V O L U M E 25, NO. 7, J U L Y 1 9 5 3 a t least 1.2 cc. per 100 grams. Theoretically, this volume of internal hydrogen could produce approximately 10% porosity. This estimate compared favorably with the amount of porosity revealed by radiographic examination of the weld. DISCLSSIOX
One of the main sources of the error in analyzing aluminum for hydrogen is the always present oxide film on the surface. The gross effect of this film can be minimized by increasing the weight to surface-area ratio. This may be accomplished by using massive samples with smooth surfaces. .i spherical sample would be ideal. The maximum weight of the sample, however, is limited by the solubility of aluminum in t i n a t 525°C. (980°F.). The use of higher bath temperatures would increase the solubility of the aluminum but the vaporization of volatile constituents would be excessive. These metallic vapors would react with any moisture adsorbed on the walls of the apparatus. Thus, a spurious source of hydrogen would be created. Rate of Adsorption of External Hydrogen. During the detrrmination of the external hydrogen, it was observed that the samples abraded after preheating began to form the hydrated oxide film almost instantaneously. The film reached a maximum value within 10 minutes of exposure to the atmosphere. However, if the surfaces of thc preheated sample were not reabraded, the oxide film readsorbed moisture vel.>-s l o ~ l yduring exposure.
1087 After 4 hours of exposure, the amount of external hydrogen reabsorbed was - Ordnance Corps, Frankford Arsenal.
Mechanical Stability Test for Rubber latices S.4MUEL H. MARON AND IRWIN N. ULEVITCH Department of Chemistry and Chemical Engineering, Case Institute of Technology, Cleveland, Ohio The high speed agitation tests employed to determine the mechanical stability of natural rubber latex are generally inapplicable to synthetic latices. To overcome this shortcoming, a new mechanical stability test was developed which works equally well with both types of latex. The new test subjects latex to a shearing force exerted by a metal disk under load rotating in contact with a polyethylene surface. The coagulum formed in the operation of the machine for a definite time and under specified conditions, when expressed as a percentage of the solids taken, is used to define the mechanical stability. The above test was used to determine the mechanical stability of eleven samples of various synthetic latices and one of natural latex as a function of total solids content. The results show that the mechanical behavior of a latex depends on the solids content, and that a true picture of this behavior cannot be obtained from a determination of the stability at a single concentration.
R
UBBER latices are frequently subjected to mechanical manipulations which may destabilize the latex to a point where partial or even total coagulation occurs. To test the &ability of latices to mechanical stresses, a reliable, convenient, and fairly rapid test is highly desirable. For determining the mechanical stability of natural latex a test frequently employed is one based on high speed agitation (1-6, 8, 9). Although this test is more or less satisfactory for natural latex, it is inapplicable to many of the synthetic latices. Natural latices may show coagulum in stirring tests in seconds or minutes, while GR-S latices do not yield coagulum on agitation a t 12,000 t o 15,000 revolutions per minute even a t the end of 1 hour. In 1939 Murphy ( 7 ) proposed a mechanical stability test for natural latex based on a simulation of the hand-rubbing test so
commonly employed by latex chemists. The apparatus consisted of a molded rubber nose rotating eccentrically on a glass plate upon which the latex was spread. The time required for the latex film to break into small pieces was taken as the end point. As far as is known, this test was never applied to synthetic latices. I n 1944 the authors developed but did not publish a mechanical stability test based on frictional coagulation which was shown to be applicable to synthetic latices. However, the test required improvements which were not made until recently. I t is the purpose of this paper to describe this test, and to present results obtained with it on eleven synthetic latices of various types as well as on a sample of natural latex. DESCRIPTION OF TEST APPARLTUS
