Analytical Methods.
While it is possible to attain a certain amount of efficiency in
determining the worth of the raw material entering into the manufacture
of soap through organoleptic methods, these are by no means accurate. It
is, therefore, necessary to revert to chemical methods to correctly
determine the selection of fats, oil or other substances used in soap
making, as well as standardizing a particular soap manufactured and to
properly regulate the glycerine recovered.
It is not our purpose to cover in detail the numerous analytical
processes which may be employed in the examination of fats and oils,
alkalis, soap and glycerine, as these are fully and accurately covered
in various texts, but rather to give briefly the necessary tests which
ought to be carried out in factories where large amounts of soap are
made. Occasion often arises where it is impossible to employ a chemist,
yet it is possible to have this work done by a competent person or to
have someone instruct himself as just how to carry out the more simple
analyses, which is not a very difficult matter. The various standard
solutions necessary to carrying out the simpler titrations can readily
be purchased from dealers in chemical apparatus and it does not take
extraordinary intelligence for anyone to operate a burette, yet in many
soap plants in this country absolutely no attention is paid to the
examining of raw material, though many thousand pounds are handled
annually, which, if they were more carefully examined would result in
the saving of much more money than it costs to examine them or have
them at least occasionally analyzed.
ANALYSIS OF FATS AND OILS.
In order to arrive at proper results in the analysis of a fat or oil, it
is necessary to have a proper sample. To obtain this a sample of several
of the packages of oil or fat is taken and these mixed or molten
together into a composite sample which is used in making the tests. If
the oil or fat is solid, a tester is used in taking the sample from the
package and if they are liquid, it is a simple matter to draw off a
uniform sample from each package and from these to form a composite
sample.
In purchasing an oil or fat for soap making, the manufacturer is usually
interested in the amount of free fatty acid contained therein, of
moisture, the titer, the percentage of unsaponifiable matter and to
previously determine the color of soap which will be obtained where
color is an object.
DETERMINATION OF FREE FATTY ACIDS.
Since the free fatty acid content of a fat or oil represents a loss of
glycerine, the greater the percentage of free fatty acid, the less
glycerine is contained in the fat or oil, it is advisable to purchase a
fat or oil with the lower free acid, other properties and the price
being the same.
While the mean molecular weight of the mixed free fatty acids varies
with the same and different oils or fats and should be determined for
any particular analysis for accuracy, the free fatty acid is usually
expressed as oleic acid, which has a molecular weight of 282.
To carry out the analysis 5 to 20 grams of the fat are weighed out into
an Erlenmeyer flask and 50 cubic centimeters of carefully neutralized
alcohol are added. In order to neutralize the alcohol add a few drops of
phenolphthalein solution to same and add a weak caustic soda solution
drop by drop until a very faint pink color is obtained upon shaking or
stirring the alcohol thoroughly. The mixture of fat and neutralized
alcohol is then heated to boiling and titrated with tenth normal alkali
solution, using phenolphthalein as an indicator. As only the free fatty
acids are readily soluble in the alcohol and the fat itself only
slightly mixes with it, the flask should be well agitated toward the end
of the titration. When a faint pink color remains after thoroughly
agitating the flask the end point is reached. In order to calculate the
percentage of free fatty acid as oleic acid, multiply the number of
cubic centimeters of tenth normal alkali used as read on the burette by
0.0282 and divide by the number of grams of fat taken for the
determination and multiply by 100.
When dark colored oils or fats are being titrated it is often difficult
to obtain a good end point with phenolphthalein. In such cases about 2
cubic centimeters of a 2 per cent. alcoholic solution of Alkali Blue 6 B
is recommended.
Another method of directly determining the free fatty acid content of
tallow or grease upon which this determination is most often made is to
weigh out into an Erlenmeyer flask exactly 5.645 grams of a sample of
tallow or grease. Add about 75 cubic centimeters of neutralized alcohol.
Heat until it boils, then titrate with tenth normal alkali and divide
the reading by 2, which gives the percentage of free fatty acid as
oleic. If a fifth normal caustic solution is used, the reading on the
burette gives the percentage of free fatty acid directly. This method,
while it eliminates the necessity of calculation, is troublesome in that
it is difficult to obtain the exact weight of fat.
