Brown straw may be bleached by boiling in a solution of washing soda, and, whilst still moist, submitting it to the action of sulphurous acid. To do this, the straw must be hung in a nearly closed chamber; a box or barrel will do if only a small quantity of straw is to be bleached. A piece of roll sulphur is placed on a saucer and set fire to by a hot iron rod; the saucer is then placed in the chamber (below the straw, but not too near it) and left burning for some time. After bleaching, the straw should be washed with warm water to remove excess of sulphurous acid.