384
ANALYTICAL CHEMISTRY
of iodide is f i s t order. The catalytic reaction can be run a t room temperature. The presence of sunlight will catalyze the reaction and is to be avoided. ACKNOWLEDGMENT
The author is indebted to Fritz Bischoff for valuable advice, and to P. A. Gray for clinical evaluation of the method, BIBLIOGRAPHY (1) (2) (3)
Barker, S. B., J . Biol.Chem., 173,715 (1948). Chaney,A. L., IND. ENG.CHEM., AVAL. ED.,12,179 (1940). Glasstone, S., Laidler, K. J., and Eyring, H., “Theory of Rate Processes,” New York, D. Van Nostrand Co., Inc., 1941.
(4)
hlellor, J. W.,“Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 11, 2nd ed., Longmans, Green and Co., New York, 1927.
(5) Ibid., Vol. V, 1924. (6) Raben, M. S., ANAL.CHEY.,22, 480 (1950). (7) Riggs, D. S., and Man, E. B., J . Biol. Chem., 134, 193 (1940). (8) Salter, W.T., and McKay, E. A., Endocrinol., 35, 380 (1944). (9) Sandell, E. B., and Kolthoff. I. M., Mikrochim. Acta, 1 , 9 (1937). (10) Talbot,, K.B., Butler, A. M., Saltsman, A. H., and Rodriguez, P. AM.,J . Biol.Chem., 153, 479 (1944). (11) Taurog, A., and Chaikoff, I. L., Ibid., 163,313 (1946). (12) Thomas, J. W., Shinn. L. A., Wiseman, H. G., and Moore, L. A., ANAL.CHEY.,22,726 (1950).
RECEIVED August 8, 1950.
Quantitative Determination of Raffinose in Mother Beets and Raw Beet Juices By Paper Chromatography ROBERT J. BROWN Research Luboratory, Great Western Sugar Co., Denver, C o b , Sugar beet breeders and others in the beet sugar industry have long sought a method for determination of raffinose, adaptable to volume operation and applicable to small samples, such as are available from single mother beets. The objects of the present investigation were to develop such a method, and to learn the raffinose content of individual roots, variations in raffinose content of different varieties, and change in raffinose content of roots during storage. The method described includes treatment of juice from the beet by mixed-bed ion exchangers, and a modification of deWhalley’s method of paper
A
PPARENTLY all juice obtained from sugar beets contains some raffinose, the absolute quantity depending on environmental conditions under which the beets are grown and stored, and possibly on hereditary factors as well. Because certain operating problems in beet sugar manufacture are increased as the raffiose content of the beet juice increases, the beet breeder has long sought a suitable method for raffinose determination in the hope that beet strains inherently low in raffinose content might be obtained through selection. Chemical methods employing acid or enzyme hydrolysis are unsuitable from the beet breeder’s viewpoint because they require large samples of material for analysis, are not readily adapted to volume operation, and do not yield dependable results on products containing a low ratio of raffinose to sucrose, as do normal sugar beets. The method for determining raffinose in raw beet sugars by paper chromatography, recently published by deWhalley (4), provided the necessary lead, and a method that meets the beet breeder’s requirements was developed. The method described, which is adaptable to volume operation, permits analysis of the small sample of rasped pulp, available from individual mother beets, for raffinose content and other components as well, with a satisfactory degree of accuracy. The raffinose test consists of pressing a small quantity of juice from a portion of the pulp sample, preparing the juice for paper chromatography, and quantitatively by measuring the raffiose content of the prepared sample. The method is applicable to
chromatography for determination of raffinose in raw beet sugars. Individual roots of a single variety showed largevariations in raffinose content, different varieties of beets showed significant differences, and all beets tested showed increase in raffinose content during storage. Use of the method enables the sugar beet breeder to test large numbers of beets for selection of those of low raffinose content. It also provides a tool, more dependable than the common hydrolytic procedures, for the study of factors that may determine the content of beet juices encountered in sugar manufacturing operations.
