Electrical Properties of NEOPRENE FELIX L. YERZLEY' E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
and 6 inches square. The HIS review is based Electrical data o n neoprene are reviewed voltage across the electrodes upon data selected from with respect to both insulating and conwas gradually increased until tests conducted over a ducting properties. The early development breakdown occurred. T h e period of years. Under the of neoprene was directed principally toward gage was then measured adcircumstances it does not mechanical applications, and very little jacent to the punctured happen that identical neospot, and the voltage and prene was used throughattention was given to its electrical properdielectric strength were calout. Several types are reties. However, early types were tested by culated by dividing ferred to in the compounds. electrical laboratories using, among others, the value of the voltage by Each group of tests is conformulas designed for the mechanical field. this gage. sistent within itself, but diMost of the results fell far short of the inrect comparison from group to group is not justified. sulating properties of natural rubber. Early Data Keither do exact values within More recent developments of neoprene, Early published informaa group have individual merit, both i n types and i n compounding techtion on the electrical properbut the trends of electrical nique, have resulted i n electrical properties ties of neoprene appeared in quantities with controlled that are entirely adequate for a large num1936 (7'). Results from this changes of the variable under report are given in study are of primary imber of uses, some of whichare nowinpractice. Table I. portance. In general, numeriIt is hoped that this summary of the inIt is immediately apparcal values reported are the sulating and conducting values of neoprene ent that the resistivities of all average of results obtained may be useful i n suggesting solutions t o a three compounds were dison two samples, but all conmiscellany of industrial problems. tinctly low in comparison with clusions have been confirmed that of rubber insulation, by numerous parallel and rewhich ordinarily has a valueaplated tests. proximating 1015 ohm-om. Also, the dielectric constant Unless otherwise specified, tests were macle a t 82" F. for all three compounds was high in comparison with that after the samples had been dried in a desiccator for a t least for most rubber insulation. Both of these trends were 16 hours. Conventional methods (1, 2 ) were used. For distinctly unfavorable from the standpoint of insulation. all tests except those on dielectric strength, tin foil electrodes On the other hand, the values for dielectric strength, except 0.001 inch thick, adhered to the test slab by a thin film of for uncompounded mlcanizate 750D-1, were roughly competrolatum, were utilized. The test specimens were usually parable with rubber. The results make it desirable to survey 6 X 6 X 0.075 inch except for occasional samples the possible methods of improving the electrical properties which were approximately 0.020 inch thick. I n the case of neoprene which follow: of the direct-current resistivity test, the upper electrode was a 3-inch-diameter disk of tin foil surrounded by a guard 1. Compounding with litharge. ring. The lower electrode was a 6-inch square of tin foil. 2. Purifying the crude neoprene. The Leeds & Northrup test set employed consisted of a 3. Including carbon black in the formula as an absorber for sensitire galvanometer and a n Ayrton shunt. An alterelectrolytes. nating-current bridge xas used for measurements of conducting stocks. For the tests of power factor and dielectric constant, the upper electrode was a 3-inch-diameter disk TABLEI. EARLY DATAOX THREE NEOPRENE COXPOUXDS of tin foil without a guard ring. The loxyer electrode n a s a Compound No. 75OD-1 75OD-3 75OD-5 6-inch square of tin foil. General radio equipment was Neoprene Type E 100 100 100 utilized, consisting of a type 716A capacitance bridge comExtra light calcined magnesia 10 2 plete with the necessary auxiliaries. A telephone headset ... 5 10 FF wood rosin Phenyl-8-naphthylamine 2 2 was used for detection of null points. All tests reported Sulfur ... 1 I ... 10 . . . Zinc oxide here were conducted a t frequencies of 1000 cycles per second. ... ... 20 Litharge For the determination of dielectric strength, an American Cure a t 307O F., min. 60 20 20 Transformer Public Utility test set, type TS, having a Electrical properties secondary voltage range from 100 to 50,000 volts was used. D. C. resistivity, ohm-em. 2 . 2 X IO3 3 . 1 X 10'1 9.0 X lo** type 'I.(2). The electrodes were of the standard A. S. T. & Dielectric constant 8.2 7.3 7.2 Dielectric strength, volts/ Ordinarily the test specimens were about 0.020 inch thick mil 380 860 720
T
.
