STATE GEOLOGIST. 301 
It was assumed that on forming silicates or aluminates 591 calories 
are given off per kilo of lime (according to Berthelot) and 827 calories 
per kilo of magnesia. 
This work has brought out several interesting points. The heat of 
combination of the clinker is very large, making 18 per cent. of the heat 
developed by the coal. The heat in the clinker is a little more than one- 
‘tenth of the heat developed in the kiln. 
The amount of heat carried out by the waste gases was found to be 
nearly 34 of the total heat developed and 85 per cent. of the heating value 
of the fuel. If the excess of air admitted were reduced to Io per cent. 
and the temperature of the gases reduced one-half by lengthening the 
kiln, the saving would amount to 60 per cent of the amount of fuel used. 
The amount of air admitted was 132 per cent. in excess over the theo- 
retically required amount. 
The maximum temperature of the flame was found to be, by calcu- 
elation, 1000° C., that is, lower by 200° than the temperature of the clinker. 
This difference is due to the heat of combination of the clinker. 
Temperature of Burning.—The clinker formation temperatures are 
given variously from 1200° to 1475° C., according to the kind of raw 
materials, the rapidity of burning, and the composition of the mixture. 
By burning slowly a much lower temperature can be employed than by 
burning more rapidly. The average temperature in rotary kilns is prob- 
ably close to 1300° C. | 
Pyrometers are not used in burning cement and in the nature of the 
case could not be well employed. They would be of little practical use, as 
the proper temperature, whatever it may be, is practically well fixed by the 
clinker itself, its appearance in the kiln, as well as by the feeding of definite 
quantities of coal determined by experience. An optical pyrometer might 
perhaps be used of the principle depending on measuring the intensity of 
light, by means of an instrument which is practically a photometer. 
Figure 53 illustrates such an apparatus consisting of a telescope with 
the necessary lenses and containing a standard incandescent lamp, g, in 
circuit with a battery, e, and resistance, w. The light admitted into the 
telescope is red, passing through the eye piece, s. On looking into a 
heated space the instrument is focused until the incandescent loop ap- 
pears sharply as a black thread. ‘The resistance, w, of the instrument 
is then so adjusted that the filament just disappears to the eye and when 
this is done the temperature may be read off from the scale attached to the 
instrument. 
These instruments, such as the Holborn and Wanner pyrometers, 
have been brought to close and satisfactory standardization, but, after all, 
their use would not help the burner enough to pay for the trouble of 
