112 ARTIFICIAL NITROGENOUS MANURES 



To read off the volume of gas, the tube B is carefully 

 adjusted so that the mercury in it is higher than that 

 in A by I mm. for every 6-5 mm. of solution in A. 

 This makes the necessary allowance for the short 

 column of added liquid. 



The volume of gas corrected for pressure and 

 temperature is 



V X (P-/)x^73 cc 

 76ox(/+273) 



Where V is the observed volume, P the barometric 

 pressure, and p the tension of aqueous vapour at f C. 



I C.C. of NO at N.T. P. = 0-000627 gram nitrogen. 



94. {b) Schlossing's Method. — In this process the nitrate 

 is decomposed by ferrous sulphate and strong sulphuric 

 acid with the formation of nitric oxide. The latter is 

 collected and measured. 



2NaN03 + 6FeSO,+ 5 H^SO, 



= 3Fe2(S04)3+2NaHS04+4H20 + 2NO. 



Apparatus. — The apparatus is shown in Fig. 19. 

 It consists of a round-bottomed flask of about 200 c.c. 

 capacity fitted with a two-holed stopper carrying a 

 dropping funnel and a delivery tube. The delivery 

 tube is made in two parts, joined together with a piece 

 of strong rubber tubing fitted with a screw-clip, and is 

 bent down in order to dip under the surface of water in 

 a trough in which is inverted a measuring tube full of 

 water. 



Procedure. — Twenty c.c. of a 10 per cent, solution of 

 ferrous sulphate are placed in the flask and mixed with 

 50 C.C. of strong HgSO^. The apparatus is fitted 

 together, the clip opened, and the solution boiled until 

 all the air has been expelled. The screw-clip is now 

 closed and at the same time the flame removed. If the 



