(1) Determine the apparent percentage of glycerol in the sample by the acetin process as described. The result will include acetylizable impurities if any are present.
(2) Determine the total residue at 160° C.
(3) Determine the acetin value of the residue at (2) in terms of glycerol.
(4) Deduct the result found at (3) from the percentage obtained at (1) and report this corrected figure asglycerol. If volatile acetylizable impurities are present these are included in this figure.
Trimethyleneglycol is more volatile than glycerine and can therefore be concentrated by fractional distillation. An approximation to the quantity can be obtained from the spread between the acetin and bichromate results on such distillates. The spread multiplied by 1.736 will give the glycol.
(A)Pure potassium bichromatepowdered and dried in air free from dust or organic vapors, at 110° to 120° C. This is taken as the standard.
(B)Dilute Bichromate Solution.—7.4564 grams of the above bichromate are dissolved in distilled water and the solution made up to one liter at 15.5° C.
(C)Ferrous Ammonium Sulphate.—It is never safe to assume this salt to be constant in composition and it must be standardized against the bichromate as follows: dissolve 3.7282 grams of bichromate (A) in 50 cc. of water. Add 50 cc. of 50 per cent. sulphuric acid (by volume), and to the cold undiluted solution add from a weighing bottle a moderate excess of the ferrous ammonium sulphate, and titrate back with the dilute bichromate (B). Calculate the value of the ferrous salt in terms of bichromate.
(D)Silver Carbonate.—This is prepared as required for each test from 140 cc. of 0.5 per cent. silver sulphate solution by precipitation, with about 4.9 cc.N/1 sodium carbonate solution (a little less than the calculated quantity ofN/1 sodium carbonate should be used as an excess to prevent rapid settling). Settle, decant and wash one by decantation.
(E)Subacetate of Lead.—Boil a 10 per cent. solutionof pure lead acetate with an excess of litharge for one hour, keeping the volume constant, and filter while hot. Disregard any precipitate which subsequently forms. Preserve out of contact with carbon dioxide.
(F)Potassium Ferricyanide.—A very dilute, freshly prepared solution containing about 0.1 per cent.
Weigh 20 grams of the glycerine, dilute to 250 cc. and take 25 cc. Add the silver carbonate, allow to stand, with occasional agitation, for about 10 minutes, and add a slight excess (about 5 cc. in most cases) of the basic lead acetate (E), allow to stand a few minutes, dilute with distilled water to 100 cc., and then add 0.15 cc. to compensate for the volume of the precipitate, mix thoroughly, filter through an air-dry filter into a suitable narrow-mouthed vessel, rejecting the first 10 cc., and return the filtrate if not clear and bright. Test a portion of the filtrate with a little basic lead acetate, which should produce no further precipitate (in the great majority of cases 5 cc. are ample, but occasionally a crude will be found requiring more, and in this case another aliquot of 25 cc. of the dilute glycerine should be taken and purified with 6 cc. of the basic acetate). Care must be taken to avoid a marked excess of basic acetate.
Measure off 25 cc. of the clear filtrate into a flask or beaker (previously cleaned with potassium bichromate and sulphuric acid). Add 12 drops of sulphuric acid (1: 4) to precipitate the small excess of lead as sulphate. Add 3.7282 grams of the powdered potassium bichromate (A). Rinse down the bichromate with 25 cc. of water and let stand with occasional shaking until all the bichromate is dissolved (no reduction will take place in the cold).
Now add 50 cc. of 50 per cent. sulphuric acid (by volume)and immerse the vessel in boiling water for two hours and keep protected from dust and organic vapors, such as alcohol, till the titration is completed. Add from a weighing bottle a slight excess of the ferrous ammonium sulphate (C), making spot tests on a porcelain plate with the potassium ferricyanide (F). Titrate back with the dilute bichromate. From the amount of bichromate reduced calculate the percentage of glycerol.
1 gram glycerol = 7.4564 grams bichromate.
1 gram bichromate = 0.13411 gram glycerol.
The percentage of glycerol obtained above includes any oxidizable impurities present after the purification. A correction for the non-volatile impurities may be made by running a bichromate test on the residue at 160° C.
(1) It is important that the concentration of acid in the oxidation mixture and the time of oxidation should be strictly adhered to.
(2) Before the bichromate is added to the glycerine solution it is essential that the slight excess of lead be precipitated with sulphuric acid, as stipulated.
(3) For crudes practically free from chlorides the quantity of silver carbonate may be reduced to one-fifth and the basic lead acetate to 0.5 cc.
(4) It is sometimes advisable to add a little potassium sulphate to insure a clear filtrate.
The usual method of sampling crude glycerine hitherto has been by means of a glass tube, which is slowly lowered into the drum with the object of taking as nearly as possible a vertical section of the glycerine contained in thedrum. This method has been found unsatisfactory, owing to the fact that in cold climates glycerine runs into the tube very slowly, so that, owing to the time occupied, it is impossible to take a complete section of the crude. Another objection to the glass tube is that it fails to take anything approaching a correct proportion of any settled salt contained in the drum.
