Excerpts from: The Gypsum of Michigan and the Plaster Industry, by G. P. Grimsley, Published by authority of the laws of Michigan under the direction of the Board of Geological Survey, Lansing, Robert Smith Printing Company, State printers and binders, Illustrated, 1904, 247 pages (page excerpts 105-106, 124 and 160)
Powers’ Mine and Mill.
This property is located within the city on the west bank of the Grand River about midway between the Pearl and Fulton street bridges. Mr. Wm. T. Powers organized the company and sunk the shaft in 1890 (Nov 1894). The mine goes 50 feet below the bed of the river and the framework of the shaft is built up 35 feet more to the floor of the mill. The record of the shaft has been lost and the section represented in Figure 14, is given from the memory of Mr. Powers of the boring made to the roof gypsum and 60 feet below it. The company owns 30 acres of this gypsum land. The upper ledge six to eight feet thick is left for a roof and the mine is worked on a room and pillar system with rooms about 50 feet square and the pillars 20 feet. It is estimated that by this system about three-fourths of the gypsum can be removed.
The mill was built on the bank above in 1898, and was burned in the spring of 1903, and the company is known as the Gypsum Products (Manufacturing) Co. The frame mill was built in an L shape, 130 feet long east and west, and 25 to 50 feet wide with a storage shed built to the east 20 by 20 feet. The wareroom to the west was two stories high and the wider portion was three stories. On the second floor were placed the nipper and cracker and the buhrs below them in two sets, one of 30-inch for ordinary grinding, and a pair of 30-inch buhrs for regrinding. A part of the flour gypsum was carried by conveyors to the west part of the room and sacked for land plaster, and part was elevated to the third story over the kettle placed in the north part of the L extension. The gypsum then passed into the Powers patent kettle which was ten feet in diameter with a new design of flues described in the chapter on Technology, and it was heated by a wood fire. The finished plaster was dumped into fire brick bins and elevated to bins over the Broughton mixer where it was mixed with retarder to form wall plaster.
In the Powers patent kettle 40 three-inch flues are built around the circumference of the inside of the kettle, each forming a segment of an oval. This arrangement gives more clear space in the kettle and is claimed to make a considerable saving in fuel. In the Powers mill at Grand Rapids, ten tons of plaster can be made in a ten-foot kettle in one batch.
Granite Plaster of the Powers’ Mill.
Lime sulphate 72.45
Lime carbonate 7.96
Iron and alumina 1.03
Magnesium carbonate 4.98
An examination of these analyses shows that the lime sulphate varies from 72.45 per cent in the Power’s mill plaster to 92.95 per cent in the Alabaster plaster. The impurities vary from 22.6 to 2.06 per cent. The water percentage varies from 4.94 to 8.81 per cent. The loss of water in the calcining of these plasters is 74, 60, 55 per cent.
These analyses compare favorably with those given of the French plasters and with those from other districts in this country.
Figure 14. Illustration from The Gypsum of Michigan and the Plaster Industry, by G. P. Grimsley, Published by authority of the laws of Michigan under the direction of the Board of Geological Survey, Lansing, Robert Smith Printing Company, State printers and binders, Illustrated, 1904, 247 pages (page 105)
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