32 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Five-eighths of the length of the tube is filled with coarse coppec 

 oxide which is kept in position by narrow plugs of oxidised copper 

 gauze. Next to the copper oxide there is a small boat (copper or 

 porcelain) of suitable size, containing a known weight of the substance, 

 and the remaining space is filled by a roll of oxidised copper gauze 

 (Fig. 1 6). This end of the tube is connected with a gasometer 



FIG. 1 6.- 



A = Oxidised Roll of Copper Gauze. 



B = Boat. 



C = Coarse Copper Oxide. 



-From Price and Twiss' " Practical Organic Chemistry ", 



containing air (or oxygen) and a current of air freed from carbon 

 dioxide and water by passing through potash and sulphuric acid or 

 calcium chloride, is passed through the combustion tube so as to drive 

 out the products of the combustion and to help in the oxidation. 

 To the other end of the combustion tube are attached absorption tubes 

 (Fig. 1 7), of which there are various forms, to collect the carbon dioxide 



Calcium Chloride Tube. Potash Absorption Bulbs. 



FIG. 17. From Price and Twiss' " Practical Organic Chemistry ". 



and water. The first absorption tube, generally of U-shape, contains 

 calcium chloride 1 or pumice wetted with concentrated sulphuric acid; 

 the second, generally complex in shape so as to give several surfaces, 

 contains caustic potash of 33 per cent, strength; a small tube con- 

 taining calcium chloride is attached so as to retain water vapour, which 

 may be carried away during the passage of the gases. These tubes are 

 weighed before and after the combustion..and their increase in weight 

 gives the required data. 



1 After filling the tube with calcium chloride dry carbon dioxide must be passed 

 through it until its weight remains constant. 



