42 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



is carried out in practice by heating a weighed quantity of the 

 substance to be analysed in a small porcelain boat placed in 

 a tube about a yard long (Fig. 9) filled with 

 granulated oxide of copper, and through which a 

 current of oxygen or air can be passed. The 

 whole tube is heated in a furnace, and any 

 partially burned vapour of the substance which 

 o5 escapes direct combustion is finally oxidised by 

 passing over the red-hot copper oxide. The 

 water is retained in a tube containing calcium 

 ^ chloride, which readily absorbs moisture, and 

 8 the C0 2 is retained in specially devised bulbs 

 | filled with caustic potash, which are weighed 

 g before and after the analysis. This process is 

 ^ known as combustion analysis and is regularly 

 2 employed in laboratories devoted to organic 

 g chemistry. Special methods, of course, are made 

 g use of in the determination of elements other 

 jjj than carbon and hydrogen, e.g., nitrogen, phos- 

 "I phorus, or sulphur. Oxygen is usually deter- 

 mined by difference, i.e., by deducting the 

 g weights of all the other elements present from 

 the weight of the substance originally taken, 

 when the remainder, if any, is assumed to be 

 oxygen. The determination of the percentage 

 composition of the substance from combustion 

 analysis will be made clear by the following 

 example : 



0-2 grm. of a substance yielded on analysis 0'290 grm. 

 C0 2 and 012 grm. H 2 0. 



Now in every 44 parts C0 2 there are 12 parts C, 

 therefore in 0'29 grm. C0 2 there will be : 



0-29 X 12 

 44 



= 0-079 parts C 



