24 SUBSTANCES SOLUBLE IN PETROLEUM SPIRIT. 



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

 distillate may be saturated with soda, concentrated and acidified 

 ■with sulphuric acid (1"5). If an oily acid separates from the 

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

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

 may 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 acids may finally be tested for (be- 

 haviour to mercuric chloride, ferric chloride and nitrate of silver, 

 the latter also reduced by acrylic acid) as well as salicylous acid. 

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

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

 its aqueous solution by shaking with ether. For hydrocyanic 

 acid see § 34. 



Tozicodendric acid, to which Maisch partly attributes the poisonous 

 properties of Rhus toxicodendron, appears to })ossess 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 salicylic and 

 henzoic 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 

 d istillate with petroleum spirit small quantities of salicylic acid are 

 removed, but ether and chloroform may be more advantageously 

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

 henzoic acid. On evaporating the ethereal or chloroformic (or 

 petroleum spirit) solution, both l)enzoic 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, xxxviii. 9 (1866). 



* For particulars of the detection of salicylic acid in Viola tricolor by Mandelin 

 in my lab oratory, sec Sitzungsber. d. Dorpater Naturf. Ge.scll.sch. Jg. 1870, j). 77, 

 and Diss. Dorpat., 1881 ; also Pharm. Journ. and Trans. [3] xii. C27. 