.
. . I
1
Present address, Western Electrio Company, Kearny, N. J.
330
I
March, 1943
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Including large amounts of superior insulating substances. Mixing with rubber insulation to provide a compromise between the electrical pro erties of rubber and the superior mechanical and chemicar)properties of neoprene. 6. Conditioning treatments of vulcanized neoprene t o improve its electrical properties. 7. Adjusting the cure. 8. Modifying the neoprene polymer.
4. 5.
Compounding with Litharge Litharge is superior to magnesia and to zinc oxide as a curing agent for neoprene insulation. For example, the data of Table I show a pronounced difference in favor of litharge. It is probable that the reaction between litharge and the degradation products of neoprene forms salts having lower dissociation constants in the presence of moisture than have the corresponding salts of zinc and magnesium. The higher resistivity of litharge compounds is attributed primarily to this factor. I n addition to the advantage of litharge electrically, neoprene compositions containing it are definitely less combustible than compositions containing zinc oxide. Purification of Crude Neoprene As various tests have shown, the amounts of chlorinebearing electrolytes that might be suspected in normal neoprene compounds are difficult to detect by chemical means. Yet the possibility remains that they may be present in sufficient amount to cause the inferior electrical characteristics of untreated neoprene. With this possibility in mind, a sample of Neoprene Type E was acetone-extracted and then water-washed. This specially purified neoprene was compounded and tested for electrical characteristics in the following formula: COMPOUND 1333N-112 Purified Neoprene Type E Extra light calcined magnesia FF wood rosin Sulfur Phenyl-a-naphthylamine Litharge D. C. resistivity, ohm-cm. Dielectric constant Power factor, Yo
100 3 5
331
the loss factor increased by the inclusion of even this small amount of carbon black. For ordinary applications of insulation the loss factor is not of prime importance. It may be preferable in many cases to make a sacrifice with respect to loss factor in order to increase the value of the resistivity. However, as the quantity of black is increased, the loss factor increases out of all proportion to the gain in resistivity. As a consequence it appears advisable to limit the carbon black content of insulating compounds to about 5 parts of carbon black.
Inclusion of Insulating Material The effect of various materials is shown in Table 111, based upon Neoprene Type E compounded with magnesia and zinc oxide. Although higher values for the resistivity would have resulted from compounding with litharge, it was thought that the effects of the fillers would be demonstrated a t least as well in the zinc oxide formulation. The inorganic fillers were compared on an equal basis of 40 volumes per 100 volumes of neoprene. The organic fillers were used in amounts approaching the maximum permissible in a practical formulation. Control formula 1333N-200 is inferior in all insulating properties with the exception of one value for resistivity, three for dielectric constant, and one for power factor. In a general way it is interesting to note that the d. c. resistivity is increased by compounding with inert, inorganic fillers but that these increase the dielectric constant. All other materials except cottonseed oil increase the d. c. resistivity, decrease the dielectric constant and power factor. It is possible that the cottonseed oil used in this test was of an inferior grade electrically and that the results are not necessarily typical of this processing material. It is also obvious that, with the exception of the stock containing cottonseed oil, the loss factor for all compounds is lower than that of the control stock.
1
2 20 2.8
x
1013 7.8 1.25
The improvement in resistivity as the result of purification was substantial: it was also suggested by Kemp (6). Although the dielectric constant was not greatly changed, the power factor was relatively low in comparison with contemporary tests of unpurified neoprene specimens. Acetone washing, however, is not practical from a production standpoint, and a t the time of these tests it could only be hoped that advances in the technique of neoprene production would result in improved electrical properties.
