658 CEMENTS, LIMES, AND PLASTERS. 



improbable, in view of the great variety of material successfully handled 

 by the modern ball and tube mills when operated continuously in Port- 

 land-cement practice. Several years ago I referred the question to a 

 leading firm of manufacturers and was informed that nothing in their 

 experience justified the unfavorable conclusion, and that their con- 

 tinuously operated tube mills had successfully pulverized mixtures 

 of slag and lime. It seems probable that the most economical prac- 

 tice would be to send the dried slag through a small crusher, Griffin 

 mill, or ball mill, mixing the crushed slag with lime and completing 

 the mixture and reduction in continuously operated tube mills. What- 

 ever system of reduction is employed, it is necessary that the slag be 

 dried as completely as possible, and, with modern dryers, the amount 

 of moisture in the dried slag can be economically kept well below 1 per 

 cent. 



In this connection it may be of service to note the results attained 

 in the grinding of basic Bessemer slag (for use as a fertilizer) by the 

 Pottstown Iron Company. A 2000-mm. Jensch ball mill was there 

 employed. This mill consumed about 13 H.P. Its normal output 

 was 20,000 Ibs. in ten hours, though a maximum of 29,000 Ibs. in ten 

 hours had been reached on perfectly dry slag. The fineness of the 

 product was such that 95 to 98 per cent would pass a 100-mesh sieve 

 and 70 to 75 per cent a 150-mesh sieve. A West tube mill in use at 

 an American slag-cement plant grinds 8^ barrels per hour of mix to 

 a fineness of 95 per cent through 200-mesh, or 10 barrels per hour to 

 a fineness of 90 per cent. In doing this it uses 67 H.P., equivalent to 

 power consumption of 8 H.P. hours or 6.7 H.P. hours, respectively. 



Regulation of set. Slag cements will normally set very slowly 

 compared to Portland cements. As this interferes with their use for 

 certain purposes, many attempts have been made by various treat- 

 ments to reduce their setting- time. There is, unfortunately, another 

 reason why the manufacturer should desire to hasten the set of his 

 product. Most of the slag cements sold in this country masquerade 

 as Portland, and it is desirable to the manufacturer, therefore, to make 

 such of their properties as are brought out in ordinary tests or analyses 

 approximate to those of true Portland cement. The set of slag cements 

 can be hastened by the addition of puzzolanic materials. Of these, 

 burned clay, certain active forms of silica, and slags high in alumina 

 are the cheapest and most generally obtainable. The most important 

 method of regulation is, in this country at least, the Whiting process, 

 which is followed at two large American plants. 



United States Patent No. 544,706, issued in 1895 to Jasper Whiting, 



