PHYSIOLOGICAL CHEMISTRY 411 



from which ultimately distillation of the ammonia is to be carried out.) 

 Add approximately 0'5 grm. copper sulphate and 2'0 grm. potassium 

 sulphate, and then 10 c.c. of pure concentrated sulphuric acid. Put 

 the flask on a rack (Fig. 238), so constructed that the neck of the flask 

 lies in a slanting position with the belly of the flask, fitting into the 

 depression made to receive it in the asbestos plate or sand-bath. Start 

 the heating with a low flame. After 10-15 minutes, if there is no 

 excessive foaming, turn up the flame and heat the mixture strongly 



FIG. 238. Apparatus for determination of total nitrogen. 



until it is a clear greenish blue. Now shake the flask with a rotary 

 motion so as to wash down from the wall any carbonaceous particles 

 which may be sticking to it. Continue heating until the liquid is 

 perfectly clear again. The stage of incineration is now complete. (1st 

 stage.) 



The chemical reaction which takes place is that the sulphuric acid 

 decomposes the organic matter, the carbon being oxidised to carbon 

 dioxide, and the nitrogen changed into ammonia, which immediately 

 on its formation combines with the excess of sulphuric acid present to 

 form ammonium hydrogen sulphate. The first effect of adding the 

 acid is to produce charring (i.e. the mixture becomes black), and the 

 reaction is complete whenever all this liberated carbon has been 

 oxidised. 



