88 PHYSIOLOGY OF NUTRITION. 



nuclein, etc. This is of great importance, especially if we take 

 into consideration the further fact that during the development 

 of the plant any particular substance may be transferred from 

 an organic to an inorganic compound, and vice versa. The study 

 of these relations, Avhich is of importance in considering the 

 function of mineral substances, and in other respects, has lately 

 been stimulated especially by Schimper, 1 and we will first of 

 all make ourselves acquainted with the method of examination, 

 confining ourselves to the detection of Phosphoric acid, potash, 

 and lime. Further details must be sought in Schimper and 

 Zimmermann. 2 



To detect mineral substances microchemically, sections, not 

 too thin, must first be treated directly with reagents, while 

 others are tested after being reduced to ash by ignition on the 

 slide. Organic mineral compounds frequently cannot be found 

 in the unaltered sections ; generally the presence of bases or acids 

 can then only be made out easily in the ash. The purity of 

 the reagents to be employed must be very carefully tested. 



To detect Calcium in the ash from the section, we dissolve it on 

 the slide in 2 per cent. Sulphuric acid, and allow to dry up slowly. 

 Then, particularly at the edges of the drop, characteristic crystals 

 of Calcium sulphate are formed. See drawings in Haushofer, 

 Microskopische Reactionen, Brunswick, 1885, and Zimmermann's 

 work, cited below, p. 64. 



The detection of Potassium is effected with Platinic chloride. 

 The reagent must be specially tested as to its purity. The 

 crystals of double chloride of Potassium and Platinum which 

 are produced, are in the form of regular octahedrons or cubes. 

 The sections are treated with a drop of the reagent, and allowed 

 to dry up. The ash is dissolved in a little acidified water, the 

 object glass is held over a spirit flame till the solution dries 

 up, and then the reagent is added. The crystals always form 

 first at the edge of the drop ; later they appear in the middle 

 also. 



Phosphoric acid we isolate microchemically as Ammonium 

 Magnesium phosphate. The section, or the ash of it (the latter 

 after solution in acidified water and evaporation of the solution 

 on the slide), is treated with a small quantity of a mixture of 

 25 vols. of a concentrated aqueous solution of Magnesium 

 sulphate, 2 vols. of concentrated aqueous solution of Ammonium 

 chloride, and 15 vols. of water. The originating crystals of 