Inclusion of Natural Rubber Rubber itself is a possible compounding ingredient for neoprene, and the following two compositions were blended by weight in the amounts indicated in Table IV to determine its possibilities. Slabs were press-cured 40 minutes a t 287' F.: CO~IPOUND 1333N-210 COMPOUND1333-50 Neoprene Type GW 100 Smoked sheets 100 Catalpo clay 100 Zino oxide 78 Blanc fixe 100 Gilder's whiting 115 Medium-process oil 5 Phenyl-a-naphthylamine 2 Cottonseed oil 5 Paraffin 5 Semireinforcing black 5 Litharge 10 Paraffin 5 Accelerator" 0 4 Phenyl-0-naphthylamine 2 Sulfur 3 Litharge 20 90% zinc salt of mercaptobenzothiaeole and 10% di-o-tolylguanidine.
Inclusion of Carbon Black The practice with certain types of rubber insulation is to The results indicate a progressive improvement in insulating properties as the percentage of rubber is increased. include moderate amounts of carbon black in the formula as an absorber for impurities and electrolytes (9). The possibility of following a similar procedure for neoTABLE 11. EFFECT OF CARBOWBLACE ON FORMULA1333N (CURED40 MINUTESAT 307" F.) prene was investigated in Formula 1333N87 88 89 90 91 Q
Neoprene Type E
t h in power factor and resistivity is slight for the compound containing 3 parts of carbon black, the trend appears to be favorable. On the other hand, the dielectric constant increased and as a consequence
Extra FF woo8 li ht rosin calcined magnesia ~
2
100 3 ~5 3 2
1 20
20
100 3 5 ..I
~h~~$$~;;$&&,e
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Electrical Properties of dry slabs D. C. resistivity, ohm-am. Dielectric constant Power factor, % Loss factor
4 . 9 X 1011 7.74
2.1 0.16
1
6.2 I
X 1011 8.43 2.0 0.17
100 3
5 10 2 1 20
100 3 5 20 2 1 20
6 . 3 X 1021 9.72 2.1 0.20
6 . 4 X 1011 13.28 2.8 0.39
~
100 3 5 30 2 1 20 6 . 5 X 1011 17.33 4.1 0.71
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
332
ON FORMULA 1333N TABLE111. EFFECTOF INSULATING MATERIALS
Formula 1333NNeoprene Type E Extra li h t calcined magnesia FF woo2 rosin Whiting Barytes Crown clay Cottonseed oil Mineral rubber Mineral oil Para5n Phenyl-@-naphthylamine Neophax Bo Zinc oxide
200 100 10 5
... ... ... ... ... ... ... ...2 10
Electrical properties after 13 days in desiccator a t 25' C. D. C. resistivity, ohm-om. Dielectric constant b Power factor b, 7% Loss factor b 4
202 100 10 5
201 100 10 5
... ...
... ... 113 ... ...
... ...
... ...
... ... ...2
...
2 100 10
10
1.7 X 1012 8 . 2 X 1011 3.1 X 10" 7.88 3.8 0.30
6.62 2.8 0.17
8.40 3.4 0.28
203 100 10 5
(PRESS-CURED
204 100 10 5
... ... ... ... ...
... ... ... 20 ... ... ...
194
.... .. ... .... ..
...2 ...
...2
6.3 X 10" 8.67 3.0 0.26
4.7 X 10"
10
206 100 10
207 100
5 ... ...
... ...
... *50 ..
...
...
...
10
10
10
1.1
... ...
... ... ...
2
9.3 X 1010 7.10 4.4 0.31
208 100 10 5
1 :
... . .2.
...
10
8.56 2.4 0.20
40 ~ ~ I N U T EBT S 307" F.)
203 100 10 5
...
11s
Vol. 35, No. 3
...
... ... ...
