In general, it may be stated that when a strong acid, such as hydrochloric, sulphuric or nitric acid, is titrated against a strong base, such as sodium hydroxide, potassium hydroxide, or barium hydroxide, any of these indicators may be used, since very little hydrolysis ensues.  It has been noted above that the color change does not occur exactly at theoretical neutrality, from which it follows that no two indicators will show exactly the same end-point when acids and alkalis are brought together.  It is plain, therefore, that the same indicator must be employed for both standardization and analysis, and that, if this is done, accurate results are obtainable.

The following table (Note 1) illustrates the variations in the volume of an alkali solution (tenth-normal sodium hydroxide) required to produce an alkaline end-point when run into 10 cc. of tenth-normal sulphuric acid, diluted with 50 cc. of water, using five drops of each of the different indicator solutions.

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|            |          |             |
Indicator   |   N/10     |   N/10   |color in acid|color in ALKA-
| H_{2}so_{4}|   NaOH   |solution     |line solution
_______________|____________|__________|_____________|______

________
|    cc.     |    cc.   |    cc.      |
Methyl orange  |    10      |   9.90   |   Red       |  Yellow
Lacmoid        |    10      |  10.00   |   Red       |  Blue
Litmus         |    10      |  10.00   |   Red       |  Blue
Rosalic acid   |    10      |  10.07   |   Yellow    |  Pink
Phenolphthalein|    10      |  10.10   |   Colorless |  Pink
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It should also be stated that there are occasionally secondary changes, other than those outlined above, which depend upon the temperature and concentration of the solutions in which the indicators are used.  These changes may influence the sensitiveness of an indicator.  It is important, therefore, to take pains to use approximately the same volume of solution when standardizing that is likely to be employed in analysis; and when it is necessary, as is often the case, to titrate the solution at boiling temperature, the standardization should take place under the same conditions.  It is also obvious that since some acid or alkali is required to react with the indicator itself, the amount of indicator used should be uniform and not excessive.  Usually a few drops of solution will suffice.

The foregoing statements with respect to the behavior of indicators present the subject in its simplest terms.  Many substances other than those named may be employed, and they have been carefully studied to determine the exact concentration of H^{+} ions at which the color change of each occurs.  It is thus possible to select an indicator for a particular purpose with considerable accuracy.  As data of this nature do not belong in an introductory manual, reference is made to the following papers or books in which a more extended treatment of the subject may be found: