The Science record; a compendium of scientific progress and discovery . le of holding 45 barrels as a are set in brick furnaces, and their bottoms are con-structed in a peculiar manner and of stout iron, to with-stand the heat of an anthracite fire. Revolving stirrers,almost in contact with the bottoms and sides, are kept inmotion to prevent caking. 176 SCIENCE RECORD. Care and skill are requisite in the calcination process, toavoid either over or under-burning. If all the water bedriven off, the plaster will not harden so rapidly as thatwhich has been heated so long as the tumultu
The Science record; a compendium of scientific progress and discovery . le of holding 45 barrels as a are set in brick furnaces, and their bottoms are con-structed in a peculiar manner and of stout iron, to with-stand the heat of an anthracite fire. Revolving stirrers,almost in contact with the bottoms and sides, are kept inmotion to prevent caking. 176 SCIENCE RECORD. Care and skill are requisite in the calcination process, toavoid either over or under-burning. If all the water bedriven off, the plaster will not harden so rapidly as thatwhich has been heated so long as the tumultuous expulsionof vapor lasts ; and if only half the contained water be ex-pelled, the plaster will have entirely lost its power of har-dening with water. Properly calcined gypsum seems toretain one fourth of its combined water. When the calci-ner judges the process to be complete, the calcined plasteris drawn out into a bin, where it is conducted to the bolt,which is a revolving cylindrical drum made up of threedifferent finenesses of wire-cloth set on an incline. The. FIG. 2.—THE SETTLING HAMMER. finest sieve is first encountered, and then the material fallsupon the others in turn. Directly below, correspondingto the width of each particular fineness of the sieve, arebins which receive the calcined plaster of three degrees offineness, known as superfine, casting, and common. Fromthese bins the article is rapidly shoveled into barrels andpacked for the trade. The method of packing is seen in the illustration, Fig. workman first prepares the barrel by lining its inte-rior by hand with a few sheets of brown paper, wideenough to overlap one another. These project above thetop of the barrel, and are folded over in a very secure TECHNOLOGY. 177 manner, thus answering the purpose of a head. Barrelsfor distant transportation are headed in the ordinarymanner. The barrel to be filled is first fitted with a wide-mouthedfunnel, and then placed on a revolving platform, and, whilerot
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