Estimation of Thiophen in Benzene

To prepare the above reagent, 20 c.cs. of pure cone, sulphuric acid are poured into 110 c.cs. distilled water, 5 gms. of finely powdered mercuric oxide are added and the mixture stirred until almost all dissolves. The solution is then filtered and the filtrate preserved in a stoppered bottle. 

The Gooch crucible is prepared with a filtering layer of good fibrous asbestos on top of which is placed a perforated porcelain plate. The asbestos should be previously purified by boiling first with aqua regia for a short time, and then with cone, hydrochloric acid for a week, the acid being renewed each day. (J. S. C. I., 38,189.) 

---