174 STATE BOARD OF AGRICULTURE. 



Standard solutions: The standard solutions used were prepared accord- 

 ing to Clark and Lubs (1), (2). The acid potassium phosphate solution was 

 made from Merck's especially prepared salt ("Scerensen's potassium phos- 

 phate") which had been recrystallized three times in triple distilled water 

 and dried to constant weight at 110-115 C. The sodium hydroxide solution 

 was made from chemically pure material, all necessary precautions being taken 

 to get it carbonate free. It was then stored in a paraffined bottle and care 

 taken to" keep it free of CO2 and moisture. The boric acid and potassium 

 chloride salts were recrj'-stallized several times and dried according to direc- 

 tions. The proper mixtures were made and stored in bottles, the more alkaline 

 series being stored in paraffined bottles. 



Indicators: Di brom ortho thymol sulphon phthalein (Brom thymol 

 ]:)lue), pH range 6.0 — 7.6, and thymol sulphon phthalein (thymol blue, 

 alkaline range), pH range 8.0 — 9.6, were made to 0.04 per cent in 50 per cent 

 alcoholic solution. Phenol sulphon phthalein (])henol red), pH range 6.8 

 —8.4 and Ortho cresol phthalein (cresol phthalein), pH range 8.2 — 9.8, 

 were made to 0.02 per cent in 50 per cent alcoholic solution. 



The color standards: Ten cubic centimeter cjuantities of the standard 

 l)uffer mixtures having the desired pH value were placed in colorless glass 

 tubes 1.8 x 15 cm. Ten drops of indicator covering the desired pH range were 

 then added. These tubes were then placed in a Cooledge comparator (3) 

 and were ready to use. The color standards were placed in the front rack of 

 the comparator and 10 cc. of the unknown solution containing ten drops of 

 the proper indicator was placed in the rear rack of the comparator. A 

 compensating blank of water and one of the unknown solution were then in- 

 serted in the rear right and front left holes, respectively, of the comparator 

 and the readings made. 



PROCEDURE. 



Procedure A. New glassware that had never been used was secured from 

 stock and without washing or treating with cleaning solution it was filled with 

 non-buffered conductivity water which had been adjusted to pH 7.0. The 

 glassware was then autoclaved for 30 minutes at 15 pounds pressure. As 

 soon as the water had cooled down to 20'' C, 10 c. c. samples of it were taken, 

 iO drops of indicator added, and the pH value determined in the Cooledge 

 comparator as previously described. This same glassware was refilled four 

 times with non-buffered conductivity water and twice with broth, autoclaved 

 after each time and the pH value determined. This was done to determine 

 the effect of the glassware on the non-buffered solution and to see if the 

 amount of alkali was sufficient to change the reaction of the buffered solution 

 after four times autoclaving with the non-})uffered solution. Six different 

 grades and kinds of glassware were treated according to this procedure and 

 were marked sets la, 2a, 3a, 4a, 5a and 6a (see tables 1 to 6). 



Procedure B. The same procedure was followed with a different set of the 

 same glassware only the glassware was refilled with broth and autoclaved six 

 times instead of four times with conductivity water and twice \x\ih. liroth. 

 It was desired to know if sufficient alkali would l^e given off by the glassware 

 to change the hydrogen-ion concentration of the buffered solution. Six 

 different grades and kinds of glassware were treated according to this procedure 

 and were marked sets lb, 2b, 3b, 4b, 5b and 6b. (see tables 1 to 6). 



Procedure C. It is common laboratory practice to wash new glassware 



