CHEMICAL TESTS AND ANALYSES 345 



rubber stopper and with a bulb tube above to prevent the possibility 

 of sodium hydrate being carried over mechanically during distilla- 

 tion. The bulbs may be about 3 c.m. in diameter, the tubes being- 

 of the same diameter as the condenser and cut off obliquely at the 

 lower end, which is fastened to the condenser by a rubber tube." 



Preparation of Reagents. 



"(a) Potassium sulphate. This reagent should be pulver- 

 ized before using. 



(b) Sulphuric acid. The sulphuric acid should have a 

 specific gravity of 1.84. It should be C. P., containing no nitrates 

 nor ammonium sulphate. 



(c) Sulphuric acid. N-10 solution. 



(d) Standard alkali solution. The strength of this solution 

 relative to the acid must be accurately determined, N-10 solution. 



(e) Metallic mercury or mercuric oxid. If mercuric oxid is 

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

 nitrate. 



(f) Granulated zinc or pumice stone. One of these reagents 

 is added to the contents of the distillation flasks, when found nec- 

 essary, in order to prevent bumping. 



(g) Potassium sulphid solution. A solution of forty grams 

 of commercial potassium sulphid in one liter of water. 



(h) Sodium hydroxid solution. A saturated solution of so- 

 dium hydroxid free from nitrates. 



(i) Indicator. A solution of cochineal is prepared by digest- 

 ing and frequently agitating three grams of pulverized cochineal in 

 a mixture of 50 c.c. of strong alcohol and 200 c.c. of distilled water 

 for a day or two at ordinary temperatures. The filtered solution is 

 employed as indicator.'* 



Determination. 



Place the substance to be analyzed in a digestion flask, employ- 

 ing from 0.7 to 3.5 grams, according to its proportion of nitrogen. 

 Add 10 grams of powdered potassium sulphate and from 15 to 25 

 c.c. (ordinarily about 20 c.c.) of sulphuric acid. Conduct the di- 

 gestion by starting with a temperature below boiling point and 