The sampler which is illustrated herewith has been devised with the object of overcoming the objections to the glass tube as far as possible. It consists of two brass tubes, one fitting closely inside the other. A number of ports are cut out in each tube in such a way that when the ports are opened a continuous slot is formed which enables a complete section to be taken throughout the entire length of the drum. By this arrangement the glycerine fills into the sampler almost instantaneously. There are a number of ports cut at the bottom of the sampler which render it possible to take a proportion of the salt at the bottom of the drum. The instrument is so constructed that all the ports, including the bottom ones, can be closed simultaneously by the simple action of turning the handle at the top; a pointer is arranged which indicates on a dial when the sampler is open or closed. In samplers of larger section (1 in.) it is possible to arrange a third motion whereby the bottom ports only are open for emptying, but in samplers of smaller dimensions (5/8 in.) this third motion must be dispensed with, otherwise the dimensions of the ports have to be so small that the sampler would not be efficient.
In using the sampler it is introduced into the drum with the ports closed, and when it has touched the bottom, the ports are opened for a second or two, then closed and withdrawn, and the sample discharged into the receiving vessel by opening the ports. When the drum contains salt whichhas deposited, the ports must be opened before the sampler is pushed through the salt, thus enabling a portion to be included in the sample. It is, however, almost impossible to obtain a correct proportion of salt after it has settled in the drum and it is therefore recommended that the drum be sampled before any salt has deposited. A sampler 1 in. in diameter withdraws approximately 10 oz. from a 110-gal. drum. A sampler 5/8 in. in diameter will withdraw about 5 oz.
FOOTNOTES:[13]Zeit. Angew. Chem. 19, 385 (1906).[14]Zeit. Angew. Chem. 27, 11-20 (1914).[15]Bull. 107, Bur. Chem. U. S. Dept. Agriculture.[16]Richards and Gies, Am. J. Physiol. (1902) 7, 129.[17]Seifensieder Ztg. (1913) No. 46.[18]Bull 107, Bur. Chem. U. S. Dept. Agriculture.[19]Carbon is readily burned off completely, without loss of chlorides, in a gas-heated muffle furnace adjusted to a dull red heat.[20]An electric oven suitable for this work, which is readily adjusted to 160 degs. C., has been made for Mr. Low and the chairman, by the Apparatus and Specialty Company, Lansing, Mich. Its size is 9-1/2 × 10 × 16 inches, and capacity 8 Petrie dishes. It gives a strong draft at constant temperature.[21]A precipitate at this point is an indication of the presence of iron or alumina, and high results will be obtained unless a correction is made as described below.
[13]Zeit. Angew. Chem. 19, 385 (1906).
[13]Zeit. Angew. Chem. 19, 385 (1906).
[14]Zeit. Angew. Chem. 27, 11-20 (1914).
[14]Zeit. Angew. Chem. 27, 11-20 (1914).
[15]Bull. 107, Bur. Chem. U. S. Dept. Agriculture.
[15]Bull. 107, Bur. Chem. U. S. Dept. Agriculture.
[16]Richards and Gies, Am. J. Physiol. (1902) 7, 129.
[16]Richards and Gies, Am. J. Physiol. (1902) 7, 129.
[17]Seifensieder Ztg. (1913) No. 46.
[17]Seifensieder Ztg. (1913) No. 46.
[18]Bull 107, Bur. Chem. U. S. Dept. Agriculture.
[18]Bull 107, Bur. Chem. U. S. Dept. Agriculture.
[19]Carbon is readily burned off completely, without loss of chlorides, in a gas-heated muffle furnace adjusted to a dull red heat.
[19]Carbon is readily burned off completely, without loss of chlorides, in a gas-heated muffle furnace adjusted to a dull red heat.
[20]An electric oven suitable for this work, which is readily adjusted to 160 degs. C., has been made for Mr. Low and the chairman, by the Apparatus and Specialty Company, Lansing, Mich. Its size is 9-1/2 × 10 × 16 inches, and capacity 8 Petrie dishes. It gives a strong draft at constant temperature.
[20]An electric oven suitable for this work, which is readily adjusted to 160 degs. C., has been made for Mr. Low and the chairman, by the Apparatus and Specialty Company, Lansing, Mich. Its size is 9-1/2 × 10 × 16 inches, and capacity 8 Petrie dishes. It gives a strong draft at constant temperature.
[21]A precipitate at this point is an indication of the presence of iron or alumina, and high results will be obtained unless a correction is made as described below.
[21]A precipitate at this point is an indication of the presence of iron or alumina, and high results will be obtained unless a correction is made as described below.
The following report of theCommittee on Analysis of Commercial Fats and Oilsof theDivision of Industrial Chemists and Chemical Engineersof the American Chemical Society was adopted April 14, 1919, by unanimous vote:
W. D. Richardson,Chairman, Swift and Co., Chicago, Ill.
R. W. Bailey, Stillwell and Gladding, New York City.
W. J. Gascoyne, W. J. Gascoyne and Co., Baltimore, Md.
I. Katz,[A] Wilson and Co., Chicago, Ill.
A. Lowenstein,[A] Morris and Co., Chicago, Ill.
H. J. Morrison, Proctor and Gamble Co., Ivorydale, Ohio.
J. R. Powell, Armour Soap Works, Chicago, Ill.
R. J. Quinn,[A] Midland Chemical Co., Argo, Ill.
Paul Rudnick, Armour and Co., Chicago, Ill.
