412 



Mr. T. Graham on the Absorption and 



Fig. 1. 



nally offered by the in- 

 ventor as the means of 

 producing a vacuum, or 

 as an air-pump. But by 

 bending the lower end 

 of the straight fall-tube, 

 the instrument may be 

 further made to deliver 

 gas into a receiver, and 

 be used with advantage 

 as the means of trans- 

 ferring small volumes 

 of gas from one vessel 

 to another. 



While the mercury in 

 the funnel A is allowed 

 to flow downward into 

 the barometer-tube CB, 

 of 2J miliims. in dia- 

 meter, by relaxing the 

 clamp upon the adapter 

 tube of rubber at C, a 

 connexion is also made 

 with the close receiver 

 to be exhausted, such 

 as an air-tight bag E, 

 by means of the branch 

 tube w. The air in E, 

 gaining access to the 

 Torricellian vacuum, is 

 swept on by the falling 

 mercury, and delivered 

 below into the small gas- 

 receiver R, previously filled with mercury and inverted over mer- 

 cury in the mortar B below. The principal difficulty in obtain- 

 ing a good vacuum in E by means of this apparatus arises from 

 the necessity of joining the glass tubes in more than one place 

 by means of adapter tubes of rubber. The directions given by 

 Dr. Sprengel on this point require to be closely followed :- — " The 

 connexions between the glass tubes are made of well-fitting black 

 vulcanized caoutchouc tubing, sold under the name of French 

 tubing. This is free from metallic oxides, which render the 

 tubing porous. Besides this all these joints are bound with coils 

 of copper wire, which is easily accomplished with a pair of pliers." 

 The joints should also be coated with gutta percha liquefied by 

 heat, or with fused rubber. An exhausting-syringe, or air-pump, 



