601
ELECTRICAL RlOISTURE TESTISG
(5) GELBACH: J . -4m. Chem. Soc. 6 5 , 4857 (1933). Text-book of Physical Chemistry, p. 1082. D. Van Nostrand Company, (6) GLASSTONE: Inc., S e w York (1940). ( 7 ) GLASSTONE, LAIDLER, ASD EYRING:T h e Theory of Rate Processes, p. 199. (8) HINSHELTVOOD: T h e Kinetics of Chemical Change in Gaseous Systems, p. 239. Clarendon Press, Oxford (1929). AND LIARTIN:J. Phys. Cheni. 38, 365 (1934). (9) IREDALE (IO) JONES ASD KAPLAN: J. Ani. Chem. Soc. 5 0 , 1845 (1928). (11) PIIOELTYN-HUGHES : T h e Kinetics of Reactions i n Solution, p. 15. Clarendon Press, Oxford (1933). (12) L~OOSEI.AND L c D L A M : Proc. Roy. Soc. Edinburgh 49, 160 (1929). (13) PAULIXG: T h e A7ature of the Chemical B o n d , 2nd edition, pp. 346,349. Cornel1 University Press, Ithaca, Xew York (1940). (14) Reference 13, p. 167. (15) POLISSAR: J. Am. Chem. SOC.62, 956 (1930). (16) POPOFF AND WHITMAN: J. .&In.Chem. SOC. 47, 2259 (1923). (17) RICE,RILPATRICK, .4m LEMKIX: J. Am. Chem. Soc. 45, 1361 (1923). (18) SCHrxhcHER A N D STIEGER: physik. Chem. 12B, 348 (1930). (19) SCHnfAcIIER AND WIIG: z. physik. Chern. 11B,45 (1930). (20) SEMENOFF: Jahresber. Fortschritte Chem. 1864, 483. (21) SLATOR:J. Chem. Soc. 86, 1697 (1904). (22) TOLMAN: J. Am. Chem. Soc. 42, 2506 (1920). (23) VOSBURGH: J . Ani. Chem. Soc. 44, 2120 (1922).
z.
RADIO-FREQI-ESC'Y DIELECTRIC PROPERTIES OF DEHTDRATED CARROTS -%PPLICATIOS 'IO ~ I O I S T T DETERMIS.~TIOS RE B Y ELECTRIC i~ METHODS K . CRAWFORD D U S L A P , J R . ,
~ Y D BESJAAIIS
RIAKOWER
K e s t e r n Regional Research l,abora20ry1, A l b a n y , California Received J u n e Y , 1945 I. INTRODUCTIOX
l'ery fen- comprehen,Qive studies have been made of the radio-frequency properties of vegetable materials containing absorbed water. Tausz and Rumm (11) have macle a fairly complete study of several materials, including starch, tobacco, and slate, but their measurements were made only a t low frequencies, in the neighborhood of 1000 cycles per second. Argue and 19aass (1) have measured the dielectric constant of a cellulose-n-ater system as a function of the moisture content, at one frequency, 500 kc., and one temperature, 25°C. Several investigations have been carried out on the radio-frequency properties of soils, which have dielectric properties similar to those of organic systems containing dispersed water. Smith-Rose (10) has measured the dielectric constant and the conductivity of various types of soil as a function of the moisture content and Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.