L. M. Tolman, Wilson and Co., Chicago, Ill.
E. Twitchell,[A] Emery Candle Co., Cincinnati, Ohio.
J. J. Vollertsen, Morris and Co., Chicago, Ill.
[Note A: Resigned.]
These methods are intended to aid in determining the commercial valuation of fats and fatty oils in their purchase and sale, based on the fundamental assumption commonly recognized in the trade, namely, that the product is true to name and is not adulterated. For methods for determining the identity of oils and fats, the absence of adulterants therein and for specific tests used in particular industries, the chemist is referred to standard works on the analysis of fats and oils.
The methods are applicable in commercial transactions involving fats and fatty oils used in the soap, candle and tanning industries, to edible fats and oils and to fats and fatty oils intended for lubricating and burning purposes. The methods are applicable to the raw oils used in the varnish and paint industry with the exceptions noted under limitations, but special methods have not been included.
The methods have not been developed with special reference to waxes (beeswax, carnauba wax, wool wax, etc.) although some of them may be found applicable to these substances. The Committee considers the Wijs method superior to the Hanus method for the determination of iodine number of linseed oil as well as other oils, although the Hanus method has been considered standard for this work for some time and has been adopted by the American Society for Testing Materials and in various specifications. It has been customary to use the Hübl method for the determination of iodine value of tung oil (China wood oil) but the Committee's work indicates that the Wijs method is satisfactory for this determination.
1.Sampling While Loading—Sample shall be taken at discharge of pipe where it enters tank car dome. The total sample taken shall be not less than 50 lbs. and shall be a composite of small samples of about 1 pound each, taken at regular intervals during the entire period of loading.
The sample thus obtained is thoroughly mixed and uniform 3-lb. portions placed in air-tight 3-lb. metal containers. At least three such samples shall be put up, one for the buyer, one for the seller, and the third to be sent to areferee chemist in case of dispute. All samples are to be promptly and correctly labeled and sealed.
2.Sampling from Car on Track[23]—(a)When contents are solid.[24]In this case the sample is taken by means of a large tryer measuring about 2 in. across and about 1-1/2 times the depth of the car in length. Several tryerfuls are taken vertically and obliquely toward the ends of the car until 50 lbs. are accumulated, when the sample is softened, mixed and handled as under (1). In case the contents of the tank car have assumed a very hard condition, as in Winter weather, so that it is impossible to insert the tryer, and it becomes necessary to soften the contents of the car by means of the closed steam coil (in nearly all tank cars the closed steam coil leaks) or by means of open steam in order to draw a proper sample, suitable arrangements must be made between buyer and seller for the sampling of the car after it is sufficiently softened, due consideration being given to the possible presence of water in the material in the car as received and also to the possible addition of water during the steaming. The Committee knows of no direct method for sampling a hard-frozen tank car of tallow in a satisfactory manner.
(b)When contents are liquid.The sample taken is to be a 50-lb. composite made up of numerous small samples taken from the top, bottom and intermediate points by means of a bottle or metal container with removable stopper or top. This device attached to a suitable pole is lowered to the various desired depths, when the stopper or top is removed and the container allowed to fill. The 50-lb. sample thus obtained is handled as under (1).
In place of the device described above, any sampler capable of taking a sample from the top, bottom, and center, or from a section through car, may be used.
(c)When contents are in semi-solid condition, or when stearine has separated from liquid portions.In this case, a combination of (a) and (b) may be used or by agreement of the parties the whole may be melted and procedure (b) followed.
All packages shall be sampled, unless by special agreement the parties arrange to sample a lesser number; but in any case not less than 10 per cent of the total number shall be sampled. The total sample taken shall be at least 20 lbs. in weight for each 100 barrels, or equivalent.
1.Barrels, Tierces and Casks—(a)When contents are solid.The small samples shall be taken by a tryer through the bunghole or through a special hole bored in the head or side for the purpose, with a 1-in. or larger auger. Care should be taken to avoid and eliminate all borings and chips from the sample. The tryer is inserted in such a way as to reach the head of the barrel, tierce, or cask. The large sample is softened, mixed and handled according totank cars(1).
(b)When contents are liquid.In this case use is made of a glass tube with constricted lower end. This is inserted slowly and allowed to fill with the liquid, when the upper end is closed and the tube withdrawn, the contents being allowed to drain into the sample container. After the entire sample is taken it is thoroughly mixed and handled according totank cars(1).
(c)When contents are semi-solid.In this case the tryer or a glass tube with larger outlet is used, depending on the degree of fluidity.
(d)Very hard materials, such as natural and artificial stearines.By preference the barrels are stripped and samples obtained by breaking up contents of at least 10 per cent of the packages. This procedure is to be followed also in the case of cakes shipped in sacks. When shipped in the form of small pieces in sacks they can be sampled by grab sampling and quartering. In all cases the final procedure is as outlined undertank cars(1).
2.Drums—Samples are to be taken as under (1), use being made of the bunghole. The tryer or tube should be sufficiently long to reach to the ends of the drum.
