260 ASPIRATOR 



lateral tube, c, instead of being connected with an open tube through which air can 

 bo drawn, bo connected with a closed receiver, the air will be gradually sucked out of 

 this vessel by the descending current of water, and a vacuum, more or less perfect, 

 may be thus obtained. This is, indeed, the principle of the admirable, though simple, 

 exhausting apparatus introduced by Dr. Sprengel, in which a vacuum is obtained by 

 the descent of a column of mercury. The mercury is placed in a large funnel, 

 A (fig. 96), which communicates with a glass tube, c, d, longer than the tube 

 of tho mercurial barometer, and open at both ends. The receiver, K, to be exhausted, 

 is connected with a lateral tube, opening into the main tube at x. On pressing a 

 spring-clamp attached to the india-rubber connection below c, the mercury flows down 

 the tube, c, d. As tho lower end of this tube opens a little below the lateral spout of 

 the bulb, B, the first portions of mercury hermetically seal this open end, and prevent 

 any ingress of air. Tho descending column of mercury is broken up into detached 

 cylinders separated by columns of air sucked in from the vessel H. Tho mercury and 

 air pass out at the lateral aperture of the bulb B ; and to economize tho mercury, it is 

 from time to time poured back from the vessel H to the funnel A. As rarefaction 

 proceeds, the quantity of air enclosed with the mercury becomes less and less, and as 

 the exhaustion approaches completion tho mercurial column is almost uninterrupted 

 by any air. At this stage of tho operation, tho falling mercury makes tho character- 

 istic sound of a liquid moving in a vacuum, familiar in the common water-hammer. 

 When the exhaustion is complete, about 30 inches of mercury will bo supported in 

 the tube, c, d, and the remaining part of the tube, together with the lateral branch x 

 and receiver K, is in the condition of the Torricellian vacuum that is to say, it is a 

 space containing nothing but vapour of mercury at very low tension. By means of 

 this mercurial pump a higher degree of rarefaction can be attained than with tho 

 ordinary air-pump. Dr. Sprengel found no difficulty, even with common cold mercury, 

 in rarefying the air to one-millionth of its original density. The inventor recommends 

 the use of an exhausting-syringe to remove tho bulk of the air, employing the 

 mercurial pump only as an auxiliary in completing the exhaustion. In practice, the 

 Sprengel pump is not so simple in construction as that previously figured, but is 

 furnished with certain accessory parts, which do not, however, affect the general 

 principles of its action. Some improvements in the pump have been introduced by 

 Prof. McLeod. (For Sprengel's original researches, see ' Journ. Chemical Soc.' 1865, 

 p. 9 : for McLeod's improvements, seo same journal, 1867, p. 307). 



Dr. Sprengel, in explaining the action of his mercurial pump, says : ' My instru- 

 ment is merely the reverse of the trompe, with this addition, that tho supply of air is 

 limited, while that of the trompo is unlimited.' 



An important application of the principle of the Sprengel pump has been recently 

 made by Professor Bunsen, in his new method of filtering. The operation of filter- 

 ing is usually very tedious, and in many branches of manufacture a rapid method of 

 filtration is highly desirable. Bunson's great improvement consists in accelerating 

 tho operation by filtering into a flask from which the air has been partially with- 

 drawn : the pressure . of the atmosphere on the surface of the liquid in the filter 

 forces the liquid through the pores of the paper, and the partial vacuum on the other 

 sido offers but little resistance to its passage. To effect tho exhaustion, the vessel 

 which receives tho filtered solution is placed in connection with a water air-pump, 

 that is, an apparatus on Sprengel's principle, but working with water instead of 

 mercury. This water air-pump is Recommended by Bunson, not only for washing pre- 

 cipitates, but for crystallising substances from syrupy mother-liquors. Both the 

 mercurial and water air-pumps may become of great use in the arts, where a ready 

 and perfect means of exhaustion may be needed. 



(For translation of Bunsen's paper on filtration with tho filter-pump, see 'Philo- 

 sophical Magazine,' Jan. 1869, p. 1.) 



Tho following form of spirator, devised by Professor Guthrie, will be found useful 

 in establishing a current of air for an indefinite length of time, by means of a con- 

 tinuous current of water. It may bo employed either as aspirator in drawing, or as 

 expirator in forcing air through an apparatus. Its action will bo readily understood 

 by referring to tho accompanying diagram (Jig. 97.)- 



A is a wide-mouthed 12-ounco bottle, whoso bottom is covered with a few milli- 

 metres of mercury, m. Through its well-fitting cork, c, four holes are bored. Into 

 the first of those, the wide tube open at both ends, g, is fitted, so that its lower 

 end is a little above the mercury, m. The upper end of g is provided with a cork, 

 through which the syphon-tube / passes. In the second hole of c tho bent tube h is 

 fixed, in such a manner that its lower end dips beneath tho surface of the mercury, m. 

 Through the third hole of tho cork c, a straight tube, c, is passed, whose office is 

 to convey water into the bottle, A ; the lower end of c is a little above the mercury, m. 

 Through the fourth hole, in c a narrow tube, e, is fastened, whose longer exterior 



