474 PRACTICAL PHYSIOLOGY 



the watch glass with a drop of the sulphate solution, when only 

 a very slight haze should be obtained. It is necessary to repeat 

 the determination several times before an accurate result can be 

 obtained. 



//. Grravimetric Method. The Total Sulphates. Boil 100 c.c. of urine 

 with 5 c.c. HC1 as before, and add to the resulting solution a solution 

 of barium chloride till no more precipitate is produced. Filter off 

 this precipitate of barium sulphate through an ash-free filter paper, 

 and wash it with boiling water till the washings no longer give a 

 precipitate with sulphuric acid. Expose the filter paper and precipitate 

 in an air-bath at 100 C., and when dry remove them to a crucible 

 which is heated, at first gradually, but afterwards with a strong flame. 

 When the mass has become white allow it to cool in a desiccator,, 

 then add a few drops of pure sulphuric acid and again heat very 

 gradually to redness, taking great care that none of the contents of the 

 crucible are lost by spirting. 



The sulphuric acid is added to convert into sulphates any sulphides 

 which may have formed. 



Now cool in a desiccator, weigh and deduct the weight of the 

 crucible, when the remainder will correspond to the amount of barium 

 sulphate formed, 100 parts of which correspond to 34-33 parts of 

 sulphuric acid (S0 3 ). 



The Ethereal Sulphates. (Salkowski's method). The inorganic 

 sulphates are precipitated by means of an alkaline solution of barium 

 chloride, the resulting barium sulphate is filtered off, and the filtrate 

 is acidified with hydrochloric acid, and heated just to boiling point over 

 an asbestos plate. The heat decomposes the ethereal sulphates, which 

 at once combine with the excess of barium salts present. 



In making a quantitative determination 100 c.c. urine should be 

 mixed with 100 c.c. barium chloride solution ; and of the filtrate only 

 100 c.c., corresponding to 50 c.c. original urine, should be taken for 

 the estimation, as, by so doing, the necessity of washing the precipitate 

 is obviated. 



CHAPTER XIV. 



THE METHODS FOR THE ESTIMATION OF 

 GENERAL METABOLISM. 



METABOLISM is the subject which treats of the changes undergone 

 by the food stuffs after they are absorbed from the intestine. There 



