By J.H. COSTE.
This has been found useful for drying substances at temperatures above
100° C. It is usually difficult to obtain a temperature much above,
say, 120° in the ordinary air oven without using a large burner, which
is generally difficult to regulate. The temperature also varies
considerably at different heights in the oven. If the substance is
attacked by air at high temperatures or gives off other substances
than water, an estimation of the water is difficult.
[Illustration: Air Bath Apparatus]
The apparatus figured--which is made from a square "tin" or copper
box, with a lid perforated at the top to take a thermometer (T), the
bulb of which is level with the tubes (A and B) passing through the
sides of the box--is heated by an Argand burner and supported on a
retort stand. Dry air (or other gas) passes through the tube, B, where
it undergoes a preliminary heating, and then through the drying tube,
A. The substance to be dried is placed in a porcelain boat, or in a
tube passing through the cork of A (by the latter means precipitates
on filter tubes can be dried). It is usually sufficient to estimate
the loss in weight of the substance in the boat; but, if necessary,
drying tubes can be used to collect the water, or special absorbing
apparatus for other volatile substances.
A temperature of over 200° C. can be easily obtained with an ordinary
Argand flame and maintained fairly constant. When a thermometer was
placed inside as well as one outside the drying tube, it was found
that the temperatures only differed by a few degrees when a water pump
was drawing air through the system at the rate of about 8 liters per
hour. If this bath is protected from draught, any temperature can be
maintained within a few degrees easily.--Journal of the Society of
Chemical Industry.
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