I. AGRICULTURE AND RURAL ECONOMY. 383 



adopting uniform methods of analysis. At a meeting, at 

 Magdeburg, of the chemists of the stations, in 1873, a definite 

 plan for the determination of phosphoric acid was agreed 

 upon, to be used by all. But differences have been found in 

 different analyses of the same fertilizer, even when the same 

 method has been followed. Dr. Marcker, director of the ex- 

 periment station at Halle, has lately sought to discover the 

 cause of these variations. Superphosphates, as commonly 

 manufactured, are by no means powder of uniform fineness, 

 but often contain large particles that have clumped together 

 in the treatment with acid. It would be natural to presume 

 that these lumps would have the same composition as the 

 fine powder. Such Dr. Marcker finds is not the case. A 

 number of superphosphates, made from guanos, bone-black, 

 and bone-dust, were sifted through a sieve whose meshes (in- 

 cluding wire) were one millimeter wide, and the coarser and 

 finer portions were analyzed separately. 



The finer portions contained from 2.8 per cent, more to 4.3 

 per cent, less phosphoric acid than the coarser. If, therefore, 

 in the analysis even of a superphosphate made from as finely 

 pulverized material as bone-dust or bone-black, the clumpy 

 portions are omitted and the finer portions analyzed, it is 

 easy to see how incorrect results may be obtained. 



From these observations Dr. Marcker concludes that " in 

 the selection of samples of fertilizers for analysis the great- 

 est caution should be observed on account of the difference 

 in composition of the coarser and finer particles. It is nec- 

 essary that the samples be so prepared and pulverized as to 

 afford a safe guarantee for the uniform mixture of larger and 

 smaller particles." "It would be just to expect manufactu- 

 rers to see to it that fertilizers be well mixed and finely pul- 

 verized. Doubtless the best way to secure this would be 

 found in the refusal on the part of consumers to buy imper- 

 fectly prepared articles." Zeitschrift des Landwirthschaftli- 

 chen Vereins der Provinz Sachsen, 1874, No. 1,12. 



ABSORPTION OF AMMONIA, ETC., FKOM SOLUTIONS BY THE SOIL. 



Among the conclusions reached by Eichhorn, from a se- 

 ries of experiments in regard to absorption by the soil, it is 

 stated that hydrous double silicates of alumina and lime, as 

 chabazite and stilbite, absorb the ammonia from solutions of 



