Experimental, Analytical, and other purposes. 19 



light \ if it exhibits much more than this, the draught is too 

 powerful. 



With one ounce of copper put into the cold furnace, and the 

 gas lighted and properly adjusted, the copper generally begins 

 to melt at about the tenth or twelfth minute, and is completely 

 melted by the fifteenth. With the heat well up, one ounce of cop- 

 per has been melted in it in 2 J minutes, one ounce of cast iron in 

 3 minutes, five ounces of copper in 4J minutes, and three ounces 

 of cast iron in 5 minutes. With the smaller hole in the top of 

 the furnace open, one ounce of copper has been melted in 3^ 

 minutes ; and several ounces of copper have been kept in fusion 

 for upwards of half an hour, and may be kept so for any length 

 of time : cast iron has also been fused and kept melted under the 

 same conditions. These various effects have also been obtained 

 in a somewhat diminished degree with the chimney standing in 

 an open room. 



When the small hole D is open, some air is drawn in that 

 way, and less air passes up with the gas through the tube ; but 

 this cold air does not much diminish the temperature of the cru- 

 cible, because it combines with the excess of gas now passing over 

 the edge of the inner cylinder; it however renders the flame 

 round the crucible white by deficiency of air, and this should be 

 partly corrected by lessening the amount of gas. An excess 

 either of air or gas renders the surface of melted copper dull. 



When it is desirable to perfectly avoid the contact of air with 

 the fused substance during manipulation, a thin and narrow ring 

 of fireclay should be placed upon the top of the tube to con- 

 tract its opening ; the flame then completely closes over the top 

 of the crucible and prevents access of air. A proper adjustment 

 of gas, together with exclusion of air in this manner, enables a 

 perfectly bright surface of melted copper, or even tin, to be con- 

 tinuously maintained, from which the images of the parts above 

 are clearly reflected. The clay ring may be withdrawn by lifting 

 the plate B. A less perfect exclusion of air may be obtained 

 by employing a narrow crucible placed rather low down in its 

 support. A small iron dish should be placed beneath the tube L, 

 to receive any melted substance that may fall. The furnace is 

 protected by letters patent, and may be obtained of the maker, 

 E. W. Ball, 11 Islington, Birmingham. The chief conditions of 

 success in the use of this furnace are, sufficient gas, proper regu- 

 lation of gas to air, and a suitable degree of draught. 



Note. — I beg to acknowledge the assistance I have received 

 from Mr. Thomas Simons, crucible-maker, Northwood Street, 

 Birmingham, in the production of suitable clay cylinders, &c. for 

 this furnace. 



C2 



