No. 434-] 



PARA FFL NE BA TH. 



turn. As constructed for our paraffine baths the coil is a some- 

 what flexible cylinder, about half an inch in diameter, with cop- 

 per covering. With its attached insulated wires such a coil is 

 shown hanging- on the wall at the left in Figure 1. The resist- 

 ance metal used in the coil was a copper-nickel alloy. In the 

 case of the paraffine baths this coil was simply shoved into the 

 bath through an inch hole made in the top of the bath. The 

 knob with connecting wires protrudes outside, and the coil rests 

 on the floor of the bath, immersed, of course, in water. In the 

 case of the thermostats used for incubating purposes, etc., a hole 

 was cut in the side or bottom of the water reservoir, and the 

 coil after being introduced was soldered in place so as to close 

 the hole. 



To devise a regulator was more difficult. The use of anwdi- 

 nary rheostat proved to be impracticable, because it was not possi- 

 ble to make sufficiently fine gradations of resistance for different 

 temperatures, nor by it to provide against fluctuations in the 

 initial current. 



The method finally adopted utilizes a one-cell relay battery to 

 magnetize an electro-magnet. The heating current is made to 

 pass through the armature, which is pulled into contact with a 



is drawn away from the post by the magnet the heating current 

 is broken. Into the circuit of the relay battery is put the regula- 

 tor ; when the relay circuit is closed at the regulator, the mag- 

 net operates on the armature and breaks the heating current ; 

 when the relay circuit is broken at the regulator, the armature 

 is drawn back by the spring to its first position thus closing the 

 heating circuit. 



Our Reichert gas regulators {R), already in use for the pur- 

 pose of regulating the gas supply to the burners, were adapted 

 by very slight changes to the new requirements. The tubular 

 glass stopper carrying the gas inlet was removed ; in its place 

 was put a cork, bored to receive one of the copper wires ( W) 

 from the single-cell battery of the Leclanche type (Samson cell 

 No. 2). The copper wire terminates with a No. 20 platinum 

 wire (Fig. 3, Pt.) which is about an inch long ; the height of the 

 lower end of this wire above the mercury in the column can be 



