248 AGRICULTURAL ANALYSIS 



grams are treated in a platinum dish with 20 cubic centimeters 

 of a 20 per cent, acetic acid on a water bath until all the carbonic 

 acid is eliminated. The mass is then evaporated to dryness and 

 ignited in order to remove the moisture and any organic substance 

 that may be present. The ignited mass is mixed with about 20 

 grams of pure ignited quartz sand, then placed in a dry flask of 

 about 250 cubic centimeters capacity and treated with 40 cubic 

 centimeters of pure concentrated monohydrate sulfuric acid. The 

 flask is stoppered in such a way as to connect with it two U-tubes 

 filled with water and is then heated for four hours to 140. 

 After the decomposition is completed a stream of warm air 

 amounting in all to about one liter is drawn slowly through the 

 apparatus. The contents of the U-tubes are poured into a beaker 

 and the hydrofluosilicic acid is treated with one-half-normal 

 soda-lye, using phenolphthalein as indicator. In case there are 

 only small quantities of fluorin, namely, only one-half of one per 

 cent., it is advisable to add some fluorid of calcium of known 

 composition and the quantity of fluorin obtained is corrected by 

 deducting the added fluorin from the total secured. In the case 

 of superphosphate there is added to the five grams of substance 

 a sufficient amount of milk of lime to produce a distinct alkaline 

 reaction. The mixture is then evaporated and ignited as above. 

 After cooling, the mass is rubbed with a pestle and poured through 

 a dry funnel into the decomposition flask above mentioned. The 

 platinum dish and funnel are repeatedly rinsed with finely ground, 

 ignited quartz powder. The rest of the process is carried on as 

 has just been described. 



218. French Method for Mineral Phosphates. The French offi- 

 cial methods are adapted to determine phosphoric acid in various 

 forms. 7 



First Mineral phosphates composed chiefly of dry calcium 

 phosphate mixed in a greater or less degree with carbonate of 

 lime, silicious materials, etc., and in different degrees of fineness 

 as secured by the usual mechanical means. 



Second Phosphate of fresh bone, phosphate of degelatinized 

 bone, animal black, char from the sugar refining factories, etc. 



7 Grandeau, Tratte d'Analyse des Matures agricoles, 3d Edition, 1897, 

 1 =443- 



