The insoluble portion remaining on the filter paper is washed with water until all the carbonate is dissolved. The washings are then titrated with N/10 sulfuric acid and expressed as sodium or potassium carbonate. Should borates or silicates be present it is possible to express in terms of these. If borax is present the carbon dioxide is boiled off after neutralizing exactly to methyl orange; cool, add mannite and phenolphthalein and titrate the boric acid with standard alkali.
(_b_) _Bosshard and Huggenberg Method._[14]
In using the alcoholic method for the determination of the free alkali or fat in soap there is a possibility of both free fat and free alkali being present. Upon boiling in an alcoholic solution the fat will be saponified, thus introducing an error in the analysis. The method of Bosshard and Huggenberg overcomes this objection. Their method is briefly as follows:
1. N/10 hydrochloric acid to standardize N/10 alcoholic sodium hydroxide.
2. Approximately N/10 alcoholic sodium hydroxide to fix and control the N/40 stearic acid.
3. N/40 stearic acid. Preparation: About 7.1 grams of stearic acid are dissolved in one liter of absolute alcohol, the solution filtered, the strength determined by titration against N/10 NaOH and then protected in a well stoppered bottle, or better still connected directly to the burette.
4. A 10 per cent. solution of barium chloride. Preparation: 100 grams of barium chloride are dissolved in one liter of distilled water and filtered. The neutrality of the solution should be proven as it must be neutral.
5. [Greek: alpha] naptholphthalein indicator according to Sorenson. Preparation: 0.1 gram of [Greek: alpha] naphtholphthalein is dissolved in 150 cubic centimeters of alcohol and 100 cubic centimeters of water. For every 10 cubic centimeters of liquid use at least 12 drops of indicator.
6. Phenolphthalein solution 1 gram to 100 cubic centimeter 96 per cent. alcohol.
7. Solvent, 50 per cent. alcohol neutralized.
First--Determine the strength of the N/10 alcoholic sodium hydroxide in terms of N/10 hydrochloric acid and calculate the factor, e. g.:
10 c.c. N/10 alcoholic NaOH = 9.95 N/10 HCl} 10 c.c. N/10 alcoholic NaOH = 9.96 N/10 HCl} 9.96