196 CAPILLARY TUBE COLORIMETRY 



1. Apparatus 



Capillary Tubes. For blood collections, plasma protein precipi- 

 tations, and for the making of pipettes, capillary tubing having an 

 outside diameter of 0.8 mm. and an inside diameter of 0.6-0.7 mm. 

 was employed by Richards et al. (1933). The capillaries in which 

 reactions were produced and colors developed were 0.5 mm. outside 

 diameter and 0.35 mm. inside. These smaller tubes must have very 

 uniform bores and hence it is necessary that they be drawn mechan- 

 ically. 



Pipettes. The pipettes are drawn from the larger capillary tub- 

 ing. Their slender tips should have an outside diameter of about 50 

 [x; the over-all length should be about 10 cm. Liquid is drawn up and 

 expelled in the pipettes by means of an attached piece of rubber 

 tubing through which suction or pressure may be applied. 



Microscope. A binocular microscope giving about fifteen fold 

 magnification with an optical field of about 1 cm. in diameter is 

 recommended. For the microscopic measurements a micrometer disc 

 is placed in one of the oculars or the disc is cemented to the glass 

 stage of the microscope. The disc should have a 10 mm. scale divided 

 in 0.1 mm. In order to reduce the chance of evaporation of fluids, 

 the glass stage, with the exception of the circle visible in the optical 

 field, is covered with wet filter paper. 



Water Manipulator. For the introduction and movement of 

 columns of fluid in the capillary tubes, controllable suction or pres- 

 sure must be applied at one end. A small syringe having a piston 3 

 mm. in diameter moved by a micrometer screw serves this purpose. 

 The tip of the syringe is connected by rubber tubing with a short 

 glass or metal tube drawn out at one end to a tip small enough to 

 enter the capillary tube. The syringe, rubber tube, and tip are filled 

 with colored water, care being taken to exclude air bubbles, and 

 mounted on a level with the microscope stage. When water is forced 

 out of the tip into the capillary tube, a water seal is formed which 

 permits the movement of water into or out of the capillary. In this 

 fashion columns of liquid may be introduced into the capillary tube 

 from the other end and their movements can be easily controlled. 



Other Accessories. A small centrifuge is required that will hold 

 the capillary tubes. A piece of unglazed milk glass (35 cm. X 35 cm. 

 X 4 mm.), two desk lamps fitted with 100 watt bulbs, and a sus- 



