September, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
by the factor 0.382 gives the fluoride normality in the original sample. In those cases in which the volume of the lead sulfate precipitate in the 250-cc. flask is appreciable, an appropriate correction should be made. This may be roughly calculated, as the volume of the lead sulfate (specific gravity 6.2) is about 0.024 cc. for each cubic centimeter of normal sulfate solution originally present. In Expts. 7 and 8 (Table I), with
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25 cc. of a 2 N nickel sulfate solution, this is equivalent to 2 x 25 X 0.024 = 1.2 cc. of PbS04-i. e., 0.5 per cent of the 250 cc. The results given for these experiments include deductions of 0.5 per cent (0.0025 gram) based on this correction.
ACKNOWLEDGMENT Acknowledgment is due to William Blum, under whose direction this work was conducted.
Variation of Stress-Strain Properties of NitrocelluloseCamphor Mix with Its Composition'" By Paul Heymans and George Calingaert MASSACHUSETTS INSTITUTE OP TECHNOLOGY, CAMBRIDGE. MASS.
I
T I S of interest for photoelastic work to be able to obtain celluloids of any specified elastic proper tie^.^ It is well known that the physical properties of celluloid vary with its composition. Nishida4 has studied the comparative elastic properties of celluloids made with cellulose of different origins. As the various materials which he examined did not have as sole variable the origin of the cellulose, his results do not allow a reliable interpretation. Nishida states, as a general qualitative condition, that the physical properties of celluloid are much affected by the several operations during the manufacturing processes, and especially depend upon the nature and properties of the loading materials.
only by varying its composition when manufactured. Different samples of celluloid were prepared, care being taken to use raw materials of the same origin and to put them through the same manufacturing processes, varying the content in camphor and adding ester gum in one case. The stress-strain curves were determined on specimens of rectangular cross section measuring 1 inch by 0.25 inch, and 4 inches in gage length. The results, together with the relative content of camphor and ester gum, are summarized in Table I and Figs. 1 and 2. The elastic limit was taken a t the point where the stressstrain curve departs from a straight line. A more accurate definition of the elastic limit, such as a given increment of the elongation per unit of charge, could not be made on account of the plasticity of the materials. Single variations of the elongation differed appreciably, while the mean slope of the stressstrain curve was still constant. TABLE I
SamDle A B C
D E
TESTSON CELLULOIDS OF VARYIXG COMPOSITION From preliminary tests it appeared that homogeneous celluloid of different chemical compositions could be obtained 1 Presented before the Division of Cellulose Chemistry at the 67th Meeting of the American Chemical Society, Washington, D . C., April 21 to 26, 1924. * T h i s work was undertaken b y the Photoelastic Laboratory of the Massachusetts Institute of Technology at the request of the Research Laboratory of the General Electric Company. a Heymans, Am. Mech. Eng., 44, 513 (1922). 4 THISJOURNAL., 8, 1099 (1916).
Camphor Per cent 9.5 8.8 17.8 24.2 38.6
Ester gum Per cent 0 7.2 0 0 0
Young's modulus of elasticity Elastic limit Lbs./su. in. Lbs./sa. in. 350,000 2450 337,000 2025 387,000 2425 308,000 1875 254,000 1825
Although the elastic limits should, therefore, not be considered too accurate, the moduli of elasticity are more reliable, since for a given stress-strain curve a slight displacement of the elastic limit will affect the value of the modulus much less. Comparing Samples A and B, in which the ratio of camphor to nitrocellulose is the same, the only difference being the addition of ester t gum, it is seen that ester gum lowers the elastic limit and the $ modulus of elasticity. & Samples A , C, D, and 8 E constitute a series in which the percentage of &#cm f " P ? camphor varies from 9.5 to 38.6. Fig. 2 shows the effect of the camphor content on the elastic limit and the modulus of elasticity. It is seen that the modulus of elasticity does not vary constantly with the.percentage of camphor. A maximum is reached a t
