Burners:
The ordinary Bunsen burner is widely employed for the attainment of moderately high temperatures. The maximum temperature is attained by adjusting the regulator so as to admit rather more air than required to produce a non-luminous flame; too much air gives a noisy flame, which is unsuitable.
Hot Plates:
The electrically-heated hot plated, preferably provided with three control - 'Low', 'Medium', and 'High' - is of great value in the analytical laboratory. The heating elements and the internal wiring should be totally enclosed; this protects them from fumes or spilled liquids. Electric hot plates with 'stepless' controls are also marketed; these permit a much greater selection of surface temperatures to be made. A combined electric hot plate and the magnetic stirrer is also available. For some purposes, a steam bath may be used.
Electric Oven:
The most convenient type is an electrically heated, thermostatically controlled drying oven having a temperature range from room temperature to about 250-300 degrees C; the temperature can be controlled to within 1 or 2 degrees Cc. They are used principally for drying precipitates or solids at comparatively low controlled temperatures and have virtually superseded the steam oven.
Microwave Ovens:
These also find application for drying and heating operations. They are particularly useful for determining the moisture content of materials since the elimination of water takes place very rapidly on exposure to microwave radiation.
Muffle Furnaces:
An electrically heated furnace of muffle from should be available in every well -equipped laboratory. the maximum temperature should be about 1200 degree C. If possible, a thermocouple and indicating pyrometer should be provided; otherwise, the ammeter in the circuit should be calibrated, and a chart constructed showing the ammeter and corresponding temperature readings. Gas-heated muffle furnaces are marketed; these may give temperatures up to about 1200 degrees C.
Air Bath:
For drying solids and precipitates at temperature up to 250 degrees C in which acid or other corrosive vapours are evolved, an electric oven should not be used. An air bath may be constructed from a cylindrical (copper, iron, or nickel) vessel with the bottom of the vessel pierced with numerous holes. A silica triangle, the legs of which are appropriately bent, is inserted inside the bath for supporting an evaporating dish, crucible, etc. The whole is heated by a Bunsen flame, which is shielded from draughts. The insulating layer of air prevents bumping by reducing the rate at which heat reaches the contents of the inner dish or crucible. An air bath of similar construction but with special heat-resistant glass sides may also be used; this possesses the obvious advantage of visibility inside the air bath.
