Biological Chemistry. 



(a) The Method of Dumas. The principle of this 

 method consists in burning the substance in contact with 

 copper oxide in a stream of dry 

 carbon dioxide, and collecting the 

 gaseous products formed in a eudio- 

 meter of special construction (nitro- 

 meter) (Fig. 12) over a strong 

 solution of sodium hydroxide. The 

 carbon and hydrogen, as in the pro- 

 cess of estimating these elements, 

 are burnt to carbon dioxide and 

 water, and the nitrogen is set free, 

 or oxidized to oxides, which latter 

 can be decomposed by hot copper ; 

 the nitrogen thus formed is carried 

 forward with the stream of carbon 

 dioxide into the nitrometer, and 

 there measured, the latter gas 

 being absorbed by the alkali. 



The form of combustion tube and furnace is similar to 

 that employed for the estimation * of carbon and hydrogen. 

 Into the front part of the combustion tube is introduced a 

 spiral of bright copper to decompose the oxides of nitrogen ; 

 behind this follows a long layer of granular copper oxide, 

 and behind this is the weighed amount of substance mixed 

 with copper oxide, c (again about 0*2 grm. is generally em- 

 ployed), and behind this again is a roll of oxidized copper, 



COARSE CuO 



FINE COARSE 



NHCO 3 



AB&ESTOS 



PLUG 



'0->1 



ASBESTOS 



PLUG 



Fig. IS. 



or coarse copper oxide (see Fig. 13). The carbon dioxide is 



* The Dennstedt furnace may also be employed, in which case copper oxide 

 is not used. The older method is here described. 



