Examples of solvents which are often used include aliphatic and alicyclic hydrocarbons such as hexane, octane and cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene, ethers such as ethyl ether and isopropyl ether, lower alcohols such as methanol, ethanol and isopropyl alcohol, and alkyl ethers of ethylene glycol such as ethylene glycol monomethyl ether and ethylene glycol monoe