24 SUBSTANCES SOLUBLE IN FETROLEUM SPIRIT. 



obtain all* including those standing lower in the series, the aqueous 

 distillate may be saturated with soda, concentrated and acidified 

 with sulphuric acid .(l'^)- If *d oily acid separates from the 

 aqueous liquid, angelic or yalerianic acid, or an acid higher in the 

 series, may be looked for. (The test of smell, bciiling-point, etc., 

 inay be applied, and the ultimate analysis made.) Further in- 

 formation on this point may be found in §§ 139, 140. If the acid 

 liberated is soluble in water, an attempt to separate it by the addi- 

 tion of chloride of calcium may meet with success. Should that not 

 be the case, formic and acetic a*ids may finally be tested for (be- 

 haviour to raercuric chlorides ferric chloride and nitrate of silver, 

 the latter also reduced by acrylic aeid) as well as salieylous acid. 

 The last-named acid strikes a violet colour with ferric chloride. 

 (See also § 33.) Salieylous acid may likewise be separated from 

 its aquesous solution by shaking with ether. Eor hydrocyanic 

 acid see § 34. 



Toxicodendric add,to which Maisch partly attributes the poisonous 

 properties of Rhus toxicodendron, appears to posses^ great simi- 

 larity with formic, acetic, and acrylic acid. . It may be isolated 

 by distillation, and like formic acid reduces nitrate of silver and 

 chloride of gold slowly in the cold, quickly On warming. But it 

 does not reduce mercurous nitrate or chromic acid as formic acid 

 does, nor does it yield the iron reaction- characteristic of acetic 

 acid, etc.; the mercuric salt dissolves with difficulty in water* 

 (formic acid reduces mercuric to mercurous chloride). 



§ 26. Salicylic, Benzoic Acid, etc. — It mUst also be. borne in mind 

 that some of the acids of the aromatic series, such' as salicylie and 

 benzoic acid (§ 55), are volatile with the vapour of water at 

 temperatures as low as 100°, and may therefore be carried over 

 with the steam in distilling the ethereal oil. On shaking the 

 distillate with petroleum spirit small quantities of salicylic aeid are 

 removed, bat ether and chlorofonn may be more advantageously 

 employed ; the latter liquid is also adapted for tJie isolation o 

 henmic add. On evaporating the ethereal or chloroformic (or 

 petroleum spirit) solution, both benzoic, and salicylic acid are 

 obtained as crystalline residues difficultly soluble in cold water 

 (salicylic acid about 1 in 300). ^ The two acids may be dis- 



^ Conf. Amer. Journal of Pharmacy, xxxvjii. 9 (1866). 



^ Vox particulars of the detection of salicylic acid in Viola tricolor by Mandelin 

 in my laboratory, see Sitznngsber. d. Dorpater Naturf. Gesellsch. Jg. 1879, p. 77, 

 and Diss. Dorpat,, 1881 ; also.Pharm. Journ. and Trans,. fS] xii. 627. 



