32 METHODS OF ANALYSIS. 



the precipitate to settle. When the liquid becomes clear, draw off one-half by 

 means of a pipette and titrate with half-normal hydrochloric acid, using phenol- 

 phthalein as indicator. This number of cubic centimeters of half-normal acid 

 multiplied by 2 gives the number of cubic centimeters of half-normal acid cor- 

 responding to the original amount taken. The last figure obtained represents 

 sodium hydroxid and the difference between the first and last figures repre- 

 sents the sodium carbonate. 



(b) CARBONATE AND HYDROXID,<* METHOD II (CAMERON). PROVISIONAL. 



(1) SOLUTIONS REQUIRED. 



A fifth-normal solution of potassium acid sulphate ; methyl orange and phenol- 

 phthalein indicators. 



(2) DETERMINATION. 



Dilute with carbon-dioxid-free water an aliquot of the solution as prepared in 

 Method I and add a few drops of phenolphthalein. Add a fifth-normal solution 

 of potassium acid sulphate at the rate of about 1 drop per second, with constant 

 stirring, until the pink color fades out and the solution becomes colorless. The 

 reading thus obtained (n) represents the sodium hydroxid and one-half of the 

 sodium carbonate present, since the sodium carbonate is changed to sodium 

 bicarbonate. Add methyl orange and continue the titration to the appearance 

 of a pink color. This reading (m) represents the sodium bicarbonate present, 

 or one-half of the sodium carbonate; 2m represents all the sodium carbonate 

 present, and n-m the sodium hydroxid. 



8. Tobacco and Tobacco Extract, 

 (a) NICOTIN, KISSLING METHOD. OFFICIAL. 



(1) SOLUTIONS REQUIRED. 



(a) Alcoholic soda. Dissolve 6 grams of sodium hydroxid in 40 cc of water 

 and GO cc of 90 per cent alcohol. 



(6) Sodium hydroxid. Dissolve 4 grams of sodium hydroxid in 1,000 cc of 

 water. 



(c) Sulphuric acid. A standard solution. 



(2) DETERMINATION. 



Weigh from 5 to G grams of tobacco extract or 20 grams of finely powdered 

 tobacco, which has been previously dried at GO C. so as to allow it to be pow- 

 dered, into a small beaker. Add 10 cc of the alcohol-soda solution and follow, 

 in the case of the tobacco extract, with enough chemically pure powdered cal- 

 cium carbonate to form a moist but not lumpy mass. Mix the whole thor- 

 oughly. Transfer this to a Soxhlet extractor and exhaust for about five hours 

 with ether. Evaporate the ether at a low temperature by holding over the 

 steam bath, and take up the residue with 50 cc of the dilute sodium hydroxid 

 solution. Transfer this residue by means of water to a Kjeldahl flask, capable 

 of holding about 500 cc, and distil in a current of steam, using a condenser 

 through which water is flowing rapidly. Use a three-bend outflow tube, a few 

 pieces of pumice, and a small piece of paraffin, to prevent bumping and frothing. 

 Continue the distillation till all the nicotin has passed over, the distillate usually 



U. S. Dept. Agr., Bureau of Soils, Bui. 18, p. 77 ; by action of the association In 1907 

 this method was dropped. 



