510 CEMENTS, LIMES, AND PLASTERS. 



value of conserving the waste heat from the clinker by heating the 

 entering air." As the clinker of the two kilns during this test carried 

 out 4,409,540 B.T.U. per hour, and the clinker regenerator returned 

 2,041,000 of this, its efficiency was 46.3 per cent. 



At a German Portland-cement plant where the stack-gases are used 

 in drying the raw materials, a large amount of very fine dust settles 

 from the stack-gases in the drying chamber. This dust has been exam- 

 ined f by Seger and Kramer, and found to consist of 43.65 per cent 

 of insoluble and 56.35 per cent of soluble matter. The insoluble matter 

 gave: silica 31.4 per cent, alumina 14.7 per cent, iron oxide 4.9 per cent, 

 lime 36.8 per cent, magnesia 1.3 per cent, loss on ignition 0.9 per cent. 

 The soluble portion consisted of potassium sulphate 61.1 per cent, and 

 potassium carbonate 38.9 per cent. Calculating these proportions to 

 percentages of the total dust, we have: 



Silica (SiO 2 ) 13.71 



Alumina (A1 2 O 3 ) 6.42 



Iron oxide (Fe 2 O 3 ) 2. 14 



Lime (CaO) 16.06 



Magnesia (MgO) . 57 



Potash carbonate 34 . 43 



Potash sulphate 21 . 92 



Loss on ignition 4 . 76 



The composition of this stack-dust has directed attention to the 

 possibility of utilizing it as a source of potash, and both American 

 and foreign patents have been taken out to cover possible processes 

 for this purpose. 



List of references on heat requirements. The following list con- 

 tains the principal papers dealing with this phase of cement-manufac- 

 ture. Those marked with an asterisk are restricted mainly to a dis- 

 cussion of clinkering temperatures, etc. 



* Bleininger, A. V. Manufacture of hydraulic cements. Bulletin No. 3, 



Ohio Geological Survey, 1904. 



* Campbell, E. D. Some preliminary experiments upon the clinkering of 



Portland cement. Journ. Amer. Chemical Soc., vol. 24, pp. 969-992, 

 Oct., 1902. 



* Campbell, E. D., and Ball, S. An experiment upon the influence of the 



fineness of grinding upon the clinkering of Portland cement. Journ. 

 Amer. Chem. Soc., vol. 25, pp. 1103-1112, Nov., 1903. 



* Campbell, E. D. Further experiments on the clinkering of Portland cement 



and on the temperature of formation of some of the constituents. Journ. 

 Amer. Chem. Soc., vol. 26, pp. 1143-1158, Sept., 1904. 



t Journ. Soc. Chem. Industry, vol. 23, p. 661. June 30, 1904. 



