These volume/counting cells are used to define precise volumes of liquid for counting particles in a specified volume. Sedgewick Rafter cell and coverglasses are for use in water analysis, culture inspection and any fluid where particles per volume need to be determined.
The glass counting chamber is a reusable tool for the professional user. The cell is made of high quality optical glass with a chromium surface image. It is intended for continued professional use and whenever using phase contrast. The lower cost plastic chambers are intended for one time use.
These chambers are 50mm long x 20mm wide and 1mm deep. Their bases are marked with a grid of one thousand 1mm squares. When filled with liquid and a coverglass placed over the chamber, a 1ml volume of liquid is trapped. When used under a low magnification light microscope, each of the grid squares equates to 1microlitre (μl) of liquid.
The Howard cell is a glass slide of 76 x 35mm with a central circular island and is used for counting mould hyphae and spores in fruit juices. With the coverglass in place, a 0.1mm thickness of liquid is contained over the central island. The coverglass has 25 calibrated fields of 1.382mm diameter through which to view the particles. It removes the necessity of precise adjustment of the microscope and eyepiece graticule in the original Howard method.