in relative humidity. This switching mechanismalso is adaptable for giving rapid and discretechanges in temperature.

It is designed to operate at test-chamber tempera-tures above 0° C, but may readily be used at tem-peratures as low as —40° C. The low temperaturesare achieved, however, at some sacrifice of the maxi-mum attainable relative humidity. For most of thetest-chamber temperature range, practically anydesired relative humidity may be produced by theapparatus.

Independent checks on the performance of the ap-

paratus by means of the gravimetric method ofmoisture determination and the psychrometric meth-od show an average agreement in relative humidityof 1.2 percent as measured and as given by the ap-paratus, eq 2.

The author gratefully acknowledges the assistanceof R. A. Baum of the Shop Division in the construc-tion of the apparatus and of E. T. Woolard in theexperimental work.

WASHINGTON, August 14, 1950.

Journal of Research of the National Bureau of Standards Vol. 45, No. 5, November 1950 Research Paper 2146

An Improved Apparatus for Determining Moisture inRubber by Distillation with Toluene

By Max TryonAn improved apparatus has been developed for the determination of water in rubber by

distillation with toluene. The volume of the water collected is measured in a graduatedcapillary tube, which allows more precise measurement than the tapered tube formerly used.The interior of the trap and condenser is coated with a water-repellent silicone polymer toprevent water droplets from adhering to the walls and to improve the accuracy. Thispaper describes the construction of the apparatus and a procedure for coating its interiorwith the silicone polymer. A method for calibration of the trap is included in a generalprocedure for use of the equipment.

I. Introduction

The water content of certain organic materials canbe determined by a method that involves the forma-tion of an azeotrope of an immiscible organic liquidwith the water, distillation of the azeotrope, andseparation of the water as a separate phase. Thevolume of water is then measured by the use of agraduated container.

For this purpose there are several devices commer-cially available for the collection and separation ofwater distilled with a liquid of low density, such astoluene. Since the time of Dean and Stark [1] 1

there have been a large number of refinements andspecial applications similar to their original apparatus[2 to 9]. These refinements are essentially attemptsto overcome! tin; following shortcomings of the origi-nal design. First, there is a tendency lor water toadhere to parts of the apparatus rather than to collectin the graduated portion. Second, there is a lack ofprecision of reading the volume of water collected(Uw to the dimensions and shape of the graduatedcontainer. Third, sharp separai ion of the immiscibleliquid and water does not always occur in apparatuswith naiTOW water-collecting tubes, because theimmiscible liquid tends to be trapped in the lube bythe water. Fourth, the apparatus must be meticu-lously clean or the water will entrap the immiscibleliquid and will not properly (ill the measuring lube,regardless of the shape or dimensions of the tube.

1 F i g u r e s i n b r o c k e t s I n d i c a t e ( l i e l i t e r a t u r e r e f e r e n c e s a i t h e e n d <>r i h i s p a p e r .

Subsequent modifications and refinements of theoriginal apparatus have overcome some of theseobjections to varying degrees. The apparatusdescribed in this paper, however, answers all theseobjections satisfactorily and also offers a few moreadvantages.

The procedure and apparatus described in thispaper was originally devised in 1947 to determinesmall amounts of water (about 1% by weight)present in certain types of synthetic rubber [10, 11]that could not be analysed with procedures standardat that time. As a result, this procedure has beenaccepted as a referee method for determining mois-ture in all types of synthetic rubbers by the Sub-committee on Test Methods, Reconstruction FinanceCorp., Office of Rubber Reserve.

It is felt that this apparatus supplies the need for arapid, simple, precise method for determining smallamounts of water in materials on a routine productionbasis and furnishes a valuable tool for research.

II. Description of Apparatus

The apparatus is shown schematically in figure 1.The distilling flask, A, contains the sample andtoluene. This flask is connected to the collectingtrap, T, by a 24/40 standard taper joint Lubricatedwith silicone stopcock grease. A West condenserequipped with a drip tip is connected to the trap bymeans of a 24/40 standard taper joint, also lubricatedwith silicone grease. The tapered portion of the trap

362

FIGURE 1. Distillation apparatus.

