BY JAMES M. PETRIE. 533 



were distilled as in (A). The distillate neutralised 68-6 cc. of 

 the standard alkali and contained 0-045 grams of formic acid and 

 i 0'35 grams of acetic acid. 



Summary of above results. — The total acid less the fixed acid 

 ;gives free acid. 



Formic acid existing free in leaves - 002 °/ ) 



f ,, , nn An 0-047 % total. 



,, as neutral formate 0-045 j /0 



Acetic acid free in leaves ... ... 0' 177 



0-527 



,, as neutral acetate ... 0-350 



Free organic acids ... .. 0-179 % driven off by heat. 



Org. acids combined as salts ... 0-395 remain in dried leaves. 



Total volatile org. acids ... 0-574% in fresh leaves. 



We have seen that two-thirds of the total acid is combined as 

 neutral salts. The next step is to determine the nature of the 

 base. Acids are found in plants combined with alkaloids, gluco- 

 sides, and metallic bases. The sting of the Giant Nettle-Tree is 

 so virulent and powerful that it has been believed to be due to a 

 poisonous principle in the sap accompanying the "formic acid." 

 A special examination was then made for such poisonous principles; 

 and most of the known methods were used, including extraction 

 with alcohol, benzene, water, &c, with precipitation of the large 

 amount of tannin present by lead acetate or lead oxide, but from 

 these no basic principle was obtained. 



By the well known Stas-Otto process more favourable results 

 were obtained. In this the dried leaves were first exhausted 

 with water acidulated with tartaric acid, and after boiling for a 

 short time the acid solution was found to become quite neutral. 

 This remarkable reaction was further examined by titrating the 

 acid solution at intervals. 



20 cc. required at first 4-9 cc. standard alkali. 



After 1 hour, cold, 4-9 cc. 



After 1 hour, boiling, 1 -8 cc. 



After successive intervals of 1 hour 1-1, 0-8, - 2, neutral. 



During the extraction abundant fumes of formic and acetic 

 acids were evolved; the tartaric is therefore able to slowly decom- 



