I-VD CSTRIAL A S D Eh’GIATEERI,VG CHEMISTR I’
June, 1925
with a concavity factor of 100 per cent a t the same concentration which produces maximum energy of resilience at rupture. At present, carbon black offers the closest approximation to this ideal. Such a combination of properties would provide the engineer with rubber structural members the behavior of which could be calculated as readily as those of steel, wood, and concrete, although, of course, offering a much wider range of elastic properties. Summary
An energy criterion for the degree of concavity of the rubber stress-strain curve is proposed in the form of the ratio between the area subtended by the curve on the strain axis and half the tensile product, expressed in energy units. This ratio-as a percentage-is called the concavity factor “C.” I t is calculated as follows: “C”
=
24 E>f X 700 per cent -
625
where E y = energy of resilience in foot-pounds per cubic inch T P = tensile strength in pounds per square inch multiplied by per cent elongation divided by 10,000 i. e., T
P
=
T X E 10,000
“C” is slightly responsive to changes in crude and cure, but very highly sensitive to pigmentation. The finer the pigment the greater its power to increase the value of “C”. Maximum reenforcement may ultimately be attained through the coincidence of 100 per cent concavity factor with high energy of resilience, a t rupture. Carbon black shows the nearest approximation to this ideal, the complete realization of which may greatly expand the application of rubber in the arts. Acknowledgment
The writer gratefully acknowledges the aid received from H. A. Braendle in the preparation and calculation of these data.
Measurement of Susceptibility of Fats to Oxidation’ By G. R. Greenbank and G. E. Holm RESEARCH LABORATORIES. BUREAUOF
HE presence of exceedingly small traces of oxidation products in fats may be shown by the application of various chemical tests. Although delicate enough to be of value in detecting the first oxidation products, these tests are hardly delicate enough to follow oxidation susceptibility changes quantitatively. The method described herein employs directly the principle of oxygen absorption, and is therefore a direct comparative measure of susceptibility. The figure illustrates the type of apparatus that has been used in these laboratories for some time. The samples of fat or materials containing fat are placed in small filtration flasks (175 cc.); the flasks are evacuated, filled with oxygen, placed in a constant-temperature oven a t 70” C., and connected to the tubes leading to the manometers. During the temperature adjustment, the pressures in the systems are adjusted by means of the 3-way stopcocks inserted in the tubes. When the systems have become stable the electrical connections are made, the platinum-tipped copper wire leading into the manometer being fixed a t a point where it is immersed to the extent of 1 to 2 mm. In the apparatus used the clock closes the circuit a t minute intervals, thereby actuating the four relays, to each of which is fastened an arm holding a marking device. Every minute, therefore, there is made upon a record sheet held upon the drum a dot for each 1
Received April 10, 1925
DAIRYING, WASHINGTON, D .
C.
circuit, so long as the pressures in the manometers remain normal. As soon as oxygen absorption begins in any one flask the circuit is broken and the relay in this circuit will not be actuated when contact is again made in the clock, though the other ,relays will function until the respective circuits are broken in the manometers. The record sheet is ruled to 10-minute intervals to facilitate the time readings. For confirmation of results, the contacts in the manometers may be reset and a second reading obtained. If the first break is due to true absorption a second break will follow within a short time. Where the experiment extends over a period longer than a working day there is danger of flow of mercury into the flasks with continued oxygen absorption. To avoid this care should be taken that the manometers do not contain too much mercury. Where a small amount is used in each manometer the air will be allowed to enter the system as soon as the mercury is depressed to the bend in the tube, thus forming a by-pass and preventing a backflow of mercury into the tubes. It is realized that every laboratory engaged in work upon fat oxidation does not possess a recording device of the type illustrated here, but numerous other devices (bells, lights, etc.) may be employed; however, these need more or less constant attention.
A Method for Measuring the Susceptibility of Fats to Oxidation
