298 LECTURES TO SCIENCE TEACHERS. 



Having got it to this condition the stop-cock is turned off. 

 Then a small quantity of solution of indigo is introduced 

 into the manometer, the stop-cock is turned so as to connect 

 the manometer with the reservoir. By opening one of 

 these stop cocks you will see that the level is easily 

 adjusted, so that the gas contained within the vessel has 

 the atmospheric pressure. When this is the case the stop- 

 cocks are left in their present position. It is connected 

 with a manometer, and into a graduated burette you intro- 

 duce some solution of potash. You then turn the stop- 

 cock and allow a drop to enter. The entrance of this drop 

 produces absorption of the carbonic anhydride and there 

 will be a rise in the level or diminution of the internal 

 pressure. You admit more and more solution of potash 

 until the pressure is restored, when you measure how much 

 liquid has been introduced which is the actual measure of 

 the gas you are absorbing. You will see that by changing 

 the burette you can introduce three or four absorbent re- 

 agents one after another, provided that those first in- 

 troduced do not interfere with the action of the following. 



Messrs. Russell and West have devised an apparatus for 

 the estimation of urea in urine. Five cubic centimetres of 

 urine are introduced into a bulb at at the bottom of a wide 

 tube, and the bulb closed with a stopper at the end of a 

 glass rod. The wide tube is then filled with an alkaline 

 solution of potassic hypobromite and water introduced into 

 the trough, through the bottom of which the wide tube 

 passes. A graduated tube is filled with water and inverted 

 in the trough, the stopper is removed from the neck of the 

 bulb, and the inverted tube placed over the wide one. The 

 urea is decomposed by the hypobromite, and by gently 

 heating the bulb the reaction is completed in five minutes. 

 From the volume of gas collected the percentage of urea 

 is determined. 



There are many important chemical processes in which 

 gases are produced, and a proper investigation of the 

 quantities and composition of these gases will doubtless be 

 useful to the manufacturer as well as to the scientific 

 chemist in following the changes taking place in various 

 operations. All improvements in apparatus adapted to the 

 analysis of gases are therefore of considerable importance 

 from an industrial as well as a scientific point of view. 



