Chemicai, Tests and Anai^yses 263 



(b) Kjeldahl digestion flasks. — These are pear-shape, round- 

 bottomed flasks, made of hard, moderately thick, well-annealed glass, 

 having a total capacity of about 250 c.c. They are 22 cm. long and 

 have a maximum diameter of 6 cm., tapering gradually to a long 

 neck, which is 2 cm. in diameter at the narrowest part and flared a 

 little at the edge. 



(c) Distillation flasks. — For distillation a flask of ordinary 

 shape, of about 550 c.c. capacity may be used. It is fitted with a 

 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 cm. 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 pulverized 

 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 am- 

 monium sulphate. 



(c) Sulphuric acid. — N-IO 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. 



(/) 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. 



(/}) 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 



