THE FOOD OF PLANTS. 81 



of clover plants. A large quantity of the clover is dried in the 

 drying chamber and cut up, the whole being then thoroughly 

 mixed together. About 100 gr. of the material will yield 

 sufficient ash for our purpose. The combustion is best effected 

 in a large platinum dish ; in absence of this a porcelain dish may 

 be used. In the combustion itself, which is effected over an open 

 flame, great care must be taken that the temperature does not 

 rise too high ; the ash should never be allowed to glow. The 

 analysis is conducted according to the directions of E. von Wolff. 1 

 I have often convinced myself that this method is satisfactory. 

 1 or. of the crude ash obtained serves for the determination of 



?T> 



Carbon dioxide, which may conveniently be carried out by means 

 of Dietrich's apparatus. 2 1 gr. of crude ash is also treated 

 with diluted Nitric acid, the solution serving for the determina- 

 tion of Chlorine. 3-4 gr. of ash is moistened in a flask with con- 

 centrated Nitric acid and then treated with strong Hydrochloric 

 acid, and digested for some time at boiling point. The whole is 

 now rinsed into a porcelain dish, and evaporated to dry ness. The 

 dry residue is placed for some time in the drying chamber, then 

 moistened with concentrated Hydrochloric acid and extracted 

 with water. The undissolved residue (Silicic acid, sand, Carbon) 

 is collected on a dried and weighed filter, well washed with hot 

 water, dried and then weighed. The contents of the filter are 

 transferred to a platinum dish, and, after addition of soda lye, 

 boiled several times with a concentrated solution of -Sodium car- 

 bonate. The fluid is now filtered through the filter paper already 

 used. The residue after being well washed consists of sand and 

 Carbon, the quantity of each being determined by combustion. 

 The alkaline solution*serves for the determination of the Silicic 

 acid. It is treated with excess of Hydrochloric acid, and evapor- 

 ated to dryness, the residue being then boiled with acidified water. 

 Silicic acid is separated and its weight is determined. 



The filtrate from the above-mentioned residue of Silicic acid, 

 sand, and Carbon is made up to a known volume, say 500 c.c., and 

 divided into two measured portions. In one portion we deter- 

 mine the Sulphuric acid by means of Barium chloride. The 

 solution separated from the Barium sulphate by filtration is 

 \vnrmed gently with ammonia Ammonium carbonate and Ammo- 

 nium oxalate, and filtered. The filtrate is evaporated to dryness, 

 the residue gently ignited and heated with Oxalic acid. The 

 ignited residue must be treated with water. The solution 



PP. G 