20
10
2
2 ... 10
X 1012 2 . 8 X 1011 5.85 6.62
2.4 0.14
7.5
3.0 0.19
x 1011 7.20 3.5 0.26
A special grade of factice (vulcanized oil). 1000 centipoises.
b At
On the other hand, the improvement is most rapid for rubber contents of more than 50 per cent. There may be many possibilities in the future for insulating mixtures of neoprene and rubber, where greater resistance is required to heat, sunlight, oil, and flame than is possible with rubber alone. The advantages of neoprene are gradually lost, however, as the percentage of rubber is increased, and the present 10
mixtures with rubber appear t o be an impractical way of improving the electrical properties of neoprene.
Conditioning Treatments Three practical compounding approaches to the insulation problem are offered by the foregoing. They are inclusion of carbon black, activation with litharge, and inclusion of proper insulating materials. The combination of these principles in a practical formula for wire insulation is exemplified by the following composition: COXPOUND 1333N-209 Neoprene Type GW Blanc fixe Catalpa clay Paraffin Medium-process oil Semireinforcing black Phenyl-&naphthylamine Litharge
-i
O I;;
100 100 100 3
5 6 2
20
1
I
Compound 1333N-209 was extruded as 3/64-inch wall insulation KO. 14, solid AWG tinned copper wire; the following history of resistance per 1000 feet of wire indicates possibilities in conditioning treatments for neoprene-insulated wire:
I 0
5 >
T
5 IC ! !
Step
W
a
NO.
d
1
n'
2
3 4 5 6
I(
7
IC
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0
1.
10
20
30 4 0
5 0 6 0 70 8 0 H O U R S AT 1 4 I 0 C .
90
100
110
I20
COMPARISON OF STOCK0,COMPOUNDED (SOLID CURVES) AND
UNCOMPOUNDED (DOTTED CURVES)
Temp., Treatment Original immersed in water After 24-hr. immersion Plus 30 min. &t 1500 volts Total immersion 44 I rs. 44-hr. immersion 4- 3.5 hr. a t 1500 volts 17-hr. drying in 70" C. oven Plye 4.5 hr. a t 1500 volts after oven drying
' C. 29 29 29 29 29 24
24
klegohms/ 1000 F t . 13.5 2.8 9.2 3.8 10.4 44.0
32.9
It is recognized that rubber insulation, which is slightly low in resistivity, can be improved by subjecting it to high voltage for a time without detracting from the other desirable insulating properties, The preceding data on neoprene insulation show that extensive exposure to high voltage likewise increases its resistance. It is also significant that the initial period of immersion caused a severe drop in the resistance per thousand feet of wire while the trend after continued immersion and extensive exposure to high voltage was to restore the d. c. resistivity almost to its initial value. The highest value attained after 17 hours of drying in the 70" C. oven was probably the combined result of reduction in moisture content and of tighter cure. Although these results would not be considered typical of any normal test procedure, they indicate gradual improvement
INDUSTRIAL AND ENGINEERING CHEMISTRY
March, 1943
333
GLASS
NEOPRENE
RUBBER PORCELAIN
D R Y H A R D WOODS ELEMENTS
METALLIC
0 Y
-6
-5
,
-4
,
,
,
-3
-2
-1
,
,
0
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I
2
,
,
3
4
,
,
,
,
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6 7 8 9 IO I1 L O G A R I T H M OF R E S I S T I V I T Y
l
12
S
I3
,
,
14
IS
I(
16
1
1
,
17
18
IS
0
FIGURE 2. RESISTIVITY SPECTRUM FOR INSULATING MATERIALS
of electrical properties under severe conditions and are reassuring from a service standpoint.
