296 LECTURES TO SCIENCE TEACHERS. 



in construction to Scheibler's, but it is simpler in one fray 

 because instead of having that complex arrangement for 

 the raising and lowering of the liquid in the tube he 

 makes one to slide, and you slide it until the column of 

 liquid is level in both. 



Then there is an apparatus described by Winkler, of 

 which there are three specimens on the table. It is an 

 absorption eudiometer ; and unfortunately one instrument 

 can only be used for the absorption of gas by one reagent 

 without washing it out again; but by using two instru- 

 ments you can use two reagents one after the other with- 

 out loss of time. There is an ordinary stop cock at the 

 top, and at the bottom a three-way-cock. The gas can be 

 blown through the measuring tube and out at the top. 

 You can fill the apparatus simply by passing the current of 

 gas through for a sufficient time. When the gas has dis- 

 placed the air entirely the india-rubber tube is closed by a 

 compression cock, and you then have the eudiometer filled 

 with the gas. The absorbent which is to be used is poured 

 into this non-graduated tube, and a small quantity of air 

 will be imprisoned between the long portion of the tube 

 and the stop-cock. The three-way-cock is turned upside 

 down, the compression-cock is opened until the reagent 

 flows out through the nozzle ; then you have the gas in one 

 tube and the reagent in the other, and all that you have to 

 do is to bring them in contact. You turn the three-way- 

 cock when the column of liquid forces a small quantity of 

 liquid into the gas. They are then well shaken together, 

 and the stop cock is turned so as to allow the liquid to flow 

 in. The readings are taken off in the usual way. When 

 only a small quantity of gas has to be measured the lower 

 part of the tube is graduated so that a small absorption 

 which may be less than ^th per cent, is shown. You see 

 it would be impossible to employ this instrument for 

 absorption by means of another reagent without trans- 

 ferring the gas into a second apparatus for a second 

 absorbent, while washing out the first ; but this instru- 

 ment of Winkler has been used several times, and washed 

 out without any accident occurring to it. 



Then there is another apparatus of Max Liebig which is 

 used for the determination of oxygen. The gas is measured 

 in a pipette containing 50 cc., and connected with a caout- 



