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XIII. Contributions to the Chemistry of the Urine . — Paper III. 
Part I. On the Variations of the Acidity of the Urine in the state of Health. 
Part II. On the simultaneous Variations of the amount of Uric Acid, and the Acidity 
of the Urine in the state of Health. 
Part III. On the Variations of the Sulphates in the state oj Health, and on the 
influence of Sulphuric Acid, Sulphur and Sulphates, on the amount of Sul- 
phates in the Urine. 
^^Hknrv Bence 5oyiE.s,M.D.,M.A. Cantab., F.R.S., Physician to St. George's Hospital. 
Received November 20, 1848, — Read January 25, 1849. 
Part I. — On the Variations of the Acidity of the Urine in the state of Health. 
In the Philosophical Transactions for 1845, I showed that not unfrequently in 
London, the urine was found in many persons to be alkaline from fixed alkali ; and 
I mentioned that Dr, Andrews, at Belfast, had found the water passed at noon of 
two-thirds of the students of his class to be alkaline. 
It appeared to me to be a matter of great interest to determine quantitatively the 
daily variations in the acidity and alkalescence of the urine in the state of health ; 
to trace, if possible, the cause of the variations ; to determine the effect of some 
medicines ; at the least until this was done I could draw no conclusions regarding 
the effect of diseases on the acidity of the urine. 
In examining quantitatively the variations at different hours of the day, it was 
immediately found that there was no fixed degree of acidity of the urine ; that the 
acidity did not vary with the specific gravity, but that there was a never-ceasing- 
change, an ebb and flow, in the acid reaction of the urine, which was quite inde- 
pendent of the specific gravity. 
The degree of acidity of the urine was found generally to be greatest a short time 
before food was taken; and after food the acidity was diminished, until about three 
hours after breakfast, and four or five, or six hours after dinner, when it reached the 
minimum point ; after which it again rose and attained its height previous to food 
being again taken. 
A healthy man was the subject of the following experiments : for three months he 
had taken strong exercise, walking above 700 miles. Food was taken twice daily. 
The exercise was moderate during the experiments, from three to four hours daily. 
The urine not unfrequently showed most marked alkalescence from fixed alkali. 
Rarely even phosphate of lime was deposited. Five or six hours afterwards the 
