§§ 99, 100. ESTIMATION OF NITRIC ACID. 



85 



graduated, and communicates with D by means of an indiarubber 

 tube. Both C and D are filled with water till the zero ill C is 

 reached, the water standing at the same height in D. The solution 

 of soda is then allowed to flow slowly into A (which already con- 

 tains the liquid and powdered aluminium), so that the experiment 

 may last from two to three hours. The hydrogen evolved causes a 

 rise of the water in D, but by occasionally opening the clip at g^ it 

 may be maintained at about the same level in both tubes. Care 

 must be taken at the end of the experiment that the level is exactly 

 the same before the final reading is taken. From the volume of 

 gas thus found the volume of the caustic soda introduced from B 

 must be deducted, and the remainder corrected for temperature, 



Fig. 4. 



pressure, and tension of water-vapour, A previous blank experi- 

 ment having shown the amount of hydrogen obtainable from the 

 aluminium taken, the nitric acid may be calculated from the 

 deficit, 4 molecules of hydrogen corresponding to 1 of nitric 

 acid or nitrate of potassium. 



§ 100. AVulfert's method is a modification of Schloessing's 

 devised by Schulze : 0-.5 to I'O gram of the powdered substance is 

 boiled with water to which a little milk of lime has been added, 

 filtered and washed ; the filtrate and washings are then evaporated 

 to 30 or 40 cc, and again filtered. The filtrate is neutralized with 

 hydrochloric acid and introduced into the flask A (Fig. 4), the 

 neck of which has been drawn out so as to admit of connection 