3.Other Packages—Tubs, pails and other small packages not mentioned above are to be sampled by tryer or tube (depending on fluidity) as outlined above, the tryer or tube being inserted diagonally whenever possible.
4.Mixed Lots and Packages—When lots of tallow or other fats are received in packages of various shapes and sizes, and especially wherein the fat itself is of variable composition, such must be left to the judgment of the sampler. If variable, the contents of each package should be mixed as thoroughly as possible and the amount of the individual samples taken made proportional to the sizes of the packages.
The sample must be representative and at least three pounds in weight and taken in accordance with thestandard methods for the sampling of commercial fats and oils. It must be kept in an air-tight container, in a dark, cool place.
Soften the sample if necessary by means of a gentle heat, taking care not to melt it. When sufficiently softened, mix the sample thoroughly by means of a mechanical egg beater or other equally effective mechanical mixer.
Apparatus:Vacuum Oven—The Committee Standard Oven.
Description—The Standard F. A. C. Vacuum Oven has been designed with the idea of affording a simple and compact vacuum oven which will give as uniform temperatures as possible on the shelf. As the figure shows, it consists of an iron casting of rectangular sections with hinged front door made tight by means of a gasket and which can be lowered on opening the oven so as to form a shelf on which samples may be rested. The oven contains but one shelf which is heated from above as well as below by means of resistance coils. Several thermometer holes are provided in order to ascertain definitely the temperature at different points on the shelf. In a vacuum oven where the heating is done almost entirely by radiation it is difficult to maintain uniform temperatures at all points, but the F. A. C. oven accomplishes this rather better than most vacuum ovens. Larger ovens containing more than one shelf have been tried by the Committee, but have been found to be lacking in temperature uniformity and means of control. The entire oven is supported by means of a 4-in. standard pipe which screws into the base of the oven and which in turn is supported by being screwed into a blind flange of suitable diameter which rests on the floor or work table.
Moisture Dish—A shallow, glass dish, lipped, beaker form, approximately 6 to 7 cm. diameter and 4 cm. deep, shall be standard.
Determination—Weigh out 5 grams (= 0.2 g. of the prepared sample) into a moisture dish. Dry to constant weight invacuoat a uniform temperature, not less than 15° C. nor more than 20° C. above the boiling point of water at the working pressure, which must not exceed 100 mm. of mercury.[25]Constant weight is attained when successive dryings for 1-hr. periods show an additional loss of not more that 0.05 per cent. Report loss in weight asmoisture and volatile matter.[26]
Standard Vacuum OvenStandard Vacuum Oven
The vacuum-oven method cannot be considered accurate in the case of fats of the coconut oil group containing free acid and the Committee recommends that it be used only for oils of this group when they contain less than 1 per cent free acid. In the case of oils of this group containing more than 1 per cent free acid, recourse should be had temporarily to the routine control method for moisture and volatile matter[27]until the Committee develops a more satisfactory method.
The air-oven method cannot be considered even approximately accurate in the case of the drying and semi-drying oils and those of the coconut oil group. Therefore, in the case of such oils as cottonseed oil, maize oil (corn oil), soy bean oil, linseed oil, coconut oil, palm kernel oil, etc., the vacuum-oven method should always be used, except in the case of fats of the coconut group containing more than 1 per cent free acid, as noted above.
Dissolve the residue from the moisture and volatile matter determination by heating it on a steam bath with 50 cc. of kerosene. Filter the solution through a Gooch crucible properly prepared with asbestos,[28]wash the insoluble matter five times with 10-cc. portions of hot kerosene, and finally wash the residual kerosene out thoroughly with petroleum ether. Dry the crucible and contents to constant weight, as in the determination of moisture and volatile matter and report results asinsoluble impurities.
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 muffle, to constant weight, taking care that the decomposition of alkaline earth carbonates is complete, and report the result assoluble 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]
Thealcohol[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 quantity in the case of dark-colored, high acid fats. Add 50 to 100 cc. hot, neutral alcohol, and titrate withN/2,N/4 orN/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.
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''' glass, 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. potassium 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 homogeneous, 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. titer tube, placed in a 16-oz. salt-mouth bottle of clear glass, fitted with a cork that is perforated so as to hold the tube rigidly when in position. Suspend the titer thermometer so that it can beused 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 titer of the fatty acids. The titer should be made at about 20° C. for all fats having a titer above 30° C. and at 10° C. below the titer for all other fats. Any convenient means may be used for obtaining a temperature of 10° below the titer of the various fats. The committee recommends first of all a chill room for this purpose; second, an artificially chilled small chamber with glass window; third, immersion of the salt-mouth bottle in water or other liquid of the desired temperature.
Extraction Cylinder—The cylinder shall be glass-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 potassium 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 roomtemperature and add 50 cc. of petroleum ether. Shakevigorouslyfor 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 glass 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 formoisture 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.
Preparation of Reagents—Wijs Iodine Solution—Dissolve 13.0 g. of resublimed iodine in one liter of C. P. glacial acetic acid and pass in washed and dried chlorine gas until the original thiosulfate titration of the solution is not quite doubled. The solution is then preserved in amber glass-stoppered bottles, sealed with paraffin until ready for use.
