7 BOTANICAL MICROTECHNIQUE. 



2. Acids. 

 a. Oxalic Acid (COOH), 



104. For the recognition of oxalic acid and its soluble 

 salts Schimper recommends (II, 215) : 



1. The addition of a solution of calcium nitrate, when 

 crystals of calcium oxalate are formed (cf. 99, i). 



2. The addition of uranyl acetate causes the formation 

 of rhombic crystals of mostly rectangular form, which, when 

 large, are plainly yellow and strongly doubly refractive, but 

 whose composition is still unknown. 



3. Acid potassium oxalate, when present in considerable 

 quantity, is often directly recognizable in dried preparations 

 by its crystalline form and strong double refraction on com- 

 parison with a dried solution of the same salt, as well as by 

 the aid of Borodin's method. 



b. Tartaric Acid, C 3 H 2 (OH) a (COOH) a . 



105. Streng (III) has recommended for the recognition 

 of tartaric acid the addition of a solution of barium chloride 

 and antimonic oxide in hydrochloric acid. This causes the 

 formation of rhombic plates of antimonyl-barium tartrate 

 whose obtuse angles measure 128. 



Schimper (II, 220) recommends the use of the two follow- 

 ing reactions : 



1. The addition of potassium acetate produces rhombic- 

 hemihedric crystals of the hardly soluble acid potassium 

 tartrate. 



2. Neutral solutions are treated with calcium chloride. 

 There are then formed rhombic crystals of calcium tartrate 

 which represent chiefly a combination of an elongated prism 

 with the dome. Concerning their reactions see 95. 



c. Betuloretic Acid, C 36 H 66 O 4 . 



106. This acid is secreted by the trichome-glands on the 

 leaves of Betula alba. It is insoluble in water, but soluble 

 in alcohol, ether, alkalies, alkaline carbonates, and concen- 

 trated sulphuric acid, in the latter with a red coloration (cf. 

 Behrens III, 379). 



