442 URINE. 



case in typhus, measles, &c., but sometimes also in inflammations 

 running their ordinary course. Thus it not unfrequently happens 

 in pneumonia, that a urine is passed in the morning, which either 

 already exhibits an alkaline reaction, or becomes alkaline in a very 

 short time, whilst the urine discharged three or four hours later 

 may have an acid reaction, and exhibit an increase of acidity on 

 standing. Now, when such different kinds of urine are mixed, we 

 can hardly be said to be conducting a very strict, or even rational, 

 method of investigation. 



In conducting an analysis of the urine, special attention must 

 be devoted to its evaporation and the drying of its residue ; and 

 here again we encounter other difficulties, which differ from those 

 presented by similar modes of investigation, as, for instance, in 

 evaporating and drying milk. I have convinced myself by direct 

 experiments* that, in evaporating the urine, its decomposition will 

 be directly proportional to the duration of the evaporation ; and I 

 have already drawn attention to the fact that the urine always 

 develops ammonia during its evaporation, although it may retain 

 its acid reaction. It is, therefore, very important to let this eva- 

 poration be effected as rapidly as possible, when it is unavoidably 

 necessary to do so by heat ; and this observation is especially ap- 

 plicable when the collective twenty-four hours' urine is evaporated, 

 since in this case the urine is rendered more susceptible of de- 

 composition from prolonged standing. Slow evaporation has, 

 however, the effect of causing the urine to become decomposed 

 with extraordinary rapidity, as we may see from the fact that urine 

 which has been thus collected and mixed together will, in four out 

 of five cases, contain no hippuric, but only benzoic acid. The urine 

 always becomes slightly decomposed when evaporated by heat, 

 in whatever manner this may have been accomplished; but the 

 following method is, I think, the best adapted to hinder, as much 

 as possible, this decomposition. The urine should be introduced 

 into a wide tubular retort, and whilst the evaporation is proceeding 

 on a sand-bath near the boiling point, atmospheric air, or hydrogen 

 gas, should be continually passed over the evaporating surface. 

 The distillate will then always be ammoniacal, although not to such 

 a degree as if the evaporation were accomplished without the em- 

 ployment of a current of air. The quantitative determination of 

 the solid residue cannot, however, be obtained by this method, 

 which simply serves for the preparation of the extract from which 



* Op. cit. 



