Abstract: A process for the preparation of a monoalkyl ether of a hydroxyphenol of the formula ##STR1## in which Z each independently is hydrogen or a substituent which is stable under the reaction conditions,R is lower alkyl, andn is 1, 2, 3 or 4,comprising reacting a hydroxyphenol of the formula ##STR2## with an alkyl halide, alkyl sulphonate or aryl sulphonate alkylating agent of the formulaR--Xin which X is a halogen atom, or an alkylsulphonyloxy or arylsulphonyloxy radical,at a temperature from about 130.degree. C. to 200.degree. C. and in the presence of an alkali metal base or alkaline earth metal base and of a diluent comprising a polyhydroxyalkyl ether having at least one OH group. Advantageously the base is sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate, the hydroxyphenol is pyrocatechol, the alkylating agent is isopropyl chloride, isopropyl C.sub.

Abstract: A method is provided for controlling the flow of liquid through a column separated by vertically spaced plates into compartments to determine the height of liquid on a plate wherein the liquid is flowed through tubes from compartment to compartment and the rate of flow through the tubes is regulated by a throttle valve responsive to gas pressure below a plate or to the height of liquid in a compartment.