AGRICULTURAL ANALYSIS 



For N : 2.125 0g = 0.32783) 



" N 2 O 5 '- 8.188 (log = 0.91318) 

 " NaNO 3 : 12.893 Og = 1.11318) 



378. Method of Devarda. The inconvenience due to slow 

 action and other causes, arising from the use of pure metals in the 

 reduction of nitrates to ammonia, has been overcome, to some 

 extent, by Devarda, by use of an alloy, in a state of fine powder, 

 consisting of aluminum, copper, and zinc. 60 The alloy consists of 

 45 per cent, of aluminum, 50 per cent, of copper, and five per 

 cent, of zinc. In dissolving, the copper is left in a finely divided 

 state, which is a great help in distillation in preventing bumping. 



The analytical process is carried out as follows : The solution 

 containing the nitrate, in quantity equivalent to about one-half 

 gram of potassium nitrate, is placed in a flask having a capacity 

 of about one liter, and diluted with 60 cubic centimeters of water 

 and five cubic centimeters of alcohol, after which 40 cubic cen- 

 timeters of caustic potash solution, of specific gravity 1.3 are 

 added. From two to two and one-half grams of the alloy de- 

 scribed above are introduced, and the flask attached to a conden- 

 ser with a receiver containing standard acid. The connection 

 between the flask and the condenser is made by means of a tube 

 having on the limb next the flask a bulb filled with glass beads 

 to prevent the contents of the flask splashing over into the receiver, 

 and on the other limb another bulb to prevent the acid in the re- 

 ceiver finding its way into the distillation flask, should regurgi- 

 tation occur. When the flask has been thus connected with the 

 condenser it is gently heated for half an hour, at the end of which 

 time the evolution of hydrogen will have slackened or ceased, and 

 the distillation is then begun, at first cautiously, until the zinc of 

 the alloy has completely dissolved, and then more vigorously, the 

 time necessary being about 20 minutes from the time when the 

 contents of the flask begin to boil. The distillate is caught in 

 standard acid and the ammonia determined by titration of the 

 residual acid in the ordinary way. It is to be noted that the 

 strength of the alkali used is of importance, as, if it be too strong, 

 the action on the alloy is unduly vigorous at the beginning of the 

 80 Chemiker-Zeitung, 1892, 16 : 1952. 



