304 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



supported in any convenient manner. The tube is filled 

 with mercury or water (according to the kind of gas 

 to be operated upon) ; it is then reversed, and the gas to 

 be operated upon suffered to ascend the tube, until a cer- 

 tain quantity has been introduced. The electric spark or 

 shock is then passed from the one wire to the other, when 

 the gas is inflamed. The result is seen by the product left. 

 Price, $3.00 ; graduated, $4.00; stand, $1.00. 



Fi s- 361. Apparatus for passing an 



Electrical Spark through 

 Gases.-Psiss a spark through 

 a vessel filled with nitrogen, 

 and it becomes intensely 

 brilliant, and of a splendid 

 blue color, equal to that of 

 burning brimstone. The ap- 

 paratus, which is convenient, 

 for trying experiments of this kind, is as follows (Fig. 361). 

 A is a glass receiver, holding about a pint ; it has a wire and 

 ball inserted in two opposite sides, B and C. B is capable 

 of sliding backwards or forwards, so that it may be made to 

 approach or recede from the other. The receiver is placed 

 in the pneumatic trough, and is filled with the required gas, 

 in the ordinary way practised by chemists. For some gases 

 a mercury or oil trough must be employed. During the 

 experiment one of the balls must be connected by a wire 

 with the prime conductor, as at D, and the wire of the other 

 held in the hand. 



An instrument is made, answering the same purpose, con- 

 sisting of a globe of glass having two necks, one of them 

 attached to a cap connected with a stop-cock, and having a 

 brass ball entering the neck of the globe. The other neck 

 a cap with sliding rod, having brass balls at each end. The 

 globe is exhausted of air by the air-pump, and the gas to 

 be experimented with introduced. 



Price, $3.00 to $6.00. 



Kinnersley^s Electrical Air Thermometer. (Fig. 362.) 

 This is an instrument for showing the expansion of air when 

 an electrical shock is passed through the instrument. It 

 consists of a glass tube, ten inches long and two inches in 



