ADVANCED PHYSIOLOGICAL CHEMISTEY 457 



If, now, the isethionic acid be treated successively with phosphorus pentachloride 

 and ammonia it yields, first chlor-ethyl-sulphonic acid, and then the Cl of this 

 becomes replaced by an amido group to form amido-isethionic acid which is taurine. 



(a) C 2 H 4 <g OH + 2 PC1 5 = C 2 H 4 <g a + 2 POC1 3 + 2 HC1. 

 Isethionic acid. Chlor-ethyl-sulphon-chloride. 



Chlor-ethyl-sulphonic acid. 

 Taurine. 



CHAPTER X. 

 URINE. 



IN the following chapter the various headings will be taken up in 

 exactly the same order as in the elementary course, and, since the theo- 

 retical points in connection with the chemistry have already been fully 

 discussed there, it will be necessary to deal here only with certain 

 technical details in connection with the separation and quantitative 

 estimation of the various urinary constituents. 



Kjeldahl's Method for the Estimation of Nitrogen. Incineration. 

 This process may be materially quickened by adding to the contents 

 of the combustion flask some metallic oxide. The oxides most com- 

 monly employed are those of mercury and copper, more especially 

 those of copper, since it has been shown that mercury combines with 

 a certain amount of the liberated ammonia to form a compound from 

 which it is not expelled by the subsequent distillation with caustic 

 alkali. The oxide itself is not added, but the sulphate and the amount 

 of this required for 5 c.c. of urine is O5 gr. 



As a rule, about 3 gr. of potassium sulphate are also added. 

 This becomes changed into potassium pyrosulphate in the heated 

 acid, and this has the property of very materially assisting the 

 oxidation. 



The addition of these two bodies is especially necessary, where bodies 

 rich in carbon are being oxidised. They are, therefore, invariably 

 added when it is necessary to burn filter paper, or where the nitrogen 

 in milk, muscle, or any other food-stuff is being determined. 



Distillation. In order to keep the end of the distilling tube just 

 touching the surface of the fluid in the receiving flask, the latter 

 should be placed on a platform which can be raised or lowered by 

 a screw (see Fig. 150). 



