYSTRENGTR TESTS FOR DIPRERENT= Poisson’s ratio, which may DIAMETER RATIOS be taken as 0.5 for gelatin
+
575
PER CENT JELLY-STRENGTH TESTSFOR DIFFERENT DIAMETER RATIOS
,576
I N D UXTRIAL A N D ENGINEERING CHEMISTRY
meter. Finally. in ( e ) , the writers have already pointed out that the limit of elasticity appears to differ but little from the tenacity, or rupture limit, so that the resilience may be B2 €32 taken as 0.5 - = - where B = breaking load, and N = E 6n” rigidity, and could be expressed in ergs per cubic centimeter if absolute units are required. While these quantities can be determined in absolute units with our torsion instrument, this is not the case with the plunger type. It is obvious, however, that the plunger type can be calibrated on the torsion instrument by comparison of the results with the same gelatin jellies. Secondly, such elasticity determinations can he made with the same precision as viscosity. It seems to us that the use of the terms “jelly strength,” !‘jell consistency,” etc., in a
Vol. 15, N o . 6
vague and undefined sense should be abandoned, and that on account of this indefiniteness and the lack of investigation of systematic error, much of the work published on this phase of the subject requires careful revision. ADDENDUM Using jellies up to 8 per cent concentration, a comparison between the plunger type described here and our torsion instrument has been made for an ash-free gelatin and for a commercial gelatin. I n both cases the ratio” of the rigidities by the two instruments remained constant, the average for the ash-free gelatin (F3-14) being 43.0, for the commercial, 43.6. This apparatus constant, for the conditions used (depth of jell~75 5 em., ratio of diameters S 4 4 , should be a definite factor for converting jelly strengths into rigidities by the plunger method.
Changes in Powdered Rosin Stored in Closed Containers‘ By F. P. Veitch and W. F, Sterling BUREAU OF CHE‘MISTRY, WASHIXGTON, D. C .
PREVIOUS W’ ORK in which the quantity of Rosin powdered and stored in partly filled closed containers will change suficiently within one week. to show on careful analysis soap made from definite EGER2found that quantities of lump rosin significantly lower acid and iodine numbers, higher saponification rosin in a thin and stearin of known soapnumber, and higher softening and melting points-and, inferentially. film exposed, to making value is compared higher specific grauity, increase in weight, and a greater proportion the air for 33 days inwith the quantity made of oxygen. creased in weight 1.58 per from a mixture of exposed Because of these facts samples should be prepared for analysis cent. Fahrion3found that wowdered rosin and the only immediately- before the analysis is begun. Dowdered rosin exDosed for known stearin. Low yields i 4 mo. to the air and stirred were obtained with powfroni time to time differed widely in some of its constants from a portion of the same dered rosin that had been exposed to the air for 2 mo., while sample exposed at the same time in lump form, which had still lower yields were obtained with powdered rosin that not changed in that time. The acid number of the powdered had been standing for the same length of time over water. rosin had decreased from 159.0 to 151.2, the iodine number The authors assume that the oxidation of the rosin leads from 132.9 to 72.6, while the saponification number had to the formation of water-soluble compounds and that the increased from 165.8 to 174.7. He also found, by combus- soap-making value of the rosin is lowered more than protion, that the oxygen had increased from 12.7 per cent in portionately. the lump to 18.0 per cent in the powder, with proportionate EXPERIMENTAL WORKAT BUREAUOF CHEMISTRY decrease in hydrogen and carbon. He found that powdered In 1921, in reanalyzing within a few weeks a sample of rosin began to increase in weight in 2 days and gained 4.2 per cent in weight during 2 mo. Solubility in petroleum rosin, the writers found that its acid, saponification, and ether decreased with increase in oxygen content. When iodine numbers, and also the melting point of the powdered the exposed samples were dissolved in dilute alkali and samples kept in partly filled corked bottles, had all changed, shaken out with petroleum ether and salt, the lump gave while the unsaponifiable matter remained practically the same. The work of Fahrion and of Goldschmidt and Weiss 92.5 per cent and the powder 29.2 per cent soluble. shows the effect of exposing powdered rosin to the air for Palmer and Boehmer4 found that the extraction of rosin some time, but so far no reference to rapid changes or to from wood by petroleum solvents was complete. Schwalbe and Schultz5 found that the longer pine wood changes within a closed receptacle such as is generally used was kept, particularly in the form of sawdust, the smaller in the laboratory for storing samples for analysis, has been was the quantity of resin that could be extracted, even by a found. This fact, while interesting in itself, explained in part, though not entirely, the wide discrepancies between the series of different solvents used successively. Goldschmidt and Weiss6 found that the soap-making value constants of rosin reported by different analysts and also the of exposed powdered rosins”was from 2 to 5 per cent less than decided differences heretofore found between the different that of lump rosins as determined by the stearin method,7 grades of rosin, differences which were not confirmed by the Bureau of Chemistry in careful work on the constants of 1 Presented before t h e Division of Industrial and Engineering Chemistry rosin, in which samples of known origin and grade were used at the 64th Meeting of the American Chemical Society, Pittsburgh. P a , and the sample for analysis taken from the lump at the time September 4 t o 8, 1922 of analysis. aChem. Rev F i t t - H a m - I n d , 6 (1898), 236. I b i d . , 22 (1915), 97. The fact that the constants of rosin do change after the 4 THISJOURNAL, 8 (1916). 695 rosin is powdered having been fully established, it evidently 6 Z . angew. ChPm., 3 1 (191S), 125 becomes important to know how soon these changes take 62.deut. bl- Felt-Ind., 4 1 (1921), 147. place and the rate a t which they take place under ordinary 7 Seqfenfabr , 39 (1919), 49.
vv
8
I
