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is their total weight which is alone valuable, and to separate the three with accuracy is not easily effected. The first can, however, be isolated by the following process, the details of which have been worked out by Dr. Muter. The process depends upon the well-known fact that the oleate of lead, Pb2CH3O2, can be separated from plumbic palmitate, Pb2C16H3102, and plumbic stearate, Pb2CH3502, by taking advantage of the solubility of

the former in ether.

33

Muter's method of estimating oleic acid is as follows:-3 grms. of the fat are saponified by means of alcoholic potash. The potash is carefully neutralised by acetic acid,

250

-200

150

100

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using phenol-phthalein as an indicator. 200 cc. of water, to which 30 cc. of a 10 per cent. solution of plumbic acetate have been added, are boiled and, while boiling, the soap solution is slowly poured in with constant stirring. The whole is allowed to cool, the supernatant fluid poured off, and the lead soap washed with hot water by decantation. The precipitate is transferred to a stoppered bottle, 80 cc. of ether added, and, finally, the ether made up to 120 cc. The bottle is allowed to stand, with occasional shaking, for twelve hours, during which time the whole of the oleate will have dissolved. The ethereal solution is now filtered into a special tube (Fig. 38), the plumbic stearate, &c., being washed with ether until free from lead; this usually entails the use of about 100 cc. of ether. Hydrochloric acid, 25 per cent. strength, is poured in up to the first mark on the tube and the contents shaken. The liquids are now allowed to separate and the acid layer drawn off by means of the stop-cock. Water is then poured in and the contents again shaken, the water being removed as before, and the whole process repeated until the washings are free from acidity. The total volume of the ether is noted, a fractional portion run off into an Erlenmeyer's flask, and the ether distilled until a very little ether remains. It is not distilled completely, so as to avoid exposing the oleic acid to the air; 50 cc. of pure alcohol are added to this residue and the solution titrated by decinormal soda, using phenolphthalein as an indicator; each cc. of d. n. acid is equal to 0.0282 oleic acid. Having thus ascertained the strength of the remaining ethereal solution in the tube, the next step is to run off as many cc. as correspond to 0.5 grm. of oleic acid into a stoppered bottle

Fig. 38. Muter's olein tube.

of at least 350 cc. capacity; this flask is also provided with a doubly perforated cork carrying two tubes, one of which is connected with a carbon dioxide apparatus. The flask is placed in warm water and the gas passed through until all trace of ether has been removed. To the residue 50 cc. of Hubl (see p. 372) are added, the stopper inserted and allowed to stand the usual time and then titrated.*

E. Twitchell † has proved that 100 cc. of ether dissolves 0·015 of the lead salts of purified commercial stearic acid at 0°, and that this is an objection to Muter's process.

He proposes a modification of Jean's process as follows, of which he gives the following example :-A lard, the liquid fatty acid of which gave when tested by Muter's process an iodine absorption of 94.1 per cent., was treated as follows:-4 grms. of the fatty acids were dissolved in 50 cc. of 95 per cent. alcohol and 2.5 grms. of lead acetate in 20 cc. of the same alcohol added, both solutions being hot. The liquid with precipitate was put on one side for two hours, the temperature being strictly 15° for the last hour. A part of the whole was then filtered into a separating funnel, treated with ether and HCl, the acids washed and dried in a current of CO2, their iodine number obtained, and their percentage in the original solution determined. The precipitate was washed with 95 per cent. alcohol, decomposed with HCl, and the solid fatty acids dried and weighed; the results

were:

Per cent.
46.24

Solid fatty acids,
Liquid fatty acids, 51.82

Iodine number.

4.9 103:37

figures indicating that all the solid acids and part of the liquid had been precipitated.

If the iodine number of the total fatty acids is obtained the method of calculating results is as in the following example:4 grms. of fatty acids gave an iodine number of 62.57; the fatty acids from the filtrate at 15° gave an iodine number of 109-35 and were equal to 46.81 per cent.

