224 Phosphoric Acid in Human Urine. 
Art. XXI—Phosphoric Acid in Normal Human Urine; by 
ae : 4 Dr. D. Breen. 
Norwirustanpine the importance of all knowledge appertain- 
ing to physiology and pathology, neither chemist nor physician 
has heretofore made any considerable research in relation to phos- 
phoric acid in urine. But the accurate and expeditious method 
for the determination of phosphoric acid, proposed by Professor 
Liebig, forbids our remaining longer in ignorance of facts which 
may be of great value in the treatment of disease. This method 
consists simply in the titrition of urine, with .a solution of the 
perchlorid of iron, until the filtrate from the mixture gives the 
well known blue reaction with ferrocyanid of potassium. It is 
based upon the fact that either a neutral or acetic acid solution 
of phosphoric acid gives with perchlorid of iron an insoluble pre- 
cipitate, whilst the peroxyd of iron is readily dissolved by acetic 
acid. If a solution of phosphoric acid containing acetate of soda 
be treated with perchlorid of iron, we have the following reac- 
tion—PO; +3(NaO, A)+Fe2Cl; =Fe20:, PO; +3(NaCl)+3A. 
The solution of perchlorid of iron is most conveniently made 
by dissolving in nitro-hydrochloric acid 15-656 grammes of iron, 
and evaporating to dryness, to expel the excess of acid, then add- — 
ing nitric acid, and again evaporating to prevent the existence of 
protochlorid, and afterward, re-dissolving the product in 2000 ce. 
of water. Every cc. of this solution will precipitate ten milli- 
grammes of phosphoric acid. Instead of the above, a solution 
of the perchlorid of iron of unknown strength may be used, and 
the iron be determined. Or, the strength of the solution of iron 
may be found by titrition with a solution of phosphoric acid of 
known strength. In all the above methods the solution of iron 
must be free from proto-chlorid. at 
If the urine, of which we would determine the phosphori¢ 
acid, has become alkaline by the decomposition of urea, some of 
the phosphoric acid may have been precipitated with lime oF 
been used) and free acetic acid are added. The urine is then 
treated with a solution of perchlorid of iron from a burette— 
frequently testing, until the phosphoric acid is saturated, and we 
have a drop of iron in excess. ‘'T'o test for iron in excess, lay # 
filter on a white porcelain plate, or on a glass supported by white 
per, and moisten it slightly with ferrocyanid of potassium; 
with a glass rod bearing a drop of urine, press a double filter upo? 
the paper containing the ferrocyanid of potassium, and if the 
be an excess of iron, in three or four seconds we have the blue 
