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.

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.