The hen's egg: Variation in shell deformation under static load with relative humidity and age of egg

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Abstract
Deformation of an intact egg shell under static load, which is used for the nondestructive estimation of shell thickness, is commonly assumed to be independent of the relative humidity of the atmosphere surrounding the egg and of the age of the egg. Two experiments are described in which these assumptions were tested. In the first it was found that deformation under a load applied at the poles depends on both factors. In the second it was found that the same was true for equatorial loading and that the change in deformation was independent of the number of times the load had been applied, the porosity of the shell and the strain of bird. Deformation increased linearly with relative humidity and decreased exponentially with the age of the egg, the half‐value period being about 3.5 d. It is suggested that the effect may be due to variation in the elastic properties of the organic moiety of the shell. The effect is small relative to that of shell thickness and curvature and may usually be neglected if relative humidity is in the normal range and the egg is more than 10 d old. With fresh eggs or extremes of relative humidity, however, it is desirable to apply corrections. A table of correction factors is given (Table 6).