any juice or liquor, raw or defecated, encountered in the beet sugar manufacturing process. PREPARATION OF SAMPLE
The beet roots from which breeding selections are to be made are carefully stored in a cellar between time of harvest and time of making selections. Tests for various components under consideration are made on a sample of rasped pulp. A wide-angle rasp, which cuts a 36” sector from the root along the axis from tip to crown, is used to rovide a sample of sufficient size from roots of minimum size. he minimum size of root normally encountered weighs about 700 grams, from which somewhat more than 60 grams of pulp may be recovered with care. After 13 grams of the pulp have been taken for determination of sugar and other components, the residual pulp is employed for the raffinose determination. Simultaneous determination of raffinose and other components will generally not be feasible, and therefore the residual pulp is placed in a small plastic bag, labeled, quick1 frozen, and stored a t a temperature below 0” F. until time for t i e raffinose determination. From results obtained to date, it appears that frozen pulp may be stored indefinitely without change. Preparation of the sample for paper chromatogra hy requires: pressing the juice from the pulp sample, deionizing &e press juice sample; and adjusting the deionized sample to standard concentration. A small hydraulic press, such as the Carver laboratory press, is suitable for rapid preparation of the desired volume of press juice. From 40 grams of pul wrapped in 16-ounce duck, more than 20 ml. of press juice maygk obtained.
5
V O L U M E 24, NO. 2, F E B R U A R Y 1 9 5 2 Partridge ( 5 ) noted a harmful effect from the presence of inorganic matter in paper chromatography of sugars and suggested use of ion exchangers for their removal. Albon and Gross ( 1 ) noted that the presence of more than 1.5% ash in raw sugars caused interference with the raffinose test, and also suggested use of ion exchangers. The amount of ash carried by beet juice is well above the critical point, and therefore deionization is required. Deionization is effected by means of a mixed bed consisting of 2 volumes of anion exchanger, such as 1R.4-400, and 1 volume of cation exchanger, such as 1R-120. Anion exchangers of the type of 1R-4B and 1R-45 gave unsatisfactory results. The ion exchanger bed absorbs a small amount of sugar and furthermore absorbs sucrose and raffinose in different ratios. Obviously, the sucrose-raffinose ratio in the effluent must be the same as that in the original juice.
385
Finally, pure raffinose has been added to beet press juice and the deionization treatment given to both the original and the fortified juices. The chromatogram showed the expected increase in raffinose content of the fortified sample. Absorbed sugars are displaced by absorption of ionic matter, of which beet juice generally contains a large quantity. The end point of the ion exchanger treatment may be taken as the point where ionic matter begins to break through the column in significant quantity, or the point where, for safety, the volume of effluent equals thrice the volume of the ion exchanger bed if ionic matter has not broken through in significant quantity a t this point. The mixed ion exchanger is placed in a column made from J//g inch glass tubing, about 5.5 inches long, having a 2.5-inch funnel fused a t the top, and a constriction a t the bottom in which a loosely fitting cotton plug is placed. Below this is attached a crude conductivity cell consisting of a 2-mm. glass tube with two fused-in platinum wires 1 cm. apart. About 5 ml. of mixed ion exchanger are washed into the column; formation of air pockets is guarded against while filling. The water level is held a t the surface of the ion exchanger bed until juice treatment starts. Figure 1 shows the deionizing column. Press juice is poured into the funnel and the flow rate is adjusted to about 1 ml. per minute, As soon as the water is displaced from the column (about 2.5 to 3 ml.), collection of the sample begins. At this point the resistance in the cell is above 100,000 ohms. Collection of the sample continues until 15 ml. are obtained or the resistance drops to 7000 to 8000 ohms. The end point may depend on the characteristics of the conductivity cell employed. One worker, operating a battery of five such columns, all connected to a suitable selector switch, encounters little difficulty after a short training period. The deionized juice from normal beets, which is generally a dark, turbid liquid, is satisfactory for spottin on the paper, after adjustment of concentration to a standard vafue. A few drops of the effluent are tested for concentration in a refractometer, and a measured volume of the effluent is carefully diluted to standard concentration with water-generally 10 or 570 dry substance, depending on the raffinose content of the samples. As results are reported as per cent raffinose on sugar, adjustment of concentration on a refractometer dry-substance basis involves some error, but not sufficiently great to be of significance in selection work. Purity determinations on a number of deionized press juice samples have given results of 95% or higher. DETERMINATION OF RAFFINOSE BY PAPER CHROMATOGRAPHY
Figure 1. Mixed-Bed Ion Exchanger Column By polariscopic analysis, in a large scale test, it was demonstrated that, although the first sugar-containing effluent from treatment of a solution containing 10% sucrose and 0.75% raffinose showed 29% raffinose on sucrose, when the volume of effluent equaled twice the volume of the mixed bed of ion exchanger, the sucrose-raffinose ratio in the total effluent did not differ significantly from that of the original solution. Chromatographic tests have shown the proper raffinose content of the various samples of effluent from 5-ml. beds of ion exchanger n-hen solutions containing 15% sucrose and 0.3, 0.5, and 0.7% raffinose on sucrose were treated and the effluents from each column were collected in three 10-ml. increments. On occasion beet juices are encountered which contain a relatively small amount of ionic matter, and therefore permit the recovery of large volumes of deionized effluent. Tests mere made on such juices to demonstrate the constancy of sucrose-raffinose ratios in the effluents. Effluents were caught in increments, each of a volume equal to twice the volume of the ion exchanger bed. The sucrose-raffinose ratio was found to be constant in all increments.
