MICROCHEMIS TR Y. 5 7 



ii. Ammonium, NH. 



84. The so-called Nesslers reagent may be used for the 

 recognition of ammonium, according to Strasburger (I, 74). 

 It is prepared in the following manner : 2 grams of pdtas- 

 sium iodide are dissolved in 5 ccm. of water, and then 

 mercuric iodide is added to the solution while warm, until 

 a part remains undissolved. After the fluid is cooled it is 

 diluted with 20 ccm. of water, allowed to stand for a time, 

 filtered, and 20 ccm. of the filtrate are diluted with 30 ccm. 

 of a concentrated caustic potash solution. If the fluid then 

 becomes turbid, it must be filtered again (Nickel I, 94). 



In the presence of ammonium this solution takes a yel- 

 low color, and with more ammonia a brown precipitate is 

 formed. But various organic compounds give the same 

 reaction (Nickel I, 94). 



12. Calcium, Ca. 



85. Calcium occurs very often within the living plant in 

 crystalline form, and these crystals, which are met with 

 sometimes in the cell-sap, sometimes within the membrane, 

 consist most commonly of calcium oxalate ; crystals of 

 calcium carbonate, gypsum, and calcium tartrate are less 

 often observed. Besides, calcium carbonate often incrusts 

 cell-membranes in greater quantities ; and finally, calcium 

 phosphate has been recognized in the vegetable organism. 

 We will describe first the methods for recognizing the 

 various calcium salts, and then the methods of recognizing 

 the presence of calcium in the ash and in the cell-sap. 



a. Calcium Oxalate, Ca(COO) a . 



86. Nearly all crystals which occur within the plant-cell 

 consist of calcium oxalate. They are found partly in the 

 cell contents, and are partly within or upon the wall. They 

 belong partly to the tetragonal, partly to the monoclinic 

 crystal system. Their most important forms are illustrated 



