§ 62.- NITKIC ACID. 91 



dip d in a glass containing a solution of ferrous chloride 

 in hydrocliloii^ acid, remove the lamp from A, and open 

 the clamp just enough to allow this solution to flow into 

 the flask rather rapidly; when about 200 c.c. of the fer- 

 rous solution have passed in, replace this solution by dilute 

 hydrochloric acid, and allow three or four portions of this 

 to flow in also, and thus wash all the ferrous salt out of the 

 tube ; finally rinse the tube into the flask with a little dis- 

 tilled water. Now, close the clamp on be, and, without 

 allowing any air to enter the tube, insert d in the tiibulure 

 of the jar B, replace the lamp under A, immediately open 

 the clamp» on be, while holding the rubber tube tightly 

 compressed between the fingers until a pressure is felt 

 from within ; then remove the fingers and allow the nitric 

 oxide gas that is generated in the flask to pass into the 

 receiver B. The reaction is generally terminated in about 

 8 minutes ; so long as nitric oxide is escaping it bubbles 

 up through the milk of lime in B, but as soon as nothing 

 but water and hydrochloric acid pass over, both are 

 absorbed by the milk of lime, and the bubbling of the gas 

 through it ceases. 



If the receiver B is filled with gas before all . the nitric 

 acid in A is decomposed, close the clamp on be, remove 

 the lamp immediately from under A, take the rubber tube 

 d out of the tubulure and let it lie in the water over the 

 mercury, while the receiver is emptied in the manner de- 

 scribed below ; then fill the receiver again with mercury 

 and milk of lime as directed above, insert d in the tubu- 

 lure again, apply heat to A while the tube be is closed 

 with the fingers only, and proceed as before, until the de- 

 composition of the nitric acid is finished. 



When the evolution of gas finally ceases, close be, re- 

 move d from the tubulure, and proceed to empty the gas 

 from B. To this end, mount another flask, C, in the same 

 manner as A was arranged, put about 100 c.c. of distilled 

 water in it, attach a rubber tube about 12 cm. long to the 



