of Benzoic Acid into Hippuric Acid. 503 



play. It occurred to me that it might be the lactate of urea, 

 instead of pure urea, which is taken up; and upon comparing 

 the formulae for hippuric acid, benzoic acid, and the lactate of 

 urea, it appeared that one equivalent of lactate of urea minus 

 three eqs. of water, gave exactly the requisite elements for the 

 conversion of 2 eqs. of benzoic acid into 2 eqs. of hippuric 

 acid. 2 eqs. of benzoic acid + 1 eq. of lactate of urea = 2 

 eqs. of hippuric acid + 3 eqs. of water. 



Hippuric acid (anhydrous) Cjg Hg O5 Nj 

 Benzoic acid (Do.) Cj4 H5 O3 



Difference C4 H3 0.j Nj 



Twice the difference . . Cg H,^- O4 Ng 



Lactic acid C^ H5 O5 



Urea C^ H^ O, N^ 



Lactate of urea Cg H9 O7 N^ 



Lactate of urea -3 H O = Cg H^ O4 K; 



Now the urea has by MM. Cap and Henry been found to 

 exist in human urine as lactate, and the separation of the 

 elements of water is a change which might be expected to 

 take place in the system under such circumstances. The ben- 

 zoic acid merely taking up the lactate of urea, and throwing 

 off water, is certainly a more probable occurrence than the 

 destruction of such a stable compound as uric acid. 



In analyses for the quantity of lactate of urea, according to 

 the method of Cap and Henry, I found that although I could 

 not obtain it in crystals, yet the quantity in a syrupy state was 

 much reduced after taking the benzoic acid, and the same ap- 

 peared on forming nitrate of urea from it. I obtained I't grs. 

 less of urea in 4i ounces of urine when the benzoic acid had 

 been taken. In another experiment I obtained 17 grs. less of 

 urea when 30 grs. of benzoic acid had been taken ; this is a 

 greater loss than can be accounted for by the formation of the 

 hippuric acid ; but this can be referred to the urine, from some 

 accidental circumstance, being of nearly as high specific gra- 

 vity in this case as when the benzoic acid had been taken. 

 30 grs. of benzoic acid, swallowed, usually increased the spe- 

 cific gravity of the urine from four to six-thousandths. 



From these results two inquiries suggest themselves : — 1st, 

 May not hippuric acid be formed artificially out of the body ? 

 2nd, If sufficient benzoic acid were swallowed at such a time 

 when least urea was contained in the urine, would the benzoic 

 acid not cease to be all converted into hippuric acid, part of 

 it then appearing in the urine unchanged? 



