PHYSICAL PROPERTIES OF CLAYS. 37 



where they can be watched through a peep-hole but 

 at the same time will not receive the direct touch of 

 the flame from the fuel. It is always well to put two 

 or more cones in the kiln so that warning can be had 

 not only of the approach of the desired temperature 

 but also of the rapidity with which the temperature 

 is rising. 



In order to determine the temperature of a kiln sev- 

 eral cones of separated numbers are put in, as for ex. 

 .07, 1, and 5. Suppose .07 and 1 are bent over in burn- 

 ng but 5 is not affected, then the temperature of the 

 kiln was between one and five; the next time 2, 3, and 

 4 are put in, and 2 and 3 may be fused but 4 remain 

 unaffected, indicating that the temperature reached 

 the fusing point of three. 



These pyramids have been much used by foregin 

 manufacturers of clay products and are coming into 

 use in the United States. Numbers .01 to 10 can be 

 obtained for one cent each from Prof. E. Orton, Jr., 

 Ohio State University, Columbus, Ohio. 



It is rather difficult to compare the thermo-electric 

 pyrometer with Seger pyramids and say that either 

 one or the other is better. The latter are well adapted 

 to judge the completion of the burning. That is it 

 may take the same amount of heat to burn a certain 

 ware to the proper condition, as it does to bend over 

 cone 5,so that when the latter goes over the burning is 

 done. 



The cones do not however show whether the itemper- 

 ature of the kiln is r'sing steadily or fast at one time 

 and slow at another, or again whether or not it may 

 'have dropped temporarily. 



All of these last mentioned conditions are shown by 

 the thermo-electric pyrometer, and a comparison of 



