Place the combined kerosene filtrate and kerosene washings from the insoluble impurities determination in a platinum dish. Place in this an ashless filter paper folded in the form of a cone, apex up. Light the apex of the cone, whereupon the bulk of the kerosene burns quietly. Ash the residue in a m.u.f.fle, to constant weight, taking care that the decomposition of alkaline earth carbonates is complete, and report the result as SOLUBLE MINERAL MATTER.[29] When the percentage of soluble mineral matter amounts to more than 0.1 per cent, multiply the percentage by 10 and add this amount to the percentage of free fatty acids as determined.[30]

FREE FATTY ACIDS.

The ALCOHOL[31] used shall be approximately 95 per cent ethyl alcohol, freshly distilled from sodium hydroxide, which with phenolphthalein gives a definite and distinct end-point.

DETERMINATION--Weigh 1 to 15 g. of the prepared sample into an Erlenmeyer flask, using the smaller quant.i.ty in the case of dark-colored, high acid fats. Add 50 to 100 cc. hot, neutral alcohol, and t.i.trate with _N_/2, _N_/4 or _N_/10 sodium hydroxide depending on the fatty acid content, using phenolphthalein as indicator. Calculate to oleic acid, except that in the case of palm oil the results may also be expressed in terms of palmitic acid, clearly indicating the two methods of calculation in the report. In the case of coconut and palm kernel oils, calculate to and report in terms of lauric acid in addition to oleic acid, clearly indicating the two methods of calculation in the report. In the case of fats or greases containing more than 0.1 per cent of soluble mineral matter, add to the percentages of free fatty acids as determined 10 times the percentage of bases in the soluble mineral matter as determined.[30] This addition gives the equivalent of fatty acids combined with the soluble mineral matter.

t.i.tER.

STANDARD THERMOMETER--The thermometer is graduated at zero and in tenth degrees from 10 C. to 65 C., with one auxiliary reservoir at the upper end and another between the zero mark and the 10 mark. The cavity in the capillary tube between the zero mark and the 10 mark is at least 1 cm. below the 10 mark, the 10 mark is about 3 or 4 cm. above the bulb, the length of the thermometer being about 37 cm. over all. The thermometer has been annealed for 75 hrs. at 450 C. and the bulb is of Jena normal 16"' gla.s.s, or its equivalent, moderately thin, so that the thermometer will be quick-acting. The bulb is about 3 cm. long and 6 mm.

in diameter. The stem of the thermometer is 6 mm. in diameter and made of the best thermometer tubing, with scale etched on the stem, the graduation is clear-cut and distinct, but quite fine. The thermometer must be certified by the U. S. Bureau of Standards.

GLYCEROL CAUSTIC SOLUTION--Dissolve 250 g. pota.s.sium hydroxide in 1900 cc. dynamite glycerin with the aid of heat.

DETERMINATION--Heat 75 cc. of the glycerol-caustic solution to 150 C.

and add 50 g. of the melted fat. Stir the mixture well and continue heating until the melt is h.o.m.ogeneous, at no time allowing the temperature to exceed 150 C. Allow to cool somewhat and carefully add 50 cc. 30 per cent sulfuric acid. Now add hot water and heat until the fatty acids separate out perfectly clear. Draw off the acid water and wash the fatty acids with hot water until free from mineral acid, then filter and heat to 130 C. as rapidly as possible while stirring.

Transfer the fatty acids, when cooled somewhat, to a 1-in. by 4-in.

t.i.ter tube, placed in a 16-oz. salt-mouth bottle of clear gla.s.s, fitted with a cork that is perforated so as to hold the tube rigidly when in position. Suspend the t.i.ter thermometer so that it can be used as a stirrer and stir the fatty acids slowly (about 100 revolutions per minute) until the mercury remains stationary for 30 seconds. Allow the thermometer to hang quietly with the bulb in the center of the tube and report the highest point to which the mercury rises as the t.i.ter of the fatty acids. The t.i.ter should be made at about 20 C. for all fats having a t.i.ter above 30 C. and at 10 C. below the t.i.ter for all other fats. Any convenient means may be used for obtaining a temperature of 10 below the t.i.ter of the various fats. The committee recommends first of all a chill room for this purpose; second, an artificially chilled small chamber with gla.s.s window; third, immersion of the salt-mouth bottle in water or other liquid of the desired temperature.

UNSAPONIFIABLE MATTER.

EXTRACTION CYLINDER--The cylinder shall be gla.s.s-stoppered, graduated at 40 cc., 80 cc. and 130 cc., and of the following dimensions: diameter about 1-3/8 in., height about 12 in.

PETROLEUM ETHER--Redistilled petroleum ether, boiling under 75 C., shall be used. A blank must be made by evaporating 250 cc. with about 0.25 g. of stearine or other hard fat (previously brought to constant weight by heating) and drying as in the actual determination. The blank must not exceed a few milligrams.

