LOSS OF PHOSPHORIC ACID BY INCINERATION 53 



oil cakes and other organic compounds, the large quantity of 

 phosphoric acid which they contain is in organic combination 

 and unless special precautions are exercised a portion of the 

 phosphorus is lost in burning. The loss of phosphoric acid which 

 takes place in cereals has lately been carefully studied by Leavitt 

 and LeClerc. 27 In the case of wheat it is shown that the 

 principal part of the organic phosphorus is in a water-soluble 

 form, known as phytin. This substance has a relatively high 

 molecular weight compared to the phosphorus molecule. A 

 comparatively large percentage of the phosphorus may be lost 

 in ashing without changing very greatly the apparent weight of 

 the ash. 



As is well known, the addition of calcium acetate previous to 

 burning prevents the volatilization of phosphoric acid. The pro- 

 portion of phosphorus lost by the ordinary incineration as com- 

 pared with the amount obtained with the previous addition of 

 calcium acetate has been found in the extreme cases to be 50 per 

 cent, of the total quantity present. The ordinary incineration 

 was conducted at redness. If, however, the incineration is ac- 

 complished without any treatment whatever at incipient redness 

 just sufficient to show a faint radiation of light from the dishes, 

 there is no appreciable loss of phosphoric acid. The results 

 show that the ashing below the point of fusion of the mineral 

 portions of the ash is not a very important factor where only the 

 percentage of ash is desired. But in order to determine the 

 quantity of the phosphorus as phosphoric acid the greatest cau- 

 tion must be observed to keep the temperature below the volatil- 

 ization point of the combined phosphorus. This is to be ac- 

 complished either by incineration at an extremely low tempera- 

 ture or by previous treatment with calcium acetate. 



Later investigations show that in reality there is no appreciable 

 loss of phosphoric acid even at bright redness. The phosphoric 

 acid is simply changed into a form which is not precipitable by 

 ammonium molybdate until the ash has been boiled a long time 

 with nitric acid, or has been treated according to Neumann's 

 method of digesting with nitric and sulfuric acid. 



27 Journal of the American Chemical Society, 1908, 30 : 391, 617. 



