156 Description of a Furnace 



Inches. 



Total height of the furnace - - - - - - - 17^ 



Height of the lower chamber, A, including the bot- 

 tom, which was an inch in thickness - - - 11 



Height of the upper chamber, B, o»- of the fire- 

 place, ------------- 5J 



Diameter, taken at the upper interior edge of the 

 fire-place, B ---------- o£ 



Diameter of the same, taken at the bottom or par- 

 tition -------------7 



This part decreases in diameter 2-J inches, tapering to- 

 wards the lower part of the furnace, A. 



The tube, C, is conical at the upper extremity and cy- 

 lindrical towards the bottom : it is 9^ inches in length, 4^- 

 in diameter at the top, and 2f towards the middle. Both 

 ends of it are open. 



The tube, C, is placed in the aperture formed in the mid- 

 dle of the partition, in such a manner as to rise 3 or 4 inches 

 into the fire-place. The place where it joins to the parti- 

 tion is luted with clay, to prevent the ashes or small coals 

 from falling down. 



When this arrangement is made, the net, D, (see fig. 2.) 

 made of brass wire worked very open, is placed in the tube. 

 It has the shape of a funnel, the upper edge of which is 

 made fast to a ring ef wire of the same diameter as the upper 

 part of the tube, C. The decrease in the diameter of the 

 tube C conduces to the stability of this net, and the conical 

 form of the latter prevents it from coming into contact with 

 "the lateral parts of the tube, which is a matter of great im- 

 portance to preserve the copal from too great alteration by 

 the heat. 



The copal is placed on this metallic filter in pieces not 

 larger than a small nut, and the whole is closed up with 

 the iron plate or cover, E, an inch in thickness, taking 

 care to lute the joining with clay, to prevent all communi- 

 cation with the exterior air. 



A shallow dish or capsule, F, filled with water, (fig. 3.) 

 is placed under the bottom of the tube, C, in such a man- 

 ner that the tube is immersed in the water two or three lines. 



The fire-place, B, being filled with burning coals so as 

 to rise above the iron cover of the tube, the first impression 

 of the hea,t on the copal is announced by a kind of crackling, 

 the consequence of its dilatation, which makes it split into 

 small pieces. This noise is a sign of beginning liquefaction, 

 which indeed takes place soon after. A small iron pallet- 

 knife 



