252 AGRICULTURAL ANALYSIS 



There is in the second precipitate mentioned above a slight loss 

 of alumina which precise experiments have shown me to 

 be 0.8 milligram. This is due to a solubility which depends 

 only on the volume of the liquid and not upon the weight of the 

 precipitate. Eight-tenths of a milligram should, therefore, be 

 added to the weight of the alumina as determined above. 



220. Comparison of Methods of Estimation of Iron and Alu- 

 mina in Phosphates. Blattner, in collaboration with Brasseur, at 

 Lille, has made a comparative examination of some of the methods 

 in use of determining the iron and alumina in natural phosphates. 

 They have examined the following processes : 



1. The process of Maret and Delattre, which is very extensively 

 employed in France. 



2. The method of E. Glaser. 



3. The method of H. Lasne. 



4. The method of J. Grueber. 



The results of their studies are as follows : 



1. The method of Maret and Delattre gives results w r hich are 

 not accurate, the quantities of iron and alumina being usually 

 too small. 



2. The method of E. Glaser, embracing separate determinations 

 for the oxid of iron and alumina is able to give exact results, 

 but if the phosphates contain manganese this substance goes also 

 in the precipitate and is counted as alumina, and as a result the 

 figures for alumina obtained by the method of Glaser are too high 

 when manganese is present. 



3. The method of Lasne gives results which are rigorously exact 

 when conducted with reagents which are perfectly pure. It is 

 the most exact method known up to the present time, and has been 

 tried by the authors in the most minute detail. It can be regarded 

 as a standard method. 



4. The method proposed by Grueber appears to be an abridge- 

 ment of the method of Lasne. The authors, however, prove that 

 it does not give correct results. Grueber applied it to phos- 

 phates which were prepared by synthesis and which contained 

 only certain of the matters, and not at all, which enter into the 

 composition of natural phosphates. Where a great deal of lime 



