140 THE SECRETIONS : 



for washing the precipitate, and super-saturated with nitric 

 acid. A solution of chloride of barium must be added, as 

 long as any sulphate of baryta continues to be precipitated. 

 The fluid is then warmed, for the more perfect separation of 

 the sulphate of baryta, which is collected on a filter, washed, 

 exposed to a strong heat, and weighed. By this means the 

 sulphuric acid contained in the urine is calculated. The acid 

 solution from which the sulphuric acid has been precipitated 

 is mixed with the water used for washing the precipitate in 

 a stoppered bottle of such a size as to be nearly filled by it ; 

 it is rendered alkaline by caustic ammonia, and chloride of 

 barium is added to it, as long as phosphate of baryta is pre- 

 cipitated. The bottle must be allowed to stand, with the stop- 

 per in it, until the precipitate is completely deposited. The 

 fluid is then poured off", and the precipitate washed out on a 

 filter with a little weak solution of ammonia. It is dried, 

 exposed to a strong heat, and weighed. The phosphoric acid 

 must be calculated from the phosphate of baryta thus obtained. 

 The ammoniacal fluid from which the sulphuric and phosphoric 

 acids have been removed by baryta is mixed with the fluid with 

 which the last precipitate was washed ; they are evaporated, the 

 residue treated with sulphuric acid, and then submitted to a high 

 temperature to expel any excess of the acid. The fixed alkalies 

 remain in combination with sulphuric acid. If these salts are 

 dissolved in water, and chloride of barium added to the filtered 

 solution as long as sulphate of baryta continues to be precipi- 

 tated, the chlorides of potassium and sodium are left in the 

 solution, from which they may be separated and estimated. 



The chlorine is determined, as I have already remarked, by 

 a separate experiment. A known quantity of the fixed salts is 

 dissolved in water, and a little nitric acid added to the filtered 

 solution; upon the addition of nitrate of silver, a curdy pre- 

 cipitate of chloride of silver is thrown down. 



The proximate constituents of the fixed salts being thus de- 

 termined, we have next to consider how they are combined. 

 The sulphuric acid is associated with the potash, and if there is 

 not a sufficient quantity of potash, with as much soda as will 

 make up the deficiency : the rest of the soda is allotted to the 

 hydrochloric and phosphoric acids. If there is more than suf- 



