no-112] Nitrogen in Nitrates 79 



by a pinchcock. The pneumatic trough, e, is filled with 

 water. 



This apparatus is arranged specially for estimating the 

 amount of nitric nitrogen in commercial nitrate of soda, and 

 has to be calibrated after each operation. The method may 

 be briefly described as follows. Make up solutions of 



1 gram pure NaN0 3 made up to 100 c.c. 



1 gram commercial NaN0 3 made up to 100 c.c. 



2 grams FeS0 4 dissolved in 50 c.c. of water and a drop 



ofH 2 S0 4 . 



When passing a slightly soluble gas like nitric oxide through 

 large quantities of water, it is practically impossible to make 

 any correct allowance for the quantity that may be lost. The 

 only plan, therefore, is to make a comparison between the 

 volume of gas obtained from a pure sample of the nitrate and 

 that obtained from the sample under consideration. 



no. Calibration. — Boil 20 c.c. of the pure NaN0 3 solu- 

 tion with 20 c.c. water as before to expel air. Close the india- 

 rubber joint d and add 25 c.c. FeS0 4 solution. Place the 

 collecting tube in position, and add 50 c.c. strong sulphuric 

 acid cautiously to the liquid in the flask, opening d at the same 

 time. Complete the reaction exactly as in the other apparatus. 

 Read off the volume of gas. 



in. The Estimation. — Wash out the apparatus imme- 

 diately the calibration is finished, and do a second operation, 

 using 20 c.c. of the commercial nitrate solution. 



112. Calculation. — This is very simple, being a mere 

 comparison of the two results. Thus, supposing the calibra- 

 tion gave x c.c. of gas and the estimation y c.c, then the 

 percentage of pure NaN0 3 in the commercial sample would 



be-'— 100. There is no need, with this apparatus, to correct 

 x 



