Abstract: A dental impression powder package and method for the preparation of material for making dental impressions. The package includes a bag that encloses dental impression powder and a valve that extends through the bag. The valve is selectively adjustable between an open state where the water is injectable into the bag and a closed state in which fluids are prevented from passing through the valve. The valve includes an open top end, a closed bottom end, a wall extending between the top and bosom ends, and a slit extending along a section of the wall. When the valve is open, the slit opens to permit fluid to be inserted into the bag. The slit closes to block fluid from passing through the slit in the valve while the contents of the bag are being mixed. A syringe is insertable into the valve to insert water into the bag and to extract air from the bag. In one embodiment of the present invention, the alginate mixture is extruded from the bag through the valve and into an impression tray.

Abstract: A casing for holding a magnetic recording disc for a computer disc drive is disclosed, and which is characterized by a read-only/write-protect capability. The casing comprises an envelope having a notch formed along one folded side edge of the envelope, and a write-protect strip positioned in the folded side edge for covering the notch and thereby preventing erasure of the disc. In each disclosed embodiment, the strip includes a lip disposed within the notch for facilitating retention of the strip in the slot and sliding movement of the strip between the write-to-disc and write-protect positions. Also, the strip may include a projection portion which is sized to fit within the notch, and thereby effectively preclude inadvertent movement of the strip in the slot.