246 ANNUAI, REPORT 
resistance furnaces, however, are quite troublesome above a temperature 
of 1200° C., owing to the conduction of the heating cylinder and con- 
sequent danger of short circuits. ‘he Hempel carbon resistance furnace 
would prove very suitable, and of late a furnace has been offered on the 
market which certainly “seems to be an exceedingly simple apparatus, 
consisting mainly of a refractory cylinder of fire-clay or basic material 
surrounded by a special resisting material, called “Kryptol.” It is 
claimed that the “Kryptol” furnace produces a temperature of 2000° C. 
quite readily, depending on the refractoriness of the cylinder. It con- 
sumes from 3 to 5 kilowatts per hour, according to the temperature 
and size. The temperature measurements must be made with an optical 
pyrometer, but can be carried out even with an ordinary photometer. 
Corrections of the Cement Composition.—In the following table 
a few general corrections are given which may be followed if the clinker 
produced, experimentally or on a large scale, shows certain defects: 
Defect of cement. Correction. 
Too difficult to vitrify. Decrease lime content, or add more ferric 
oxide in the shape of an ore, or add 
fluorspar to raw cement. 
Vitrified too rapidly. Increase silica content of clay base and lime 
content. 
Yellowish clinker. Increase silica content in clay base. 
Sets too rapidly. Increase silica content in clay base, or add 
fluorspar to raw mix, or add ferric oxide 
toraw mix, or add ground gypsum to 
burnt cement. 
Sets too slowly. Reduce silica content. 
Not constant in volume (does not stand | Store longer. Decrease lime content or in- 
boiling test.) crease content of ferric oxide, or increase 
silica content in clay base; grind raw mix- 
ture finer; reduce sulphur content. 
Tendency to dust. Increase lime content; quench clinker in 
water or cool rapidly in air; add ferric 
oxide to raw mix. 
