]98 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS decompositions can readily be initiated at pressures above 0-6 arm. above atmospheric pressure, and special precautions and techniques have to be adopted to avoid the associated hazards. Indeed, such operations are governed by legislation issued under Orders in Council, which only permit the handling of acetylene at pressures up to 9 lb. per sq. inch normally very special precautions are called for at higher pressures. For chemical purposes, pressures up to 20 atmospheres may be used, subject to the approval by H.M. Chief Inspector of Explosives of the equipment and the techniques used. The equipment illustrated, particularly in Fig. 8, has been designed to meet these requirements. This equipment is probably amongst the most advanced in design with regard to safety existing at this time. •,• .:• •?"•'•. . •. ,- . ß . .•-:. •':• '• ....• ß • • •-•'.•.• :•.:.: 2• •:. .} -•.. .:•,• ..q. :.:..:.:.: j.'•:. ?5 ':'. :• :. -: . j..-',. , . •' .•: .-•...•.:.• • ..... ...?. '•:-.. :- ...: •:..•:.-. :':.. [ :..::•:.: ß .'j .j• • •.-, ..:.: :.:. ..:'. • • ::- •. . •.-.. --• :.... . .. ,, .•:•.... -¾•.•(• .... -• ... :: ... Fig. 3. View of the reactor and vessel used in the production of gamma butyrolactone.

I:OLYVINYLI:YRROLIDONE IN COSMETICS 199 In proc•ucing polyvinylpyrrolidone, acetylene and formaldehyde are first reacted under pressure in the presence of a. suitable catalyst to prepare 2-butyne-1 '4-dio,1. This is then hydrogenated to butane-1 ß 4-diol, which in the presence of-another catalyst is simultaneously dehydrogenated and ring closure effected to give gamma butyrolactone. This, in turn, is then reacted with ammonia under pressure to give alpha pyrrolidone, and further reaction with acetylene under pressure then gives vinyl pyrrolidone monomer. The monomer is polymerised under carefully controlled conditions to give an aqueous solution of polyvinylpyrrolidone of the desired molecular •veight. This solution can then either be sold as such or submitted to a spray-drying operation to remove ,the water and trace volatile impurities, Fig. 4. The reactooe for pyrrolidone production with a vacuum still in the background.