ASPIRATOR 



259 



obtained 1>y evaporating off the more volatile portions of gas-tor, sand, chalk or lime 

 are mixed, it is called artificial asphaltum. The mineral substances arc strongly 

 heatod to expel all moisture, and then added to the pitch while in the melted state, 

 This is used for pavements, for lining tanks, &c. 



ASPIRATOR. An apparatus used for drawing a stream .of air through a tube 

 or other vessel. There are several varieties used by chemists in the analyses of air. 

 One or two only need be mentioned hero. 



Brumier's consists of two equal cylindrical vessels placed one above another 

 and communicating by tubes, which can be opened or closed, so that when the water 

 has run from the upper to the lower vessel, the apparatus, turning for tho purpose 

 on a horizontal axis, may be inverted, so as to repeat the process. 



An aspirator devised some years ago by Mr. M. W. Johnson is of considerable 

 interest, as the principle of its action has of late received extensive application 

 in the construction of certain forms of exhausting apparatus. The arrangement 

 of Johnson's aspirator will be readily understood from the accompanying figure 

 (jig. 95). A tip in connection with a supply of water is fitted by means of a piece of 

 india-rubber tubing to a small cylinder, A. opening below into a long straight glass 

 tube, n, and communicating by means of a lateral branch, c, with the vessel through 

 which the stream of air is to bo drawn. On opening the tap, the water runs down 

 the tubes AB, carrying with it air, which it sucks in through the branch-tube, c ; in 

 this way a stream of air continues to flow in at c as long as water is allowed to run 

 through A B. An aspirator of this form was fitted up by Mr. Johnson at the Eoyal 

 College of Chemistry, and was desc] ibed before the Chemical Society in 1852. (' Journ. 

 Chem. Soc.' vol. iv. p. 186.) 



Johnson's aspirator is similar in 

 principle to tho water-blowing machine 

 known as the trompe, used with the old 

 Catalan iron-furnaces, still working 

 in the Pyrenees and other parts of 

 Southern Europe. In the trompe, a 

 cistern of water is connected with 

 wooden pipes haying small openings 

 called aspirateurs, communicating with 

 the external atmosphere. As the stream 

 of water descends from the cistern 



95 



through the pipes, it draws down with it a current of air entering through these 

 aspirateurs, and tho mixed air and water passes into a vessel below, whence tho 

 water flows out through a special aperture, whilst the air passes to the tuyere. 



On referring to the previous figure of Johnson's aspirator, it is clear that if the 



,s2 



