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. White 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.
