July,
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
1920
713
NOTES AND CORRELSPONDENCE UNSAPONIFIABLE MATTERS Editor of the Journal of Industrial and Engineering Chemistry: I n THIS JOURNAL, 11 ( ~ g ~ g )1 1, 6 1 , is given the final report of the Committee on Analysis of Commercial Fats and Oils of the Division of Industrial and Engineering Chemistry of the AMERICAN CHEMICAL SOCIETY, as adopted April 1 4 , 1919, b y unanimous vote. Anyone who has served on such a committee knows the great amount of work required of its members and the difficulty of ’harmonizing varying ideas, with the result t h a t the final conclusions are apt, t o some extent, to be compromises. Owing t o the difficulties of getting members together and actually illustrating certain points by tests, all points cannot be satisfactorily worked out, without unduly prolonging the time required t o make a report. We wish here to call particular attention to the method adopted for the determination of unsaponifiable matters. Although this method is better than any other published commercial method with which we are acquainted, in t h a t i t is easy to carry out and gives fairly concordant results, i t contains a source of error which may not be constant, and which is very easily eliminated with practically no additional work. We refer to the presence of free fatty acids in the final residue recorded as “unsaponifiable matter.” By the method of extraction and washing employed this final residue always contains more or less free fatty acids, yet the committee made no mention of the fact nor suggested any method of correction. Although this point was called to the attention of the committee and illustrated by examples, they did not see fit t o add to their method the operation which would eliminate the error in question. During the petroleum ether extractions the amount of alcohol in the solution are not over 30 per cent by volume. Fifty per cent of alcohol are required to prevent hydrolysis of most soap solutions. Therefore, unless there is a sufficient excess of alkali a t this point, the soap is bound to undergo hydrolysis to some extent, with the result that the petroleum ether extracts will contain some free fatty acids. They will also, probably, contain some soaps. The combined extracts are washed with I O per cent alcohol washes, with the result that any soaps present in the petroleum ether extracts may undergo some hydrolysis. The final residue is, therefore, bound to contain free fatty acids, and not necessarily in constant proportional amounts. Actual tests show this t o be the case. Twitchell’s method,’ which is much the same as the committee method but employs ethyl ether for extraction, takes into account the free fatty acids left with the final residue and deducts their amount, calculated as oleic acid. The objection to this method is that these free fatty acids are not oleic acid, and in many cases a serious error is introduced by so considering them. On trying the committee method we have always found the final residue to contain titratable amounts of free fatty acids, and it is obvious that any free fatty acids in this residue should be deducted from unsaponifiable matter. I t might be claimed t h a t the amount of free fatty acids would be practically constant and t h a t they would make little difference in a commercial method. But the amount of free fatty acids left is not constant and the residue may contain more free fatty acids than it does true unsaponifiable matter. Using the committee method as a basis, we modified the method of washing the petroleum ether extracts, by introducing a wash with dilute caustic solution, whereby free fatty acids are removed from the petroleum ether and hydrolysis of any soap TX16 JOURWAL,
7 (1915), 217,
prevented, a t least t o a great extent. Our residues contain either no titratable amounts of free fatty acids, or such small amounts t h a t considering them as oleic acid will introduce no appreciable error. Our method is as follows: Five g. of the fat or oil are saponified according to the committee method, which is followed in all details up to obtaining the petroleum ether extracts. The extracts are washed with 2 5 cc. portions of I O per cent ( I O cc. diluted to IOO cc.) alcohol as directed, then with 0 . 5 N sodium or potassium hydroxide solution, followed by I O per cent alcohol again, and then with water until all alkali has been washed out. Determinations by the committee method and our modification are given below: SAPONIFIABLE MATTER IN SOY-BEAN OIL B Y COMMITTEE METHOD
Five petroleum ether extractions were made and the extracts combined before washing. After three washes with I O per cent alcohol (25 cc. each time), the extracts were transferred to a weighed flask, the ether evaporated off, and the residue dried in a n air oven at 105’ C. for about half an hour, cooled, and weighed. Gram Residue recovered. . . . . . . . . . . . . . . . . . 0.0422 Free fatty acid titrated with 0 . 1 N NaOH ( 0 . 2 9 cc.), combining weight of 279 (found lor pure soy-bean oil fatty acids). ..................... 0 0081 Net unsaponifiable matter.. .