The percentage of liquid acids multiplied by the iodine number of these acids and deducted from the iodine number of the total acids equals oleic acid. Dividing this by 0-9 gives the percentage of oleic acid precipitated with the solid acids. Thus 46.81 × 109.35 in the above case -51.1962.57 = 11.38. Divid

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100

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ing 11:38 by 0.9 12.64 in the precipitate, which, added to 46.81, represents the total liquid acids, 59.45.

*Analyst, April, 1889.

+Journ. Amer. Chem. Soc., 1895, xviii., 289 to 295; Analyst, July, 1895.

Mr. Wanklyn* has proposed estimating butyric acid derived from the formation of butyric ether in saponifying with alcoholic potash as follows:-The butter is clarified in the usual way, and then 5 grms. are weighed and taken for the analysis. The butter is placed in a small retort of about 200 cc. capacity, and fitted to a condenser. About 100 cc. of alcohol (specific gravity 0-838) is added to the butter in the retort, and then 0.5 grm. of solid potash is added. The retort is then gently heated, and the contents are distilled, the distillation being continued to dryness. The distillate is received in a bottle fitted with a stopper, and containing 40 cc. of accurately measured normal caustic potash or soda. When the distillation is complete, the stopper is placed in the bottle and the contents are shaken for a short time, and presently it will be found that the smell of butyric ether has vanished. Phenol-phthalein is now added to serve as an indicator, and the solution is titrated with normal sulphuric acid.

Good butters treated in this way yield from 2.8 to 34 per cent. of butyric acid as ether, while common butterine yields no trace.

Estimation of Glycerin.—The determination of glycerin in fats, hitherto most unsatisfactory, can now, thanks to the labours of Wanklyn, Fox, Benedikt, and Zsigmondy, be accomplished with fair accuracy.

The process is based upon the oxidation of the glycerin by alkaline permanganate, the consequent formation of oxalic acid, carbon dioxide, and water; and the estimation of the oxalic acid; whence the glycerin is calculated according to the formula

C3H8O3 + 302 = C2H2O4 + CO2 + 3H2O

100 parts of oxalic acid are equal to 102.2 parts of glycerin, or, since the oxalic acid is usually determined as lime carbonate, 100 parts of lime carbonate equal 92 parts of glycerin.

The details of the process are as follows:-10 grms. of the filtered butter-fat are saponified by a known volume of a solution of KHO in pure methyl alcohol,† or, better still, by a strong aqueous solution of potash. Mr. Allen has recommended saponifying the fat by means of 25 cc. of a 16 per cent. potash solution in a flask well stoppered down by means of an indiarubber stopper, heat being applied by means of a water-bath for

1884.

"The Analysis of Butter," by W. Fox and J. A. Wanklyn. Analyst,

Ethyl alcohol cannot be used, for on treatment with boiling alkaline permanganate, some oxalic acid is produced.

The

several hours, until from the homogeneous appearance of the liquid it is certain that saponification has been effected. The soap is now decomposed in the usual way by means of dilute sulphuric acid; the fatty acids separated; the filtrate made up to a known bulk, and a fractional part of this taken for oxidation. The oxidation is carried out as follows:-The solution is alkalised by potash solution containing at least 5 per cent. of free alkali, and then a 5 per cent. solution of potassic permanganate is added until the liquid is blackish in colour. solution is boiled, whereupon manganese oxide is precipitated, but the excess still tinges the liquid red, the red colour is discharged by adding sulphurous acid, the whole is then filtered and the precipitate well washed with boiling water. filtrate is boiled, and, while boiling, an excess of calcium acetate is added. The precipitate, consisting of an impure calcic oxalate, is collected, washed, dissolved in dilute sulphuric acid, and titrated with permanganate solution, or it may be ignited, and the resulting calcic carbonate dissolved in d. n. HCl, titrating back with a known volume of a solution of d. n. soda, and using orange methyl as an indicator. The best results are obtained when the amount of glycerin to be oxidised is from 3 to 5 grm., and the dilution not greater than 1 per cent.*

