MEASUREMENTS 



317 



duces the variations of temperature during the experiment. 

 The atmospheric pressure at the moment is also ascertained. 



As a precaution, two readings should be made to ensure that 

 each absorption has been complete, whilst beforehand the free 

 air should be analysed, and should give 21% of oxygen and 

 practically no carbonic gas (0-03%). The slightest trace of tur- 

 pentine should be avoided, because it destroys the absorbent 

 power of the phosphorus. The cocks should be greased. 



244. 2. Bonnier and Mangin's Eudiometer The principle of 

 this apparatus is the same as that of the preceding, except that 

 the absorption of oxygen is effected by a concentrated solution of 

 potassium pyrogallate instead of phosphorus. It comprises- a 

 capillary tube df bent into U-shape at its free extremity, which 

 enters a vessel of mercury (fig. 226), the other extremity being 

 soldered to a metal cylinder also filled with mercury and closed 

 by an air-tight piston actuated by a hand wheel a. The capillary 

 tube is accurately graduated from to 600. By pushing in the 

 piston the tube of mercury is filled to its orifice i, which should 

 be a few millimetres below the mercury level. 



FMJ. 226. 

 Bonnier and Mangin's Eudiometer. 



The solutions of the reagents are prepared in small test tubes 

 inverted in mercury (/). The solution of potash is made by 

 melting tablets of potash in a test tube containing water. The 

 solution of pyrogallate is made by dissolving pyrogallic acid and 

 adding a few tablets of potassium to the test tube containing 

 the liquid, the solution has a clear brown colour. It is essential 

 that the two solutions be saturated. 



Operation. To make an analysis, the test tube (m) is sunk over 

 the tube i until the point of the latter appears within it. If the 

 piston be slightly pressed in, a sample of gas can be taken. The 

 test tube is withdrawn, and by the movement of the piston, the 

 air to be analysed is brought into the graduated tube and enclosed 

 between the final division marked 600 and a division which will 

 be read to the left, say 150. Therefore there are 600 150= 450 