....
Per cent 0.844
0.162 0.682
I n a second test the method was modified to include a wash with dilute hydrochloric acid, as in Twitchell’s method. Gram
. . . . . . . . . . . . . . . . 0,0532 ............................ 0.OZOl
Residue recovered., Free fatty acid titrated as before ( 0 . 7 2 cc.). N e t unsaponifiable matter. . . . . . . .
Per cent 1.064 0.402 0.662
MODIFICATION O F T H E COMMITTEE METHOD
Five grams of oil were saponified as directed by the committee, and their method followed until after the first set of alcohol washes. The extract was then washed with 25 cc. of 0.5 N sodium hydroxide solution, followed by alcohol washes and water until alkali was all washed out. Gram Residue recovered (No 0 . 1 N NaOH required for free fatty acids), , , , , 0,0337
.
Per cent 0.6740
A second test followed, modified to include a wash with dilute hydrochloric acid after the first set of alcohol washes, followed by our regular method, including an alkaline wash. Gram Residue obtained ( N o 0 , l A’ NaOH required for any free fatty acids left in residue). 0.0325
.....................
Per cent 0.6500
These illustrations are sufficient to show that free fatty acids are left in the residue obtained by the committee method, while by our modification no titratable amount of free fatty acids is left in most cases, but sometimes there are very small amounts. When we heat the residues with neutral alcohol, add phenolphthalein and one drop, or a fraction of a drop, of 0 .I N sodium hydroxide and obtain a strong permanent red coloration, we consider that there is no titratable amount of free fatty acids present. The above matter illustrates our point, but i t may be of interest t o compare the above methods with a similar method, using ethyl ether instead of petroleum ether for extractions. It is to be noted t h a t ether always gives higher results than petroleum ether. This is t o be expected, as petroleum ether is a poorer solvent than ether for oxidized and hydroxy fatty matters. Ether probably gives more accurate results, but for a commercial method petroleum ether appears more satisfactory.
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TEST1-Five grams were saponified as usual, transferred t o an extraction cylinder, made up t o 40 cc. with alcohol, treated with 120 cc. of water and 50 cc. of purified (water- and alcohol-free) ether, shaken, and separated. After five extractions the ether extracts were joined and washed with dilute hydrochloric acid as in Twitchell’s method, then with N KOH, and then with water until free from alkali. Gram Per cent 0.8900 Residue obtained.. . . . . . . . . . . . . . . . . 0.0445 Free fatty acid titrated with 0 . 1 A‘ NaOH. . . 0.0056 0 . I116 Net unsaponifiable matter.. Test 11-This
Net unsaponifiable matter..
.... .... .. . . . .
Reground again: Third extract with 150 cc. dry e t h e r . . . . Free fatty acid, 0.05 cc., 0 . 1 N N a O H .
. Total unsaponifiable matter. . . . . . . . .
0.79
TEST111-This
was the same as Tests I and 11, except t h a t 75 cc. of ether were used the first time and three additional 50 cc. extractions were made. Gram Per cent Residue obtain 0.0498 0.9960 Free fatty acid 0.0073 0.1460 Net unsaponifiable matter.
. .. . . . .
0.0004
N e t unsaponifiable Reground again: Fourth extract with 150 cc. dry e t h e r . . Free fatty acid too small to titrate
Per cent 0.90 0.11
12,
No. 7
Per cent
.
1.082 0.016
1.066 0.070
0.0018 0.0014
~
0.7784 Gram 0.0450 0.0056
-
. .
N e t unsaponifiable.. . . . . . . . . . . . . . 0.0533 Reground mixture and extracted again: Second extract with 150 cc. dry e t h e r . . . 0.0035 N o free fatty acid indicated.
was a duplicate of Test I.
Residue obtaine Free fatty acids
Gram 0.0541 0.0008
.
First extract with 150 cc. dry e t h e r . . . . Free f a t t y acids, 0.03 cc. 0 . 1 N NaOH.
-
.. . ..
Vol.