The

The Iodine Value.-Hubl (Dingl. polyt. Journ., 253, 281-295) has proposed a method which is of the greatest value in the examination of oils and fats generally, and can be applied to the analysis of butter. The melted fat is treated with an alcoholic solution of iodine in presence of an alcoholic solution of mercury bichloride; under these circumstances the unsaturated fatty acids or their glycerides absorb iodine in a regular and definite manner. With regard to butter, the only unsaturated fatty acid is oleic acid; hence the amount of iodine absorbed has relation to the content of olein or to oleic acid.

The following solutions are required :

*See papers by Messrs. Fox & Wanklyn, Chem. News, Jan. 8, 1886; by R. Benedikt & R. Zsigmondy, Analyst, x., 205; and by Allen, op. cit., xi., 52.

J. David, Compt. Rend. 94, 1477-1479, estimates glycerin as follows:100 grms. of the fat are melted, 65 grms. of barium hydrate are added, with brisk stirring; when most of the water has been expelled the heating is discontinued; 80 cc. of alcohol of 95° are poured on the mass, and the whole stirred; 1 litre of water is then added, and the mixture boiled for an hour. The barium soap remains insoluble, whilst the glycerol is dissolved by the water, which is freed from the excess of barium, reduced in volume by boiling, and finally evaporated in a vacuum at a low temperature. The glycerin might evidently be estimated by the oxalic method.“

(1) Solution of iodine and mercury bichloride. 25 grms. of iodine are dissolved in half a litre of alcohol of 95 per cent. strength, and 30 grms. of mercury bichloride are dissolved in another half litre of alcohol; the two solutions are now mixed, and allowed to stand, before standardising, for twenty-four hours. (2) Solution of sodium hyposulphite, 24 grms. to the litre. (3) 3·8747 grms. of potassium bichromate dissolved in a litre

of water.

(4) A solution of potassium iodide, 10 per cent. strength.

The thiosulphate is standardised as follows:-10 cc. of the potassium iodide solution are placed in a stoppered bottle, and 5 cc. of HCl added, together with 20 cc. of the bichromate solution. This will liberate exactly 0.2 grm. of iodine. The thiosulphate solution is run in carefully until a light straw colour only remains, then a little freshly-prepared starch solution is added, and the thiosulphate run in until the blue colour disappears. The number of cubic centimetres added will, of course, be equal to 0.2 grm. of iodine. The next thing is to titrate with the thiosulphate the solution of iodine and mercury bichloride. It is best to take for this purpose 25 cc. of the iodine solution, and to operate in a similar way—that is, running in the thiosulphate until there is only a pale straw colour, and finishing with starch as an indicator.

To obtain the iodine value of butter-fat, from 0.6 to 0.8 grm. of the clear melted fat is dropped on to the bottom of a tared flask, the flask and its contents weighed. The fat is dissolved in 10 cc. of chloroform, and 25 cc. of the iodine solution run into the flask, which should be at least 500 cc. in capacity; the flask is now stoppered and put in the dark for four hours. Should the iodine solution become decidedly pale at the end of two hours, a second 25 cc. of iodine is run in, for unless an excess is present, accurate results will not be obtained. At the end of the stated time, 20 cc. of the potassium iodide solution are added (or, should there be a red precipitate of mercury iodide, even more), the liquid diluted with from 300 to 500 cc. of water, well shaken and titrated with the thiosulphate, using as an indicator starch solution. The difference in the number of cubic centimetres of thiosulphate used on the original iodine solution, and that on the solution which has acted on the fat, gives the requisite data from which to calculate the amount of iodine the fat has absorbed ; this is calculated into per cent. of the fat.

Rowland Williams* has examined in this way thirty butters, the mean of which gave 35.34 per cent. of iodine absorbed, the extremes being 23.6 and 40-3. Seven margarines gave from 62.29 to 75.22 per cent. Analyst, June, 1894.

*

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