602
K. CRAWFORD DUNLAP, JR., A S D BEXJAMIS MAKOWER
of the frequency (10 kc. to 10 me.) a t one temperature. Fricke and his collaborators (4, 5, 6) have made nieasurements on gelatin-water systems and on various other systems, such as kaolin-n ater and quartz-water suspensions, a t frequencies from 2 kc. to 65 mc. Errera and Sack (3) haye recently measured dielectric properties of animal fibers at frequencies from S kc. to 13 mc. S o previous work has been done upon dehydrated vegetables in this field; a t least there is no information available in the literature. The work reported in the present inveFtigation deals n i t h the dielectric properties of dehydrated carrots, especially with the radio-frequency properties.' The dielectric constant and thc electrical conductivity have been measured n-ith respect t o changes of moisture content, temperature, frequency, bulk density, and particle size. Some ~i-ork has also been done on the effect of electrode polarization upon the results a t low frequencies. These properties are of especial importance for the measurement of moisture content by electrical methods, including d.c., low-frequency, and radio-frequency methcds. Folloir ing presentation of the results a discu3sion is given of various electrical methods of measuring moisture content. The results reported in the present paper mag also have some interest in connection n.ith the problem of the nature of the dielectric properties of dispersed materials of biological origin containing absorbed water. 11. RIETHOD, .1PP.\R i T U S ,
\SD JI l T C R I - ? L S
The preliminary mcasiwmenty of capacity w r c made by determination of the change of capacity required in 3 parallel standard condenser to restore resonance. Although the method TI-ahfound to give exellent preckion for capacity nieasurements at low moisture contents, the broadening of the resonance curve caused by the lealiage conducti-\-ityof the cell at high moisture contents (aborc 12-14 per cent) led t o abandonment of this method in favor of a radio-frequency bridge type of measurement. Thi. bridge ciicuit has been discussed by Oncley (8) and T. 11. Shaw (9). The frequency range obtainable by use of an all-n-ave receiver as detector n-as from 18 kc. to 5 mc. -1bol.e 5 mc. the shielding of the bridge became very poor, and balance T ~ difficult. S In the racgc 18 kc. to 5 mc., with this bridge and a General Radio Co. Type i 2 2 D standard condenser, and with the cell described belon, capacities from 10 to 1100 ppf and conductivities of the order to mho per centimeter could be 2 It is necessary in some cases t o correct results obtained f r o m a high-frequency bridge T h e most commonly required correction is that for the inductance L of the leads of the cell. This inductance affects the capacity according t o the following equation.
c, =
C 1 - 02LC
where C i s the true capacity, C, the messured value, and w = 27r X frequency of oscillation. I n the present work this correction is not needed, since a t high frequencies, where the correction is most likely t o be needed, the capacity is small, and \Then the capacity is large t h e frequency is small. This conclusion has been checked by measurement of t h e inductance of the leads and calculation of the correction for several typical cases In all these cases the correction was negligible I t has also been noticed t h a t there were slight irregularities in e when small changes of capacity were being measured, owing t o lack of constancy of inductance of the standard resistor, for different resistance values
ELECTRICAL MOISTURE TESTIKG
603
The experiments were carried out by use of the cell represented in figure 1. The outer diameter of the inner electrode was 3.49 em. and the inner diameter of the outer electrode was 5.60 cm. The annular region containing the sample was 5.06 cm. in length. The cell vias ordinarily filled with a constant weight of 45 g. of dehydrated material. Thus the bulk density was equal to 0.760 g. per ~ m This . ~ value for the bulk density is to be assumed in the remainder of this paper, unless othern-ise specified. The outer electrode was grounded in all the measurements to avoid errors due to presence of stray capacities. Fiducial marks on each cap and on the shell enabled one to screTr the caps on to the same point for each experiment and thus to reproduce accurately the end capacities. The measurements were made in a room maintained at a temperature of 22°C. & 1.0" and a relative humidity of 50 per cent. For control of the temperature of
1h -
r///1
BRONZE
2 CM.
POLYSTYRENE
FIG.1. Longitudinal section of cell used in t h e dielectric measurements
the cell, n-ater was circulated through the coil indicated in figure 1. This coil was connected with another coil immersed in a bath whose temperature could be held constant to fC.2"C'. Circulation was obtained by use of a centrifugal pump, The temperature 11-as read from a mercury thermometer immersed in the liquid as it returned to the bath. Pince the reading on this thermometer ~ r a 40.2" or O.3"C. different from the reading of that in the bath, the average temperature was used in tabulation of the results. -411 the measurements were begun after a 1ap.e of a t least 30-40 min. after beginning of circulation, which was the time required to bring the cell to constant temperature. The preliminary experiments n-ere carried out by use of the cell equipped with bakelite-impregnated fabric insulators. The considerable variation in the "empty" capacitance value of the cell, caused by water absorption of this insulation, led to replacement of these insulators with others made of polystyrene.
