P R E F A C E S.I. Units Papers are beginning to appear in primary publications in which all units used are SI; most papers, however, continue to be written in a mixture of metric systems. Because of the labour that would be involved at a time when Reporters are already hard pressed, The Chemical Society has not yet requested them to use SI exclusively in articles. Some Reporters have used SI, others follow the traditional mixture. There is therefore lack of consistency between one article and another, and sometimes between an article and the scientific paper being reported. The Society’s policy on units is being announced in ‘Notices to Authors’, published on the inside of the covers of issues of The Journal of The Chemical Society.P R E F A C E S.I. Units Papers are beginning to appear in primary publications in which all units used are SI; most papers, however, continue to be written in a mixture of metric systems. Because of the labour that would be involved at a time when Reporters are already hard pressed, The Chemical Society has not yet requested them to use SI exclusively in articles. Some Reporters have used SI, others follow the traditional mixture. There is therefore lack of consistency between one article and another, and sometimes between an article and the scientific paper being reported. The Society’s policy on units is being announced in ‘Notices to Authors’, published on the inside of the covers of issues of The Journal of The Chemical Society.