SCHULZE-TIEMANN METHOD 405 



boiled soda-lye, which is obtained by dissolving 12.9 parts of 

 sodium hydroxid in 100 parts of water. 



The liquid which is to be examined for nitric acid (the pinch- 

 cocks being opened and the tube g h not dipping into the crys- 

 tallizing dish), is boiled for one hour in order to drive the air 

 out of the flask A. The end of the tube e f g h is then brought 

 into the crystallizing dish containing the sodium hydroxid solu- 

 tion so that the steam escaping from the flask, A, escapes partly 

 through the tube bed and partly through the tube f g h, not 

 allowing, however, the bubbles to enter the measuring tube C. 

 To determine whether the air is all expelled, the pinch-cock at g 

 is closed and the soda-lye will thereupon rise to g in case no air 

 interferes. It is best to close the tube at g first with the thumb 

 and finger, and then the rise of the soda-lye to that point can be 

 determined by the impulse felt The tube is then firmly closed by 

 means of the pinch-cock g. The rest of the steam is allowed 

 to escape through the tube abed, and the evaporation is con- 

 tinued until the contents of the flask are evaporated to about 10 

 cubic centimeters.* The flask into which the tube c d dips is 

 filled with freshly boiled water. The lamp is removed from the 

 flask A, the pinch-cock is closed, whereupon the tube c d be- 

 comes filled with the freshly boiled water. The measuring tube, 

 C, filled with freshly boiled soda-lye, is closed with the thumb 

 and brought into the dish B, care being taken that no bubble 

 of air enters. It is placed over the end of the tube g h. 



The pressure of the external air will now flatten the rubber 

 tubes at c and g. The flask at the end of c d, holding freshly 

 boiled water, is then replaced with one filled with a nearly satu- 

 rated solution of ferrous chlorid containing some hydrochloric 

 acid. The flask containing the ferrous chlorid solution should 

 be graduated so that the amount which is sucked into the flask 

 A can be determined. The pinch-cock c is opened and from 

 15 to 20 cubic centimeters of the ferrous chlorid solution allowed 

 to flow into A. The end of the tube c d is then placed in an- 

 other flask containing strong hydrochloric acid, and the latter al- 

 lowed to flow into the tube in small quantities at a time until 

 all the ferrous chlorid is washed out of the tube bed into A. 