Adjustment of Cure
A further possibility with respect to electrical properties is the adjustment of cure. The following data illustrate the idea that more extensive knowledge of compounding principles for neoprene may result in superior electrical properties even with the present types of neoprene. The data also indicate the stability of the electrical properties of neoprene under severe aging conditions. The compounds compared (cured 30 minutes a t 40 pounds) are as follows: Compound No. 1333N-216 Neoprene Type G N 100 Hexamethylene ammonium hexamethylene dithiooarbamate . .. .. . Paraffin 5 Phenyl-@-naphthylamine 2 Semireinforcing black 6 Catalpo clay 100 Blanc fixe 100 Medium-process oil 10 Litharge 20
Modification of the Polymer The history of neoprene is a series of eventful improvements in physical properties. Thus, as a further possibility it can be expected that future modifications of neoprene will have electrical properties vastly superior to those displayed by current types. Neoprene Type FR, the latest addition, shows interesting possibilities: Compound No
1333N-218
0 ..~ 25
.... .... .... .... .... .... .... ~
...
... ...3
100 0.1
100
2 100
100
100 a
0
1333N-217 100
1333N-219
100
Litharge
10 5 20
10 5 20
Cure at 287' F., min.
40
30
~
Measurements were made of d. c. resistivity, dielectric constant, and power factor after aging for various intervals in a 141' C. oven. The trends of these various quantities for the two compounds are shown in Figure 1. Comparison of the resistivity curves for the compounded and uncompounded stocks indicates conclusively that neither was cured to its maximum effectiveness electrically as originally prepared. The maximum attained by the compounded sample after 48 hours was 5.7 X l0ls ohm-cm., while that attained by the uncompounded specimen after 120 hours was 3.2 X 1013 ohm-cm. The discrepancy between the two may be the result either of the difference in state of cure or of the presence of insulating extenders in the compounded stock. Also, the dielectric constant for the uncompounded material is lower a t all points than that of the compounded material. I n per cent power factor, the compounded stock is definitely superior at all aging intervals to that of the uncompounded stock although it appears possible that a longer exposure a t 141' C. might bring these two values together. On the other hand, the uncompounded material had become hard and brittle by the end of 121 hours, and more extensive exposure would not have been practical.
Eleotricel properties D. C. resistivity, ohm-cm. Power factor, % Dielectric constant Loss factor
1.2
x 10'8 0.9 7.3 0.066
4.2 X 10'2 1.6 8.3 0.12
Effect of Temperature o n Resistivity The effect of temperature upon the resistivity of neoprene is indicated by the following compound and data: COMPOUND 1333N-220 Neoprene Type G N Piperidine pentamethylene dithiocarbamate Phenyl-p-naphth ylamine G a s t i (carbon black) Ground mica Paraffin Shellac Medium-process oil Litharge Cure a t 287' F., min. Temyrature, C.
25 40 60
80 100
100 0.25 2 5 150 5 16 10 20 30
Resistivity, Ohm-Cm. 5.46 X 10'2 1.13 X 10'2 1.62 X IO" 6.01 X 10'0 1.89 x 10'0
INDUSTRIAL AND ENGINEERING CHEMISTRY
334
Vol. 35, No. 3
~~
TABLE IV. ELECTRICAL PROPERTIIN OF NEOPRENE-RUBBER MIXTURES Formula 1333K-
1333N-210
1333N-211
1333N-212
1333X-213
1333N-214
1333N-215
100
95
75 25
50
25 75
6 93
2 . 4 X loi4 5.94 0.9 0.053
9 . 4 X loi4
Ne0 rene (1333N-210: Rubter (1333-60)
...
Electrical properties D. C. resistivity, ohm-em. Dieleotric constant Power factor, 70 Loss factor
5
6 . 6 X 1012 8.2 1.3 0.106
8.0 X
loiz
8.14 1.2 0.098
x 101% 7.36 1.3 0.095
9.0
50
2 . 9 X lola 6.41
1.2
0.077
5.05 0.5 0.025
1333 -60
io0 9.4 X lOl4 5.03 0.5 0,025
There are electrical conditions under which the decrease of resistivity with rising temperature even up to 100” C. could be permitted, and there are more severe conditions under which high-temperature applications would invite failure. It is not easy to state in a general way what the allowable limits are, and it would be beyond the scope of this paper to attempt to do so. The limits depend upon many factors, and careful analysis of high-temperature applications should be made to determine their practicability.
