TREATMENT OF THE COMSTOCK ORES. 257 



is connected with it by two side flues, that branch off from the main flue 

 about ten feet from the stack, leaving space for a platform between the stack 

 and the end of the main flue, which is open, or only closed by a sheet-iron 

 door. The firing being in progress in the several fireplaces, the heat passes 

 along the main flue and then by the branch flues to the stack. The material 

 to be roasted is put on the platform at the end of the flue near the stack, and 

 is moved, by the mechanical appliances referred to, into the flue and slowly 

 along its whole length, at such speed as may be desired, and, at the same 

 time, subjected to constant stirring and turning. This is effected by means 

 of an endless chain, passing through the flue, and carrying a number of 

 scrapers, which, as they move along the flue, just rest on the bottom. 

 The cliain moves over two pulleys, one at each end of the flue, and is so 

 arranged as to pass, in one direction, in and through the flue, and, in the 

 opposite direction, outside of and above it. At two opposite parts of the 

 chain are two circular pieces of iron, having the form of a ring, with a diam- 

 eter about equal to the width of the flue. To each of these circles are attached 

 the scrapers, six or eight in number. They are shaped something like a plow- 

 share. As they pass through the stuif spread on the flue bottom they move 

 it along and turn the particles with which they come in contact. The scra- 

 pers may be so set on the ring that the entire surface of the flue bottom is 

 covered at some time by one or another of them. According to the angle 

 which the face of the scraper makes with the larger axis of the flue the for- 

 ward movement of the material will be greater or less. By this means, as 

 well as by the speed at which the chain is caused to move, the length of time 

 which a given portion of the material shall occupy in passing through the flue 

 may be determined. The rings, carrying the scrapers, are jointed or hinged 

 so as to pass over the pulleys on which the chain moves. At each end of the 

 flue is a sheet-iron door, the lower part of which is hinged so that the rings 

 may pass. There are also slots cut in the hinged parts for the passage of 

 the chain. 



This furnace, although devised several years since and affording then 

 satisfactory results with experimental trials, has not yet come into general use. 

 Some furnaces of this kind, but difiering in some details of construction, were 

 33 