The procedure employed on beet juice follows generally that described by deWhalley ( 4 ) and by Albon and Gross (1) for raw beet sugars. It is necessary to select standards of the proper range for the beets under investigation. When working with freshly harvested beets, standards carrying 10% sucrose and from 0.2 to 1.0% raffinose on sugar in steps of 0.2% have been found satisfactory. Twenty microliters of a 10% sugar solution, containing 1.0% raffinose on sucrose, carry 20 micrograms of raffinose-this is about the maximum quantity of raffinose per spot found by deWhalley ( 4 ) suitable for quantitative measurement. This quantity of sample applied in a single drop produces too large a spot for best results. Therefore the sample is applied to the paper in three approximately equal increments, and each increment is permitted t o dry before application of another. A micropipet control, such as S o . 293, Size A, marketed by the Micro Chemical Specialties Co., Berkeley, Calif., provides satisfactory control of delivery of the sample. The micropipets used in this work were prepared in the laboratory and all delivered 17.0 =k 0.25 microliters. Little study of filter papers was made, and nothing superior t o Rhatman No. 1 was found. The 22.5 X 18.25 inch sheets are cut to form two 22.5 X 9.125 inch sheets. The papers are spotted along a line 8 cm. from one end, a t 3-cm. intervals; 5 spots of the standard raffinose solutions and 12 spots of juice samples are placed on each sheet. As a tendency often exists for the sample to climb the outside of the pipet ti the paper is lifted to come in contact with the pipet tip before t t e micro-pipet control screw is turned to cause delivery of the sample. Mild heating, provided by a 60-1vatt silver bowl light globe, placed under the point of spotting, is used to hasten
ANALYTICAL CHEMISTRY
396 drying. The spotting benoh carries three micropipets and heaters, all ooerated by one worker.
rlolda uf spotting, spraying of paper, and heating to bring out colors is observed, replicates generally produce spots of the same intensities, and the standards invariablyshow the expected gradation in colors. The deionized beet juice carries more or less colloi" ~~~~~~~" ~~~~~~~~~~. .~ vap& of the &ent em&yed, and requires care to maintain in dal matter, which a t times appears to cause some interference proper condition. Stainless steel. or glass as described bv dowith the running of the sugars, with accompanying changes in the shape and size of the raffinose spot. An idea of the accuracy of the method may be obtained from used-to support the troughs.' The troughs a r e made bycutting Table I, whioh shows observed differences in duplicate tests made stainless steel pipe, 2 inches in outside diameter, along its axis, on deionized juices from 204 individnsl beets. The mean of all and welding on rectangular ends which serve as supports. Notches tests was 1.33% ratkinase on sucrose. are cut just above the edges of the trough, and glass rods are held These results are satisfactory far purposes of selection. The in the notches. This device prevents accidental siphoning oi solvent from the trough to thc filter papcr sheet. beets being tested were abnormally high in raffinose contcnt, and a given variation in intensity of spot color, between duplirates, resulted in twice the normal variation in raffinose found as xII tests were N U a t a concentration of 50% of standard. In ot.her words, when working with normal beets, using solutions :xt, 10% dry substance, a maximum variation of 0.2% raffinose on sugar is expected in duplicate tests, and this variation hut rarely. Oocasionally interference with the ra&iase test arises fmnr aa cvtraneous mgar sometimes observed d j a c e n t to the ritfinose spot. While all normal beets shoa only suoroae, r s 5 o s e , and iovulose, when 1-naphthol is used to develop the chmmetogram, niter too long storage of the beet roots or juice samples obtained therefrom, extraneous ketose-containing 8ugara may appear on the chromatogram. If any of these extraneous sugars appear, one is invariably observed which has ttn R, value slightly greater than that of raffiose, and because the spot often borders that of raffinose i t may interfere with the estimation of raffinose inten.;it.y. Conceivably thia sugar is one, described by Blanohard .wd Albon (5),which is found in mugar liquors incompletely hydrolyzed by invertase. Bacon and Edehnan ( 8 ) have noted t h e presence of three sugars with R, values less than than of mcrosc in sugar Sirups partially hydrolyzed by invertase. The interfering sugar is well &own in Figure 3, sample 8, The solvent used is a modification of that described by dLL though it has run farther, in relation to raffinose, than commonly !