604
W. CRAWFORD DUSLAP, JR., .YTD BENJAMIS JIAKOWER
The polystyrene-insulated cell retained high insulation resistance and low power factor even a t 100 per cent humidity. It is important to know fairly accurately the value of the cell constant, CO, which may be defined by the relation
As a first approximation, COis the capacity of the empty cell minus lead capacity and edge-effect capacity. C, is the capacity of the empty cell. Cf is the capacity of the cell filled with material. E is the dielectric constant of the material. Co can be calculated fairly accurately for an infinitely long cylindrical condenser by the formula
co =
1.111 ~
Wf
2 log a where b = the inside diameter of the outer electrode, a = the outside diameter of the inner electrode, and 1 = the length of the cylinder in centimeters. For the present cell this value was 8.35 ppf, but edge effects made this value inaccurate. The value of Co was also determined by calibration with water, amyl alcohol, and caprylic alcohol (2-octanol). The dielectric constants of the alcohols were separately determined in a three-plate parallel-plate condenser vith quartz insulation. This condenser was calibrated by use of purified acetone and benzene. Acetone and benzene could not be used in the cell of figure 1, because they dissolved the polystyrene insulation. The values of Co obtained by the above procedure varied from 8.35 for n-ater to 9.01 for caprylic alcohol. It seems that changes in the end capacities caused by the presence of material of high dielectric constant caused the cell constant to decrease ivith increase in dielectric constant of the contents. The value for water is approsimately equal to the calculated value. The value obtained by use of caprylic alcohol (CO = 9.04 ppf) wa? used for all E from 1 to 10. When the uncorrected E obtained from equation 1 with Co = 9.04 varied from 10 to 30, E v-as recalculated Tyith a value of Co equal to 8.90. Similarly, for uncorrected E in the range of 30 to 50, CO= 8.70; for E = 50 to 70, Co = 8.50; and for e > 70, Co was taken to be 8.35 ppf. No attempt was made to calibrate the cell for conductivity measurements. Instead, the calculated cell constant for conductivity T V ~ Pused. Thus, the specific conductivity is calculated from the obserred value of the resistance, K , by means of the formula g=-
b log a 2nlR
The use of this equation is justified, since the observed variations in the conductivity are usually very great, often involving changes by factors of several powers of ten; hence high accuracy is not needed.
ELECTRICAL MOISTURE T E S T I S G
605
Accurate measurement and even definition of d.c. conductivity of non-conductors is in general rather difficult, because the result may vary with applied voltage, time of application of voltage, and other factors. Electrode polarization also affects the results, since for high moistures readings of resistance obtained with a d.c. ohmmeter showed immediate increase with time upon application of voltage. S o special precautions have been taken in this work with respect to any of the above factors, and the results for d.c. resistance cannot be considered to be of high precision. The higher conductivities were measured with a multitester ohmmeter and the conductivities in the range lo-’ to 10-lo ohm-’ with an electronic ohmmeter. A ballistic galvanometer method was used for conductivities in the range 10-lo t o ohmp1. Conductance of the polystyrene insulation was found to be much less than that of the sample in all cases. The carrots used in the present vork were obtained from t v o different sources. One type was obtained on the open market and consisted of a mixture of varieties, but was probably mostly of the Chantenay variety. The other type consisted of the Tendersweet variety. Although it has been found in other work that dielectric properties, and especially the conductivity, vary with variety, the two types used in the present work were found to have practically identical properties. The carrots were