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KXTENSIMETERs

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i _bbie is blown in a thin layer of dough. This is (•uoposed to imitate the behavioiir in fermentation; _but actually, as Scott Blair and Potel show, it measures first and foremost the, water-absorbing capacity, sińce all doughs are tested at the same moisture content. In so far as the amount of swelling of the bubble is concemed, this method measures a complicated function of viscosity and shear modulus, a function which is certainly not the particular combination of these properties which is reąuired to assess good baking ąualities. The German-Hungarian | farinograph,” which measures the work done in stirring and so gradually dis-integrating a dough, gives data which are affected by stickiness as well as consistency. Rupture properties of materials are always exceedingly hard to measure because they are so much infłuenced by the strength of the weakest point. The sooner a direct connection can be found between them and such properties as viscosity and modulus, the better for everyone concerned.

It is worth noting that the tensile strength of metals (crystalline systems) can be calculated from the attractive and repulsive forces acting between the atoms. The theoretical figures are always very much higher than the experimental ones (500-1,000 times as high). Smekal attempts to explain this in terms of “ Lockerstellen,” or points of weakness. A very smali flow will make a very considerable weakening. There certainly are zones of weakness within the crystal lattice. Chalmers gives evidence that, in the case of tin, these planes of weakness are not amorphous, but rather a type of anomalous crystal lattice. In the case of glass, it appears that the Iow tensile strength obtained in practice compared with that calculated from theory, is