%lley (4) and is preuared by mixina 50 volumes of n-butvl &Iooours. ~.ohol,30 volume3 6: ~.)ridine,~RIlvolumrs oi water, and 4.5 w The method, as given above, is presented as a practical, mtisumrd ai benrmr. Thir mixture forms R single phase whirl) ~ d 1 nut, h r d into ~eporntcphases i f the hborntory cools I Z I ~ ~ I I I Jover' factory method for large scale tests on roots of the quality nornight. mally enconntered in breeding work. Spotted nhecrn offilter pxpcr are placed in Lhe troughs, snd 1I1v Roots in abnormal condition may be encountered, which yield chnmisrograms me rtnned without prrlrrQtnltllt of l l w pnpelr ~n deionized juices unsuitable for paper chromatography because pnturntrd VRDOIB. A large pan oi used rulvent is plnrrrl ~n the. bottom~ofth'e cabinel of the presence of too large an amount of colloidal matter. Such Chromatogrnsns are permitted t o develop overnight and ~LII: juices require a clarification step as well &B the deionization then removed from the cabinet, drjed in air, and finally in an oven treatment. The clarification step is &]sodesirablewhen maximum a t 90" C. for 1hour, accuracy in the raffiose determination is wished. Maximum Various color indicators have been tried, but none found equal accuracy is obtained when clarified, deionized juice is run hy the to the 1Yq solution of 1-naphthol in ethyl alcohol plus 1volume of phos honc mid to 10 volumes of 1-naphthol solution, recomupflow procedure. Upflori has not given satisfactory resu1t.s on menfled by Albon and Gross ( 1 ) . press juice treated by deionixation only. Uniform spraying of the sheet is highly important and both sides are sprayed. After spraying, the sheet is permitted t.o dry in air for a t least 30 minutes.before heating. This drying treatment increases the sensitivity of the test and decreases relative 1 'able 1. Comparison of Duplicate Tests on 204 Single Beet background intensity. The sheet is then placed in a large oven at. Roots 90" C. and heated far 5 minutes for color development. Unifarmity of oven temperature in the area where the sheet is placed is Spread in Ob~
a1.n
~~
~~~
~
No. of Roots
hilrhlv imnnrtant
i n Olm," .~ . ~
102
box covered with B milk ala& olaie uniformlv illu;hihated from beneath serves well
68 29 4
1
.
~
~
served % Raffin. "" SllrFnaa ..... 0
0.1 0.2
0.3 0.4
Figure 3 is a photograph of a finished chromatogram. Samples 1, 2, 8, and 9 are beet juices; No. 8 was held until decided deterioration had developed. Samples 3 to 7 are standards containing 0.2 to 1.0% raffinose on sucrose.
The following methods have been employed successfully f o r preparation of a clarified, deionieed ssmple:
accuracy of results proper attention to
Add 0.4 to 0.5% calcium oxide on beet juice as milk of lime. heat to 80' t o 85' C., add filter aid, filter on a Biichner funnel, cool, and deionize filtrate. Clarify the juice with bade lead acetate, filter, and deionize t h e filtrate.
V O L U M E 24, NO. 2, F E B R U A R Y 1 9 5 2 Deioniee the juice sample, coawlt~tecolloidal matter with aliiminum hydrosol, and filter. The procedures described may he applied to any beet juice or liquor, raw or defecated. On these products, where size df sample available is not a. factor, doioniastion of a lead acetateclarified filtrate and employment of upflorr, technique are ret-
ommended for greatest. accuracy. Concentrations of solutions must be selected to provide suitable Quantity of raffinose in the spot placed on thepaper, and stand&ds modified to the same ~ucrosecontent and proper range of raffinose content. When products very high in raffinose content are tested, dry substance of the deionized effluent is not a satisfactory basis. Deionization is performed on a somewhat larger sede, and all samples are prepared for spotting a t constant polarization. After raffinose has been determined chromatog raphieally, its polarieation is estimated and the sucrose oonteint of the sample is taken by difference. This procedure has proved very satisfactory 011
.