dehydrated by commercial dehydration methods by the Engineering Division of this laboratory. The samples were brought to their final moisture content by placing them in desiccators over solutions of various concentrations of sulfuric acid (7). The moisture content was determined a t intervals during the work by heating for 22 hr. at 70°C. in a vacuum oven after grinding in a Wiley mill through a C.S. KO.40 sieve. Moisture content is expressed throughout this paper in terms of percentage of dry weight. Although there is some doubt as to the degree of correspondence of the “water” determined by this method and the “water” involved in a dielectric measurement, it was considered that the accuracy of the determination v a s satisfactory for determination of the moisture differences among the samples used The initial experiments consisted of measurements on loosely packed carrots (bulk density 0.76 g. per cm.9 ground to pass a U. S.KO,18 screen but not a V. S.S o . 25 screcn (18-26 mesh). Later a distribution of S o . 18 to No. 35 was used. S o significant differences in results were found for either dielectric constant or conductivity for the same density of packing for these two distributions. A discussion will be given later of the effect of using smaller particles than those present in the above distributions. 111. PRECISIOS O F RESULTS
idea of the precision of the results may be obtained from the following experiment : The dielectric constant and electrical conductivity of a sample of carrots containing 6.1 per cent moisture were measured a t 1.8 mc. after each of four successive fillings of the cell. The values for e were 2.779,2.777, 2.781, and 2.779. These values indicate that for materials ground t o fairly narrow particlesize distribution (18-25 mesh) the dielectric constant is reproducible to better than 1 per cent. Horn-ever, fluctuations in temperature and in moisture content,
606
W. CRAWFORD DUXL.LP, J R . , h X D BESJAMIK 3 f 1 K O W E R
and errors in the bridge itself, probably make the accuracy for the dielectric constant no better than 1-2 per cent. The results for the specific conductivity in the above experiment were: 3.43, 2.54, 4.05, and 2.17 X lov8. It is clear that the agreement is not as good as it is n-ith the dielectric constant, especially a t TABLE 1 V a r i a t i o n of the dielectric constant of dehydrated carrots w i t h change of moisture content, temperature, and frequency MOISTURE
(PER CENT, DRY 'vEIGHT)
1 1
F R C Q L T X Y IY KILOCYCLES
5000
I
1800
1
1000
-
2.32 2.38 2.42 2.66 2.64 2.78 4.29 5.23 6.05
1.5 4.2 6.1 8.5 9.2 10.3 16.3 18.7 20.4
!i
2.33 2.40 2.44 2.71 2.69 2.87 4.62 5.82 6.96
1
1
2.34 2.41 2.46
1
1 1
500
1
2.34 2.42 2.47
180
1
100
1
50
I
18
2.37 2.44 2.50
2.35 2.46 2.52 2.91 2.89 3.19 6.44 9.26 11.55
2.39 2.48 2.53 2.97 2.95 3.29 7.27 10.8 14.8
2.41 2.51 2.56 3.08 3.05 3.46 8.99 13.8 19.2
2.39 2.55 2.57 2.79 3.59 3.73 10.25 13.43
2.41 2.57 2.59 2.83 3.80 3.87 11.83 15.18
2.42 2.60 2.61 2.88 4.00 4.06 14.5 18.1
2.44 2.63 2.64 2.90 4.37 4.46 19.7 24.3
2.60 2.84 2.90 3.37 4.G7 6.25
2.61 2.88 2.94 3.45 5.03 7.00 16.25 19.09 21.4 28.9
2.63 2.93 3.00 3.60 5.58 8.25 19.2 24.2 26.3 38.8
2.65 3.01 3.09 3.88 6.77 10.78 24.9 35.0 37.1 64.4
(b) 20.7"C. 2.34 2.45 2.47 2.64 3.14 3.16 5.84 7.12
1.5 3.8 4.2 6.1 8.52 8.59 16.3 18.5
2.35 2.48 2.50 2.66 3.29 3.31 6.59 8.31
2.35 2.49 2.52 2.70 3.38 3.39 7.26 9.15
2.37 2.52 2.53 2.74 3.50 3.52 8.21 10.7
(c) 353°C 1.5 2.6 4.2 6.1 8'52 10.2 15.6
20.4
I
1
I
1 1
2.51 2.66 2.72 2.95 3.66 4.14 7.13
9.90
2.52 2.73 2.77 3.07 3.88 4.60 8.48 9.05 10.83 12.11
2.54 2.76 2.80 3.13 3.99 4.81 9.56 10.23 12.13 14.05
2.55 2.80 2.84 3.23 4.22 5.29
14.10
1
1
I,
the low moisture levels. Thus, whereas the maximum variations in dielectric constant are equivalent to 0.05 per cent moisture, the maximum variations for conductivity correspond to 0.15 per cent moisture. Bridge errors arking from manipulation a t balance in the measurements of conductivity probably exceed those for dielectric-constant measurements.
