THE CAUSE OF ITS ACID REACTION. 405 



soda which it contained. The observations necessary for deter- 

 mining this question are not, however, so easily conducted as one 

 might at first sight suppose ; for when the urine has been treated 

 with so much alkali that its reaction is neither acid nor alka- 

 line, there must obviously still remain the acid phosphate of 

 soda in the solution ; for the neutral phosphate of soda has an 

 alkaline reaction, and, therefore, the acid salt cannot be neutralised 

 whilst the urine continues to exhibit no reaction towards vegetable 

 colours. On this account, I have endeavoured to determine the 

 quantity of the free acid in the urine by the following method : 

 1 precipitate the urine with an excess of chloride of barium, and 

 after boiling the precipitate with a very weak solution of sulphuric 

 acid, determine the weight of the sulphate of baryta. I next 

 digest equal quantities of urine with freshly precipitated car- 

 bonate of baryta until the acid reaction has entirely disappeared, 

 and after acidifying the filtered fluid with a little acetic acid, preci- 

 pitate by means of chloride of barium. This precipitate also is 

 boiled in an extremely dilute solution of sulphuric acid, and then 

 weighed ; the quantity of the latter is far smaller than that of 

 the sulphate of baryta first weighed, and this difference between 

 the two weights gives the quantity of sulphate of baryta 

 necessary to yield a sufficient amount of base to saturate the free 

 acid contained in the urine. Hence we may easily calculate from 

 the chemical equivalents the amount of the free acid or of the acid 

 phosphate of soda. If this method did not lead us to calculate a 

 larger quantity of acid phosphate of soda in the urine than it 

 would appear from another mode of analysis there actually existed, 

 the acid reaction would depend solely upon the acid phosphate. 

 Although this was not unfrequently the case, I found still oftener 

 that the opposite condition existed in healthy as well as in morbid 

 urine ; that is to say, a comparison of the baryta salts commonly 

 yielded a higher number for the quantity of the acid phosphate of 

 soda than was found by direct analysis to be present, and hence 

 there must, in most cases, be some free organic acid present in 

 addition to the acid phosphate of soda, or some other acid salt 

 which reddens litmus paper. We must, however, beware of draw- 

 ing too hasty a conclusion in reference to this subject, for the 

 acidity of the urine often increases so rapidly after its discharge, 

 owing to the formation of lactic or acetic acid, that the excess of 

 free acid observed in the above mentioned experiments may 

 perhaps be owing to the lactic acid formed after the urine has left 

 the body. On the other hand, we frequently find such an excess 