0.0004
0.008 0.008
__ 1,150
To all appearances the unsaponifiable matter obtained by the dry method was the same as that obtained by the wet method referred to below. It is noticeable how much higher, the unsaponifiable matter is than is shown by either the committee method or by our modification.
0,850
TESTIV-This
was the same as Test 111, except that a wash with hydrochloric acid was included. Per cent Corrected unsaponifiable matter. . , , . . , . . . . . . . 0.8361 DRY EXTRACTION METHOD
Comparison with a dry extraction method may be of interest, particularly in cbnnection with another extraction of soy-bean oil of which we will speak later. Our method of making a dry extraction uses a special arrangement of apparatus and ethyl ether purified from water and alcohol. This is obtained by adding a good excess of dry granular calcium chloride, shaking well a t intervals, and allowing to stand overnight. Filter off the ether (protecting from circulation of air) and t o each liter of ether add 50 g. of dry rosin and distil off theether. The apparatus is illustrated. GENERAL METHOD OF OPERATION-The fat or oil is saponified by boiling with excess of alcoholic alkali, the alcohol evaporated off, and drying finished in a vacuum oven a t as high a heat as the material will stand. When perfectly dry and free from alcohol (usually within a short time) the material is mixed with a t least twice its weight of dry soda ash and finely ground in a glass mortar and placed in the extraction tube. About 75 cc. of ether, purified from water and alcohol, are run in on top of the material to be extracted and allowed to percolate through it. The percolate will generally be so strong in unsaponifiable matter by the time it reaches the end of this tube that it is ready t o crystallize. After one or two percolations the material is removed from the tube, dried for a short time, and repulverized to expose new surfaces. This is the only drawback to the dry extraction method, but is not as much trouble as it would appear. There is generally no trouble with the percolation, if the ether is properly purified, but suction may be used, if necessary. APPLICATION TO SOY-BEAN OIL-Five grams of the oil were saponified as usual, the alcohol driven off, and the resulting mass dried and mixed with 2 0 g. of anhydrous sodium carbonate, ground finely in a mortar and put in the tube. One hundred and fifty cc. of purified ether were used for the first extraction. Percolation was steady and became faster as extraction proceeded. Each ether extract was washed first with neutral water to see if there was any indication of alkali in solution, as shown by phenolphthalein. A little was shown each time, but with other stocks these extracts are often free from any soap or other alkali. The water wash was then followed by a wash with 0 . 5 N NaOH solution to remove any soaps and prevent hydrolysis as much as possible. Finally all sodium hydroxide was washed out with pure water and the matter remaining in solution recovered.
A-Large tube filled with granular calcium chloride, t o keep moisture of air from entering apparatus
B-Extraction tube with several small holes through bottom. I n t o this tube is p u t the powder t o be extracted. There is a plug of cotton wool in the bottom and a perforated lead plate just above i t t o hold i t in place and make a seat for the substance t o be extracted. It also facilitates removal of the substance for regrinding
C-Adapter t o allow extraction tube t o be connected with 500 cc. (or other size) separatory funnel
D-Squibb’s form of separatory funnel. portions are about as shown, diameters of varying from an inch t o an inch and a half
Protubes
WET EXTRACTION METHOD
WET
EXTRACTIOS
O F UNSAPONIFIABLE
MATTER
FROM
SOY-
oIL-Soy-bean oil was filtered through paper and 50 g. of the filtered oil used. Without going into details, the general method was to saponify with excess of alcoholic potash solution, and dilute with water so that the resulting solution would contain about one-fourth of its volume of alcohol. After making
BEAN
July,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
about three ether extractions a t this dilution, more water was added t o reduce the alcohol content t o about one-sixth of the total volume, and further extractions with ethyl ether were made. The various residues obtained were reboiled with excess of alcoholic potash and the unsaponifiable matter reextracted. Cnfortunately the first and main residue was not tested for free fatty acids, and so probably appears higher than it should, and the spread, after resaponification and extraction, is greater than i t would be had the fatty acids been deducted. SUMMARY OF OPERATIOXS
The residue (uncorrected for free fatty acids) amounted to I . 1 6 per cent unsaponifiable matter, which checks with that found by the dry method, which, however, was corrected for a n y free fatty acids. This residue was resaponified with the following results: from
Per cent Per cent alcohol from 1/0 alcohol 1 1.500
0 0100
Per cent Total 1 1600
0,8420
0.0036
0.8456
~
Recovered npon first resaponification, , , , . . . . Recovered upon second resaponification. . . . . . . Recovered upon third resaponification. . . . . . . Recovered upon fourth resaponification. . . . . .