has a volume of about 10 ml below the overflowtube, U. The overflow tube slopes upward from thetapered portion and so prevents drops of water, fall-ing from the condenser tip, from returning to thedistilling flask. A capillary tube, C, 56 cm long andof about 1.5-ml volume is sealed to the bottom ofthe tapered portion of the trap. This capillary isgraduated at 1-mm intervals between the points Xand Y (50-cm length) and has a 12/3 ball joint atthe top end. This joint, lubricated witii siliconegrease, serves to connect the capillary to a wastereceiver, II, which has a drain stopcock at the bottom.The waste receiver is connected by rubber tubing toa bottle of water, P, which is in turn connected byrubber tubing to a leveling bulb, L. The levelingbulb has both a coarse and a fine adjustment. Rais-ing or lowering the clamp, S, affords the coarseadjustment, and the threaded tube, H, allows thefine adjustment. Thermometer reading lenses provevery useful for reading the scale on the graduatedcapillary tube.

The capillary tube, the trap, and the condenserare coated with a thin film of silicone polymer toprevent water droplets from adhering to the walls ofthe apparatus. The effect of this coating is to reversethe usual water-glass meniscus, and the result is amercury-type meniscus that is easily seen in thecapillary. The silicone coating is applied by pouringa solution, 5 ml of mixed methylchlorosilanes (Dri-filin) dissolved in 100 ml of dry toluene, into theclean air-dried apparatus and allowing it. to stand incontact approximately 15 min before pouring outthe excess solution. It is important that the glass-ware be air-dry and not oven-dry, as a very thinlayer of adsorbed water on the glass surface is essen-

tial to form the coating [14]. Caution: It is recom-mended that this operation be carried out in a hood, asthe methyl chlorosilanes are toxic, flammable, and corro-sive. The apparatus is then air-dried and heatedovernight in an oven at 105° C. The apparatusmay be used indefinitely and may even be rinsedwith acid-dichromate cleaning solution without dis-turbing the film or the calibration of the capillary.However, the film may be removed by soaking theequipment for 10 to 15 min in alcoholic potassiumhydroxide.

The distilling flask may be heated by any suitableheat source, but an electric enveloping heater isrecommended for best control of the distillation.

III. Operation of Apparatus

1. Calibration

The capillary is calibrated by adding, progres-sively, weighed increments of water to the taperedportion of the trap, which has been filled previouslywith dry toluene up to the overflow tul^. Aftereach increment has been added, the water in thetrap is raised up into the graduated capillary bylowering the leveling bulb. The fine adjustmentaffords a simple and quick method for adjusting thebottom of the water column to a zero point on thecapillary. The height of the column is noted andthe leveling bulb raised to return the water to thetapered portion of the trap. Another weighed incre-ment of water is added and the process repeated.The size and number of the increments to be meas-ured depends on the accuracy and precision desired.

Because toluene is present in the trap, the watercolumn is confined between two columns of toluenewhile being measured. This prevents evaporationloss and also aids in obtaining a sharp mercury-typemeniscus at both ends of the water column. Varyingthe weight of the water added and measuring thecolumn lengths obtained allows precise calibration ofthe capillary. If the capillary is uniform, a simplelength-to-weight factor is all that is required. How-ever, if the capillary is nonuniform, a simple graph-ical calibration curve is readily made from suchmeasurements.

2. Distillation of Sample

The sample is weighed to the desired accuracy andplaced in the distilling flask with a sufficient amountof toluene to keep the sample covered. The tolueneis dried by passing it through a column of activatedsilica gel. The trap is filled up to the overflow tubewith dry toluene and the distilling flask heatedslowly until Liquid begins to drop from the tip of thecondenser. The distillation is continued at theproper rate, depending on the type of sample used,until no more water droplets appear in the distillatedropping into the large part of the trap. Five milli-liters of dry toluene is poured in the top of the con-denser to wash any water adhering to the condenserdown into the trap. The heater is then turned offand the water in the trap allowed to cool to room

363

temperature, or a beaker with cool water may belifted around the trap to aid in adjusting the temper-ature to a predetermined value, dependent on thetemperature of the calibration procedure. Aftercooling, the leveling bulb is lowered to draw thedistilled water into the capillary and to adjust thebottom of the water column to the zero point usedas a reference in the calibration of the graduatedcapillary. The length of the water column is read,and then the leveling bulb is lowered further todraw the water and toluene in the trap into thewaste receiver. The trap is again filled up to theoverflow tube with dry toluene, and the distillingflask is replaced with another flask containing asample and toluene. This procedure allows anothersample to be run almost immediately. Cleaning thetrap at intervals by flushing with toluene is accom-plished by pouring toluene in the trap through thecondenser and lowering the leveling bulb to drawthe solvent through the capillary into the wastereceiver. The stopcock on the bottom of the wastereceiver allows removal of the accumulation of waterand tolufne.

IV. Accuracy and Precision

Several experiments, designed for statistical analy-sis, in which a number of possible variables werestudied, were used to evaluate the method. Theknown samples were prepared in batches by taking a200-g batch of GR-S-10 synthetic rubber and millingit for approximately 5 min., after which it was sheetedout at a setting of 0.02-in. distance between themill rolls and then placed in a vacuum oven at 90° Cfor 4 hrs. After the rubber was dried, it was storedin a desiccator overnight. The rubber was thenweighed to the nearest milligram and passed throughthe mill at a 0.02-in. setting several times, taking carethat no rubber was lost from the mill. The samplewas reweighed to check for loss of rubber. Afterthe rubber was checked for loss in weight, it wasbanded on the mill, and two 10-ml portions of dis-tilled water were milled into the sample and the mix-ture thoroughly blended. The sample was next re-moved from the mill and placed on an electricallygrounded sheet of aluminum to cool and discharge thestatic charge formed during the milling operation.After approximately 10 min., t he rubber was weighed.A portion of the rubber was cut into pieces smallenough (o pass through the opening of (he distillingflask and placed as quickly as possible in a. weighedtin wi th an air-tigh1 cover. The remaining portionof t he wet rubber was reweighed and stored in an air-tight container . The tin. containing the sample wasweighed and the sample then removed and placedin the flask containing the toluene. This proceduregave several checks for t h(moisture content, by Weig]moisture during handlingthe loss of moisture duringless than. I mg.

The da ta shown in tableanalysis , indicated that then

Weight of the sample, the, and the possible loss of

Under these condit ionshandl ing was found to he

pendence of the precision and accuracy, within thelimits of this experiment, on the size of the sampleor on the time of distillation after the water dropletscease to appear in the distillate. The slope and inter-cept of each curve shown in figures 2,3, and 4 indicate

3 4 5 6 7 8 9 10 II 12

AMOUNT OF WATER ADDED,GRAMS13 14 15

FIGURE 2. Amount of water recovered versus the amount ofwater added for untreated drum toluene used directly.

O, 45-min distillation; • , 90-min distillation; • 120-rnin distillation. Inter-cept, 0.070 g; slope, 1.03.

- 1 0 -

3 4 5 6 7 8 9 10 II 12

AMOUNT OF WATER ADDED.GRAMS

13 14 15

was no siafter statistical

nilicanl de-

FlGURB -5. A in<imil of water recovered versus amount of wateradded for drum toluene filtered through a Ili-fl column ofactivated .silica gel.

O, 4.r>-min distillation; I I, 90-min distillation; • . L20-min distillation! Inter-cept, 0.028 n; slope, 0.1157.

364

3 4 5 6 7 8 9 10

AMOUNT OF WATER ADDED, GRAMS

II 12 13 14 15

FICURE 4. Amount of water recovered versus the amount ofwater added for drum toluene distilled and the wet forerunremoved.

O, 45-min distillation; • , 90-min distillation; #120-min distillation. Inter-cept, 0.085 g; slope, 0.986.

the recovery and correction for water in each of thetoluenes listed in table 1. The toluene treated withsilica gel showed a recovery significantly less than 100percent but also showed no significant water correc-tion for the toluene. That the other toluenes did notshow a significant difference from 100-percent re-covery is probably due to the lower precision in thesecases. However, the water correction was appre-ciable for these two toluenes. Further, the toluenetreated with silica gel gave the lowest standarddeviation of the three toluenes.

TABLE 1. Standard deviation, water correction, and recoveryas affected by treatment of the toluene

Std.dev.* (g)Water (blank)

correct Ion <:• JRecovery (%)

Toluene passedthrough silica gel

Weight of« ater Inrubber

gI. 16850. 1633

.6122. 7T> 11.3488

.8064

. 7289

.31668061

Weight orw : i l e r re-covered

gI. 13390. 4650

. 6058

. 7703

.3714

8 3 5 7

. 7053

.3316

. 7628

i). 02:!

