Whip the whites of eggs very stiff

From 1922:

Whip the whites of eggs very stiff, and just as they are becoming stiff add as much bicarbonate of soda as will go on a threepenny piece. When the, whites are stiff, stir in about a tablespoonful of castor sugar, but do not beat the sugar in, and be careful not to break down the whites too much when adding it. Pile the meringue as lightly as possible on the pudding. Do not attempt to smooth it over. Put it into a moderately hot oven. A very hot oven will burn it quickly; a cool one will make it tough. Brown it very lightly. The meringue should be made and put into the oven as late as possible. The quicker it can be got to table the better, but it ought to be able to stand without spoiling for a quarter of an hour or twenty minutes.