558 NEW YOEK STAtE MUSEUM 



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

 indicating that the temperature reached the fusing point of 3. 



These pyramids have been much used by foreign manufacturers 

 of clay products and are' coming into use in the United States. 



There are several indirect methods of determining temperatures, 

 but that of Bischof (Dingler's Polyt jour. 196: 438, 525; 198: 

 396) is perhaps the best known. This consists in increasing the 

 refractoriness of weighed samples by adding to them increasing 

 quantities of an intimate mixture of equal parts of chemically pure 

 silica and alumina, and heating them with a prism of Saarau fire 

 clay (whose fusing point is Seger cone 36) to above the melting 

 point of wrought iron. While involving more labor than the direct 

 method, it has the advantage of requiring only one standard. 



This method was tried by Hofman and Demond (" Further ex- 

 periments for determining the fusibility of fire clays ", Trans. 

 Amer. inst. min. eng. Mar. 1895) who mixed various samples of 

 fire clays with varying proportions of calcium carbonate, and 

 calcium carbonate and silica, to render them fusible at temperatures 

 below the melting point of platinum, while common brick clays 

 were mixed with alumina and silica tO' decrease their fusibility, the 

 object of this being tO' arrive at a standard temperature at which 

 both refractory and fusible clays could be tested. The results ob- 

 tained at first were very satisfactory, but subsequent ones did not 

 result as was desired and the method had to be abandoned. More 

 recently however this method has been tried by J. L. JSTewell and 

 G. A. Rockwell with much better results {Trans. Amer. inst. min. 

 eng. Oct. 1898, " A modification of Bischof's method for determin- 

 ing the fusibility of clays, as applied to nonrefractory ones, and 

 the resistance of fire clays to fluxes ", H. 0. Hofman) 



In the last experiments the Seger cone 26 was used as a standard, 

 as it forms the line between refractory and nonrefractory clays, 

 the nonrefractory ones being toned up till they show the same 

 behavior in the fire as cone 26. The amount of toner added then 

 gave an idea how far the clay stood below the lower limit of 

 refractoriness. 



