- 37 



solutions of sulphuric acid were made up in two liter quantities 

 to a strength of approximately 0.5 normal for the 1 part in 

 1000 tests and approximately 0,1 normal for the 1 part in 200 

 tests. The exact normality of each solution was determined 

 through comparison with the standard sodium carbonate solution. 

 The standard sodium carbonate solution in turn was titrated 

 against the intermediate standard acid solution. It was found 

 that the acid prepared for the 1 part in 200 tests was 9»94 

 times as concentrated as the intermediate standard acid and that 

 the acid prepared for the 1 part in 1000 tests was 50,2 times as 

 concentrated as the intermediate standard acid. The entire mass 

 of ambient water in the model was rendered suitably alkaline by 

 addition of sodium carbonate. It was found that approximately 

 2,0 milliliters of the intermediate standard acid solution pro- 

 duced the blue-green to blue change of color in the brom cresol 

 green indicator and that approximately 3.1 milliliters of inter- 

 mediate standard acid produced the green-yellow color change 

 when added to 50 mil.liliters of the sodium carbonate solution 

 used as the ambient water. This ratio of concentrations was moni- 

 tored by titrations throughout the model tests. During each 

 test the dilution factor inevitably tended to shift. The aver^ 

 age dilution factor was calculated for each run and the results 

 of these calculations are tabulated in the log sheets and 

 entered on the smooth plots of the results for each test. Two 

 values are given; the value for the ycllcw-green change repre- 

 senting the highest measurable concentration of simulated bleed 



