Reports and notes of the Public Health Laboratories, Cairo. No. 1, 1917.

Date:
1918
Catalogue details

Licence: In copyright

Credit: Reports and notes of the Public Health Laboratories, Cairo. No. 1, 1917. Source: Wellcome Collection.

    61/144 page 49
    WAALS THE EXAMINATION OF THE MrIxepD Fatty AcIpDs.. About 20 grammes of the oil were saponified with an excess of 8 per cent alcoholic potash. The alcohol was evaporated off from the soap, the soap dissolved in water and the fatty acids liberated by acidifying with sulphuric acid. The liberated fatty acids were extracted with petroleum ether, the petroleum ether washed and finally dried by standing over anhydrous sodium sulphate. The dried petroleum ether solution of. the mixed fatty acids was filtered through a dry folded filter and preserved in a dry stoppered bottle in an ice chest. For the examination of the mixed fatty acids suitable quantities of this solution were transferred to a stoppered weighing flask; the flask was then closed with a rubber stopper fitted with two exit tubes, and the ether evaporated off in a current of CO, over a boiling water bath, the heating being continued under the suction pump for half an hour after the ether appeared to have boiled off. The flask was allowed to cool while still attached to the pump, and when cool was transferred to a desiccator and weighed after standing there about fifteen minutes. ‘The Determination of the Mean Molecular Weight and Neutralization Number. An amount of the petroleum ether solution equivalent to about 5 to 6 grammes of the fatty acids was evaporated as detailed above. The weighed fatty acids were dissolved in 50 c.c. of neutralized pure alcohol, and titrated with normal KOH, using phenolphthalein as indicator, until a slight pink colour persisted on stoppering the flask and shaking. Closely agreeing results were obtained thus :— Mat PU ae 5°542 grammes Witsot fatty acids’...° 2. «.. ..., O° Soo grammes No. of cc. of N/I KOH Routed.” TOM. No. of c.c. of N/I KOH required 19°05 c.c. Seo 2. ve. ree eee 2916 M.W.. Seip REPRE emmy wen Roe ee ee Neutralization No. .:. “...\\ 2. 2.5 192°4 Nentralizatton No. remy aga Ooo When nearing the end of the titration N/10 KOH was substituted for the normal solution. HEXABROMIDE TEST. A weighed quantity of the fatty acids, prepared as above, was dissolved in glacial acetic acid and cooled to below 5°C. in an ice bath. Bromine was then added from a finely pointed pipette until the yellow colour persisted. The flask was stoppered and allowed to stand in ice-water for three hours. The precipitate formed was filtered through a tared filter and washed with cooled ether. The precipitate dissolved completely. In order to make certain that the solubility of the precipitate was not partially due to the elevation of the temperature of the ether during the washing (the room temperature was about 30°C.) the ether solution was kept in a stoppered flask over night. The ether solution remained perfectly clear. The bromine titration was repeated on a fresh portion of the fatty acids, ether being added along with the glacial acetic acid before the addition of the bromine. No precipitate was formed on pro!onged standing in ice. - It was therefore, concluded that no linoleic acid was present. A further portion of the fatty acids was dissolved in glacial acetic acid and the bromination carried out as before. The brominated product was allowed to stand in the ice chest overnight. The flask was then warmed gently and stood on one side in order to allow the acetic acid to partially evaporate. Crystals in the form of small flakes were obtained. The crystals were removed from the mother liquor and recrystallized from glacial acetic acid. A rough melting-point determination was made after the first crystallization. The crystals melted between 112 and 113°C. After the recrystallization the melting-point was 113-113°5° C, This melting-point agrees closely with that given for linoleic acid, namely 114° C.
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