Exercise 93. Lead Tetraphenyl

To 70 g. of ether, thoroughly dried over metallic sodium, add 25 g. of brombenzene and 3.7 g. of magnesium ribbon that has been rubbed bright with fine sandpaper. Close the flask with a calcium chloride tube 

When the magnesium has disappeared, add 24 g. of dry, carefully powdered lead chloride in small quantities at a time and with frequent shaking. Allow the mixture to stand two days with occasional shaking. 

In small portions at a time, add 200 cc. of water, faintly acidulated with hydrochloric acid. Collect the dark precipitate on a Buchner funnel and dry it thoroughly. Place the dark solid in a flask with a reflux condenser and boil with 100 cc. of benzene. Filter off the benzene through a folded filter, leaving the solid in the flask. Repeat the extraction with benzene several times. Combine the filtrates and concentrate to a volume of about 75 cc. On cooling, lead tetraphenyl separates from the solution in colorless needles which melt at 222°  

Intermediate between undoubted suspensions and undoubted solutions is a class of dispersed systems called colloids. A beam of light passed through a 

It will be observed that a colloid is not a member of a particular class of substances but a state of matter and that any substance under the proper conditions may become a colloid, just as it may become a solid, a liquid, a gas, or a solution. 

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