Conducting Xeoprene The insulating qualities of neoprene do not cover the entire range of electrical properties that are of technical interest today. Electrical conductivity in neoprene is also important, and is attainable by the same means and to the same extent as for rubber. The following data are based upon established commercial products and do not indicate the possibilities of new blacks which have recently been offered and may soon be developed. The data illustrate the range of values attainable with several types of carbon black. Litharge was not used in these formulas since its effect on insulating qualities was not required. BABEC o m a u x n 100
Neoprene Type G N Hexamethylene ammonium hexamethylene dithiooarbamate St&c acid Pheny1:a-naphthylamine Extra linht calcined magnesia Eight-pfocess oil Zinc oxide Carbon black
0.25 0.5
2
4 8 6
As indicated
30
Cure a t 287’ F., min.
A. C. Resistivity, 50 parts 2.7 x 10% 1 . 6 x 108
Type of Black Acetylene Boft carbon Semireinf arcing Channel
1.0 8.5
x x
108
107
Ohm-Cm. 100 parts 1 . 2 x 102 2.0 x 107 6 . 7 x 104 1 . 7 X 108
As a further illustration of the conductivity obtainable, the following data show the trend in A. C. resistivity values with increasing amounts of acetylene black: BASECOMPOUXD Neoprene Type G N Hexamethylene ammonium hexamethylene dithiocarbamate Phenyl-a-naphthylamine Extra light calcined magnesia Acetylene black Light-process oil Zinc oxide
100
0.3 1 4 As indicated 1 5
Cure at 287O F., min. Parts of Acetylene Black 0 10 20 30 40 50
76
FIGURE 3. SUPERIOR RESISTANCE TO HEAT SHOWN BY NEOPRENE OYER RUBBER
30 A. C. Resistivity, Ohm-Cm. 1 x 10’2 2 x 108 9 x 107 3 x 104 6 . 4 X 10* 1 . 4 x lo* 1 . 4 X 102
It is not intended to go extensively into the phenomena of conducting neoprene compositions, but the effects appear
similar to those for rubber which are covered extensively elsewhere (for example, by Juve, 4). The fact should be kept in mind that whether a material is a resistor OT a conductor is relative. Rubber is an insulator in comparison with most metals, but it is a conductor in comparison with fused quartz and purified ceresin wax. Keoprene likewise is an insulator in comparison with most metallic elements, but whether it is an insulator or conductor with respect to rubber depends upon the particular compounds compared. Figure 2 illustrates what might be called the “resistivity spectrum” for electrical materials. The horizontal axis shows the range of resistivity which has been measured, plotted logarithmically to provide a practical spread of values on the chart. At the various vertical levels the horizontal lines show the range of resistivity values which have been published in various reference works ( 3 ) in comparison x i t h neoprene and rubber for which values have been assumed in this paper. The range for rubber is taken to be 50-5 X 1015ohm-cm. although higher values have been reported for purified rubber (6). The range for neoprene is taken to be 50-5 X The range for metallic elements begins with silver a t 1.47 X 10-6 and may be extended to the value for the metalloid boron a t 8 X lo4. Both neoprene and rubber overlap this range. At the other end of the range, neoprene overlaps published values for such insulating materials as slate, phenolic resins, fiber, Lavite, glass, porcelain, and dry wood. It does not quite attain the published value for enamel, and is distinctly inferior to the high values attained by various waxes, mica, rosin, and sulfur. This i ~ o u l dseem t o indicate rather con-
March, 1943
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