607
ELECTRICAL MOISTURE TESTIKG IV. RESULTS
In tables 1 and 2 are presented values of the dielectric constant and total conductivity (a.c. and d.c.) as functions of moisture content, temperature, and ThBLE 2 V a r i a t i o n of the total Conductivity of deh,ydrated carrots with change of moisture content, temperature, and frequency Conductivities in mhos per centimeter X 10'
___ hroIsrunE
(PERCEST D K S
I~EIGH')
1 I
FKEQCESCS IN KILOCYCLES
jO00
I
1800
I
I
1000
5on
I
180
I
100
I
50
I
__ 18
(a) 1.5"C. ~~
1.5 4.2 6.1 8.5 9.2 10.3 16.3 18.7 20.4
~
I
1 1
1 I
1.45 1.70 1.78 3.30 3.82 4.95 23.4 33.7 53.7
I
0.482 0.540 1 1.20 1 1.36 1.95 8.80 16.5 28.9
~
' i
0.124 0.124 0.093 0.420 0.374 0.576 3.59 8.06 16.4
0.280 0.295 0.260 0.980 0.779 1.15 5.75 11.7 21.3
0.046 0.039 0.047 0.140 0.125 0.205 2.01 5.27 11.9
0.031 0.0311 0.031 0.078 0.078 0.125 1.46 4.35 10.3
0.016 I 0.008 0.016 , 0.047 0.031 ' 0.031 1.09 3.66 9.10 1
0,047 0.062 0.047 0.093 0.452 0.470 10.1 29.3
0.016 1 0.016 1 0.031 0.062 0.264 0.310 8.75 , 27.7
1
0.016
I
0.008 0.016 0.015 0.793 3.02 8.20
(b) 20.7"C. 1.5 3.8 4.2 6.1 8.52 8.59 16.3 18.7
, , 1
1 1
1
1.59 2.22 2.29 3.16 7.26 7.20 45.0 82.0
'
' 1
0.700 1 .04 2.94 1 2.74 1 25.2 50.9
0.202 0.420 0.404 0.622 1.73 1.85 18.7 41.6
~
1 '
0.140 0.185 0.202 0.280 0.996 1.01 14.2 33.3
1
1 ~
~
0.016 0.031 0.016 0.031 0.171 0.170 7.57 26.4
0.016 0.109 0.093 6.63 25.2
0.016 0.031 0.047 0.125 0.607 1.52 34.8 42.4 97.5 127.2
0.031 0.023 0.062 0.374 1.04 33.8 40.5 95.5 121,
( c ) 35.S"C. ~~~
1.5 2.6 4.2 6.1 8.52 10.3 15.6 16.3 18.7 20.4
, '
0 751 1 0 362 2.37 1 07 1 0 624 3.10 1.24 0 747 3.70 2 15 1 23 5.51 1 12.7 1 4 2 7 1 3 2 7 9 92 6 87 20.6 64 4 54 1 101.0 ' 6 3 3 I 7 4 7 114. 1 141 122 191. 1 179 1 160 246. ~
1 1
I
0 164 0 05871 0 039 0 327 0 062 0 327 0 110 0 717 0 327 I 0 187 208 0 904 4 66 2 06 45 2 38 5 36 2 543 1 4 7 2 ,44.6 111 103 100 146 135 131
;:!
56"
~
frequency. By total conductivity is meant the conductivity measured by an ax. bridge. In figure 2 are shown curves for carrots representing the variation of the dielectric constant, E, with moisture content a t three temperatures, and a t one frequency, 1.8 mc. Figure 3 shows the variation of E with frequency for differ-
608
W, CRAWFORD DUNL.\P,
JR., .ASD BENJAMIN MAKOTVER
FIG.2. Variation of E of dehydrated carrots with changes in moisture content for three temperatures, a t 1.8 mc. There is considerably greater variation of E a t low moistures a t 35.8"C.than a t 20.7" or 1.5"C. All moisture contents refer t o dry basis. 20.7'G.
100 b-
z a
-
z
-
+ C n 0 0
10
2 (L
+ 0 w
-I
:
--
8.5
-
wn I1 5
1.5
I
I
I I I l l
I
I
I
L
I
I
50 FREQUENCY
t
I
I
500
-
I
I
I
I I I I
5000
KILOCYCLES
FIG.3. Variation of the dielectric constant with frequency a t various moisture contents a t 20.7"C. The frequency variation of e is very slight a t low moisture contents,. but is large for high moisture contents.
