a condition as possible throughout the entire process of crush- 

 ing" and mixing; and, if the raw materials originally contained 

 a little moisture, they are dried before being powdered and 

 mixed. In the wet method, on the other hand, the materials are 

 powdered and mixed while in a very fluid state, containing 60 

 per cent, or more of water. 



DRYING THE RAW MATERIALS. With the exception of the 

 marls and clays used in the wet method of manufacture, Port- 

 land cement materials are usually dried before the grinding is 

 commenced. This is necessary because the raw materials, as 

 they come from the 1 quarry, pit or mine, will almost invariably 

 carry appreciable, though often very small, percentages of 

 water, which greatly reduces the efficiency of most modern types 

 of grinding mills, and tenclls to clog the discharge screens. 



PERCENTAGE OF WATER IN RAW MATERIALS. The percent- 

 age of water thus carried by the crude raw material will depend 

 largely on the character of the material ; partly on the method 

 of handling and storing it ; and partly on weather conditions. 



Im the case of hard limestones, freshly quarried, the water 

 will commonly range from 1-2 per cent, to 3 per cent., rarely 

 reaching or exceeding the higher figure except in the very wet 

 quarries or during a rainy season. Such limestones, compara- 

 tively dry when quarried, are frequently sent to the grinding 

 mills without artificial drying. 



With the soft, chalky limestones, which absorb water very 

 rapidly, the percentage can usually be kept down to. 5 per cent, 

 or less in dry weather; while prolonged wet weather may ne- 

 cessitate the handling at the mill of material carrying as high 

 as 15 to 20 per cent, of water. 



The clays present a much more complicated case. In addi- 

 tion to the hydroscopic or mechanically-held water that they 

 may contain, there is also always present a certain percentage 

 of chemically combined water. The amount of hydroscopic 

 water present will depnd on the treatment and exposure of the 

 clay ; and may vary from I per cent, or so in clays which have 

 been stored and air-dried to as high as 30 per cent, in fresh 

 clays. The chemically combined water will depend largely on 

 the composition of the clay, and may vary from 5 to 12 per 

 cent. The hygroscopic or mechanically held water of clays can 

 be driven off at a temperature of 212 F., while the chemically 



