APPENDIX J 



DETERMINATION OF TOTAL NITROGEN BY A MODIFICATION 

 OF KJELDAHL'S METHOD, TO INCLUDE THE NITROGEN OF 



NITRATES 



This method in some form is used by most chemists for the de- 

 termination of the total nitrogen, and is useful in many ways in bac- 

 teriological work. 



REAGENTS REQUIRED 



1. Standard hydrochloric acid solution. For careful work the abso- 

 lute strength of the solution may be determined by precipitation 

 with silver nitrate and by weighing the silver chloride. 



2. Standard sulphuric acid solution. For ordinary work half-normal 

 acid is used, but for work where small amounts of nitrogen are 

 involved, decinormal acid is better. 



3. Sulphuric acid. This should be the strong acid, sp. g. 1.84, and 

 should be free from nitrates and ammonium sulphate. 



4. Zinc dust. This should be an impalpable powder. Granulated 

 zinc or zinc filings will not answer. 



5. Sodium thiosulphate. 



6. Commercial salicylic acid. 



7. Metallic mercury or mercuric oxide. If mercuric oxide is used 

 it should be prepared in the wet way, but not from mercuric nitrate. 



8. Potassium permanganate. This is used as a fine powder. 



9. Granulated zinc or pumice stone. One of these substances should 

 be added to the contents of the distillation flasks to prevent bumping. 



10. Potassium sulphide solution. A 4 per cent solution of com- 

 mercial potassium sulphide. 



11. Sodium hydroxide solution. A saturated solution of sodium 

 hydroxide free from nitrates. 



12. An indicator. A solution of cochineal prepared by digesting and 

 frequently agitating 3 g. of pulverized cochineal in a mixture of 50 cc. 

 of strong alcohol and 200 cc. of distilled water for a day or two at 

 room temperature. The filtered solution is employed as an indicator. 



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