ELECTRICAL M O I S T r R E TESTING
609
ent moisture contents at 20.7"C. From figure 2 one notes that there is only a small increase of the dielectric constant with increasing moisture until the mois1
1.5OC.
'I 0'10 I
I-
> Io
2
z
0
0 0 -
LL -
0
-8
IO n v)
-I
a
IO I-
-9
IO 0
4 8 MOISTURE
12 16 20 C O N T E N T (%I- DRY BASIS
FIG.4. Total conductivity of dehydrated carrots as a function of moisture content for various moisture contents and frequencies, a t 15°C. As the frequency increases the conductivity also increases, hut for all frequencies there is little or no change in conductivity until a moisture region of 6-8 per cent is attained. Although no work has been done upon very high moisture contents, it is pi-ohable that the curves flatten out a t moistures slightly higher than the highest used in this ivork.
ture reaches about 8 per cent. It is also clear that the slope of the dielectric constant-moisture curve increases with temperature.
610
W. CRSWFORD DU411.1P, J R . , r\ND BENJAMIR' MAKOWER
Figure 4 shows the variation of the total conductivity of the material as a function of moisture content for various frequencies, a t 1.5"C. Figure 5 shows the same curves for 20.7"C., and figure 6 the curves for 35.8"C. The three sets
MOIST U R E C 0 NT E NT-( %)-DRY BAS IS FIG.5 . Total conductivity cs. moisture a t 20.7"C. The rapid variation a t 6-8 per cent a t 1.5"C. has changed into a much slower one a t 20.7 and there is considerably greater variation of
u
with moisture a t low moisture contents.
of curves show a marked transition in conductivity a t low moistures as the temperature is increased. Thus at 1.5"C.,there is almost no change of conductivity with change of moisture content until the moisture content reaches 6-8 per cent, a t which moisture level the conductivity begins to rise rapidly. At 20.7"C.
611
ELECTRICAL MOISTURE TESTIKG
there is considerably greater variation of conductivity with moisture content, but there remains a definite sharp inflection in the curves. At 35.S°C. the sharp inflections have disappeared and the variation of conductivity with change of
MOISTURE
CONTENT (%)- DRY
BASIS
E'rc,. G Totnl conductivity L'S moisture at 35.8"C. The sharp variations of figure 5 now appear only as a mild inflection of the curves. Coincidental with this change of shape of the curves, the slope in general decreases at high moistures with increase in temperature. Change 111 temperature, of course, also produces a general upward shift of all t h e curves.
moisture is of the same order of magnitude a t low and high moisture contents. In figure 7 some of the conductivity results have been replotted t o show variation of conductivity with frequency a t various moisture contents. It seems evident that a t low moisture levels the conductivity is nearly linear with respect
612
W. CRAWFORD DUXLAP, JR., B X D BEKJAMIS MMAKOWER
to frequency change but that a t high moisture levels the conductivity begins-to increase markedly only above about 1000 kc.
20.7" C -5
IO
J
t
>.
I-
-I
I-
* /
-
a
//
-9
I O ,
//
I
/
'1
I
I
I
l
l
I
I
I
l
l
FREQUENCY - KILOCYGL-ES FIG.7. Variation of total conductivity with frequency at 20.7"C. This figure is a replot of figure 6 t o show the linear variation of u at low-moisture conductivities upon a log-log scale. Thus the specific conductivity is proportional t o frequency at low moisture contents.
Figure 8 shows the d.c. conductivity as a function of moisture content a t three different temperatures. It is interesting to note that the 1.2"C. curve shows a sharp inflection similar to that for the radio-frequency curves of figures 4 and 5, but that the sharp inflections are not present in the 20.7"C. and 353°C. curves.
ELECTRICAL MOISTCRE TESTING
613
The d.c. conductivity was found to vary with the age of the sample. For this reason the curves in figure 8 are not identical with the d.c. curves in figures
0
4 8 12 16 20 MOISTURE CONTENT-(%)-DRY BASIS
FIG.5. D.C. conductivity of dehydrated carrots at three temperatures. KOelaborate precautions have been taken in the measurement of the d.c. conductivity, so that results are not of high precision. The results are thought precise enough, however, so that the pronounced bend in the curve at 1.2"C. has some significance.
