182 



CHEMICAL TECHNIQUES 



closed chambers containing strips of wet filter paper, or a layer of 

 water on the floor. 



Holter (1945) described a large moist chamber into which the 

 hands may be placed for various operations, and into the top of 

 which a binocular dissecting microscope is fitted to enable observa- 

 tion of the material being manipulated. The humidity is kept con- 

 stant through the regulation afforded by an electrically fitted hy- 

 grometer connected to a circulation pump which supplies an adjust- 

 able proportion of wet and dry air. 



Holter Moist Chamber. The chamber is illustrated in Figure 

 67. It is made of varnished plywood ; the dimensions of the box are 

 64 X 35 X 30 cm., not considering the bevelled surfaces on the ends 

 of the front which contain doors 12 X 12 cm. The hands may be 

 inserted through tight-fitting rubber cuffs attached in the openings 

 of the doors. A slanting glass window (20 X 20 cm.) is fitted into 

 the front of the box and is hinged so that larger objects can be 



f^\-^ 



Fig. 67. Air-conditioning chamber. 

 From Holter (1945) 



Fig. 68. Arrangement of 



air-conditioning apparatus. 



From Holter (1945) 



placed inside. The edges of a sheet of rubber are sealed into a hole 

 ( 15 X 15 cm.) cut in the top of the box; holes in the rubber fit tightly 

 around the tubes of a binocular dissecting microscope. The sheet of 

 rubber is rather limp and bulging so that vertical movements of the 

 microscope will not cause it to stretch unduly. Illumination of the 

 interior is supplied through a window in the back wall which, for 

 some purposes, should be screened with a heat-absorbing device. 

 A moist atmosphere is maintained in the box by means of the 



