Pyrolysis of orthoboric acid, ammonium borate, borax and tetramino cupric borate hexahydrate (Cu(NI15)4. )B4,07.6H10 under reduced pressure (0.8-1.0x10-1 mm Hg) has been studied over the temperature. range 28-850C, employing the Linseis Vacuum Thermobalance. In almost all case the temperatures of commencement and completion of pyrolysis is considerably lowered due to the partial vacuum and it is possible to obtain the compound Na113407.3H20 by simple vacuum dehydration of borax at room temperature. Dehydration of boric acid is accompanied by sublimation but in case of the borates no volatilization of 13103 occurs. The first two compounds yield BLOB while borax and the copper compound produce Natty? and Cul1407 respectively as end products.