clusively that, since slate, fiber, Lavite, phenolic resins, glass, and porcelain are useful as insulation for low-voltage service, neoprene may have parallel utility in combination with its other desirable properties. An aspect of the superior resistance of neoprene to heat is shown by Figure 3. A length of No. 14 AWG copper wire was covered with 3/&nch neoprene insulation, and another length was similarly insulated with heat-resistant rubber. After 15 months in a 70’ C. air oven, both samples were wound on a half-inch mandrel. The rubber was brittle enough to crack badly, while the neoprene showed no signs of failure. Code specifications based upon the characteristics of a given material are not necessarily proper criteria for other materials. For example, a code wire specification of 1500 megohms per thousand feet (8) for rubber-insulated wire is not based upon the electrical demands made upon this insulation but upon a characteristic value of rubber as a quality control. Specifications for neoprene-insulated wire based upon its electrical properties would be adequate to ensure satisfactory performance of the wire under many conditions of low-voltage service. The dielectric strength test specified for code wire, on the contrary, is not indicative of the electrical properties of rubber, but is set up as a means of detecting pinholes and other flaws in the extruding coating. The test applied to 3/e4-inch wall insulation a t 1500 volts works out to 32 volts per mil. This is obviously a trivial exposure for a solid film of either rubber or neoprene, which
33s
can be made to have a dielectric strength of a t least 800 volts per mil. Acknowledgment The author takes pleasure in acknowledging the important contributions of A. J. Northam and J. P. Nowlen of the du Pont Company to the progress of this work. He is also indebted to Millard Gass, who made most of the measurements, and to representatives of the wire and cable industry for helpful discussions.
Literature Cited (1) Am. SOC.Testing Materials, Tentative Methods D149-36T and D 160-36T. (2) Ib%d., D267-37T. (3) Hodgman and Holmes, Handbook of Chemistry and Physics, 23rd ed., p. 1662 (1939-40); Perry, Chemical Engineers Handbook, p. 2228 (1934) ; International Critical Tables, Vol. 11, pp. 310-11 (1927). (4) Juve, A. E., I n d i a Rubber World, 103, 47 (Feb., 1941). (6) Kemp, A. R., in Davis and Blake’s “Chemistry and Technology of Rubber”. p. 666, New York, Reinhold Pub. Corp., 1937. (6) McPherson. A. T.. Ibid.. Chaoter 15. i7j Miles, J. B., Jr., Natl. Reseahh Council, Div. of Eng. and Ind. Research, Comm. on Electriral Insulation, Rept. on Electrical Insulating Properties of Duprene, 1936. (8) Underwriters’ Laboratories, Standard for Rubber-Covered Wires and Cables, Subject 44. (9) Wiegand, W. B., and Boggs, C. R., IND. EKQ. CHEM.,22, 822 (1930). PRESENTED before the Division of Rubber Chemistry at the 102nd Meeting of the AMERICAN CHEMICAL SOCIETY. Atlantic City, N. J.
LAZARUS ERCKER, THE ASSAYER
By R. W h i t e N 1683 Sir John Pettus published in
I London
his “Fleta Minor: The Laws of Art and Nature in Knowing, Judging, Assaying, Fining, Refining, and Inlarging the Bodies of Confined Metals”. This is a free translation of the earlier German “Assays” (Beschreibung allerfurnemisten mineralischen Ertzt und Bcrgwcrcksartcn, Prague, 1574) of Lazarus Ercker (Erskerus), whose portrait is reproduced here as “The Assayer”, a copy from White’s engraving. This is No. 147 in the Berolzheimer series of Alchemical and Historical Reproductions. T h e numbered articles are: (2) Scales; (3) Cases for the Weights; (4) Bottles for Aqua Regis, Aqua Fortis, Aqua Vitrioli, Aqua Argentea or Quicksilver.
D.I).BEROLZHEIMER 50 East 41st Street New York, N. Y.
The lists of reproductions and directions for obtaining copies appear aa follows: 1 to 96, January, 1939, page 124; 97 to 120, January, 1941, page 114; 121 to 144, January, 1943, page 106. An additional reproduction appears each month.
