GENERAL APPARATUS AND MANIPULATION 



181 



ameter, 4 in. deep), embedding in insulating material, and surround- 

 ing with iron or brass pipe. 



Linderstr0m-Lang (1936) employed an incineration oven for the 

 ashing of samples in small tubes. The oven (Fig. 65) is made of a 

 solid copper block containing holes 18 mm. deep and about 7 mm. 

 in diameter. Two electric heaters placed at the sides of the block 

 enable a temperature of 440-460° to be maintained. A rheostat is 

 used to obtain lower temperatures and to regulate the heating. The 

 sides and bottom of the oven are insulated with asbestos. The tubes 

 used with this oven were of quartz and had an inner diameter of 

 3.8 mm., an outer diameter of 6 mm., and a length of 20 mm. A 

 solid copper block with holes drilled to accept small tubes for 

 Kjeldahl digestions was used with gas heat by Borsook and Dubnoff 

 (1939), as shown in Figure 66. 



Copp' 



Fig. 65. Incineration oven 



to accommodate small tubes. 



From Linderstr0m-Lang (1936) 



8 mm. H h- 



Fig. 66. Digestion rack and Kjeldahl tubes. 

 From Borsook and Dubnoff (1939) 



Naturally, modifications in the micro furnaces and ovens may be 

 made, and commercially available types such as that of Micro- 

 chemical Specialties Co. are also often suitable. 



F. MOIST CHAMBERS 



When working with small volumes of liquid it is necessary in 

 certain instances to maintain a moist atmosphere around the liquid 

 to prevent evaporation. The various forms of the moist chambers 

 employed on the stage of a microscope have been described by 

 Chambers and Kopac (1937). In general these are partially en- 



