Abstract: Spheres are released from within plurospheres by mixing a fluid with fly ash or bottom ash particulate material obtained by burning coal to form a slurry. The slurry is vibrated at an ultrasonic frequency and with sufficient power that plurospheres in the particulate material are cracked open to release spheres of the material which are encapsulated within the plurospheres. The so-treated material is separated from the slurry to obtain the released spheres.

Abstract: An aluminium foil electrode 11 is secured to a flexible insulating sheet 10 by pressure sensitive adhesive. The foil has a slot 14 extending for the major portion of the foil's length from a contact edge 12b. To test for cracks in the foil which might cause poor electrical contact with the patient and thus cause diathermy burns, the resistance around the U-shaped pathway from the contact edge on one side of the slot to the other side of the slot is monitored.The adhesive is exposed through the slot 14 and through cut-out apertures 15,15a in the foil 11, to improve contact of the patient plate with the patient. A removable cover sheet 16 protects the exposed adhesive when not in use.