DETERMINATION--Weigh 5 g. (0.20 g.) of the prepared sample into a 200-cc. Erlenmeyer flask, add 30 cc. of redistilled 95 per cent (approximately) ethyl alcohol and 5 cc. of 50 per cent aqueous pota.s.sium hydroxide, and boil the mixture for one hour under a reflux condenser.

Transfer to the extraction cylinder and wash to the 40-cc. mark with redistilled 95 per cent ethyl alcohol. Complete the transfer, first with warm, then with cold water, till the total volume amounts to 80 cc. Cool the cylinder and contents to room temperature and add 50 cc. of petroleum ether. Shake _vigorously_ for one minute and allow to settle until both layers are clear, when the volume of the upper layer should be about 40 cc. Draw off the petroleum ether layer as closely as possible by means of a slender gla.s.s siphon into a separatory funnel of 500 cc. capacity. Repeat extraction at least four more times, using 50 cc. of petroleum ether each time. More extractions than five are necessary where the unsaponifiable matter runs high, say over 5 per cent, and also in some cases where it is lower than 5 per cent, but is extracted with difficulty. Wash the combined extracts in a separatory funnel three times with 25-cc. portions of 10 per cent alcohol, shaking vigorously each time. Transfer the petroleum ether extract to a wide-mouth tared flask or beaker, and evaporate the petroleum ether on a steam bath in an air current. Dry as in the method for MOISTURE AND VOLATILE MATTER. Any blank must be deducted from the weight before calculating unsaponifiable matter. Test the final residue for solubility in 50 cc. petroleum ether at room temperature. Filter and wash free from the insoluble residue, if any, evaporate and dry in the same manner as before. The Committee wishes to emphasize the necessity of thorough and vigorous shaking in order to secure accurate results. The two phases must be brought into the most intimate contact possible, otherwise low and disagreeing results may be obtained.

IODINE NUMBER--WIJS METHOD.

PREPARATION OF REAGENTS--_Wijs Iodine Solution_--Dissolve 13.0 g. of resublimed iodine in one liter of C. P. glacial acetic acid and pa.s.s in washed and dried chlorine gas until the original thiosulfate t.i.tration of the solution is not quite doubled. The solution is then preserved in amber gla.s.s-stoppered bottles, sealed with paraffin until ready for use.

Mark the date on which the solution is prepared on the bottle or bottles and do not use Wijs solution which is more than 30 days old.

There should be no more than a slight excess of iodine, and no excess of chlorine. When the solution is made from iodine and chlorine, this point can be ascertained by not quite doubling the t.i.tration.[32]

The glacial acetic acid used for preparation of the Wijs solution should be of 99.0 to 99.5 per cent strength. In case of glacial acetic acids of somewhat lower strength, the Committee recommends freezing and centrifuging or draining as a means of purification.

_N_/10 _Sodium Thiosulfate Solution_--Dissolve 24.8 g. of C. P. sodium thiosulfate in recently boiled distilled water and dilute with the same to one liter at the temperature at which the t.i.trations are to be made.

_Starch Paste_--Boil 1 g. of starch in 200 cc. of distilled water for 10 min. and cool to room temperature.

An improved starch solution may be prepared by autoclaving 2 g. of starch and 6 g. of boric acid dissolved in 200 cc. water at 15 lbs.

pressure for 15 min. This solution has good keeping qualities.

_Pota.s.sium Iodide Solution_--Dissolve 150 g. of pota.s.sium iodide in water and make up to one liter.

_N_/10 _Pota.s.sium Bichromate_--Dissolve 4.903 g. of C. P. pota.s.sium bichromate in water and make the volume up to one liter at the temperature at which t.i.trations are to be made.

The Committee calls attention to the fact that occasionally pota.s.sium bichromate is found containing sodium bichromate, although this is of rare occurrence. If the a.n.a.lyst suspects that he is dealing with an impure pota.s.sium bichromate, the purity can be ascertained by t.i.tration against re-sublimed iodine. However, this is unnecessary in the great majority of cases.

_Standardization of the Sodium Thiosulfate Solution_--Place 40 cc. of the pota.s.sium bichromate solution, to which has been added 10 cc. of the solution of pota.s.sium iodide, in a gla.s.s-stoppered flask. Add to this 5 cc. of strong hydro-chloric acid. Dilute with 100 cc. of water, and allow the _N_/10 sodium thiosulfate to flow slowly into the flask until the yellow color of the liquid has almost disappeared. Add a few drops of the starch paste, and with constant shaking continue to add the _N_/10 sodium thiosulfate solution until the blue color just disappears.

