678 URINE. 



acidity and the ion acidity it follows that no direct relation exists between 

 these and that the extent of these two acidities may be independent of 

 each other. 



The osmotic pressure of the urine varies considerably even under 

 physiological conditions. The limit for the freezing-point depression 

 has been found by a number of investigators to be A 1.3 to 2.3 C. After 

 partaking of considerable water it may be markedly lower, and on 

 diminished supply of water it may be considerably higher. 



In regard to the further physical-chemical imvestigations of the urine 

 and as to the conclusions drawn from a combination of the chemical 

 and the physico-chemical investigations of the urine, we must refer to 

 the extensive work of CARL NEUBERG. 1 



The specific gravity of urine, which is dependent upon the relation 

 existing between the quantity of water secreted and the solid urinary 

 constituents, especially the urea and sodium chloride, may vary con- 

 siderably, but is generally 1.017-1.020. After drinking large quantities 

 of water it may fall to 1.002, while after profuse perspiration or after 

 drinking very little water it may rise to 1.035-1.040. In new-born 

 infants the specific gravity is low, 1.007-1.005. The determination 

 of the specific gravity is an important means of learning the average 

 amount of solids eliminated from the organism in the urine, and on this 

 account the determination becomes of true value only when at the same 

 time the quantity of urine voided in a given time is determined. The 

 different portions of urine voided in the course of the twenty-four hours 

 are collected, mixed together, the total quantity measured, and then the 

 specific gravity taken. 



The -determination of the specific gravity is most accurately obtained 

 with the pycnometer. For ordinary cases the specific gravity may be 

 determined with sufficient accuracy by means of areometers. The 

 areometers found in the trade, or urinometers, are graduated from 1.000 

 to 1.040; for exact observations it is better to use two urinometers, one 

 graduated from 1.000 to 1.020, and the other from 1.020 to 1.040. 



To determine the specific gravity of urine, if necessary filter the 

 urine, or if it contains a urate sediment, first dissolve it by gentle heat, 

 then pour the clear urine into a dry cylinder, avoiding the formation of 

 froth. Air bubbles or froth, when present, must be removed with a glass 

 rod or filter-paper. The cylinder, which should be about four-fifths full, 

 must be wide enough to allow the urinometer to swim freely in the liquid 

 without touching the sides. The cylinder and urinometer should both 

 be dry or previously washed with the urine. On reading, the eye is 

 brought on a level with the lower meniscus which occurs when the sur- 

 face of the liquid and the lower limb of the meniscus coincide; the read- 



1 Der Harn sowie die iibrigen Ausscheidungen und Korperflussigkeiten von Mensch 

 und Tier. Teil. 2, Berlin, 1911. 



