To weigh the caustic soda or potash place about five grams on a watch glass on a balance and weigh as rapidly as possible. Wash into a 500 cubic centimeter volumetric flask and bring to the mark with distilled water. Pipette off 50 cubic centimeters into a 200 cubic centimeter beaker, dilute slightly with distilled water, add a few drops of methyl orange indicator and titrate with normal acid. For the carbonates about 1 gram may be weighed, washed into a 400 cubic centimeter beaker, diluted with distilled water, methyl orange indicator added and titrated with normal acid. It is advisable to use methyl orange indicator in these titrations as phenolphthalein is affected by the carbon dioxide generated when an acid reacts with a carbonate and does not give the proper end point, unless the solution is boiled to expel the carbon dioxide. Litmus may also be used as the indicator, but here again it is necessary to boil as carbon dioxide also affects this substance. As an aid to the action of these common indicators the following table may be helpful:
_Color in _Color in _Indicator._ Acid Alkaline _Action of Solution._ Solution._ CO_{ 2}._
Methyl orange Red Yellow Very slightly acid Phenolphthalein Colorless Red Acid Litmus Red Blue Acid
It may be further stated that methyl orange at the neutral point is orange in color.
To calculate the percentage of effective alkali from the above titrations, it must be first pointed out that in the case of caustic potash or soda aliquot portions are taken. This is done to reduce the error necessarily involved by weighing, as the absorption of water is decided. Thus we had, say, exactly 5 grams which weighed 5.05 grams by the time it was balanced. This was dissolved in 500 cubic centimeters of water and 50 cubic centimeters or one tenth of the amount of the solution was taken, or in each 50 cubic centimeters there were 0.505 grams of the sample. We thus reduced the error of weighing by one tenth provided other conditions introduce no error. In the case of the carbonates the weight is taken directly.
One cubic centimeter of a normal acid solution is the equivalent of:
Grams. Sodium Carbonate, Na_{ 2}CO_{ 3} 0.05305 Sodium Hydroxide, NaOH 0.04006 Sodium Oxide, Na_{ 2}O 0.02905 Carbonate K_{ 2}CO_{ 3} 0.06908 Potassium Hydroxide, KOH 0.05616 Potassium Oxide, K_{ 2}O 0.04715