DETERMINATION--Weigh accurately from 0.10 to 0.50 g. (depending on the iodine number) of the melted and filtered sample into a clean, dry, 16-oz. gla.s.s-stoppered bottle containing 15-20 cc. of carbon tetrachloride or chloroform. Add 25 cc. of iodine solution from a pipette, allowing to drain for a definite time. The excess of iodine should be from 50 per cent to 60 per cent of the amount added, that is, from 100 per cent to 150 per cent of the amount absorbed. Moisten the stopper with a 15 per cent pota.s.sium iodide solution to prevent loss of iodine or chlorine but guard against an amount sufficient to run down inside the bottle. Let the bottle stand in a dark place for 1/2 hr. at a uniform temperature. At the end of that time add 20 cc. of 15 per cent pota.s.sium iodide solution and 100 cc. of distilled water. t.i.trate the iodine with _N_/10 sodium thiosulfate solution which is added gradually, with constant shaking, until the yellow color of the solution has almost disappeared. Add a few drops of starch paste and continue t.i.tration until the blue color has entirely disappeared. Toward the end of the reaction stopper the bottle and shake violently so that any iodine remaining in solution in the tetrachloride or chloroform may be taken up by the pota.s.sium iodide solution. Conduct two determinations on blanks which must be run in the same manner as the sample except that no fat is used in the blanks. Slight variations in temperature quite appreciably affect the t.i.ter of the iodine solution, as acetic acid has a high coefficient of expansion. It is, therefore, essential that the blanks and determinations on the sample be made at the same time. The number of cc. of standard thiosulfate solution required by the blank, less the amount used in the determination, gives the thiosulfate equivalent of the iodine absorbed by the amount of sample used in the determination.

Calculate to centigrams of iodine absorbed by 1 g. of sample (= per cent iodine absorbed).

DETERMINATION, TUNG OIL--Tung oil shows an erratic behavior with most iodine reagents and this is particularly noticeable in the case of the Ha.n.u.s reagent which is entirely unsuitable for determining the iodine number of this oil since extremely high and irregular results are obtained. The Hubl solution shows a progressive absorption up to 24 hrs.

and probably for a longer time but the period required is entirely too long for a chemical determination. The Wijs solution gives good results if the following precautions are observed:

Weigh out 0.15 0.05 g., use an excess of 55 3 per cent Wijs solution. Conduct the absorption at a temperature of 20-25 C. for 1 hr.

In other respects follow the instructions detailed above.

SAPONIFICATION NUMBER (KOETTSTORFER NUMBER).

PREPARATION OF REAGENTS. _N/2 Hydrochloric Acid_--Carefully standardized.

_Alcoholic Pota.s.sium Hydroxide Solution_--Dissolve 40 g. of pure pota.s.sium hydroxide in one liter of 95 per cent redistilled alcohol (by volume). The alcohol should be redistilled from pota.s.sium hydroxide over which it has been standing for some time, or with which it has been boiled for some time, using a reflux condenser. The solution must be clear and the pota.s.sium hydroxide free from carbonates.

DETERMINATION--Weigh accurate about 5 g. of the filtered sample into a 250 to 300 cc. Erlenmeyer flask. Pipette 50 cc. of the alcoholic pota.s.sium hydroxide solution into the flask, allowing the pipette to drain for a definite time. Connect the flask with an air condenser and boil until the fat is completely saponified (about 30 minutes). Cool and t.i.trate with the _N_/2 hydrochloric acid, using phenolphthalein as an indicator. Calculate the Koettstorfer number (mg. of pota.s.sium hydroxide required to saponify 1 g. of fat). Conduct 2 or 3 blank determinations, using the same pipette and draining for the same length of time as above.

MELTING POINT.

APPARATUS--_Capillary tubes_ made from 5 mm. inside diameter thin-walled gla.s.s tubing drawn out to 1 mm. inside diameter. Length of capillary part of tubes to be about 5 cm. Length of tube over all 8 cm.

_Standard thermometer_ graduated in tenths of a degree.

_600 cc. beaker._

DETERMINATION--The sample should be clear when melted and entirely free from moisture, or incorrect results will be obtained.

Melt and thoroughly mix the sample. Dip three of the capillary tubes above described in the oil so that the fat in the tube stands about 1 cm. in height. Now fuse the capillary end carefully by means of a small blast flame and allow to cool. These tubes are placed in a refrigerator over night at a temperature of from 40 to 50 F. They are then fastened by means of a rubber band or other suitable means to the bulb of a thermometer graduated in tenths of a degree. The thermometer is suspended in a beaker of water (which is agitated by air or other suitable means) so that the bottom of the bulb of the thermometer is immersed to a depth of about 3 cm. The temperature of the water is increased gradually at the rate of about 1 per minute.

The point at which the sample becomes opalescent is first noted and the heating continued until the contents of the tube becomes uniformly transparent. The latter temperature is reported as the melting point.

Before finally melting to a perfectly clear fluid, the sample becomes opalescent and usually appears clear at the top, bottom, and sides before becoming clear at the center. The heating is continued until the contents of the tube become uniformly clear and transparent. This temperature is reported as the melting point.[33] It is usually only a fraction of a degree above the opalescent point noted. The thermometer should be read to the nearest 1/2 C., and in addition this temperature may be reported to the nearest degree Fahrenheit if desired.

CLOUD TEST.

PRECAUTIONS--(1) The oil must be perfectly dry, because the presence of moisture will produce a turbidity before the clouding point is reached.

(2) The oil must be heated to 150 C. over a free flame, immediately before making the test.