. 028295. 66

1 (istilled toluene

Weighi ofwater inrubber

g1). 96961. 28660 3327

. .r>i;.r>(i

. 1285

. 9839

. 4896

. 9737

. 3887

Weighi ofwater re-covered

g0.98881. 10710. 3865

. 6070

. 5231

1.048811. 59281 0135n. 1878

0.035

. 084998 63

Untreated toluene

Weight ofwater inrubber

g0.4847

. 8672

. 9008

. 2601

.6991

1 2306(i 2598

. 64221. HIM

Weight "i« ater re-covered

g

0. 5743. 9748

I.0S210. 3564

. 7586

1 29470.3159

. 70691.2188

0. mo

1704103.01

Comparisons were also made between this methodand those involving the mastication of the sampleson hot rolls or oven-drying of thin sheets. Thedata from such a comparison is shown in table 2.The weights of sample used for the water determi-nation in the four methods were quite different,ranging from a few grams for the Mill-oven methodto 450 g for the hot-mill method. However, a com-parison of the standard deviations of the methodsindicates that the distillation method is more precisethan either the Goodrich method or the SpecificationHot-mill method. The Specification Mill-ovenmethod is more precise than the distillation method,but the operating factors of the mill method are toits disadvantage [12].

TABLE 2. Comparison of methods for the determination ofmoisture in synthetic rubbers

Method.

Distillation

Specification Mill-oven Method (C-l-c)[12]

Specification Hot-mill Method (C-l-a)[12]

Goodrich [12, 13]

Toluenetreatment

(Silica geL-•^Distilled-.(.Untreated-

Standard devi-ation of a singledetermination

of water

Percent0.023.035.040

.045

.05

Single determinai [on.

The author is very grateful to Patricia CusterJackson and Aurelia Arnold for making numerousmeasurements for the purpose of evaluating the im-provements in the apparatus, and also to JohnMandel for advice and assistance in designing sta-tistical experiments to show quantitatively the valueof the improvements.

V. References[1] E. W. Dean and D. D. Stark, A convenient method for

the determination of water in petroleum and otherorganic emulsions, Ind. Eng. ('hem. 12, 480 (1920).

[2] G. L. Bidwell and W. V. Sterling, Preliminary notes onthe direct determination of moisture, End. Eng, ('hem.17, 147 (1925).

[3] .). A. DeLoureiro, An improved technic in the toluenedistillation method Tor the determination of moisturein foods! nil's, .1. A.8SOC. Official Agr. ( 'hem. 21 , 645(1938).

[4] .). K. Cleland and YV. U. Fetzer, Determination ofmoisture in sugar products, Ind. Eng. ( 'hem. Anal.Ed. 14, 12 1 (1942).

[5] W. (!. Marskell and J. E. Etayner, An improved apparatusfo r t h e d e t e r m i n a t i o n of w a t e r in o i l s a n d f u e l s , F u e l2«, 49 (1947).

| ( ) | \ Y . X o r m a n n , Z u r w a s s e r b e s ! i n i i n u n i ; i n f e t l e n u n danderen stoffen, Z. angew. Chem. 38, 380 (l(.)2.r>).

|7| A. ('. Beckel, A. G. Sharp, and 1!. T. Milner, Apparatusfor determining moisture by the distillation method,Ind. Eng. Chem. Anal. Ed. 11, 425 (1939).

[8] I1'.. I!. Caley and L. Gordon, Trap for the determinationof w a t e r b y t h e d i s t i l l a t i o n m e t h o d , A n a l . C h e m . 2 1 ,7 4 9 (\»\\)).

|U| ,1. Mitchell and I >. M. Smith, Aquametry, pp. I to 5( I n t e r s c i e n c e P u b l i s h e r s , I n c . , N e w Y o r k , X . Y . , I ( . ) I S ) .

|K)| M. Try on and I'. Custer, National Bureau of Standards,unpublished repori to Office of Rubber Reserve (May24, L948).

907877 50 365

[11] M. Tryon, P. C. Jackson, and J. Mandel, NationalBureau of Standards, unpublished report to Office ofRubber Reserve (Feb. 28, 1949).

[12] P. Custer, National Bureau of Standards, unpublishedreport to Office of Rubber Reserve (Feb. 6, 1947).

[13] P. C. Baker, B. F. Goodrich Chemical Co., unpublishedreport to Office of Rubber Reserve (Aug. 20, 1946).

[14] E. G. Rochow, Introduction to the chemistry of thesilicones, p. 32 and 83 to 88 (John Wiley and Sons,Inc., New York, N. Y., 1946).

