316 GASOMETRIC-VOLUMETRIC METHODS 



are drilled symmetrically P/ie in. apart and Vs in. diameter, and a 

 machined rim is made around each chamber. Threaded bolts are 

 placed at each end of the block as shown and a flat head plate (B) 

 of Lucite (Vs in. thick) is drilled to fit over the bolts. The head plate 

 has the same dimensions as the top of the block and has a 1 mm. 

 hole drilled over the center of each chamber. A glass capillary tube 



(D) with a bore 0.1-1.0 mm. and a length of 1% in. is flattened on 

 one side by grinding to a width of Ys to Vie in. and the ground sur- 

 face is polished on a smooth stone to remove the frosting. Two holes 

 separated by l^^/ie in. are drilled through the flat side into the capil- 

 lary lumen ; a blunt 27 gauge hypodermic needle may be used to drill 

 the holes. Rubber gaskets (C), perforated by a short length of 27 

 gauge needle, are used to seal the capillary tube to the head plate. 

 The capillary is cleaned with chromic acid mixture and the ends are 

 plugged with paraffin and sealed by warming. A channel brass strip 



(E) is drilled to fit over the bolts so that by means of thin knurled 

 nuts (F) it may be used to hold the capillary tube, head plate, and 

 chamber block tightly together. The bottom of the channel brass is 

 slotted over the entire length of the capillary to press only on the 

 sides of the latter. The screws have to be slowly and evenly tightened 

 to prevent the index droplet from being forced into one of the vertical 

 connecting holes. All the surfaces to be sealed are coated with stop- 

 cock grease. 



A paper scale may be placed under the center part of the capillary 

 to enable reading of the displacement of the index droplet, or a low- 

 power microscope fitted with an ocular micrometer may be used. The 

 index droplet consists of kerosene which has been treated for several 

 days with concentrated sulfuric acid and then stored over pellets of 

 sodium hydroxide in a closed vessel in order to remove unsaturated 

 compounds which might lead to resin formation. [Tobias and 

 Gerard, 1941, claim that isodecane (2,7-dimethyloctane) is the 

 index fluid of choice for use in small capillaries.] 



The size of the chambers may be varied by filling them with 

 paraffin to any chosen level. The surface of the paraffin is then 

 smoothed out with the flat end of a metal rod. Both chambers are ad- 

 justed to about the some volume. A disc of Lucite with one depres- 

 sion to hold the biological material and another to hold the droplet 

 of alkali used to absorb carbon dioxide is placed in each chamber. 



Both chambers are charged in exactly the same manner with the 