Mark the date on which the solution is prepared on thebottle 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 titration.[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/10Sodium 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 titrations 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.
Potassium Iodide Solution—Dissolve 150 g. of potassium iodide in water and make up to one liter.
N/10Potassium Bichromate—Dissolve 4.903 g. of C. P. potassium bichromate in water and make the volume up to one liter at the temperature at which titrations are to be made.
The Committee calls attention to the fact that occasionally potassium bichromate is found containing sodium bichromate, although this is of rare occurrence. If the analyst suspects that he is dealing with an impure potassium bichromate, the purity can be ascertained by titration 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 potassium bichromate solution, to which has been added 10 cc. of the solution of potassium iodide, in a glass-stoppered flask. Add to this 5 cc. of strong hydro-chloric acid. Dilute with 100 cc. of water, and allow theN/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 theN/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. glass-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 potassium iodide solution to prevent loss of iodine or chlorine but guard against an amount sufficient to run down inside the bottle. Letthe 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 potassium iodide solution and 100 cc. of distilled water. Titrate the iodine withN/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 titration 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 potassium 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 titer 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 Hanus reagent which is entirely unsuitable for determining the iodine number of this oil since extremely high and irregular results are obtained. The Hübl 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 percent Wijs solution. Conduct the absorption at a temperature of 20-25° C. for 1 hr. In other respects follow the instructions detailed above.
Preparation of Reagents.N/2 Hydrochloric Acid—Carefully standardized.
Alcoholic Potassium Hydroxide Solution—Dissolve 40 g. of pure potassium hydroxide in one liter of 95 per cent redistilled alcohol (by volume). The alcohol should be redistilled from potassium 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 potassium 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 potassium 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 titrate with theN/2 hydrochloric acid, using phenolphthalein as an indicator. Calculate the Koettstorfer number (mg. of potassium 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.
Apparatus—Capillary tubesmade from 5 mm. inside diameter thin-walled glass 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 thermometergraduated in tenths of a degree.
600 cc. beaker.
Determination—The sample should be clear when meltedand 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.
Precautions—(1) The oil must be perfectly dry, becausethe 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.
(3) There must not be too much discrepancy between the temperature of the bath and the clouding point of the oil. An oil that will cloud at the temperature of hydrant water should be tested in a bath of that temperature. An oil that will cloud in a mixture of ice and water should be tested in such a bath. An oil that will not cloud in a bath of ice and water must be tested in a bath of salt, ice, and water.
Determination—The oil is heated in a porcelain casserole over a free flame to 150° C., stirring with the thermometer. As soon as it can be done with safety, the oil is transferred to a 4 oz. oil bottle, which must be perfectly dry. One and one-half ounces of the oil are sufficient for the test. A dry centigrade thermometer is placed in the oil, and the bottle is then cooled by immersion in a suitable bath. The oil is constantly stirred with the thermometer, taking care not to remove the thermometer from the oil at any time during the test, so as to avoid stirring air bubbles into the oil. The bottle is frequently removed from the bath for a few moments. The oil must not be allowed to chill on the sides and bottom of the bottle. This is effected by constant and vigorous stirring with the thermometer. As soon as the first permanent cloud shows in the body of the oil, the temperature at which this cloud occurs is noted.
With care, results concordant to within 1/2° C. can be obtained by this method. A Fahrenheit thermometer is sometimes used because it has become customary to report results in degrees Fahrenheit.
The oil must be tested within a short time after heating to 150° C. and a re-test must always be preceded by reheating to that temperature. The cloud point should beapproached as quickly as possible, yet not so fast that the oil is frozen on the sides or bottom of the bottle before the cloud test is reached.
The standard size of sample adopted by the committee is at least 3 lbs. in weight. The committee realizes that this amount is larger than any samples usually furnished even when representing shipments of from 20,000 to 60,000 lbs. but it believes that the requirement of a larger sample is desirable and will work toward uniform and more concordant results in analysis. It will probably continue to be the custom of the trade to submit smaller buyers' samples than required by the committee, but these are to be considered only as samples for inspection and not for analysis. The standard analytical sample must consist of 3 lbs. or more.
The reasons for keeping samples in a dark, cool place are obvious. This is to prevent any increase in rancidity and any undue increase in free fatty acids. In the case of many fats the committee has found in its co-operative analytical work that free acid tends to increase very rapidly. This tendency is minimized by low temperatures.
After careful consideration the committee has decided that moisture is best determined in a vacuum oven of the design which accompanies the above report. Numerous results on check samples have confirmed the committee's conclusions. The oven recommended by the committee is constructed on the basis of well-known principles and it is hoped that this type will be adopted generally by chemists who are called upon to analyze fats and oils. The experiments of the committee indicate that it is a most difficult matter to design a vacuum oven which will produce uniform temperaturesthroughout; and one of the principal ideas in the design adopted is uniformity of temperature over the entire single shelf. This idea has not quite been realized in practice but, nevertheless, the present design approaches much closer to the ideal than other vacuum ovens commonly used. In the drawing the essential dimensions are those between the heating units and the shelf and the length and breadth of the outer casting. The standard Fat Analysis Committee Oven (F. A. C. Oven) can be furnished by Messrs. E. H. Sargent & Company, 125 West Lake street, Chicago.
