182 FORMIC ACID IN STINGING NETTLES. 
thought of was that which, by means of stinging hairs or 
similar organs, produces an analogous effect to the sting of 
certain insects. 
About a pound of the collected plants, Urtica urens and 
dioica, was cut small and pressed, and submitted to distilla- 
tion with about four times the quantity of water and a few 
drops of concentrated sulphuric acid. The distillate was 
opalescent ; a few oil-drops floated on its surface ; it had a 
very offensive odor and a scarcely perceptible acid reac- 
tion. Mixed with carbonate of soda and evaporated to 
dryness in the water bath, it furnished a brownish mass, a 
very small portion of which was deliquescent, the greater 
consisting of the excess of carbonate of soda. 
The mass was now very cautiously decomposed in a 
glass retort by the gradual addition of dilute sulphuric acid, 
when a distinctly acid distillate was obtained in the well- 
cooled receiver, which, neutralized with ammonia, gave|all 
the reactions characteristic of formic acid. This experiment 
however did not appear to me to furnish a satisfactory 
proof of the presence of ready formed formic acid in the 
plant, as formic acid can be produced from the most differ- 
ent organic substances by concentrated sulphuric acid ; 
and it was possible that in the present case the formic acid 
might have been produced by decomposition towards the 
end of the operation. 
Five pounds of stinging nettles were therefore distilled 
with a corresponding quantity of water without any addi- 
tion of sulphuric acid, and a product obtained perfectly 
similar to the one above mentioned. It was neutralized 
with carbonate of soda, evaporated to dryness, the residue 
decomposed with dilute sulphuric acid, and the acid distil- 
ate digested with carbonate of lime, in order to avoid the 
excess of carbonic acid and excess of alkali, which rendered 
the reactions very indistinct, and filtered. The yellowish 
solution, concentrated in the water-bath, proved to be for- 
miate of lime. It reduced salts of silver and mercury, gave 
