132 AGRICULTURAL ANALYSIS 



has therefore, but little practical value for agricultural purposes. 

 In all volumetric analyses the accuracy of the burettes, pipettes, 

 and other graduated vessels should be proved by careful calibra- 

 tion. Many of the disagreements in laboratories where the 

 analytical work is conducted equally well can be due to no other 

 cause than the inaccuracy of the graduated vessels which are often 

 found in commerce. Burettes should not only be calibrated for 

 the whole volume but for at least every five cubic centimeters of 

 the graduation. 



URANIUM METHOD AS PRACTISED BY THE FRENCH 

 CHEMISTS. 



118. The Uranium Method. Since the phosphoric acid of prac- 

 tical use for agricultural purposes is nearly always combined with 

 lime, alumina and iron, its volumetric estimation by means of a 

 standard solution of a uranium salt is to be preceded by a pre- 

 liminary separation by means of an ammoniacal magnesium 

 citrate solution. The phosphoric acid may also be separated by 

 means of molybdic solution or by tin or bismuth. The principle 

 of the method was almost simultaneously published by Sutton, 

 Neubauer, and Pincus. 6 In practise, however, it has been found 

 that when the uranium method is to be used, the magnesium cit- 

 rate separation is the most convenient. Since this is the method 

 until lately practised almost universally in France, it will be given 

 in detail. It is based essentially on the process of Joulie, 7 as 

 described by Munro. 8 



119. Preparation of Sample. (i) Incineration. Since the or- 

 ganic matters present in a phosphatic fertilizer often interfere 

 with the employment of uranium as a reagent, it is necessary to 

 incinerate the sample before analysis. 



(2) Solution of the Material. All phosphates, with the excep- 

 tion of certain aluminum phosphates, amblygonite for example, 

 are easily dissolved in nitric and hydrochloric acids more or less 



6 Chemical News, 1860, 1 197, 122; Sutton, Volumetric Analysis, gth 

 Edition, 1904 : 298. 



Archive fur wissenschaftliche Heilkunde, 1860, 4 : 228. 

 Journal fur praktische Chemie, 1859, 76 : 104. 



1 Bulletin de la Socie'te' des Agriculteurs de France, 1876 : 53 ; Ency- 

 clope"die chimique, 1888, 4 : TO. 

 " Chemical News, 1885. 52 : 85. 

 Manuel agenda des Fabricants de Sucre, 1889 : 307. 