The test to be described subjects latex to a shearing force exerted by a metal disk under load, rotating in contact with a polyethylene surface. The coagulum formed in the operation of the machine for a definite time and under specified conditions is taken as a measure of the mechanical stability of the latex. The complete test apparatus is shown in Figure 1 and coneists of a drill press, A , a platform scale, B , a special cup assembly, C, and a rotor disk, D. The drill press is powered by a l/a-hp. motor, and is provided with a belt drive and pulleys by means of which the speeds can be varied. .in 8.5 X 24 inch platform, E, has been substituted for the table of the drill press. It is made from 2 X 2 inch angle iron, which is bolted to the base of the drill press, and in which is set the Model 4644-T Toledo scale. This scale has a total capacity of 40 pounds, and reads to 0.1 pound. The pan supplied with the scale has been removed, and for i t was substituted the cup holder plate shown in Figure 2. Details of the rotor construction are shown in Figure 3. The disk is of stainless steel, and is 2 inches in diameter and 0.5 inch thick. The center of the disk is hollom-ed out to a depth of 3/!16 inch to leave a circular rubbing surface 0.5 inch wide. Into this rubbing surface have been cut four grooves, as shown, to facilitate the flow of latex under the disk and to aid in the removal of any coagulum formed. The cup for holding the sample, shown in Figure 4, is also made
ANALYTICAL CHEMISTRY
1088 of stainless steel, and consists of three parts, the cup proper, a, a bottom plate, b, and a circular slip flange, c. Between b and the bottom edge of c is inserted the liner, d , upon which the rotor disk revolves. Details of the bottom plate construction and of the liner are shown in Figure 5. The plate is 5 inches in diameter and inch thick, and is cut along the circumference in the manner shown for mounting in the pegs indicated in Figure 2. The center of the plate has a 7/8-inch diameter cut made to a depth of '/I6 inch. Radiating from this cut are four channels, inch wide by 1/18 inch deep, which terminate in a circular groove, 6/32 inch wide and l / 1 6 inch deep, at a distance of 29/16 inches from the center of the plate. The holes in the liner correspond to the intersections of the radial channels with the circular groove, and thus permit passage of latex through the grooves from the cup to the under portion of the rotor, Finally, the four holes in the bottom plate are threaded to accommodate screws which pass through the flange c and hold together the entire cup assembly.
I%
Figure 2. Cup Holder Plate F
I
Figure 3.
Figure 1.
Mechanical Stability Test Assembly
Rotor Disk
on the amounts of coagulum formed. For this purpose a single X-695 synthetic latex was used. Times were varied from 1.5 to 10 minutes and loads from 10 to 30 pounds. The speeds used were 620 and 1000 revolutions per minute. The results obtained are given in Table I and Figure 6. Each
After trying a number of liner materials, the one found most satisfactory was inch polyethylene sheeting. The liner circles are cut from the sheets, and the holes are then drilled in them with the aid of a master template. TEST PROCEDURE
Experience has shown t h a t new liners must be conditioned before use. This conditioning consists of assembling the cup and liner, adding 75 ml. of water to the cup, lowering the rotor onto the liner until the scale registers a load of 25 pounds, and locking the drill press in this position. The motor, set for 1000 revolutions per minute, is then started, and allowed to run for 10 minutes. At the end of this time the cup, liner, and rotor are washed and wiped dry prior to actual test runs. Such a pretreatment is required only of new liners. When so treated, the same liner will operate satisfactorily for weeks a t a time. Test runs are made in essentially the same manner. Seventyfive milliliters of latex are placed in the cup, the rotor is lowered until the scale reads the desired load, and the drill press is