.
.
~~
~
~~~
~
~~~~
0.7840
....
0.7840
9 . 7 183
0.0240
0.7423
0.6770
trace
0.6770
It is evident that we have continually lost weight and it would seem that this loss cannot be satisfactorily explained by failure to extract each time the full amount of unsaponifiable matter left, but rather points to the action of alcoholic alkali on the residues, either in decomposing some of the true unsaponifiable matter or in completing the saponification o€ some very difficultly saponifiable matter, which would then be present in all ordinary residues and reckoned as unsaponifiable matter. The resaponifications and reextractions were stopped a t the above point because the amount of free fatty acids to be corrected for had apparently reached a constant figure in the last two cases. Whether this was the true end we doubt. The point happens t o give the same final result as the determination by the committee method, but this may be considered only a coincidence. THECUDAHYPACKING COMPANY WILSONH. Low OMAHA, h-EBRASKA
December 15, 1919
............
Editor of the Journal of Industrial and Engineering Chemistry: Mr. Low’s remarks in the early part of his paper, entitled “Unsaponifiable Matters,” on the difficulties which confront committees working on analytical methods are interesting but do not apply to the committee of which I am chairman. This committee made a practice of meeting regularly once a month during its period of greatest activity, and thereafter meetings were held whenever a sufficient number of results from cooperative work had accumulated to warrant calling a meeting. Conferences in various laboratories were held from time to time for the purpose of cooperating on one or another moot point in the various methods, several members of the committee meeting in this way first in one laboratory and then in another until the point was settled and unanimity reached. Such cooperative work was done on the unsaponifiable method. It is difficult for any committee to adopt a method of analysis satisfactory to all workers and this is perhaps particularly true of the unsaponifiable determination. I n my opinion, however, the method finally adopted by the committee in point of accuracy, convenience, simplicity, speed, and reliability in various hands comes as near perfection as we can hope for in the present state of our knowledge. The point which Mr. Low discusses was brought to the committee’s attention by him. After careful consideration the committee decided t h a t it was not necessary to add the manipulation advocated by Mr. Low. Mr. Low states t h a t “By the method of extraction and washing employed this final residue
71.5
always contains more or less free fatty acids, yet the committee made no mention of the fact nor suggested any method of correction.” The answer t o this statement is that the amount retained is very small; so small, in fact, as t o make no appreciable difference in the results, particularly for commercial purposes. In the majority of samples of oils, fats and greases the amount of free fatty acids a t this point usually varies from 0 . 0 2 to 0 . 0 7 per cent, rarely i t amounts to as much as 0 . I per cent, and the high figures are generally found in the case of an oil whose general peculiarities are well known-soy-bean oil. Considered as an absolute error on the positive side, this amount is not great and not worth taking into consideration in the commercial analysis of oils and fats. On the other hand, from the point of view that it may be a counter-balancing error working against incomplete extraction, i t is of still less moment. Good manipulation reduces the amount, poor manipulation increases it. Judging by his own figures in comparison with the results by members of the F a t Analysis Committee, Mr. Low’s manipulation is open to criticism. Mr. H. J. Morrison, of the Procter and Gamble Company, writes as follows in regards to Mr. Low’s argument: I have read over carefully Mr. Low’s paper in which he cr method for determining the unsaponifiable matter in the Standard Methods for the Analysis of Commercial Fats and Oils. Mr. Low’s paper is worded unfortunately in that one gets the impression that the committee did not accept criticisms and did nothing t o investigate them, This, of course, is quite wide of the mark. On t h a t particular point raised by Mr. Low I believe we did more work than on any other point raised by outside criticism. The committee was quite alive t o the danger of high results due t o hydrolysis. One point which we discussed was the amount of caustic alkali t o be used for the saponification, and the amount was fixed a t a very large excess over the theoretical for the purpose of rapid and complete saponification, on the one hand, and t o have a n excess present t o prevent hydrolysis when diluted for extraction, on the other hand. Mr. Low mentions an excess as a preventive of hydrolysis but either has not calculated the amount of excess the method calls for or must consider a very excessive amount necessary t o prevent hydrolysis. Doubtless Mr. Low has many more than the one analysis by the committee method on which he bases his contention t h a t a serious error is introduced by this hydrolysis. From the experience of this laboratory I cannot help but feel that the source of Mr. Low’s error is due t o faulty technique. I n order to protect our results from carelessness we have practiced having the unsaponifiable titrated and in 445 such titrations on the great varipty of fats, oils and greases which pass through our laboratory the average titration was 0.076 cc. 0 . 