MAY, 1947
EXPERIMENTS WITH ASH
r. PROMM
'
College of the Sacred Heart, Santurce, Puerto Rico
THOUGH the extraction of potash from ashes is mentioned in all textbooks, instructions for its preparation and use are not included in the laboratory manuals. In this laboratory it has been used for a series of student experiments in the same way as the preparation and refining of cane sugar [THISJOURNAL, 22, 502 (1945)l and might he of interest to other small laboratories. The experiment as such does not offer anything new or especially interesting; however, it is believed that the use of local resources is something i n which the future teacher a t the high-school and college lsvel as well as the chemist in smaller factories ought to be trained a t the earliest possible moment lest he fail in his first professional work when the well-equipped university laboratory is no longer a t his disposal. Raw material for these experiments has been charcoal ash which was obtained in large quantities from rural households or tobacco ash of which a cigar smoker can easily collect several hundred grams in one semester. 1. Estirnate of potash content in the ash. A direct acidmetric determination of the potassium carbonate content of the ash is not feasible because the other carbonates present react also; moreover, the unburped particles of carbon and other materials which are gray or black and insoluble in water and acids do not allow a satisfactory observation of the end point of the titration. A good estimate of the potash content of the ash can be obtained as follows: Treat 0.1 to 0.2 g. of ash with 25 ml. of 0.1 N HCI, filter, and wash with distilled water untii neutral to litmus. Titrate the united filtrates and washings with A ml. of 0.1 N NaOH and
methyl orange. Add 30 ml. of 1.5 M ammonium oxalate, boil for five minutes, and let stand overnight. Then, filter and wash. Dissolve the precipitate in 30 ml. of 6 N sulfuric acid and titrate-with B ml. of 0.1 N KMn04. (25 - . A - B)O.O0691 gives the grams of potash found if all solutions are exactly 0.1 N. On the average charcoal ash contained 19 per cent, and tobacco ash 30 per cent potassium carbonate. 9. Preparation of potash. Extraction of the ash with cold water or in the Soxhlet apparatus gave poor results. Boiling of 50 g. of ash with 25'0 ml. of water extracted 60 per cent of the potash, a second extraction yielded another 28 per cent, and a third one an additional 4 per cent, so that two or three extractions with 250 ml. of boiling water each are recommended. The residue of the evaporation of these extracts should be dried at 110' to 120' for the detkrmination of the yield. 3. Soap from potash. The insolubility of potash in alcohol does not allow an alcoholic saponification as generally practiced in the student laboratory. The low pH of the watery solution of potash also makes its direct use time consuming and inadvisable. Good results are obtained by preparation of potassium hydroxide as follows: Dissolve 13 g. of potash in 100 ml. of water, add 6 g. of quick lime, heat to boiling, and filter. Mix the filtrate with 10 g. of coconut oil in an evaporating dish and evaporate with constant stirring to a small volume of sticky mass, add 100 ml. of water, and repeat the evaporation. Pour the hot residue into 100 ml. of saturated salt solution and separate the soap cake from the solution on the next morning.