The committee realizes that for routine work a quicker method is desirable and has added one such method and has also stated the conditions under which comparable results can be obtained by means of the ordinary well-ventilated air oven held at 105 to 110° C. However, in accordance with a fundamental principle adopted by the committee at its first meeting, only one standard method is adopted and declared official for each determination.
The committee realizes that in the case of all methods for determining moisture by means of loss on heating there may be a loss due to volatile matter (especially fatty acids) other than water. The title of the determinationmoisture and volatile matterindicates this idea, but any considerable error from this source may occur only in the case of high acid fats and oils and particularly those containing lower fatty acids such as coconut and palm kernel oil. In the case of extracted greases which have not been properly purified, some of the solvent may also be included in the moisture and volatile matter determination, but inasmuch as the solvent, usually a petroleum product, can only be considered as foreign matter, for commercial purposes, it is entirely proper to include it with the moisture.
The committee has also considered the various distillation methods for the determination of moisture in fats and oils,but since according to the fundamental principles which it was endeavoring to follow it could only standardize one method, it was decided that the most desirable one on the whole was the vacuum-oven method as given. There are cases wherein a chemist may find it desirable to check a moisture determination or investigate the moisture content of a fat or oil further by means of one of the distillation methods.
However, in co-operative work the distillation method in various types of apparatus has not yielded satisfactory results. The difficulties appear to be connected with a proper choice of solvent and particularly with the tendency of drops of water to adhere to various parts of the glass apparatus instead of passing on to the measuring device. When working on coconut oil containing a high percentage of free fatty acids, concordant results could not be obtained by the various members of the committee when working with identical samples, solvents and apparatus.
On the other hand, the committee found by individual work, co-operative work and collaborative work by several members of the committee in one laboratory, that the old, well-known direct heating method (which the committee has designated the hot plate method) yielded very satisfactory results on all sorts of fats and oils including emulsions such as butter and oleomargarine and even on coconut oil samples containing 15 to 20 per cent free fatty acids and 5 to 6 per cent of moisture. Unfortunately, this method depends altogether on the operator's skill and while the method may be taught to any person whether a chemist or not so that he can obtain excellent results with it, it is difficult to give a sufficiently, complete description of it so that any chemist anywhere after reading the description could follow it successfully. The method is undoubtedly worthy of much confidence in careful hands. It is quick, accurate and reliable.It is probably the best single method for the determination of moisture in all sorts of samples for routine laboratory work. On account of this fact the committee desires to announce its willingness to instruct any person in the proper use of the method who desires to become acquainted with it and who will visit any committee member's laboratory.
This determination, the title for which was adopted after careful consideration, determines the impurities which have generally been known as dirt, suspended matter, suspended solids, foreign solids, foreign matter, etc., in the past. The first solvent recommended by the committee is hot kerosene to be followed by petroleum ether kept at ordinary room temperature. Petroleum ether, cold or only slightly warm, is not a good fat and metallic soap solvent, whereas hot kerosene dissolves these substances readily, and for this reason the committee has recommended the double solvent method so as to exclude metallic soaps which are determined below as soluble mineral matter.
Soluble mineral matter represents mineral matter combined with fatty acids in the form of soaps in solution in the fat or oil. Formerly, this mineral matter was often determined in combination by weighing the separated metallic soap or by weighing it in conjunction with the insoluble impurities. Since the soaps present consist mostly of lime soap, it has been customary to calculate the lime present therein by taking 0.1 the weight of the total metallic soaps. The standard method as given above is direct and involves no calculation. The routine method given in the note has been placed among the methods for the reason that it is used in some laboratories, but has not been adopted as a standard method in view of the fact that the committee hasmade it a rule to adopt only one standard method. It should be pointed out, however, that the method cannot be considered accurate for the reason that insoluble impurities may vary from sample to sample to a considerable extent and the error due to the presence of large particles of insoluble impurities is thus transferred to the soluble mineral matter. The committee has found one type of grease (naphtha bone grease) which shows most unusual characteristics. The type sample contains 4.3 per cent soluble mineral matter by the committee method which would be equivalent to 43.0 per cent free fatty acid. The kerosene and gasoline filtrate was particularly clear, nevertheless the ash was found to contain 36.43 per cent P2O5equivalent to 79.60 per cent of Ca3(PO4)2and 9.63 per cent of Fe2O3. The method, therefore, determines the soluble mineral matter in this case satisfactorily but the factor 10 is not applicable for calculating the fatty acids combined therewith. It is necessary, therefore, in order to determine the fatty acids combined with soluble mineral matter in the original sample to determine the actual bases in the soluble mineral matter as obtained by ashing the kerosene and gasoline filtrate. To the bases so determined the factor 10 can then be applied.
