154 



ELEMENTARY CHEMICAL MICROSCOPY 



the tiny flame B (reserve flame) employed for microchemical 

 work is furnished by a small brass tube inside the Bunsen tube. 

 This flame is always burning when the gas is turned on at the 

 gas main; its height is regulated by the screw S so as to be from 

 3 to 4 millimeters high. If, as often happens, this tiny flame 

 cannot be lowered to the proper size, remove the screw S, and 

 drop into the hole a small fragment of very soft annealed copper 

 wire, replace the screw and turn until the copper fragment has 

 been crushed sufficiently to partially obstruct the flow of gas. 



Fig. 88. Type of Small Blast Lamp for Microchemical Analysis. (Xi) 



Turning the stopcock A lights the large burner and serves to 

 regulate the size of the Bunsen flame. The burner is not sold 

 with the ring R, as shown in the figure, but this attachment can 

 be made in a few minutes by fastening a bent copper or brass 

 wire to a split brass ring which may be raised or lowered and 

 maintains its position through friction, or, if possible, a heavier 

 ring with thumb-screw is substituted for the simple ring. This 

 wire ring is useful as a support when moderately long heating 

 must be practiced or when evaporations over a tiny flame at 

 moderate temperatures are required. 



For the production of higher temperatures than are possible 

 with the flame of the Bunsen burner, a blowpipe will be found 