4, 5, and 6, n-hich were obtained at an earlier date. There appeared to be an increase of conductivity with age of sample, although there was no change in moisture content. This change in conductivity can probably be attributed to deterioration of the sample. The dielectric constant appeared to be much less sensitive to aging of the sample.
614
XV. CRAWFORD DUNLAP, JR., A K D BEKJ.4MIX M.\KOWER
To determine the effect of particle size upon the dielectric constant and conductivity, a set of experiments was carried out upon samples of 16.3 per cent and 15.5 per cent moisture and having particle-size distributions of 18-35 and l.4.4ss, 0.: Can. J . Research 13B, 156 (1038).
(2) EBERT,L.: Angew. Cheni. 47, 305 (1931). (3) ERRERA, J., ASD SACK, H. S.: Ind. Eng. Chem. 36, 112 (1943). (4) FRICKE, H., BND CuRus, H. J . : J . Phys. Chem. 41, 729 (1937). (5) FRICKE, H., A N D JACOBSEN, L . E . : J. Phys. Chem. 43, 78 (1030). (6) FRICKE, H., A N D P A R K E R , E . : J. Phys. Chem. 44, 716 (19.10). (7)MAKOWER, B.,. ~ K DDEHORITY, G . I,.: Ind. Eng. Chem. 36, 193 (1943). (8) OSCLEY,J . L . : J. Am. Chem. Soc. 60, 1115 (1038). (9) SHAW,T. bl.: J. Chem. Phys. 10, 609 (1942). (10) SMITH-ROSE, R. L.: Proc. Roy. SOC. (London) A140, 359 (1933). (11) T a v s z , J . , ASD Rvxai, H . : Kolloid-Beihefte 39, 58 (1933). (12) VAN STEEKBERGES, A . B.:Het Gas 66, 137-9 (1935).
S E W BOOKS Fundamentals of Immunology. By WILLIAMC. BOYD. 446 pp. Xew York: Interscience Publishers, Inc., 1943. Price: $5.50. This book covers the fundamental principles involved in immunological reactions, together with a brief discussion of practical applications. A chapter of the book is devoted t o laboratory techniques commonly used in serological laboratories. The author states t h a t the purpose of the book is t o serve as a n introduction t o immunology for medical students, chemists, biologists, and others interested in a n understanding of the basic principles of the science. The introductory chapter of the book serves t o introduce the reader t o the science of immunity and immunology. In this chapter the author discusses the various kinds of immunity, the methods of measurement, and the mechanisms involved. Chapter two is a somewhat detailed description of antibodies and their specificity. The subject matter in this chapter is approached from the point of view of the chemist. The author wishes t o make the student familiar with the fundamental principles involved before introducing him t o the theories and nomenclature inherent in older immunological literature. From the point of view of the chemist, he discusses the nature of the antibodies. the chemical behavior, methods of measurement, and purification. Chapters three and four deal with antigens. A distinction is made between cell antigens and others, the former being taken up separately in chapter three. Here, again, the subject matter is treated from the point of view of the chemist. The author discusses in some detail the nature of the chemical groupings which are responsible for antigenic specificity. Chapter five takes up the question of human blood groupings. This chapter is rather brief, and therefore the subject matter is not taken up in as much detail as are some of the other topics included in the book. The author discusses the basis for the four classical blood groups and treats briefly the question of other antigenic principles, in addition t o the ones involved in the four basic groups. Chapter six deals with antibody-antigen reactions. I n this chapter the author has followed somevhat the scheme used by Marrack, in treating the antibody-antigen reaction as a two-stage reaction. The first stage concerns the combination of antibody with antigen, and the second stage involves those changes which make the reaction apparent t o the observer, such as precipitation, agglutination, neutralization of toxin, complement fixation, etc. The author’s presentation of the various theories that have been advanced concerning antibody-antigen reactions is excellent. The subject material in this chapter is developed almost entirely from the point of view of the chemist.