The fatty acid method adopted is sufficiently accurate for commercial purposes. In many routine laboratories the fat or oil is measured and not weighed, but the committee recommends weighing the sample in all cases. For scientific purposes the result is often expressed as "acid number," meaning the number of milligrams of KOH required to neutralize the free acids in one gram of fat, but the commercial practice has been, and is, to express the fatty acids as oleic acid or in the case of palm oil, as palmitic acid, in some instances. The committee sees no objection to thecontinuation of this custom so long as the analytical report clearly indicates how the free acid is expressed. For a more exact expression of the free acid in a given fat, the committee recommends that the ratio of acid number to saponification number be used. This method of expressing results is subject to error when unsaponifiable fatty matter is present, since the result expresses the ratio of free fatty acid to total saponifiable fatty matter present.
At the present time the prices of glycerol and caustic potash are abnormally high, but the committee has considered that the methods adopted are for normal times and normal prices. For routine work during the period of high prices the following method may be used for preparing the fatty acids and is recommended by the committee:
Fifty grams of fat are saponified with 60 cc. of a solution of 2 parts of methyl alcohol to 1 of 50 per cent NaOH. The soap is dried, pulverized and dissolved in 1000 cc. of water in a porcelain dish and then decomposed with 25 cc. of 75 per cent sulphuric acid. The fatty acids are boiled until clear oil is formed and then collected and settled in a 150-cc. beaker and filtered into a 50-cc. beaker. They are then heated to 130° C. as rapidly as possible with stirring, and transferred, after they have cooled somewhat, to the usual 1-in. by 4-in. titer tube.
The method of taking the titer, including handling the thermometer, to be followed is the same as that described in the standard method. Even at present high prices many laboratories are using the glycerol-caustic potash method for preparing the fatty acids, figuring that the saving of time more than compensates for the extra cost of the reagents. Caustic soda cannot be substituted for caustic potash in the glycerol method.
The committee has considered unsaponifiable matter to include those substances frequently found dissolved in fats and oils which are not saponified by the caustic alkalies and which at the same time are soluble in the ordinary fat solvents. The term includes such substances as the higher alcohols, such as cholesterol which is found in animal fats, phytosterol found in some vegetable fats, paraffin and petroleum oils, etc.Unsaponifiable mattershould not be confused in the lay mind withinsoluble impurities or soluble mineral matter.
The method adopted by the committee has been selected only after the most careful consideration of other methods, such as the dry extraction method and the wet method making use of the separatory funnel. At first consideration the dry extraction process would seem to offer the best basis for an unsaponifiable matter method, but in practice it has been found absolutely impossible for different analysts to obtain agreeing results when using any of the dry extraction methods proposed. Therefore, this method had to be abandoned after numerous trials, although several members of the committee strongly favored it in the beginning.
Iodine Number—The iodine number adopted by the committee is that determined by the well-known Wijs method. This method was adopted after careful comparison with the Hanus and Hübl methods. The Hübl method was eliminated from consideration almost at the beginning of the committee's work for the reason that the time required for complete absorption of the iodine is unnecessarily long and, in fact, even after absorption has gone on over night, it is apparently not complete. In the case of the Hanus and Wijs methods complete absorption takes place in from 15 minutes to an hour, depending on conditions. Formerly, many chemists thought the Hanus solution rather easier to preparethan the Wijs solution, but the experience of the committee was that the Wijs solution was no more difficult to prepare than the Hanus. Furthermore, absorption of iodine from the Wijs solution appeared to take place with greater promptness and certainty than from the Hanus and was complete in a shorter time. Results by the Wijs method were also in better agreement in the case of oils showing high iodine absorption than with the Hanus solution and showed a slightly higher iodine absorption for the same length of time. However, the difference was not great. The committee investigated the question of substitution since it has been suggested that in case of the Wijs solution substitution of iodine in the organic molecule might occur, and found no evidence of this in the time required for the determination, namely, 1/2 hr., or even for a somewhat longer period. One member of the committee felt that it was not desirable to introduce the Wijs method into these standard methods since the Hanus method was already standardized by the Association of Official Agricultural Chemists, but the committee felt that it must follow the principle established at the commencement of its work, namely, that of adopting the method which appeared to be the best from all standpoints, taking into consideration accuracy, convenience, simplicity, time, expense, etc., without allowing precedent to have the deciding vote.
Iodine Number, Tung Oil—The committee has made an extensive study of the application of the Wijs method to the determination of iodine value in the case of tung oil with the result that it recommends the method for this oil but has thought it desirable to limit the conditions under which the determination is conducted rather narrowly, although reasonably good results are obtained by the committee method without making use of the special limitations.
The co-operative work of the committee and the specialinvestigations conducted by individual members bring out the following points:
Influence of Temperature—From 16° C. to 30° C. there is a moderate increase in the absorption, but above 30° the increase is rather rapid so that it was thought best to limit the temperature in the case of tung oil to 20° to 25° C.
Influence of Time—The absorption increases with the time but apparently complete absorption, so far as unsaturated bonds are concerned, occurs well within one hour's time. Consequently, one hour was set as the practical limit.
Influence of Excess—The excess of iodine solution also tends to increase the iodine number, hence the Committee thought it necessary to limit the excess rather rigidly to 55 ± 3 per cent, although with greater latitude results were reasonably good.
Influence of Age of Solution—Old solutions tend to give low results although up to 2 mo. no great differences were observed. Nevertheless, it was thought best to limit the age of the solution to 30 days—long enough for all practical purposes.
