ORGANIC SULPHATES. 175 



Putrefaction of nitrogenous compounds in the small in- 

 testine seems to be more productive of indican than when 

 it goes on in the large intestine. Sometimes the indican is 

 decomposed in the urine, the indigo being set free in the 

 form of blue or red microscopic crystals. It is usually dis- 

 solved as a sulphate, however, until the indigo is formed 

 by an oxidizing agent. It is normally present in large 

 quantities in the urine of the horse, where, because of the 

 long intestine, the residue from the food requires a con- 

 siderable time to pass from the body. 



371. PREPARATION OF POTASSIUM PHENOL SULPHATE 

 (KC 6 H 5 SO 4 ). First prepare, if it is not at hand, potassium pyro- 

 sulphate by mixing 25 grammes of finely-powdered potassium 

 sulphate with 15 grammes of concentrated sulphuric acid, then 

 heating (best in platinum dish). The heating should be done 

 under a hood, to avoid the acid fumes. The heat should be 

 gently applied at first, stirring until all the crystals have dissolved. 

 When it ceases to bubble increase the heat to low redness. Allow 

 it to cool, but before it solidifies it is best to carefully pour it upon 

 a piece of clean sheet iron. Powder finely the potassium pyro- 

 sulphate (K2S 2 O 7 ) thus obtained. 



In a, thin glass flask holding about a liter dissolve 15 grammes 

 of potassium hydrate in 20 or 25 cubic centimeters of water, then 

 add 25 grammes of crystallized phenol (carbolic acid, C fi H 5 OH). 

 When it has dissolved let it cool to 60 or 70 C., and, while stir- 

 ring well, add gradually in small quantities 30 grammes of potas- 

 sium pyrosulphate powdered as finely as possible. Keep it at a 

 temperature of "from 60 to 70 for from eight to ten hours, shak- 

 ing often. Then add about 125 cubic centimeters of boiling 95- 

 per-cent. alcohol, and filter while it is hot. This filtration is best 

 performed in a hot-water funnel that is, one which is surrounded 

 with a hot-water jacket. Otherwise the salt will crystallize out 

 before the liquid has passed through the filter. As soon as the 

 filtrate cools, the potassium phenyl sulphate crystallizes in pearly 

 plates. It should be filtered out and recrystallized from a small 

 quantity of boiling alcohol. 



