A PRELIMINARY REPORT ON CLAYS Or VLORIDA 97

C onduits ............................................................. 7-8
W hite earthenw are .................................................. 8-9
Fire bricks ........................................................... 5-14
P orcelain ............................................................ 11-13
Red earthenw are ..................................................... 010-05
Stonew are ........................................................... 5-8
E lectric porcelain .................................................... 10-12

 For the composition and fusion temperatures of the Seger cone series see Appendix B. A comparison of various temperatures used in the different kinds of products is shown in Fig. 1.
 The thermoelectric pyrometer is to a great extent replacing the use of the Seger cones in measuring temperatures. The greatest difficulty with its use is the cost of the apparatus. The type most widely used consists of two wires, one of platinum and the other of an alloy of platinum and rhodium or platinum and iridium, which are fused together at one end while the free ends are connected with a galvanometer. One of the wires is encased in a small quartz tube to insulate it from the other. The two wires are then placed in a larger quartz or porcelain tube which is inserted into the kiln. The heating of the thermopile in the furnace generates an electric current which is conducted to the galvanometer which measures the intensity of the current. The degrees of temperature are measured by the amount of deflection of the needle. of the galvanometer. The galvanometer may be installed in the office some distance from the kiln and the temperature may thus be observed at will. Some types of this instrument have an automatic recording device.
 The optical pyrometer is used to some extent in measuring temperatures. There are several forms on the market. The principle of some of these is to compare the intensity of light in a furnace with that from some other source. In others the light emitted from the furnace is refracted by means of prisms and a comparison is then made with some standard.
 POROSITY
 The porosity of a clay is the volume of pore space existing between the clay particles and thus depends upon the size and shape of the particles making up the mass. Spherical grains would give a maximum porosity, but clays of this type are probably unknown. In clays the grains vary in size and are irregular in shape, which greatly reduces the porosity. It has been shown, however, that increasing fineness means increasing pore space. Porosity determines the amount of water a clay will