THE OFFICIAL METHOD 339 



nia. In addition to carbon dioxid, ammonia, and free hydrogen 

 there may also be found among the products of combustion 

 marsh and olefiant gases and other hydrocarbon compounds 

 which dilute, to a greater or less extent, the ammonia formed 

 and help to carry it out of the combustion tube and into the 

 standard acid. 



299. The Official Method. Reagents and Apparatus. (i) 

 Standard solutions and indicator the same as for the kjeldahl 

 method. 



(2) Dry granulated soda-lime, fine enough to pass a 2.5 milli- 

 meter sieve. 



(3) Soda-lime, fine enough to pass a 1.25 millimeter sieve. 

 Soda-lime may be easily and cheaply prepared by slaking two 



and one-half parts of quicklime with a strong solution of one part 

 of commercial caustic soda, care being taken that there is enough 

 water in the solution to slake the lime. The mixture is then 

 dried and heated in an iron pot to incipient fusion, and, when 

 cold, ground and sifted as above. 



(4) Sodium Carbonate and Lime or Slaked Lime. Instead of 

 soda-lime Johnson's mixture of sodium and calcium carbonate, 

 or slaked lime, may be used. Slaked lime may be granulated- by 

 mixing it with a little water to form a thick mass, which is dried 

 in the water-oven until hard and brittle. It is then ground and 

 sifted as above. Slaked lime is much easier to work with than 

 soda-lime, and gives excellent results, though it is probable that 

 more of it should be used in proportion to the substance to be 

 analyzed than is the case with soda-lime. 



(5) Asbestos. The asbestos used should be ignited and kept in 

 a glass-stoppered bottle. 



(6) Combustion Tubes. These are about 40 centimeters long 

 and with an internal diameter of 12 millimeters, drawn out to 

 a closed point at one end. 



(7) U-Tubes. Large-bulbed U-tubes with glass stop-cock, or 

 Will's tubes with four bulbs. 



Manipulation. The substance to be analyzed should be pow- 

 dered finely enough to pass through a sieve of one millimeter 

 mesh ; from 0.7 to 1.4 gram, according to the amount of nitrogen 



