84 



To estimate the amount of Formic acid, over-saturate a weighed 

 or measiu^ed quantity of the distillate with carbonate of soda, 

 evaporate to dryness, expose the triturated mass to a temperature 

 of 110° until thoroughly dry; weigh; extract with alcohol of 

 95%, and note down the weight of the residue, consisting of 

 carbonate of soda, chloride of sodium, &c. The dijfference of the 

 two weights represents the Formate of soda, which contains 

 54-38% Formic acid. 



On the other hand, should, as frequently happens, such organic 

 acids, as likewise yield soda-compounds soluble m strong alcohol, 

 be present in the aqueous distillate, then the alcoholic solution of 

 the soda-salts is evaporated to drpiess, and the residue mixed 

 with nitrate of silver in the proportion of 1 })art residue to 2^ 

 parts nitrate of silvei- ; the whole is then gently heated, until the 

 reduction of the resulting Formate of silver to the metallic state 

 is completed ; 100 parts of this reduced silver, washed and diied 

 on a filter, indicate 34*26 parts Formic acid. 



The Formate of silver, like all compomads of that acid, is freely 

 soluble in water, and only separates from very concentrated solu- 

 tions as a white, curdled mass, which, on addition of water, 

 dissolves again. As the silver salts of acids, belonging to the 

 same series as Formic (like acetic, propionic, valerianic, &c.), do 

 not undergo reduction under the same conditions, theh- presence 

 does not interfere with the above result. 



If the reduced silver, obtained by this process, should be found 

 to contain chloride of silver, it is necessaiy to treat it with nitric 

 acid, which leaves the chloride behind. The latter is collected, 

 weighed, and serves to correct the estimate by deducting for every 

 100 parts of chloride, 25 '8 parts Formic acid, or the amount of 

 the Foi-mic acid is calculated from the reduced silver, minus the 

 chloride of silver. 



Fraiiji'uliii = Rhamnoxanthin. 



Fmxiu = C54 H30 O34 -|- HO. Glucosid of the barks of Fi'axinus 

 excelsior, Aesculus Hippocastaniim, A. Pavia, and of allied species 

 of those genera. Precipitate the decoction of ash-bark, collected 

 in spring during the floral season of the tree, Avith acetate of lead, 

 the filtered liquid with subacetate of lead ; pi'ess the latter deposit^ 

 decompose under watei- with sulphuret of hydrogen, filter, evapo- 

 rate the filtrate to syrup consistence, collect any crystals formed, 

 wash the latter with water, afterwards with a little spirit of wine, 

 and purify by recrystallisation. — ^Tuftily united, white, lustrous 

 needles, inodorous, slightly bitter and acerb, losing the water at 

 110°, fusing at 320° under decomposition; dissolve in 1000 parts 

 cold, readily in hot water, little in cold, readily in hot alcohol, 

 not in ether; the largely-diluted alcoholic or aqueous solution shows, 

 especially in the presence of traces of alkalies, a blue or bluish- 



