392 H. L. Wells — Self-feeding Sprengel Pump. 



enough to deliver mercury rapidly, for otherwise the efficiency 



of the apparatus will suffer. 



3 Fig. 3 represents a Sprengel pump, with 



the mercury elevator, now in use in this 

 laboratory. The artist has relatively short- 

 ened most of the tubes, and has exaggerated 

 some parts of the apparatus for the sake of 

 clearness of detail. 



The whole apparatus can be easily con- 

 structed with the materials usually at hand 

 in a chemical laboratory. Water enters at 

 E, carries mercury up through H and over- 

 flows through F, while the mercury goes 

 through a trap into the reservoir C of the 

 Sprengel pump. 



The total height of the apparatus is 

 2400 mm . The bore of the tubes E, H and F 

 is 5-6 mm . The tube H, where it leaves the 

 bottle A, takes a downward curve, thus 

 increasing the length of the intermittent 

 column of mercury raised. The inverted 

 siphon* formed by the tubes I and J pre- 

 vents air, water or sulphuric acid, which 

 may be in C, from being carried over into 

 the pump proper, no matter how slowly 



has a bore of 

 is 850^ long 



mercury may be delivered. I 

 8-10 mm " and "is 900 mm long ; J 

 with a bore of 3^ mm . 



The Sprengel tube K is about 1500 mm 

 long with a bore of 3 mm . It is very im- 

 portant for the sake of rapid pumping, that 

 this " fall-tube" should be long and have a 

 bore as large as consistent with good working. f If this tube 

 is larger at one end than the other, as it may be advantageously, 

 the smaller end should be uppermost, because it is at the top, 

 if anywhere, that mercury fails to till the bore of the tube, and 

 also because this form of tube prevents the atmospheric pres- 

 sure from forcing a column of mercury upwards out of it, since 

 the column lengthens when it rises. 



* A Sprengel pump with this modification is described and figured in Sutton's 

 " Yolumetric Analysis," edition of 1871, p. 262. 



f The proper caliber of the fall-tube is given by Sprengel (Jour. Ohem. Soc, 

 1865, p. 15) as 2£ mm . He says that with larger tubes his vacuua were -J-l mm less 

 than the barometric height, hence where the most perfect exhaustion was re- 

 quired it would be advisable to use a tube of the size which he gives. Sprengel 

 limited the length of his fall-tube by the height at which it was convenient to 

 pour back the mercury into the reservoir at the top, but it is evident that much 

 longer fall-tubes could be used conveniently with the " mercury elevator." 



