﻿the Vulcanite Tube used with Blanches Air-pump. 443 



is screwed on air-tight. In order that the cylinder shall be 

 free to oscillate, it is evident that the tube A does not admit of 

 being rigidly attached to any fixed piece of apparatus ; and ac- 

 cordingly, to connect A with the tube B communicating with 

 the pressure-gauge and air-pump plate, M. Bianchi employs a 

 flexible tube of vulcanite, which is prevented, by a helix of wire 

 inside, from collapsing with the pressure of the atmosphere when 

 the pump is working. 



Such a vulcanite connector, when of the quality furnished by 

 M. Bianchi and when new, answers its end most satisfactorily ; 

 but, like all other vulcanite tubes, in course of time it becomes 

 brittle, and, especially where it is attached to the metal tubes 

 A and B, it begins to leak. Thus it happens, when an experi- 

 ment is to be made, that the pump, in every other respect in 

 perfect order, may be found to be useless until the vulcanite has 

 had its ends cut off and is again attached, or until it is replaced 

 by a new tube. I believe all who have been in the habit of using 

 this form of air-pump must have experienced the inconvenience 

 thus arising, and will agree with me in thinking that, although 

 the use of a vulcanite tube may sometimes be convenient, the 

 necessity of employing it always is the only objectionable feature 

 of Blanches otherwise most excellent instrument. 



In order to remedy this defect, I have recently constructed a 

 metallic connector for the Bianchi air-pump belonging to the 

 Natural-Philosophy Museum of the United College, St. An- 

 drews. This consists of a brass tube, H (fig. 1), about 6 feet 

 long, \ of an inch bore, and ^ of an inch outside diameter, 

 coiled into a helix of three and a half turns about 6 inches in 

 diameter. To the air-tubes, A of the pump and B of the pres- 

 sure-gauge and pump-plate, are attached, by soldering, tubes 

 with conical ends. That which is soldered into the air-tube A 

 is carefully centered. It is represented at D (fig. 2). The 

 D are fitted air-tight, by grinding, into hollow conical pieces, 

 E, F, attached by soldering to the ends of the connecting helix H. 

 To prepare the pump for working, the cones D having been 

 slightly oiled, the piece E of the connector is slipped on to the 

 cone D of the pump at A ; and the pump-plate and gauge are slid 

 on the table on which they stand towards the pump until the 

 conical tube D at B (not seen in the figure) entering the hollow 

 piece F, takes its seat and slightly compresses the helix H length- 

 wise. The helix of brass tube, although quite rigid enough from 

 point to point to preserve its shape, yet possesses ample elasticity 

 as well as flexibility to keep the cones D in their places, notwith- 

 standing any jolting motion which may occur, even when the 

 pump, for rapid exhaustion, is driven with the utmost speed. 

 It need scarcely be further explained that the cone D at A turns 



