82 PHYSIOLOGY OF NUTRITION. 



obtained is filtered and treated with Hydrochloric acid, and then 

 again evaporated to dryness. The residue is slightly ignited, and 

 we determine the weight of the now pure alkaline chloride left. 

 The Potassium is separated from the Sodium in the usual manner 

 by means of Platinic chloride. The second portion of the solution 

 mast be nearly saturated with ammonia, treated with Ammonium 

 acetate, and gently warmed in order to precipitate the Ferric 

 phosphate present. The Phosphoric acid and the Ferric oxide 

 are then estimated according to the formula Feo(P0 4 ) 2 . To the 

 nitrate from the Ferric phosphate we add Ammonium oxalate, 

 and heat till it begins to boil in order to separate out the Calcium 

 (lime determination). After evaporating down to about 150 c.c., 

 the filtrate is treated with large excess of ammonia. After 24t 

 hours the precipitated Ammonium Magnesium phosphate is 

 collected on a filter, and we estimate the quantity of Phosphoric 

 acid and magnesia in it. The filtrate will give a precipitate 

 with magnesia mixture (prepared by mixing 1 part of crystallised 

 Magnesium sulphate with 2 parts of Ammonium chloride, 8 parts 

 of water, and 4 parts of ammonia) if it still contains Phosphoric 

 acid, or with Sodium phosphate if magnesia is still present. 



In tabulating the results of quantitative analyses of ash, the 

 amount of crude ash present in the dry substance must be given 

 as well as the quantity of pure ash (i.e. crude ash less Carbonic 

 acid, sand, and Carbon). The percentage composition of the pure 

 ash must also be calculated. 



The ash of some plants, e.g. that of the tobacco plant, contains 

 also Lithium. We can easily prepare a pretty lecture experiment 

 by moistening cigar ash with dilute Nitric acid, and holding a 

 little of the mixture in the non-luminous flame of a Bunsen 

 burner or spirit lamp on a loop of platinum wire fused into a 

 glass rod. Spectroscopic examination of the flame, e.g. by means 

 of a small pocket spectroscope, almost always discloses at once 

 the very characteristic red Lithium line. 



1 See E. von Wolff, Anleitung zur diem. Untersuchung landwirthschl. 

 iciehtiger Stoffe, 1875, p. 159. 



2 See Dietrich, Zeitschrift f. analytische Chemie, Bd. 3 and 4. The Dietrich 

 apparatus can be obtained from J. H. Biichler, Breslau. 



30. The Higher Plants Need to be Supplied with Mineral 



Substances. Sodium and Silicon are not Essential. 

 The problems here under consideration can be studied most 

 conveniently and accurately by the water culture method. The 



