摘要:

A modified colorimetric procedure showed that phosphorus content of Canadian lard (12 dry rendered samples and 21 wet rendered samples) was generally less than 0.001%, and did not appear to be definitely related to method of rendering or to keeping quality. Color of lard was conveniently measured with the Evelyn photoelectric colorimeter; photoelectric transmission values were most closely related to Lovibond color values in the yellow region. Lovibond color could be predicted only approximately from transmission. No association of color with processing conditions or with keeping quality was found. The criterion of an indicator change by volatile fatty acids in the Swift stability test rather than the attainment of an arbitrary peroxide value by the fat gave a closer association of Swift stability test values with organoleptic storage life of lard.

ISSN:1923-4287    

DOI:10.1139/cjr50f-002

出版商:NRC Research Press    

年代:1950

数据来源: NRC

摘要:

It is shown that with natural rubber, vulcanized to soft "gum" rings, extension curves after the first are in two parts, and that the second part does not develop except after severe previous extensions.With molded rings, stretched initially a few per cent short of rupture, these effects are very marked, and the fifth extension curve is in two clearly separate parts with a sharp inflection at 380% elongation. The equations fitting both parts of this curve are of the form:In these equations, the twoK0Lterms intersect atL = 0, and the equations also show a number of other coincidences which strongly suggest that they must be of significance as related to the elasticity of rubber after fatigue has produced a stabilized structure.It is also shown that with these fatigued rings no hysteresis occurs within the range from 0 to 110% elongation, irrespective of the range of the elongation and retraction cycle; that extensions within the range from 0 to 380% elongation show no hysteresis on retraction; but that hysteresis commences abruptly if 380% elongation is exceeded.Hysteresis effects for a "small loop" also differ markedly, depending on whether the loop is initiated from an elongation or retraction curve, and continued cycling round this "small loop" does not remove this difference.Since the equations for both parts of these extension curves are of exactly identical form, although hysteresis occurs in one part but not in the other, it is suggested that the basic cause of elasticity of rubber cannot be considered as in any way related to any molecular arrangement factors, but must be of a kinetic nature, and it is shown that if it is assumed that the rubber chain is vibrating, and that tension in the chain restricts this vibration, the forces developed would be quite adequate to explain the elasticity.It is also shown that with fatigued rubber the S shape of the extension curves is entirely destroyed if forces are calculated on the basis of force per unit area under stress, while this is only approximately the case for the usual extension curves.It is suggested that if the extension curve for rubber, and possibly other substances, is extended back toL = 0, it should give an intercept equal to the internal pressure in the substance, i.e., that Young's modulus represents the internal pressure of the substance.

ISSN:1923-4287    

DOI:10.1139/cjr50f-003

出版商:NRC Research Press    

年代:1950

数据来源: NRC