EXAMPLE 1.
A concentrated solution of sodium metaborate (obtained for example by boiling borax with a solution of sodium hydroxide) is allowed to react at a low temperature with a 3% solution of hydrogen peroxide, 90 grams MgSO,.7 1120 [MgSO47H2O] per kilogram of boric acid treated being added to the hydrogen peroxide. The metaborate solution may be added to the hydrogen peroxide either all at once or in portions. The sodium perborate formed is allowed to crystallise out at a low temperature and it is separated from the mother-liquor by filtration or centrifuging, the product obtained washed with cold water and subsequently dried at a low temperature.
Patent GB434991 (http://l2.espacenet.com/dips/viewer?PN=GB434991&CY=gb&LG=en&DB=EPD)
and Patent US2491789 (http://l2.espacenet.com/dips/viewer?PN=US2491789&CY=gb&LG=en&DB=EPD)
describes the prepn of the more active monohydrate.