locked. The motor is then started and the time of run is observed on a stopwatch. At the end of the desired time the motor is shut off and the lock on the drill press is opened simultaneously. The cup and contents are removed from the press, the latex is diluted with some water, and filtered through a piece of nylon hosiery or fine cheese cloth. Any coagulum formed is washed with water until free from latex, transferred to tared aluminum pans, dried for 2 hours a t 80" C. in a vacuum oven, and weighed. The weight of coagulum obtained under specified conditions is used to express the mechanical stability of the latex in the manner to be discussed below. b
EFFECTS OF TIME, LOAD, AND SPEED
Before defining standard conditions for the test, a study was made of the effects of time, loading, and speed of rotor revolution
Figure 4. Details of Cup Assembly
1089
V O L U M E 25, NO. 7, J U L Y 1 9 5 3
load. A cross-plot of the data, given in Figure 7 , indicates Speed, R.P.M. further that the coagulum 1000 reight increases e s s e n t i a l 1y Load, Lb. linearly with load a t constant 30 10 20 30 time for each speed used. Coagulum Weight, Grsms f % Consideration of the above 0.424zt5.9 0.223f7.0 0.418f4.5 0.294*1.7 0.760zk4.6 0 . 8 6 5 1 2 . 4 0 . 7 5 8 1 2 . 2 0.664f4.5 data from the standpoint of 1.41 1 2 . 8 0 , 9 0 2 1 1 . 1 0 . 9 4 9 f 6 . 5 1.21 1 2 . 5 reproducibility, convenience of 1.41 f 4 . 3 1.55 1 2 . 6 1.86 3 ~ 0 . 5 1.28 f O . O 1.60 f 1 . 3 1.59 f O . 0 1.97 i O . 5 2.30 1 0 . 4 operation, and amount of coagulum obtained led to the followingspecification of standard operating conditions for the test: Speed of rotor revolution, 1000 revolutions per minute Load, 25 pounds Running time, 5 minutes
Table I. Effects of Time, Loading, and Speed on Coagulum Formation 620
Time, Minutes 1.5 3.0 5.0 7.5 10.0
10
20
0.130f4.6 0.522f4.6 0.669f6.4 0.969f2.8 1.31 1 1 . 5
0.277f1.4 0.646f8.7 0.839f0.7 1.19 f 1 . 7 1.54 z k 2 . 0
These are the conditions which were employed in all further work. KO attempt was made to control temperature, since previous work showed such control to be relatively unimportant, However, should it be found necessary with some latices, such control can readily be provided by jacketing the cup and circulating water through the jacket. EFFECT OF SOLIDS CONTENT
To ascertain the effect of solids content on the mechanical stability of the X-695 latex, the latex as received was diluted with distilled water to various concentrations, and the mechanical stability of each of these was determined. The results obtained are shown in Table 11. These indicate that the weight of coagulum obtained during the test increases with concentration 8.5fold as the latex solids are varied fivefold. However, use of coagulum weight alone takes no cognizance of the fact that different weights of solids were involved in the test a t the various concentrations. To correct for these it is suggested that a better criterion of the mechanical stability M of the latex would be the quantity (Equation 1):
BOTTOM PLATE
Figure 5. Details of Bottom Plate Construction and Liner
of the coagulum weights is an average of three runs, and from the deviations it is evident that in most instances the test is reproducible to better than 5%. Again, the data show that the coagulum weight increases with time of run, speed of revolution, and
,,MI" 0
Figure 7.
1
P
I
0
I
I I L O A D 20 P O U N D S25
-
I
1
10
s5
I .O
Coagulum Formation as a Function of Load at Constant Time X-695latex
Table 11. Effect of Solids Content on iMechanica1 Stability of X-695 Latex
I 29
4.0
I
I
I
6.3
PO
100
- MINUTES Figure 6. Coagulum Formation as a Function of Time at Constant Load TIME
X-695 latex
I
Solids, % 5.70 7.60 11.40 17.04 22.70 25.00 28.40
Weight of Coagulum-W, Grams 0.15 0.23 0.38 0.69 1.03 1.15 1.28
Weight Solids Taken-3, Gram 4.27 5.70 8.55 12.80 17.02 18.75 21.30
=
W S 3.51 4.04 4.45 5.39 6.05 6.13 6.01
ANALYTICAL CHEMISTRY
1090 Table 111. Description of Latices Studied Initial Solids,
Latex 1
2 3 4 5 6 7 8 9 10
Emulsifier F a t t v acid soau
2s ;:
Type V Type Type \ H I X-617 X-667 Hycar 1612-3 Neoprene 571 Natural = butadiene, S t = styrene.
y
11
12 0
Contained Polymer"
%
Latex X-695 Special
NO.
