DRYING APPARATUS. 101 



Various forms of air-baths, with a regulator for maintaining a 

 constant temperature of 100 C. (212 F.), have been proposed ; 

 of these, the best are those of Griffin and Adams. These do not 

 give quite satisfactory results for milk analysis, because the 

 temperature for which they are regulated is the temperature of 

 the air in the bath, while the basins in which the milk is dried, 

 are heated to a somewhat higher temperature "b^fc6tfductiom ' 



The following figures were obtained with a Grifrm's air-bath ; 

 a porcelain capsule filled with mercury ' was ;pjaceicr' ion "xprfifyiy 

 shelves in the bath, and the temperature' of the mercury hefted! 

 The air had a constant temperature of 100 C. : 



Temperature on bottom, . . . . . .136 



,, on cork on bottom, .... 102 



on shelf, 104 



,, in upper part, ..... 96 



Constancy of temperature cannot be depended upon in an air- 

 bath ; it is, therefore, preferable to use a water-oven. The 

 author has devised a water-oven for milk analysis, which has 

 given highly satisfactory results. 



Tt consists of a jacketed copper box, opening only at the top, 

 and closed with a movable lid ; on the lid is a chimney about 

 1 foot high. The bottom portion of the jacket c< ntains four 

 8-foot coils of thin copper tubing, which communicate with the 

 exterior by four holes at the side of the bath, and with the interior 

 by four holes, one in each corner. The jacket is closed, except 

 for one opening, in which a condenser is placed. About 1 inch 

 from the bottom a sheet of copper is fixed, in which is a round 

 hole of diameter equal to half the width of the interior. 



The jacket is filled with distilled water, which is heated either 

 by a steam coil or a gas flame ; perforated copper shelves are 

 used to support the basins, etc., containing the substances to be 

 dried. The heating is chiefly done by conduction from the sides 

 of the bath through the shelves ; a current of hot air, approach- 

 ing in temperature to that of boiling water, is always passing 

 through the bath, and rapidly removes the vapour. 



The condenser is supplied with cold water, and prevents loss 

 of water. It conduces greatly to the efficiency of the bath to 

 use distilled water, as no scale is produced on the coils and sides 

 of the oven. To prevent loss of heat the oven may be lagged 

 with felt, asbestos, or kieselguhr. 



The most efficient condenser has been found to be a spiral coil 

 of tubing (preferably copper), which fits rather closely into a 

 tube. The cold water enters at the top, and passes by a straight 

 portion of the tubing to the lowest coil, whence it circulates 

 upwards, and finds an exit at the top. 