1 N NaOH, equal on 5 g. of fat t o 0 . 0 4 percent. This is quite within the limit of error of this particular operation, and I may point out that these 445 results are of course the daily routine analyses, by routine men such as are employed in such laboratories. Mr. Low seems t o explain the error and its necessary correction in the ethyl ether extraction method by the hydrolysis theory. This is not a t all the case as I think we demonstrated. It is due t o actual solution of soap, owing t o the solubility of both water and alcohol. in the ethyl ether phase. Mr. Low’s error when using the committee method, as stated above, is due, I believe, t o technique, possibly by not allowing su5cient time for a thorough separation or by drawing off the petroleum ether extract too close. I am not going t o enter a discussion here concerning the other methods iMr. Low speaks of, as I think i t patent to anyone conversant with fats and Our committee, their analysis wherein they cannot give correct results. I believe, cannot be accused of not trying o u t any suggestions and I feel are willing now at any time to t r y out anything which promises a n improvement, but I feel that this should be done by direct appeal t o the committee and not by the method of rushing into print, unless the author has irrefutable proof.
The amount of free fatty acids left in the final residue is usually neutralized by one drop of 0 . I N alkali. The one drop of 0 . I Ai alkali may or may not be an excess but frequently does amount to an excess. This point is indicated in Mr. Morrison’s letter and is considered more a t length in a letter received from Mr. Rudnick, of Armour and Company’s laboratory, which follows: The assumptions made in the first paragraph of the paper by Wilson H. Low on unsaponifiable matters are not warranted by the facts. The methods adopted by the F a t and Oil Committee were not based merely on ideas, but on the outcome of actual tests, so t h a t the final conclusions are not compromises of varying ideas. Indeed the outcome of the cooperative work done by the committee more than once upset long-held views
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
and while these views were ,,.netimes abandoned with reluctance, in the end the votes of the members were always based on the facts developed. This committee had no particular difficulty in point of attendance of its members. Occasionally differences in results became apparently irreconcilable by the usual cooperative procedure and in such cases special subcommittees were appointed t o carry out the required tests jointly in t h e several laboratories in order t o develop under personal observation the facts necessary t o cover the disputed points. None of the members of the committee reported any unusual difficulties in determining the unsaponifiable matter in soy-bean oil, t o which the entire discussion in Low’s paper is devoted, although i t is well understood that some samples of soy-bean oil show a n erratic behavior in other respects, notably in the determination of the titer. It is difficult to see how a n y sound criticism of the committee method for determining unsaponifiable matter can be based on the d a t a presented in Mr. Low’s paper. The total amount of unsaponifiable matter obtained by him in accordance with the committee method and without applying his corrections for fatty acids, is well within the normal limits for natural unsaponifiable matter in soy-bean oil. In order t o determine, however, whether such corrections as described by him were true of other samples of soy-bean oil than the one on which he reports, a sample of crude oil was tested in this laboratory with the following results: Unsaponifiable Matter WeiKht of SamDle Gram Per cent 1.00 5 . 0 1 5 grams.. . . . . . . . . . . . . 0.050 1.11 5 . 0 1 2 grams., . . . . . . . . . . . . 0 . 0 5 6 Mean . . . . . . . . . . . . . . 1.06 Fifty milligrams of unsaponifiable matter is a very small amount t o titrate for free fatty acids and i t was therefore not surprising t h a t titration with 0.1 N alkali, observing the precautions directed in the committee method, should amount t o 0 . 4 cc , equivalent t o 0 . 2 2 per cent of free f a t t y acids, calculated as oleic, on the basis of the weight of the first sample. On repeating the titration with 0 . 0 2 N alkali and carrying along a blank titration, matching as closely as possible the final color of the phenolphthalein, the net titration amounted to 0.72 cc. of 0.02 N alkali, equivalent to 0.08 per cent of free fatty acids, calculated as oleic, on the basis of the weight of the second sample. It would seem, therefore, that if the corrections developed in Low’s paper had been determined with a standard alkali of more appropriate concentration relative t o the welght of material titrated, he might have obtained results on his sample of soy-bean oil of about the same order as those which the members of the committee obtained in their original cobperative work on which the method adopted was based. There is nothing new in the work described in Low’s paper on the Twitchell and the dry extraction methods Both these methods were thoroughly tested by the committee and were rejected on the basis of the results obtained with them in codperative work Summing up, there seems t o be no good ground for criticism of the committee method for determining unsaponifiable matter, either on the basis of the data presented in this paper or the method by which they were obtained.
