Nitrogen & Hide Substance in Leather
OUTLINE OF METHOD:-
The nitrogenous substances present in the leather are converted to ammonium sulfate by digestion with concentrated sulfuric acid in the presence of a catalyst by the Kjeldahl method. The ammonia is liberated by the addition of excess of caustic soda, distilled into an absorbent solution and estimated by titration using mixed indicator. From this percentage of nitrogen and hide substances are calculated.
- Distillation apparatus with heating arrangement.
- Receiver Flask- 500 ml
- Concentrated sulfuric acid.
- Catalyst mixture of 100 mg copper Sulfate in 6-8 gm of potassium Sulfate.
- Phenolphthalein indicator
- Sodium Hydroxide 35 percent.
- Saturated solution of boric acid.
- Mixed indicator – methyl red/methyl blue
- Standard sulphuric acid 0.5 N
- Sample the leather specimen to grounded form in leather mill machine.
- Weigh about 0.5 g of test specimen and place in Kjeldahl flask.
- Add 20 ml of concentrated sulphuric acid followed by 2.5 g of catalyst mixture and cover flask with a funnel.
- Heat the flask and its content first with low flame and later with a high flame, for one hour until carbon is oxidized.
- Cool and add approximately 60 ml of water.
- Add few drops of phenolphthalein indicator.
- Add about 70 ml of sodium hydroxide 35% to make the solution slightly alkaline carefully down the side of flask and check pH.
- Now connect the flask with vertical condenser by means of tube bents and place a 300 ml conical flask at end of condenser tube.
- Pour 100ml of saturated boric acid and add 1-2 ml of mixed indicator to it.
- Distill until 150 to 200 ml of distillate is collected in receiver flask. The distilled Ammonia colors the indicator green.
- Distil for another 3 minutes; rinse the end of the condenser with distilled water.
- Titrate the distillate with standard sulphuric acid (0.5N) using mixed indicator to the first constant pink color.
- Note the volume of standard sulphuric acid consumed by distillate during titration.
Calculate the nitrogen content as follows:
Nitrogen content, percent by weight = 1.4 x V x N / W
- V = Volume in ml, of sulphuric acid used in titration,
- W=weight in g of the material taken for the test.
- N = Normality of Sulphuric acid.
Calculate the hide substance as follows:
Hide substance, percent by weight = 5.62 x nitrogen content
PERMISSIBLE ERROR –
The result of a duplicate determination shall not differ from one another by more than 0.1 percent calculated on the original weight of the material taken for the test.