14 BULLETIN 90S, U. S. DEPARTMENT OF AGRICULTURE. 



SEPARATION OF AMMONIA FROM AMINES (6). 



Unite the distillates obtained by the preceding method in a large dish, make dis- 

 tinctly acid, and evaporate until the volume is about 400 cc. Wash into a 500-cc 

 graduated flask, and cool. If the total volatile nitrogen exceeds a strength equiva- 

 lent to 30 cc N/10 in amount, make up to 500 cc, and transfer a portion equivalent to 

 20 to 30 cc of N/10 to another 500-cc flask. If the amount of total volatile nitrogen is 

 less than the equivalent of 20 cc N/10, add enough of a standard solution of ammonia 

 to raise the content to that point. Add to the liquid in the 500-cc graduated flask 10 cc 

 of a solution made by mixing equal parts of 20 per cent sodium hydroxid and 30 per 

 cent sodium carbonate. Fill to the mark with water. Now add 0.1 gram of yellow 

 mercuric oxid for each cc of N/10 acid to which the total volatile nitrogen present in 

 the solution is equivalent. Stopper tightly, cover with a black cloth to exclude light, 

 and shake one hour. Allow to stand 12 hours, or overnight, to permit the oxid of mer- 

 cury to settle. Separate from the mercuric oxid by forcing the liquid through a tube 

 containing a little absorbent cotton, using a moderate blast. Discard the first 20-30 

 cc. Distill 200 cc of the filtrate in duplicate into standardized acid. The amount of 

 acid required is equivalent to the nitrogen present as amines. The total volatile 

 nitrogen minus the amine nitrogen equals ammonia nitrogen. Express the quantities 

 as milligrams of nitrogen per 100 grams of sample. 



AMINO ACID NITROGEN. 



The few determinations of amino acid reported were made in Klein's (14) modifica- 

 tion of Van Slyke's apparatus, before the latest Van Slyke method was published. 



VOLATILE SULPHUR. 



Weigh 100-gram samples into 800-cc Erlenmeyer flasks, to which have been added 

 400 cc of water and 10 cc of a 20 per cent solution of phosphoric acid. Distill 150 cc 

 into an excess of N/20 potassium hydroxid by steam distillation in 45 minutes. 

 Neutralize the excess of alkali by titration with N/20 hydrochloric acid. To the dis- 

 tillate add 25 cc of approximately N/100 iodin solution, and, after allowing it to stand 

 from 5 to 10 minutes, titrate the unreduced iodin with N/100 thiosulphate solution. 

 Calculate the volatile sulphur as cubic centimeters of N/100 iodin per 100 grams of fish. 



CHLORIN. 



Sodium chlorid (salt). — Determine by the Volhard method(31), after the samples 

 have been ashed at a low temperature with an excess of bicarbonate of soda, free from 

 chlorin. 



TIN. 



Add 50 cc of concentrated sulphuric acid to the material in a Kjeldahl flask, and add 

 concentrated nitric acid, boiling until all organic matter is destroyed. Rinse out the 

 flask into a 600-cc beaker with boiling water, diluting to 400 cc. Neutralize with 

 ammonium hydroxid, and add 5 cc hydrochloric acid. Heat on hot plate to 95° C, 

 cover with a watch glass, and pass in a slow stream of hydrogen sulphid for one hour. 

 Digest on a hot plate for two hours. Filter, using an 11-cm S. & S. filter. Wash with 

 three portions of a wash solution (composed of 100 cc saturated ammonium acetate, 

 50 cc glacial acetic acid, 850 cc water) alternated with three portions of hot water. 

 Place filter and precipitate in a 50-cc beaker and digest with three successive portions 

 of ammonium polysulphid, bringing to a boil each time and filtering through a 9 cm 

 filter. Wash with hot water. Acidify with acetic acid, digest on a hot plate for one 

 hour, and filter through a double 11-cm filter. Wash with two portions of wash solu- 

 tion alternated with two portions of hot water. Place filter and precipitate in weighed 

 porcelain crucible and dry at 110° C. Ignite very gently at first, later with the full 

 burner. Finally heat strongly with a large Meeker burner or blast lamp. Weigh as 

 oxid of tin, and calculate percentage of milligrams of tin. 