BD
M
=
Rosin soap K-stearate K-oleate
... ...
wx
-
S
Figure 9. JIechanical Stability of Various Latices 100
(1)
where W is the weight of coagulum obtained and S the weight of solids taken. Values of S and M for the various solids contents are given in the last two columns of Table 11. On this basis the fivefold variation in the latex solids content leads only to a 1.7fold decrease in the mechanical stability of the latex. Furthermore, the data show that the mechanical stability of this latex is essentially constant between 22.70 and 28.40% solids. MECHANICAL STABILITY OF VARIOUS LATlCES
With the test conditions and method of expressing results established, a study was made of the mechanical stability of eleven other latices of various types as a function of concentration. A4description of these latices is given in Table 111, while the results obtained are shown in Figures 8 to 11.
I
I
3
0
I
I
I
I
I
5
20
25
30
35
PER CENT SOLIDS T A K E N
Figure 10. Mechanical Stability of Various Latices ?
mechanical stability of a latex at a single concentration does not characterize fully the mechanical behavior of the latex Rather, in order to obtain a more complete picture, this stability has to be measured as a function of the solids content. Finally, the proposed test is also applicable to natural latices, and shows these to have a mechanical stability comparable to that of the synthetic ones. This conclusion is in closer accord with practical experience than the results of the agitation test, which indicate the mechanical stability of natural latex to be very much lower than that of most synthetic latices.
I
1,PC
/
IV.3
ooo SIMPLIFICATION OF TEST APPARATUS
20
M
40
F E R CENT SOLIDS TAKEN
For routine operation of the test under the standard conditions proposed here, it is possible to simplify the test assembly by elimination of the Toledo scale. and substitution for it of the load-
Figure 8. Mechanical Stability of Various Latices -,
There are several points of interest revealed by these data. First, there is considerable difference in the mechanical stability of various latices. Taking the latices a t their initial solids contents, the measurements indicate that the per cent of contained solids coagulated during the test may vary from essentially zero for Type V, Type VIII, and Neoprene Type 571 latex, up to 8.770 for Hycar-1512 and 10.070for the special latex No. 2. Second, in all instances the mechanical stability of the latices varies with the solids content. However, the dependence of stability on solids is not the same for all, but falls into essentially three categories: Latices whose mechanical stability decreases with increasing concentration (X-695, Special, and Hycar-1512). Latices whose mechanical stability increases with increasing concentration (Type IV, Type V, Type VIII, Seoprene 571). Latices whose mechanical stability passes through a maximum as concentration is increased (X-617 a t 15% solids, X-667 a t 47% solids, and natural rubber latex a t 37.5Y0 solids). These observations indicate that the determination of the
F E R C E N T S O L I D S TAKEN
Figure 11. Mechanical Stability of Various Latices
1091
V O L U M E 25, NO. 7, J U L Y 1 9 5 3 ing apparatus shown in Figure 12. I t consists of a base, K , into which are threaded the four posts, L. Over these posts are slipped matched springs, M , whose total load capacity is about 40 to 50 pounds. On top of these springs is placed the cup holder plate, F, shown in Figure 2, after four holes have been drilled in it so as t o slip over the posts.
