Salts of Ammonia at ordinary Temperatures. 235 



or by leaving healthy urine to stand until it becomes alka- 

 line, the above-mentioned reactions may always be observed. 

 Slightly blue litmus paper is then at first made more strongly 

 blue, and on drying in the air the paper becomes as red as if 

 the urine were fresh, or no ammonia had been added. 



This seemed to show that no free acid existed in the urine, 

 but that the acid reaction was caused by some ammoniacal 

 salt having this property of reddening litmus. 



Pure urate of ammonia, when dissolved in water or with 

 excess of ammonia, showed a similar reaction as the solution 

 evaporated from the blue litmus paper, and hence it seemed 

 probable that urate of ammonia was one cause of the acid 

 reaction of the urine. Hippuric acid having been observed 

 by Liebig to be present in healthy urine, I formed hippurate 

 of ammonia with a slight excess of ammonia in the solution, 

 and I found that when this dried on litmus paper it gave a 

 strong acid reaction. 



It occurred to me to make the same experiment with other 

 salts of ammonia dissolved in cold water with an excess of 

 ammonia, and I found in all a similar reaction. The salts 

 used were the acetate, oxalate, nitrate, sulphate, hydrochlo- 

 rate, hydrosulphate, benzoate, phosphate, and carbonate. The 

 last produced much the feeblest acid reaction. 



Some sulphate of ammonia was dissolved in water: at first 

 it was neutral to test-paper; a drop of a solution of litmus was 

 added to a small cupful of this solution ; after standing some 

 hours in the air the blue colour disappeared, and a pink solu- 

 tion was formed long before all the fluid had evaporated. The 

 temperature was about 67° F. 



The same experiment was repeated with urate of ammonia. 

 A warm solution was made, and whilst warm it was poured 

 into a basin with a drop of litmus solution; after standing 

 eight hours a marked change of colour had taken place. A 

 line of pink had formed where the fluid had evaporated, and 

 there was a decided pink tint in the violet-coloured solution. 

 After twelve hours no violet colour was seen, but a well-marked 

 pink tint. The temperature was rather lower than in the 

 previous experiment. 



A solution of urate of ammonia when cold was filtered into 

 a watch-glass : on examining the edge of the fluid as it evapo- 

 rated a granular deposit mixed with very small needles was 

 seen with the microscope, and single crystals and tufts of cry- 

 stals of uric acid were present in considerable numbers. 



Another solution was made with a marked excess of am- 

 monia : on evaporation in a watch-glass, uric acid crystals, as 

 before, were found at the edge. 



R2 



