DRYING APPARATUS. 79 



suspended in a beaker of water. This is connected with another 

 weighed U-tube filled with pumice moistened with strong sul- 

 sphuric acid, and provided with a bulb in which the bulk of the 

 water can condense. A current of air (or preferably, hydrogen) 

 dried by sulphuric acid should be passed through the tubes, and 

 the water in the beaker boiled. After about three hours' heating, 

 the sulphuric acid tube should be removed, and, after cooUng, 

 weighed. The increase of weight of the sulphuric acid tube will 

 give the weight of the water in the milk taken. 



It is not advisable to dry the total solids at temperatures 

 exceeding 100° C, as the decomposition of the residue by heat 

 is increased at higher temperatures. 



Drying Apparatus. — For the drying of total solids the 

 following conditions may be laid down for the drying apparatus : — 



(1) The temperature must not exceed lOU' C. (212° F.). 



(2) The moisture must be removed as soon as it is converted 

 into vapour. 



The usual form of water-oven used consists of a water-jacketed 

 metal box with a door to it ; very little provision is made for 

 the removal of the moisturi', as no current of air is allowed to 

 circulate through the whole of the interior. 



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

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

 of these, the l)e.st are those of Glriffin 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 dnvd 

 are heated to a somewhat higher temperature by conduction. 



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

 a porcelain capsule filletl with mercury was placed on various 

 shelves in the bath, and the temperature of the mercury noted. 

 The air had a constant temperature of lt)0^ C. : — 



'i'i'ni|ic'i'atuix' on bottom, . KiC^ 



,, on cork on bottom, Ui2' 



,, on .-^lielf, . . . I(j4" 



,, 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. 



It 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 contains four 

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

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