Amount of Sample—As a practical amount of sample to be weighed out the Committee decided on 0.15 g. with a tolerance of 0.05 g. in either direction according to preference. In other words, the amount of sample to be taken for the determination to be from 0.1 to 0.2 g. in the discretion of the analyst.
The Committee's study of the Hübl method which has been adopted by the Society for Testing Materials in the case of tung oil indicates that this method when applied to tung oil is subject to the same influences as the Wijs method and it has the additional very serious disadvantage of requiring a long period of time for absorption which cannot be considered reasonable for a modern analytical method. When using the Hübl solution, the absorption isnot complete in the case of tung oil at 3, 7, 18 or even 24 hrs.
The Hanus method in the case of tung oil gives very high and erratic results, as high as 180 to 240 in ordinary cases for an oil whose true iodine number is about 165.
A melting point is the temperature at which a solid substance assumes the liquid condition. If the solid is a pure substance in the crystalline condition the melting point is sharp and well defined for any given pressure. With increased pressure the melting point is lowered or raised, depending on whether the substance contracts or expands in melting. The lowering or raising of the melting point with pressure is very slight and ordinarily is not taken into consideration. Melting-point determinations are commonly carried out under ordinary atmospheric pressures without correction. The general effect of soluble impurities is to lower the melting point, and this holds true whether the impurity has a higher or lower melting point than the pure substance (solvent). Thus if a small amount of stearic acid be added to liquid palmitic acid and the solution frozen, the melting point of this solid will be lower than that of palmitic acid. Likewise the melting point of stearic acid is lowered by the addition of a small amount of palmitic acid. A eutectic mixture results when two components solidify simultaneously at a definite temperature. Such a mixture has a constant melting point and because of this and also because both solid and liquid phases have the same composition, eutectic mixtures were formerly looked upon as compounds. The phenomenon of double melting points has been observed in the case of a number of glycerides. Such a glyceride when placed in the usual capillary tube and subjected to increasing temperature quickly resolidifies onlyto melt again and remain melted at a still higher temperature. This phenomenon has not yet been sufficiently investigated to afford a satisfactory explanation.
Non-crystalline substances such as glass, sealing wax and various other waxes and wax mixtures, and most colloidal substances do not exhibit a sharp melting point, but under the application of heat first soften very gradually and at a considerably higher temperature melt sufficiently to flow. This phenomenon of melting through a long range of temperature may be due to the amorphous nature of the substance or to the fact that it consists of a very large number of components of many different melting points.
The fats and oils of natural origin, that is, the animal and vegetable fats and oils, consist of mixtures of glycerides and, generally speaking, of a considerable number of such components. These components are crystalline and when separated in the pure state have definite melting points, although some exhibit the phenomenon of double melting point. For the most part the naturally occurring glycerides are mixed glycerides. In the natural fats and oils there are present also certain higher alcohols, of which cholesterol is characteristic of the animal fats and oils and phytosterol of many of the vegetable fats and oils. In addition to the crystalline glycerides and the higher alcohols present in neutral fats, there are in fats of lower grade, fatty acids, which are crystalline, and also various non-crystalline impurities of an unsaponifiable nature, and the presence of these impurities tends to lower the melting point. They also tend to induce undercooling and when the liquid fat or oil is being chilled for purposes of solidification or in determination of titer.
The presence of water, especially when this is thoroughly mixed or emulsified with a fat or oil, also influences the melting point to a marked extent, causing the mixture tomelt through a longer range of temperatures than would be the case if the water were absent. This is particularly true of emulsified fats and oils, such as butter and oleomargarine, both of which contain, besides water, the solids naturally present in milk or cream and including casein, milk sugar, and salts. The melting-point method recommended by the Committee is not applicable to such emulsions or other watery mixtures and the Committee has found it impossible to devise an accurate method for making softening-point or melting-point determinations on products of this nature. Not only the amount of water present but also the fineness of its particles, that is, its state of subdivision and distribution, in a fat or oil influences the softening point or melting point and causes it to vary widely in different samples.
As a consequence of the foregoing facts, natural fats and oils do not exhibit a definite melting point, composed as they are of mixtures of various crystalline glycerides, higher alcohols, fatty acids, and non-crystalline substances. Therefore, the term melting point when applied to them requires further definition. They exhibit first a lower melting point (the melting point of the lowest melting component) or what might be called the softening point and following this the fat softens through a shorter or longer range of temperature to the final melting point at which temperature the fat is entirely liquid. This is the melting point determined by the Committee's melting-point method. The range between the softening point and the final melting point varies greatly with the different fats and oils depending on their chemical components, the water associated with them, emulsification, etc. In the case of coconut oil the range between softening point and final melting point is rather short; in the case of butter, long. Various methods have been devised to determine the so-called melting point of fats and oils. Most of these methods, however, determine, notthe melting point, but the softening point or the flow point of the fat and the great difficulty has been in the past to devise a method which would determine even this point with reasonable accuracy and so that results could be easily duplicated. It has been the aim of the Committee to devise a simple method for the determination of the melting point of fats and oils, but it should be understood that the term melting point in the scientific sense is not applicable to natural fats and oils.