URINE. 26l 



delicate thermometer (D), graduated in hundredths of a degree 

 is introduced into the inner tube and is held in place by means of 

 a cork so that the mercury bulb is immersed in the fluid under ex- 

 amination but does not come in contact with any glass surface. A 

 small platinum wire stirrer serves to keep the fluid under examina- 

 tion well mixed while a larger stirrer is used to manipulate the freez- 

 ing mixture. (Rock salt and ice in the proportion i : 3 form a very 

 satisfactory freezing mixture.) 



In making a determination of the freezing-point of a fluid by 

 means of the Beckmann-Heidenhain apparatus proceed as follows : 

 Place the freezing mixture in the battery jar and add water (if 

 necessary) to secure a temperature not lower than 3 C. In- 

 troduce the fluid to be tested into tube A, place the thermometer 

 and platinum wire stirrer in position and insert the tube into the 

 air jacket which has previously been inserted through the metal 

 cover of the battery jar. Manipulate the two stirrers in order to 

 insure an equalization of temperature and observe the course of 

 the mercury column of the thermometer very carefully. The mer- 

 cury will gradually fall and this gradual lowering of the tempera- 

 ture will be followed by a sudden rise. The point at which the 

 mercury rests after this sudden rise is the freezing-point. This 

 rise is due to the fact that previous to freezing, a fluid is always 

 more or less over cooled and the thermometer temporarily registers 

 a temperature somewhat below, the freezing- point. As the fluid 

 freezes however there is a very sudden change in the temperature 

 of the liquid and this change is imparted to the thermometer and 

 causes the rise as indicated. It occasionally occurs that the fluid 

 under examination is very much over cooled and does not freeze. 

 Under such circumstances a small piece of ice is introduced into it 

 by means of the side tube noted in the figure. This so-called 

 "inoculation" causes the fluid to freeze instantaneously. (For 

 details of the method of determining the freezing-point consult 

 standard works on physical or organic chemistry.) 



Electrical Conductivity. The electrical conductivity of the 

 urine is dependent upon the number of inorganic molecules or ions 

 present, and in this differs from the freezing-point which is de- 

 pendent upon the total number of molecules both inorganic and 

 organic which are in solution. The conductivity of .the urine has 

 been investigated but slightly, and this very recently, but from the 

 data secured it seems that the value generally falls below K = 0.03. 

 The conductivity of blood serum has been determined as K = 0.012. 



