532 THE STINGING PROPERTY OF THE GIANT NETTLE-TREE, 



The rest of the acid distillate was next treated for the separa- 

 tion of the acetic series. Lead oxide separates the latter from 

 all other organic acids. The solution, after removal of the lead, 

 is shaken out with ether; the lower members remain in aqueous 

 solution, while those higher than butyric are found in the ethereal 

 solution. Lead formate and acetate are next formed, and after 

 evaporation are separated by alcohol in which the latter is soluble. 

 Each of these salts was then distilled with phosphoric acid, the 

 distillates neutralised with Ba hydroxide and the molecular 

 weights of the acids determined : — 



Formic acid — required 46, found 51 -7. 

 Acetic acid „ 60, ,, 59*4. 



The Ba acetate was tested for purity and found to contain a 

 trace of formate which had lowered the mol. weight. It is clear 

 from these results that the process separates nearly pure acetic 

 acid, but leaves much of the latter associated with formic acid. 



The ethereal extract yielded only traces of the higher members 

 of the acetic series. 



The two principal acids present are therefore formic and acetic, 

 with traces of the higher homologues. 



Estimation of the free acids. — For this purpose a sample of 

 fresh leaves was obtained, and treated within a few hours of 

 pulling to ensure the minimum of loss by drying. Then by 

 cutting each leaf in halves two similar samples were obtained 

 and these were treated separately as in A and B. 



(A) For total volatile organic acids. — 100 grams were distilled 

 in a current of steam with phosphoric acid. The acid distillate 

 neutralised 98 - 6 cc.y^- sodium hydroxide. 



Formic acid. — The exactly neutral solution was boiled with 

 standard silver nitrate, the reduced silver estimated, and from 

 the latter the equivalent of formic acid was found to be 047 

 grams per cent.; the acetic acid was calculated from the difference 

 and gave 0-527 per cent. 



(B) Acids existing as fixed salts. — 100 grams of leaves were 

 dried at 120°C. for three days. The free acids being volatile are 

 thus driven off. The dried leaves weighing 22 grams (loss = 78%) 



