272 



URINE. 



[CH. XII. 



To obtain the best results two separate instruments 

 should be at hand, the one calibrated from 1000 to 1020 

 and the other from 1020 to 1040. 



The total amount of solids in the urine can be roughly 

 calculated from the specific gravity by Long's coefficient. The 

 last two figures of the specific gravity x 2-6 gives total solids 

 in 1000 cc. 



Thus specific gravity at 25 C = 1017. 



Total solids in 1000 cc. = 17 x 2-6 = 44-2 grams. 



Haser's coefficient (2-33) on a similar basis, but calculated 

 for 15 C. is probably inaccurate. 



321. Take the specific gravity of normal urine by 

 means of a urinometer. Wipe the instrument clean, 

 and float it in the centre of a cylinder containing the 

 urine. Remove all froth, by means of filter paper or 

 by placing a single drop of ether on the surface of the 

 urine. Take care that the instrument does not touch 

 the sides of the vessel. Place the eye level with the 

 surface of the fluid and read the division of the scale 

 to which the latter reaches. Read the level of the true 

 surface of the urine, not the top of the meniscus 

 around the stem. 



///. The Osmotic Pressure (Cryoscopy). 



The method of taking the freezing point of 

 a fluid is described on p. 8, and the subject has 

 been considered from a theoretical standpoint 

 on p. 5. 



Fl g- 36. i n ur ine the concentrations of certain sub- 



Urmometer. stances ^ such as urea ^ are muc h greater than 



they are in the blood. The work done by the kidney 

 in effecting this concentration can be calculated from a 

 consideration of the osmotic concentration, i.e. A, of 

 each substance in blood and urine. It is quite erroneous 

 to imagine that the work done can be calculated from 

 a knowledge of the total osmotic concentration of the 

 blood and urine respectively. But, at the same time, 

 the determination of A of the blood and of the urine 

 secreted by each kidney in certain renal diseases may 



