BY WILLIAM A. HASWELL. 



435 



Two bottles of similar size are connected together by tubing in 

 the way represented in the woodcut. One of these, a, we 



call the mixing bottle ; the 

 other, b, contains the objects, 

 and must have a capacity 

 equal to at least a hundred 

 times the bulk of the latter. 

 The objects are in fluid 1, 

 and it is desired to substitute 

 fluid 2. Both bottles are 

 filled, or partially filled, 

 according to circumstances, 

 with fluid 1, and bottle A is 

 connected with a reservoir 

 of fluid 2. It is somewhat 

 difficult by means of a tap 

 to regulate the flow so that, 

 let us say, one drop in five 

 seconds will pass out of the 

 reservoir ; and it is much 

 more convenient to effect 

 this by intercalating in the 

 supply pipe a section of glass 

 tubing drawn out to the 

 required degree of fineness 

 (represented in the figure as 

 disconnected from the proxi- 

 mal portion of the supply 

 tube). The rate of flow through this narrow section of the tube 

 can be further regulated by raising or lowering the reservoir or 

 the mixing bottle, thus altering the pressure. With bottle B is 

 connected an over-flow tube. Above the narrow section of glass 

 tubing in the supply pipe it is well to have a piece of filter paper 

 stretched across the mouth of the piece of tubing in the form of a 

 diaphragm, and held in place by the overlapping india-rubber 

 tubing. This prevents the possibility of the narrow part of the 

 tube being choked up by any minute particles 

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