MINERAL RESOURCES OF THE STATE OF NEW YORK 2gi 



for the finishing or final stage, in which revolving cylinders are used. 

 The Alsing cylinder has the preference in most of the installations, 

 although in the later plants the equipment consists of tube mills. 

 The difference is mainly one of size. The cylinder is from 8 to lo 

 feet long and 6 feet in diameter, turned 20 to 25 times a minute. 

 It is loaded with i ton of talc and 3 tons of pebbles. The grinding 

 operation lasts 2 to 5 hours, depending upon the degree of fineness 

 that is required. The cylinder is idle for the time necessary to 

 charge and discharge it ; the tube mill is of the same general pattern 

 as that employed in the reduction of cement materials and its opera- 

 tion does not differ materially in the present case from that in ordi- 

 nary practice, but the tube must be lined with a material free of 

 iron to prevent contamination. It has a decided advantage over 

 the cylinder in its continuous feed and discharge, but it is not so 

 easily regulated to give the desired finish to the product. 



Two tube mills arranged in tandem, so that the discharge of the 

 first goes to the second, may be used for the entire grinding opera- 

 tion, the first mill taking the place of buhrstones or the centrifugal 

 grinder. 



The product obtained by grinding of the fibrous talc is an impalp- 

 able powder called mineral pulp; under the microscope the particles 

 still show the fibrous texture of the original. For paper filler and 

 for most other purposes uniform fineness is highly desirable. The 

 color should be as nearly dead white as possible; freedom from hard 

 particles like quartz is another factor which is important in grading 

 the talc. The product of the Edwards district is notably free of 

 discoloring impurities and compares favorably with the talc from 

 any other source in that respect. A little grit is present in most 

 of the fibrous talc; less of it in the foliated variety. Unaltered 

 tremolite and quartz are the sources of the grit. 



A coarser grade of talc known as buhr stock is made from the 

 fibrous talc by omitting the last stage of grinding in the tube or 

 cylinder mill. This has a distinctly fibrous appearance and feel, 

 the grinding being carried only so far that the material is thoroughly 

 shredded. Buhr stock supplies the place of asbestos in the manu- 

 facture of insulating materials. 



The ground talc is put up in 50-pound sacks and 2oo-poimd 

 burlap bags for shipment. 



Uses. The paper trade is the largest consumer of ground talc, 



and its requirements have determined more or less the course of 



technical development in the district. Talc functions as a filler 



chiefly, but adds other desirable qualities to paper. In its pliancy 



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