BENZENE SERIES. AROMATIC COMPOUNDS. 573 



a strong acid, forming salts known as picratcs, most of which an- 

 explosives. 



Phenolsulphonic acid, C 6 H 4 (OH)SO 3 H (Sulphocarbolic acid). 

 There are three varieties of this acid, namely, ortho, meta, and para. 

 The ortho and para acid are most easily obtained. When pure phenol 

 is mixed with an equal weight of sulphuric acid in the cold, only the 

 ortho acid is formed : 



C 6 H 5 OH + H 2 S0 4 : C 6 H 4 (OH)S0 3 H + H 2 O. 



At 100 C. (212 F.) only the para acid results. Both varieties form 

 clear solutions with water, but differ from each other in the character 

 of their salts, both as regards solubility and form of the crystals. 

 They are monobasic acids. 



Ortho-phenohulphonic acid (Sozolic acid, Aseptol) occurs on the 

 market as a 33 per cent, solution. It is a syrupy liquid, having a 

 reddish color and a feeble odor. It is used as an antiseptic. 



Sodium phenolsulphonate, Sodii phenolsulphonas (Sodium sulpho- 

 carbolate), C 6 H 4 (OH)SO 3 Na -f 2H 2 O, and Zinc phenolsulphonate, Zinci 

 phenolsulphonas (Zinc sulphocarbolate), (C 6 H 4 (OH)SO 3 ) 2 Zn -f- 8H 2 O, 

 are official salts of para-phenolsulphonic acid. They are obtained by 

 precipitating a solution of barium para-phenolsulphonate by sodium 

 carbonate and zinc sulphate respectively, filtering off the precipitate 

 of barium carbonate or sulphate, and evaporating the filtrate to crys- 

 tallization. Both salts are readily soluble and have antiseptic and 

 astringent properties. 



Sulphonic acid has been spoken of before, when it was shown that inercap- 

 tans are converted into compounds termed sulphonic acids. These acids may 

 be looked upon as derivatives of sulphurous acid, obtained from it by replace- 

 ment of hydrogen by radicals. The relation existing between carbonic and 

 sulphonic acids may be represented by the following formulas : 



Carbonic acid, c CoH Sulphuric acid, SO 2\OH 



Formic acid, CO \QH Sulphurous acid, SO *\OH 



Acetic acid, CO \OH 3 Methyl -sulphonic acid, 



Any compound CO^w Anv sulphonic acid, 



carbonic acid, 



According to this view, phenolsulphonic acid is represented by the formula, 



so / Q>H 4 OH 

 5Ua \OH 



Ichthyol, Sodium ichthyo-sulphonate, C.^H^Na-Pe. Ichthyol is the sodium or 

 ammonium salt of a complex sulphonic acid, obtained by the dry distillation 



