RASKINS' MODIFICATION 31 



be examined within an hour after being passed. The urine must 

 not be treated in any other way, not even filtered. If it is turbid it 

 may be centrifuged. 



2. Urines containing hemoglobin, bile or great excess of pig- 

 ment may be dialyzed in a collodion sac against neutral 1 per 

 cent sodium chloride solution for thirty minutes, as in Rowntree's 

 method for PH of blood. The PH of the salt solution is then 

 determined in the same way as urine. 



3. The room must be free from fumes of ammonia, hydrochloric 

 or nitric acid when estimations are made. Excess of CO2 (from 

 flames) should be avoided. 



4. For measuring amaranth and paranitrophenol solutions and 

 also the urine, 1 c.c. pipettes marked in 0.01 c.c. are needed. 



5. When the temperature of the room is above 22 an error may 

 be made in estimation due to the temperature (the permanent 

 standards do not change perceptibly), for instance, if the urine test 

 mixture is at 30 the P H figure will be greater (more alkaline) than 

 at 20 by about 0.05 (in the case of a distinctly acid urine) up to 

 even 0.20 (in the case of an alkaline urine). This can be obviated 

 readily by cooling the distilled water to about 15 before using it. 



6. The presence of protein in the urine does not interfere with 

 the use of the indicator. 



7. The phosphates for the preparation of the buffer solution 

 must be pure for this purpose. Baker's C. P. KH^PO* and 

 Merck's pure KgHPCU may be used. The buffer solution must 

 have a PH of 6.8 when estimated by the same dilution method 

 as in the case of urine. 



Dissolve each phosphate separately in about 200 c.c. of dis- 

 tilled water, taking 6.808 gms. of powdered KH^PCU and 8.712 gms. 

 of powdered K2HPO4. Mix the solutions and dilute to exactly 

 500 c.c., saturate with chloroform and filter. Keep the solution 

 in a pyrex flask tightly corked. 



8. A slight precipitate may appear after a time in the per- 

 manent standards, but this need not interfere with their use if 

 they are not shaken up. 



9. Test the indicator solution at least once a month by making 

 PH estimations with Sorensen's phosphate mixture (1 c.c. diluted 

 as in estimating urine), using for methyl red the P H 5.3 mixture 

 and for neutral red the P H 7.15 mixture. For rosolic acid the 

 buffer phosphate mixture can be used (Pa 6.8). This procedure 



