28 METHODS FOR THE ANALYSIS OF URINE 



in pyrex or nonsol flasks. They do not fade when exposed to dif- 

 fused light of moderate intensity. The permanent standards do 

 not change appreciably if properly cared for. They should not 

 be kept standing in direct sunlight, and should be kept in a box 

 or cupboard when not in use. Even after nine months the stand- 

 ards are in excellent condition, the color changes being so slight as 

 to cause practically no error in estimation of the PH of a urine. 



Each standard is prepared to match somewhat closely the 

 color given by 1 c.c. of a Sorensen's phosphate mixture diluted with 

 20 c.c. of boiled distilled water after the addition of 1 c.c. of indi- 

 cator, when at ordinary room temperature (15 to 22). Absolute 

 matching of the colors is not at all necessary. The use of rosolic 

 acid with urine is possible only with the aid of the permanent 

 standards. Sorensen's phosphate standards with rosolic acid 

 change color too rapidly for practical use. For these permanent 

 standards 20 c.c. of the buffer phosphate solution is put into each 

 of the two-ounce square bottles and various amounts of amaranth 

 and paranitrophenol are added as indicated below, and a little 

 preservative (0.2 c.c. 10 per cent thymol in chloroform) is added, 

 then the bottle is corked (but not with a rubber stopper) and 

 sealed with hot paraffin. 



The exact PH figures for the Sorensen phosphate mixtures are 

 those given in the parentheses. The approximate figures can be 

 used for most work, since it is impossible to detect differences 

 between solutions that vary less than 0.05 in their P H figures. 



The concentrations of amaranth in indicator solutions are as 

 follows: Amaranth (amaranth No. 107, Eimer & Amend), 8 mg. 

 dissolved in 100 c.c. of distilled water to which is added 0.5 c.c. of 

 the thymol-chloroform preservative. 



Paranitrophenol (Eimer & Amend), 20 mg. dissolved in 10 c.c. 

 of alcohol and diluted with 90 c.c. of distilled water. 



Methyl red (Hynson, Wescott & Dunning), very finely pow- 

 dered, 2.4 mg. dissolved in 100 c.c. of 60 per cent alcohol. 



Rosolic acid (Hynson, Wescott & Dunning), powdered, 16 mg. 

 dissolved in 100 c.c. of 95 per cent alcohol. 



Neutral red (Hynson, Wescott & Dunning), finely powdered, 

 3.2 mg. dissolved in 100 c.c. of 50 per cent alcohol. 



For these solutions the concentrations of alcohol need not be 

 exact. The last three indicator solutions must be protected from 

 the light, preferably by painting the flasks black. These indicator 