as in the effect of solids content upon this property. Depending on the latex, dilution may decrease or increase stability, or the stability may pass through a maximum a t a particular concentration. KO explanation is available a t present for the mechanical stability behavior of the various latices. It is quite certain, however, that the test described here does not involve plastometer action. During the running of the test the indicator on the scale remains constant to ca. *O.l pound. If coagulum accumulated under the rotor and plastometer action entered, the load would rise appreciably. As this is not observed, plastometer action cannot be responsible for the results obtained, and an explanation has to he sought in the colloidal character of the latices. ACKNOW LEDGMEKT
Figure 12. Simplified Loading Mechanism for Mechanical Stability Tester
A rule mounted in front of the loading apparatus permits determination of the state of loading of the springs. To obtain the desired loading, the rup and 25 pounds in weights are placed on plate F , and the depression of the springs is observed on the rule. Pressing the rotor against the cup bottom until this reading is reproduced will give then the 25-pound load required for the test operation. COICLUSIOhS
The new test described for the determination of the mechanical stability of rubber latices is rapid, reliable, and reproducible to within 5%. I t is applicable to both natural and synthetic latices. L-sing this test, a study has been made of the effect of solids content on the mechanical stability of a natural latex and eleven synthetic latices of various types. The results show that the various latices differ considerably in mechanical stability as well
The work discussed herein was performed as a part of the research project sponsored by the Reconstruction Finance Corp., Office of Synthetic Rubber, in connection with the government synthetic rubber program. LITERATURE CITED
(1) Crude Rubber Committee, Division of Rubber Chemistry, Rubber Chem. and Technol., 14, 299 (1941). (2) Davey, W.S., and Coker, F. J., Trans. Inst. Rubber Ind., 13, 368 (1938). (3) Dawson, H. G., AXIL. CHEM.,21, 1066-71 (1949). (4) Jordan, W. F., Brass, P. D., and Roe, C. P., IWD.ENG.CHEM., - 4 N I L . ED.,9, 182 (1937). (5) Madge, E. W., Trans. Inst. Rubber Ind., 28, 207 (1952). (6) Madge, E. W., Collier, H. M., and Duckworth. I. H., Ibid., 28, 15 (1952). (7) Murphy, E. -4., Rubbe? Chem. and Technol., 12, 893 (1939). (8) Noble, R. J., “Latex in Industry,” New York, Palmerton Publishing Co., 1936. (9) Novotny, C. K., and Jordan, W. F., IXD.ENG.CHEY.,ANAL.ED. 13, 189 (1941). RECEIVEDfor review December 8, 1952. Accepted March 5 , 1353.
Quantitative Organic Precipitants for Osmium I. HOFFILIN, J. E. SCHWEITZER, D. E. RYANL, AND F. E. BEAMISH C-niversity of Toronto, Toronto, Ont., Canada This research arises from a general investigation of the characteristics of organic precipitants for the platinum metals. The results obtained with osmium were of some significance because organic reagents have not been used successfully for the gravimetric determination of osmium; indeed no approved microgravimetric method for osmium has been recorded. The present report deals with the successful application of a substituted thiazole and
T
HESE investigations were made to develop a microgravimetric procedure whereby osmium in ores could be determined after extraction by fire assay, with lead as a collector. Allan and Beamish ( 1 ) used a hydrolytic procedure for micro quantities of osmium based on the method used by Gilchrist ( 3 ) for macro amounts, but reported a significant error, characteristic of “hydrolytic methods.” True blanks could not be determined owing to retention of osmium by the residue after oxidizing ignitions. Although certain organic reagents for the precipitation of osmium had been discovered by the authors they were not applicable because the precipitates could not be purified by washing, and ignition in air was inadmissible. However, the observation had been made in this laboratory that palladium dimethyl1 Present address, Dalhousie University. Halifax, N. S.. Canada.
indicates the applicability of certain substituted thioureas and thiazoles to colorimetric or gravimetric determinations. The use of strychnine sulfate as a gravimetric reagent and a completed procedure for the precipitation of the osmium-thionalide complex are reported. Besides providing the first gravimetric organic precipitants for osmium, the data obtained indicate the direction to be taken in the search for new reagents for the platinum metals.
glyoxime could be ignited in hydrogen to produce the metal (6). It is probable that palladium acts as the catalyst for this reduction. Osmium is known as an active catalyst, and it seemed likely that the metal could be recovered from organic complexes in a similar manner. Allan and Beamish ( 1 ) made preliminary tests on the possible use of thionalide as a precipitating reagent. The authors record below their data on the efficiency of thionalide, 2-phenylbenzothiaeole, and strychnine sulfate, and their successful application of these compounds to the determination of osmium. DETERMINATION OF OSMIUM
By Thionalide. REAGENTS. Ammonium Bromo-osmate. A purified sample of ammonium bromo-osmate was analyzed for
