538 AGRICULTURAL ANALYSIS 



METHODS OF ANALYSIS 



PREPARATION OF SAMPLE 



458. Destruction of Organic Matter by Direct Ignition. The 



simplest and most direct method for destroying organic matter is 

 by direct ignition. The incineration may be conducted in the 

 open air or in a muffle and the temperature should be as low as 

 possible. In no case should a low red heat be exceeded. By 

 reason of the moderate draft produced in a muffle and the more 

 even heat which can be maintained this method of burning is to 

 be preferred. With the exercise of due care, excellent results 

 can be obtained in an open dish or one partly closed with a lid. At 

 first, with many samples, the organic matter will burn of its own 

 accord after it is once ignited, and during this combustion the 

 lamp should be withdrawn. The ignition in most cases should 

 be continued in a platinum dish but should the sample contain any 

 reducible metal capable of injuring the platinum a porcelain vessel 

 should be used. The lamp should give a diffused flame to avoid 

 overheating of any portions of the dish and to secure more uni- 

 form combustion. In using a muffle the heat employed should 

 be only great enough to secure combustion and the draft should 

 be so regulated as to avoid loss due to the mechanical deportation 

 of the ash particles. 



459. Ignition with Sulfuric Acid. The favorable action of 

 sulfuric acid in securing a perfect incineration may also be util- 

 ized in the preparation of samples containing organic matter for 

 potash determinations. In this case the bases which by direct 

 ignition would be secured as carbonates are obtained as sulfates. 

 In the method adopted by the official chemists it is directed to 

 saturate the sample with sulfuric acid and to ignite in a muffle 

 until all organic matter is destroyed. 28 Afterwards, when cool 

 the ash is moistened with a little hydrochloric acid and warmed, 

 whereby it is more easily detached from the dish. The pot- 

 ash is then determined by any one of the standard methods. 

 This method has several advantages over the direct ignition. 

 Where any chlorids of the alkalies are present in the ash there 



18 Bureau of Chemistry, Bulletin 107, 1907 : n. 