. . .
3 ON SUGAR BEETS
387 were stored loosely in crates in a cellar a t about 8' C. until February 26, 1951, a total of 4 months. On this date the various stored samples were composited to form three composite8 of each of the ten varieties and the 30 samples were tested for raffinose. Table I1 shows the mean percentage raffiose on sucro8e found in each variety a t harvest time and after 4 months' storage, and the percentage increase in raffinose content in each variety. All varieties show increases in raffinose content ou storage, and although they are not constant, pight of the ten varieties show an increase of 0.4 =k 0.14% raffinose on sugar during the 4 months' storage period. All varieties lost sugar during storage, but the loss was not great enough to have a significant effect on raffinose gain, The mean loss in polarization \vas about 4% of the value a t harvest time.
T a h l e 111. Change in Raffinoae Content of Beets Stored in Outdoor Pile % Ra*aem . Roots entorinx
Sarrrpie NO.
,de
0.38
1
t,hc oampaign progresses, the raffiose content of the liquors tends to increase. The absolute value of raffiose in the liquors shows seasonal variations. The plant breeder is interested in selection of beets that will produce liquors with a minimum of raffiose. Furthermore, he is interested in the relation between raffinose in beets as harvested and the increase on storage, as beet# are commonly stored for long periods before testing for selection as mothers. A few tests have been made to gain information regarding increase in raffinose during storage.
Table 11.
Ratlinose on Sucrose in Fresh and Stored Beeta
!?.a!?
32 4
Swsr Roots leaving pile 0.47
0%
xea
Data on Ck ~" ... proup of individual beets.
--.
I-~._cll
~ - --.---I-.--
tent The mean of the 20 tests showed 0.80%7raffiose on sugar, and the extremas ranged from 0.53% minimum to 1.05% miximum. About January 15, 1951, raffinose tests were made on move 200 d e o t e d roots of this aame ~ O U D . Durine this . ..... than .~~~~~~ storage period of 7 weeks, the mean raffiose:ont&t increased t o 1.33Y0 on sucrose. or 0.53%. There is good reason for thinking T a r_--"_ mate that'ihe raffinose content of the selected &oup did not dif.". rially from that of the mean of the mhole~ T h e individnal tests a maxion the latter group ranged fror mum of slightly above 1.51 ~~~
~~~~~~~
~~~
~
These roots, which were decidedly high in raffiose at the time of the first testing, gained raffinose on storage much more rapidly than did those of the group shown in Table 11. The beets in the two series of tests were grown on fields located in two different weas. All results thus far presented have shown extremely high percentage of raffiose on sugar. Welldeveloped roots grown near On October 27-28,1950, twelve replicate aamples of each of t.en Iknver, Colo., were dugand tested on August 1, and showed from varieties were harvested and six replicates of each variety were n.on to 0.35% raffiose on sugar. Roots grown in the Billings, tested immediately. The remaining six replicates of each vxriety Mont., area, dug on August 14, varied from 0.1 to 0.80/,, and averaged 0.54% raffinose on sugar. P 4 5 6 7 In the Rocky Mountsin area it is necessary to harvest all beets before a heavy freeze sets them permanently in the ground. Therefore, many beets are stored in piles which are worked out later during the campaign. While one such storage pile was being formed in the Denver area, the beets entpring the pile were sampled once a week over a period of 4 weeks, during which the pile was being formed. The pile w-as tnkeu out during 8 3 d a y period, after an average storage period of about 9 we&. At the time the pile was taken out, the roots were carefully sampled. 0.2 The results of the tests for raffinose % RAFFINOSE ON SUCROSE on the beets entering and leaving the Tile are given in Table 111. e ?I. Finished Chron~utogramof Beet Juices and RnfIinnse S t a n d a r d s
ANALYTICAL CHEMISTRY
388 The results show an increase in raffinose during storage in the pile, but the rate of increase is much less than in roots stored in the cellar. DISCUSSION
That the raffinose content of sugar beets increases during storage appears to be demonstrated without question, but it is too early to attempt an authoritative discussion of the factors which determine the absolute level of raffinose in the roots a t harvest time or the rate a t which the raffinose content increases during storage. Environmental factors during the growth of the beet may be of major importance. Heredity appears to be a factor. Much additional information is needed on the whole subject. The quantities of raffinose found in most beets tested during the past season were far above the expected value. However, it has been demonstrated that the quantities of certain other components may differ widely between beets grown on average commercial fields and beets grown on highly fertile experimental fields, and since only the results given in Table I11 were obtained on commercially grown beets, it is possible that the data presented herein may tend to create a false impression of the normal raffinose content of commercial beets. Most of the beets encountered in the present investigation were far above the normal for commercial beets of the Rocky Mountain area. As a check on the above observation, press juice was obtained from a large batch of pulp from the same group of beets considered in Table I (average, 1.33% raffinose on sugar). The press juice was given the standard lime defecation and carbonation treatments, and a pan was boiled from the juice in order to produce a green sirup in which the raffinose content would be sufficiently great to ensure accuracy of the raffinose determination by