WASHINGTON, January 24, 1950.

Journal of Research of the National Bureau of Standards Vol. 45, No. 5, November 1950 Research Paper 2147

Porcelains Within the Beryllia Field of the SystemBeryllia-Alumina-Zirconia

By Stewart M. Lang, Laurel H. Maxwell, and Milton D. Burdick

The general physical properties of practically impervious porcelains within the beryllia(BeO) field of the system beryllia-alumina-zirconia (BeO-Al2O3-ZrO2), whose base composi-tions approximate that of NBS Body No. 4811C, were found to be: maturing range, 1,500°to 1,600° C; apparent density, 2.9 to 3.4 g/cm3; shrinkage, 17.8 to 20.5 percent; room-temperature compressive strength, 238,000 to 305,000 lb/in.2; room-temperature transversestrength, 17,200 to 34,100 lb/in.2; room-temperature transverse strength after thermalshocking, 17,800 to 31,900 lb/in.2; transverse strength at 1,800° F (982° C), 15,100 to 25,100lb/in.2; approximate Young's modulus at 1,800° F, 28,000,000 to 38,000,000 lb/in.2; relativethermal shock resistance, good; and Knoop hardness numbers (500-g load), 550 to 830. Anadmixture of 2 weight percent of calcia (CaO) to the base compositions of these porcelains(without which the specimens would not mature to an impervious structure) caused theappearance of unidentified isotropic phases.

I. Introduction

Because of the advantageous high-temperaturestrength characteristics of "glass-free" bodies com-posed of the ceramic oxides, singly or in combination,as compared to similar strength properties of themetallic alloys, many refractory porcelains may beparticularly well adapted for diversified uses in suchpower-plants as the gas-turbine and jet-propulsionengines.

Previous work at this Bureau [1, 2, 3],1 at theOhio State University Experiment Station [4], at theUniversity- of Illinois [5], and at the Lewis FlightPropulsion Laboratory of the National AdivsoryCommittee for Aeronautics [6] has shown NBS BodyNo. 481 lC [3], whose composition is within thesystem berylUa-alumina-zirconia (BeO-Al2(VZK)2),to be outstanding in many high-temperature prop-erties when compared with other refractory white-wares. Such comparisons made it seem advisableto investigate and report some of the physicalproperties of porcelains whose compositions approxi-mate that of body 481 LC.

A previous report [3] gives in some detail (lie phaserelations of (he system Be()-AI,,().;-Zr().,. The failureof these oxide bodies to mature to nonporous struc-tures was discussed in the Bureau report, but it wasshown that the addition of small quantities ofauxiliary (luxes to the base compositions did permitmaturing of the bodies to a, practically imperviouscondition. An addition of 4 percent of magensia, tobody 4811, whose mole composition ratio is 48BeO: 1ALO..,: l / i ()2 , caused the most pronounced

Figures in l .rackets Indicate the l i terature references ;ii the end of this paper.

effect on the maturing range. Experience has shownthat the use of magnesia tends to increase the particlesizes or distort the particle shapes and thereby todecrease the body strength. Considering all of theproperties studied, an addition of 2 weight percentof calcia (CaO) produced the most satisfactory 4811bodies, and this particular body composition is cor-rectly designated as Body No. 4811C. All but oneof the porcelain compositions given in this reportcontain a 2-percent addition of calcia to the basecomposition; the exception, for comparative pur-poses, is body 4811M, which contains an addition of4 percent of magnesia.

II. Materials and EquipmentThe oxides used in the preparation of the test

specimens were commercially available materials ofhigh purity. The beryllia (BeO) was of nominal99.7-percent purity, and spectrograms showed onlytraces of copper, iron, and magnesium, and veryweak lines of silicon. Ground, washed, and sievedtabular alumina (AI2O3) of 99.5-percent purity wassupplied through the courtesy of the ChampionSpark Plug Co. Commercial zirconia (Zr()2) ofnominal 99-percent purity was recalcined at 1,4-40°C, after which spectrograms showed medium linesfor niobium (columbium) and t i tan ium, and onlyvery weak lines or traces for calcium, copper, iron,magnesium, lead, and silicon. Calcia (CaO) wasadded as (he pure chemically precipitated carbonate.As prepared for use, the materials were, in all in-stances, sufficiently finely divided to pass the No.;!2r> []. S. Standard Sieve. Comminution procedureshave been given [7].

366