33O AGRICULTURAL ANALYSIS 



gauze, 10 to 15; copper oxid, eight; and asbestos plug, five centi- 

 meters, respectively. 



The copper oxid should be heated for a considerable time to 

 redness in a muffle with free access of air before using, and the 

 copper gauze be reduced to pure metallic copper in a current of 

 hydrogen at a low red heat. The anterior layer of copper oxid 

 serves to oxidize any hydrogen that may have been occluded by 

 the copper. When a sample is burned containing all or a con- 

 siderable part of the nitrogen as nitrates, the longer piece of cop- 

 per gauze is used. 



290. The Combustion. The tube having been charged and 

 connected with the pump, it is first freed from air by running the 

 pump until the mercury no longer rises in the manometer. The 

 end of the tube containing the sodium bicarbonate is then gently 

 heated, so that the evolution of carbon dioxid will be at 

 such a rate, as to slowly depress the mercury in the manome- 

 ter, but never fast enough to exceed the capacity of the pump to 

 remove it. The lamp is extinguished under the sodium car- 

 bonate and the carbon dioxid completely removed by means of 

 the pump. The delivery tube is then connected^ with the azotom- 

 eter, and the combustion tube carefully heated from the front 

 end backwards, the copper gauze and coarse copper oxid being 

 raised to a red heat before the part containing the sample is 

 reached. When the nitrogen begins to come off, its flow should 

 be so regulated by means of the lamps under the tube, as to be 

 regular and not too rapid. From half an hour to an hour should 

 be employed in completing the combustion. Since most sam- 

 ples of fertilizer contain organic matter, the nitrogen will be 

 mixed with aqueous vapor and carbon dioxid. The former is con- 

 densed before reaching the azotometer, and the latter is absorbed 

 by the potassium hydroxid. When the sample is wholly of a min- 

 eral nature it should be mixed with some pure sugar, about half 

 a gram, before being placed in the tube. When bubbles of gas no 

 longer come over, the heat should be carried back until there is 

 a gradual evolution of carbon dioxid under the conditions above 

 noted. Finally, the gas is turned off and the pump kept in opera- 

 tion until the manometer again shows a perfect vacuum, when 