invertase and melibiase hydrolysis. The green sirup showed 82.6% sucrose and 2.25% raffiose on dry substance, equivalent to 13y0 raffiose on impurities. On further crystallization of eugar, this raffinose would be found in the molasses a t the same per cent on molasses impurities. The average raffinose content of molasses from beets in the Great Western Sugar Co. area in 1950 was about 4.5% on impurities. While the mother beets that were tested averaged abnormally high in raffinose content, a few of relatively low rafFmose content were found, and possibly the plant breeders may develop a strain of low raffiose beets from those few. ACKNOWLEDGMENT
The writer is indebted to numerous persons for assistance in this investigation. First, he gives his thanks to H. C. S. deWhalley, director of the Tate and Lyle Research Laboratories, for information, in advance of publication, on his work on the determination of raffinose in raw beet sugars. Various members of the staffs of the Research Laboratory and the Experiment Station of the Great Western Sugar have given valuable assistance, especially Ralph Wood. LITERATURE CITED (1) Albon, N., and Gross, D., Analyst, 75,454-7 (1950). (2) Bacon, J. S. D., and Edelman, J., Arch. B i o c h m . , 28,467 (1950). ( 3 ) Blanchard, P. H., and Albon, N., Ibid., 2 9 , 2 7 0 (1950). (4) deWhalley, H. C. S., Intern. Sugar J . , 52, 127-9, 151-2, 267 (1950). (5) Partridge, S. M., Biochem. J.,42, 258 (1948). RECEIVED April 27, 1951. Presented before the Division of Sugar Chemistry at the 119th Meeting of ANERICAN CHEMICAL SOCIETY, Boston, Maas.
Determination of Geometric Surface Area of Crushed Porous Solids Gas Flow Method SABRI ERGUN Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, Pa.
D
ETERMINATION of specific surface area of solids has long been the subject of numerous investigations in connection with correlating the energy spent in crushing with new surface created. Although the establishment of such a relationship would be of great practical use to the process industries of crushing, the interest in surface determination has by no means been limited to crushing. Surface determinations are generally a means to an end-i.e., the knowledge of surface in itself is not so important as the application of such knowledge to estimation of reaction, heat and mass transfer rates, and pressure drop, and to numerous processes in industrial operations. Most solids possess, in addition to their external visible surface, an internal surface due to existence of empty spaces within their boundaries. If these internal spaces are considerably larger than molecular sizes, they are referred to as pores, and the material is spoken of as being porous. Differentiation between the external surface and the internal surface of porous particles is often important, but is difficult to make, as there exists no definite boundary between them. A geometric surface, as distinct from external surface, may be visualized as the surface of an impervious envelope surrounding
the body in an aerodynamic sense. Irregularities and striae on the surface would not be taken into account in a geometric surface in contrast to external surface. Whether the value of the internal, or the external, or the geometric surface area is desired will depend on the objective. Geometric surface areas are required in connection with sedimentation rates, resistance to the flow of fluids, bulk density and packing problems, and heat and mass transfer rates in flow processes. If rates of solution and reaction, and hygroscopic or total adsorptive properties are in question, the total accessible area is the relevant area. Diversified interests in surface area measurements have led t o the development of various methods, and in recent years the literature on the subject has grown rapidly. Dissolution methods developed by Wolff (83), and Martin and coworkers (YO),and later extended by Schelte (76) and Gross and Zimmerley (38), have been used to measure surface areas of glass beads, crushed quartz, etc. These methods, however, are limited t o materials for which a suitable solvent exists; even then critics have regarded the method as doubtful (S, 7 4 ) . The proportionality of heat of wetting for a given solid-liquid pair to the surface area of the solid has been utilized by various
