340 ANALYSIS OF URINE. [CH. XIII. 



Calculation. If (a) cc. of urine have been taken originally, the amount 



actually used corresponds to ift. If the standard is set at 15 mm., and the 



10 

 " U " tube reads at U, then mg. of (creatine + creatinine) in 



15 x 10 



i cc. - r<u" x ( fl ). 



The rest of the calculation is the same as that of the previous exercise. 



NOTE. The above method is a slight modification of that published by 

 Benedict, but it does not differ in any essential. 



405. The removal of aceto-acetic acid (Graham and Poulton). 



Principle. Aceto-acetic acid is converted by heat to acetone, which is 

 distilled off at low pressure. The following account is slightly modified from 

 the original. 



Solutions and apparatus required. 

 (i.) A 10 per cent, solution of phosphoric acid. 



(ii.) A solution of soda of such a strength that i cc. of it neutralises i cc. 

 of the phosphoric acid, phenol phthalein being used as the indicator. 

 A 15 per cent, solution of soda is a convenient starting point for the 

 preparation of this. When it is correctly adjusted, 1-5 cc. of it will 

 neutralise all three valencies of i cc. of the phosphoric acid, only two 

 of which are neutralised to phenol phthalein. 



(iii.) A suction pump and gauge (see fig. 9, p. 74). 



(iv.) A thick walled tube (25 to 30 mm. by 200 mm.) similar to the tube E 

 of fig. 44, but in place of F is substituted a tube drawn out to a fine 

 capillary, which must reach nearly to the bottom of E. (The 

 upper end of the tube may be fitted with a piece of pressure tubing 

 and a screw clip similar to that shown in C of fig. 8.) 



Method. Into the tube measure 10 cc. of the urine and add i cc. 

 of the 10 per cent, phosphoric acid. Fit the stopper carrying the 

 capillary tube and connect the other outlet tube to the tube E of 

 the apparatus shewn in fig. 9 and have C turned to make connexion 

 with A. Turn on the pump and note the pressure obtained, which 

 depends on the size of the capillary, on the size of A and on the 

 water pressure. It is necessary to maintain a pressure of about 

 210 mm. of mercury. Immerse the tube containing the acidified 

 urine in a water bath kept between 65 and 70 C., and leave it for 

 about three-quarters of an hour, seeing that the temperature does 

 not rise above 70 C., nor the pressure fall below 210 mm. of mercury. 

 Release the pressure by turning the tap C to connect with B, and 

 then turn off the water. Disconnect and cool the solution under the 

 tap. Add i -5 cc. of the standardised soda to completely neutralise 



