Most of these methods, however, determine, not the 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.

FOOTNOTES:

[22] Approved by the Supervisory Committee on Standard Methods of a.n.a.lysis of the American Chemical Society.

[23] Live steam must not be turned into tank cars or coils before samples are drawn, since there is no certain way of telling when coils are free from leaks.

[24] If there is water present under the solid material this must be noted and estimated separately.

[25] Boiling point of water at reduced pressures.

Pressure Boiling Point Boiling Point Boiling Point Mm. Hg. to 1 C. +15 C. +20 C.

100 52 C. 67 C. 72 C.

90 50 65 70 80 47 62 67 70 45 60 65 60 42 57 62 50 38 53 58 40 34 49 54

[26] Results comparable to those of the Standard Method may be obtained on most fats and oils by drying 5-g. portions of the sample, prepared and weighed as above, to constant weight in a well-constructed and well-ventilated air oven held uniformly at a temperature of 105 to 110 C. The thermometer bulb should be close to the sample. The definition of constant weight is the same as for the Standard Method.

[27] The following method is suggested by the Committee for routine control work: Weigh out 5- to 25-g. portions of prepared sample into a gla.s.s or aluminum (_Caution_: Aluminum soap may be formed) beaker or ca.s.serole and heat on a heavy asbestos board over burner or hot plate, taking care that the temperature of the sample does not go above 130 C.

at any time. During the heating rotate the vessel gently on the board by hand to avoid sputtering or too rapid evolution of moisture. The proper length of time of heating is judged by absence of rising bubbles of steam, by the absence of foam or by other signs known to the operator.

Avoid overheating of sample as indicated by smoking or darkening. Cool in desiccator and weigh.

By co-operative work in several laboratories, the Committee has demonstrated that this method can be used and satisfactory results obtained on coconut oil even when a considerable percentage of free fatty acids is present, and the method is recommended for this purpose.

Unfortunately on account of the very great personal factor involved, the Committee cannot establish this method as a preferred method.

Nevertheless, after an operator has learned the technique of the method, it gives perfectly satisfactory results for ordinary oils and fats, b.u.t.ter, oleomargarine and coconut oil, and deserves more recognition than it has heretofore received.

[28] For routine control work, filter paper is sometimes more convenient than the prepared Gooch crucible, but must be very carefully washed, especially around the rim, to remove the last traces of fat.

[29] For routine work, an ash may be run on the original fat, and the soluble mineral matter obtained by deducting the ash on the insoluble impurities from this. In this case the Gooch crucible should be prepared with an ignited asbestos mat so that the impurities may be ashed directly after being weighed. In all cases ignition should be to constant weight so as to insure complete decomposition of carbonates.

[30] See note on Soluble Mineral Matter following these methods. When the ash contains phosphates the factor 10 cannot be applied, but the bases consisting of calcium oxide, etc., must be determined, and the factor 10 applied to them.

[31] For routine work methyl or denatured ethyl alcohol of approximately 95 per cent strength may be used. With these reagents the end-point is not sharp.

[32] P. C. McIlhiney, _J. Am. Chem. Soc._, 29 (1917), 1222, gives the following details for the preparation of the iodine monochloride solution:

The preparation of the iodine monochloride solution presents no great difficulty, but it must be done with care and accuracy in order to obtain satisfactory results. There must be in the solution no sensible excess either of iodine or more particularly of chlorine, over that required to form the monochloride. This condition is most satisfactorily attained by dissolving in the whole of the acetic acid to be used the requisite quant.i.ty of iodine, using a gentle heat to a.s.sist the solution, if it is found necessary, setting aside a small portion of this solution, while pure and dry chlorine is pa.s.sed into the remainder until the halogen content of the whole solution is doubled. Ordinarily it will be found that by pa.s.sing the chlorine into the main part of the solution until the characteristic color of free iodine has just been discharged there will be a slight excess of chlorine which is corrected by the addition of the requisite amount of the unchlorinated portion until all free chlorine has been destroyed. A slight excess of iodine does little or no harm, but excess of chlorine must be avoided.

[33] The melting point of oils may be determined in general according to the above procedure, taking into consideration the lower temperature required.

PLANT AND MACHINERY

Ill.u.s.trations of machinery and layouts of the plant of a modern soap-making establishment.

[Ill.u.s.tration: HOIST, LYE TANK, ETC.]

[Ill.u.s.tration: MELTING-OUT TROUGH]

[Ill.u.s.tration: LAUNDRY SOAP PLANT]

[Ill.u.s.tration: DRYING RACK]

[Ill.u.s.tration: SOAP KETTLE]

[Ill.u.s.tration: REMELTER]

[Ill.u.s.tration: CRUTCHER (Cross Section)]

[Ill.u.s.tration: HORIZONTAL CRUTCHER]

[Ill.u.s.tration: CRUTCHER]

[Ill.u.s.tration: WRAPPING MACHINE (LAUNDRY SOAP)]

[Ill.u.s.tration: SLABBER]

[Ill.u.s.tration: CUTTING TABLE]

[Ill.u.s.tration: AUTOMATIC POWER CUTTING TABLE]

[Ill.u.s.tration: AUTOMATIC PRESS (LAUNDRY)]

[Ill.u.s.tration: CUTTING TABLE (HAND)]

[Ill.u.s.tration: CARTON WRAPPING MACHINE]

[Ill.u.s.tration: DRYING RACKS]

[Ill.u.s.tration: SOAP POWDER BOX]

[Ill.u.s.tration: SCOURING SOAP PRESS]

[Ill.u.s.tration: FRAME]

[Ill.u.s.tration: SOAP POWDER EQUIPMENT]

[Ill.u.s.tration: FLUFFY SOAP POWDER EQUIPMENT]

[Ill.u.s.tration: SOAP POWDER MIXER]

[Ill.u.s.tration: SOAP POWDER MILL]

[Ill.u.s.tration: TOILET SOAP EQUIPMENT]

[Ill.u.s.tration: TOILET SOAP DRYER]

[Ill.u.s.tration: MILLING BOX]