Mr. Low speaks of Twitchell’s method “which is much the same as the committee method.” Anyone who is acquainted with the two methods must realize that the methods are distinctly and decidedly different in principle. As to the dry extraction method mentioned by Mr. Low, this has been tried out in this laboratory off and on for the past fifteen years and has been found on the whole t o be inaccurate and unreliable. The Committee on the Analysis of Commercial Fats and Oils also tried the method out and arrived a t the conclusion that the method was wholly impossible and had no place among modern methods of analysis. Since the adoption of the committee method, agreements on unsaponifiable determinations which were impossible before, have been reached between various laboratories and the method has proved a great advantage to the oil and fat trade. The committee does not consider the additional alkali wash advocated by Mr. Low as either necessary or desirable if the committee method is followed and a moderate degree of skill acquired in manipulation. CHEXICAL LABORATORY OF W. D. RICHARDSON, SWIFT& COMPANY Chairman, Committee on the AnalCHICAGO, ILLINOIS ysis of Commercial Fats and Oils March 31, 1920
AWARDS FOR THESES ON FOODS AND BEVERAGES
In order to stimulate more general research along the lines of better preparation and packing of foods and beverages, and t o increase OUT knowledge of changes induced by preparation or
Vol.
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No. 7
storage of food products, Dr. A. W. Bitting, Director of Research of the Glass Container Association of America, Chicago, Ill., has announced that awards will be made for theses on these subjects. A thesis may cover any phase of the subject of foods or beverages-technological, bacteriological, or chemical. It may treat of any legitimate method of preparation, as sterilization by heat, pasteurization, salting, drying, smoking, pickling, sugaring, etc., the product to be packed in glass. The thesis may be bibliographical with abstracts, or may be a translation from work along the lines indicated. It must be submitted prior to June IO, 1921.
The awards will be as follows:
One . . . . . . . . . . . . . . . . . dl50 One . . . . . . . . . . . . . . . . . . 125 O n e . . . . . . . . . . . . . . . . . . 100 Two .................. 75 Two . . . . . . . . . . . . . . . . . . 50
Any student or graduate student working for a degree in a n y college or university is eligible to compete. The awards will be made by a competent committee and as soon after June IO, 192I , as practicable.
THE INDUSTRIAL FELLOWSHIPS OF THE MELLON INSTITUTE Under the above title there has been issued recently by t h e Director of the Mellon Institute for Industrial Research, Dr. Raymond F. Bacon, a n attractive pamphlet covering the progress of the industrial fellowship system during the past fiscab year. The growth of the Institute’s system is described in detail and shown graphically in the accompanying figure, which THE GROWTHO F THE INDUSTRIAL FELLOWSHIP SYSTEM
1912 1913
1914 1915
1916
1917 1918
1919 1920
has been reproduced from the booklet. The new form of E Q ~ tract, which replaces the one reprinted in THISJOURNAL, 11 (rgrg), 371, is included, also a list of the fellowships in operation on March I, 1920. The following fellowships have been established since the issuance of the 1 9 1 9 report:
-
