NATURAL PHILOSOPHY. 



181 



is the subject of this article. This pump consists of a barometer tube about 



33 inches long, and 5-16 to 3-8 of an inch 



in diameter. Its lower end, C, is bent in the 

 form of an S, and it is closed by a cock. 

 The upper end of the tube is firmly secured 

 to. a glass egg-shaped vessel, B, containing 

 from half a pint to one quart, and is pro- 

 vided with a stop-cock below and with an- 

 other one above; this latter faucet being 

 covered by a funnel, A. The several fasten- 

 ings and cocks are all made of iron, and 

 the apparatus is screwed on a table. 



To set the pump in operation, it is filled 

 with mercury through the funnel on the 

 top, and the upper cock is closed. By open- 

 ing the stop-cock at the lower end of the 

 tube, the mercury escapes into a vessel 

 placed underneath, a column of 30 inches 

 remaining in the tube; and a complete 

 vacuum is obtained in the egg-shaped ves- 

 sel, forming in this case the vacuum of 

 Torricclli. 



To apply this apparatus to the Magdeburg 

 hemispheres, the lower one is secured to 

 the top of the tube, and a hole is drilled in 

 the upper one, which is stopped up by a 

 cock, so that it can be filled with mercury 

 and closed. By Opening the stop-cock at 

 the lower end of the tube, a perfect vacuum 

 is attained in the hemispheres. 



To exhaust or to rarefy the air in a com- 

 mon receiver, this apparatus is also superior 

 to the common air-pump, as by its aid the 

 rarefication can be carried on ad infinitum. 

 The receiver is placed on the table and 

 made to communicate with the glass egg- 

 shaped vessel on the top of the tube by means of an iron pipe which is 

 provided with a stop-cock. If the contents of the receiver and of the glass 

 e^g-shaped vessel are equal, the density of the air is reduced one-half by 

 each operation ; and after repeating the operation ten times, its density is 

 not more than 1-1024; and after twenty times, it is not more than 1-104877(3 

 of its original density. In this case, however, it is desirable to place the 

 receiver on a ring or dish of India-rubber, instead of closing the joint by 

 means of tallow. 



This apparatus is much cheaper than any of the common air-pumps; and 

 by the aid of 20 or 25 Ibs. of mercury, all the usual experiments can be per- 

 formed. It would l)e still less expensive if made of gutta-percha. If the 

 tube is long and large cnou :h, water may be used instead of mercury, and 

 the apparatus may be employed for exhausting the air wherever it it desira- 

 ble to make use of the atmo-phcric pressure, or in order to boii certain sub- 

 stances in a partial vacuum. Diiujkr's Polylcclimc Jvurual. Scientijic 

 American. 



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