68 THE JOURNAL OF PHARMACOLOGY. 



with it some organic substances. These may act as reducing agents dui- 

 ing the ignition, and a part of the barium sulphate may thus become re- 

 duced. The residue in the crucible should therefore be moistened with a 

 very small quantity of diluted sulphuric acid and carefully heated over a 

 low flame until vapors of sulphur trioxide cease to be given off. Then ig- 

 nite again, and after cooling in a desiccator, weigh. From the weight so 

 obtained, deduct the weight of the crucible and that of the filter ash, if an 

 ashless filter was not employed. The difference in weight represents 

 barium sulphate, and each loo parts of this are equivalent to 34.331 parts 

 of sulphur trioxide (SO3). The average quantity of sulphuric acid found 

 in urine in the form of simple sulphates equals 0.2-0.25^ SO3. 



B. Conjugate or ethereal sulphates. 



The filtrate from the foregoing operation is employed for the purpose of 

 estimating the quantity of sulphuric acid, occurring in the form of conjugate 

 or ethereal sulphates. It is strongly acidified with hydrochloric acid, 

 heated to boiling, and allowed to boil for some time, and then treated with 

 barium chloride, as in the previous operation. The precipitate is treated 

 in the same manner as before. The total sulphates, that is both simple 

 and conjugate, are then obtained by adding together the results of both 

 estimations. The relation of simple to conjugate sulphates can readily be 

 ascertained by comparing the results obtained from each operation. Total 

 sulphuric acid may also be estimated in a single operation. The urine is 

 acidified with hydrochloric acid, and heated to boiling, and solution of 

 barium chloride added. The precipitate of barium sulphate which results 

 is further treated, as described before. 



2. Estimation of total sulphuric acid volumetrically. 



To a measured quantity of urine, which has been strongly acidified with 

 hydrochloric acid, and boiled, barium chloride solution of known strength 

 is added, in quantities sufficient to cause a complete precipitation of all 

 sulphuric acid, in the form of barium sulphate. 



Reagent Required. 



A. 30.5 grammes of chemically pure barium chloride (BaCU + 2H2O) 

 are dissolved in enough distilled water to make one liter. Kach cubic 

 centimeter is the equivalent of 10 milligrammes of sulphur trioxide (i cc. ^ 

 o.oi SO3). 



The method is executed as follows : 50-100 cubic centimeters of urine 

 are placed in a beaker, 5-10 cubic centimeters of hydrochloric acid added, 

 and the mixture boiled for one half hour ( = decomposition of conjugate 

 sulphates). Then add, from a burette, the barium chloride solution i cc. 

 at a time, until no further precipitation occurs. The mixture must be 

 boiled after each addition of reagent. Allow the precipitate to subside and 

 withdraw a small quantity of clear liquid (about i cc), and add to this a 