MOISTURE.
To calculate the amount of moisture contained in a fat or oil 5 to 10
grams are weighed into a flat bottom dish, together with a known amount
of clean, dry sand, if it is so desired. The dish is then heated over a
water bath, or at a temperature of 100-110 degs. C., until it no longer
loses weight upon drying and reweighing the dish. One hour should elapse
between the time the dish is put on the water bath and the time it is
taken off to reweigh. The difference between the weight of the dish is
put on the water bath and the time it is taken off when it reaches a
constant weight is moisture. This difference divided by the original
weight of the fat or oil x 100 gives the percentage of moisture.
When highly unsaturated fats or oils are being analyzed for moisture, an
error may be introduced either by the absorption of oxygen, which is
accelerated at higher temperature, or by the formation of volatile fatty
acids. The former causes an increase in weight, the latter causes a
decrease. To obviate this, the above operation of drying should be
carried out in the presence of some inert gas like hydrogen, carbon
dioxide, or nitrogen.
TITER.
The titer of a fat or oil is really an indication of the amount of
stearic acid contained therein. The titer, expressed in degrees
Centigrade, is the solidification point of the fatty acids of an oil or
fat. In order to carry out the operation a Centigrade thermometer
graduated in one or two-tenths of a degree is necessary. A thermometer
graduated between 10 degs. centigrade to 60 degs. centigrade is best
adapted and the graduations should be clear cut and distinct.
To make the determination about 30 grams of fat are roughly weighed in a
metal dish and 30-40 cubic centimeters of a 30 per cent. (36 degs.
Baume) solution of sodium hydroxide, together with 30-40 cubic
centimeters of alcohol, denatured alcohol will do, are added and the
mass heated until saponified. Heat over a low flame or over an asbestos
plate until the soap thus formed is dry, constantly stirring the
contents of the dish to prevent burning. The dried soap is then
dissolved in about 1000 cubic centimeters of water, being certain that
all the alcohol has been expelled by boiling the soap solution for about
half an hour. When the soap is in solution add sufficient sulphuric acid
to decompose the soap, approximately 100 cubic centimeters of 25 degs.
Baume sulphuric acid, and boil until the fatty acids form a clear layer
on top of the liquid. A few pieces of pumice stone put into the mixture
will prevent the bumping caused by boiling. Siphon off the water from
the bottom of the dish and wash the fatty acids with boiling water until
free from sulphuric acid. Collect the fatty acids in a small casserole
or beaker and dry them over a steam bath or drying oven at 110 degs.
Centigrade. When the fatty acids are dry, cool them to about 10 degs.
above the titer expected and transfer them to a titer tube or short test
tube which is firmly supported by a cork in the opening of a salt mouth
bottle. Hang the thermometer by a cord from above the supported tube so
it reaches close to the bottom when in the titer tube containing the
fatty acids and so that it may be used as a stirrer. Stir the mass
rather slowly, closely noting the temperature. The temperature will
gradually fall during the stirring operation and finally remain
stationary for half a minute or so then rise from 0.1 to 0.5 degs. The
highest point to which the mercury rises after having been stationary is
taken as the reading of the titer.
DETERMINATION OF UNSAPONIFIABLE MATTER.
In order to determine the unsaponifiable matter in fats and oils they
are first saponified, then the unsaponifiable, which consists mainly of
hydrocarbons and the higher alcohols cholesterol or phytosterol, is
extracted with ether or petroleum ether, the ether evaporated and the
residue weighed as unsaponifiable.
To carry out the process first saponify about 5 grams of fat or oil with
an excess of alcoholic potassium hydrate, 20-30 cubic centimeters of a 1
to 10 solution of potassium hydroxide in alcohol until the alcohol is
evaporated over a steam bath. Wash the soap thus formed into a
separatory funnel of 200 cubic centimeters capacity with 80-100 cubic
centimeters water. Then add about 60 cubic centimeters of ether,
petroleum ether or 86 degs. gasoline and thoroughly shake the funnel to
extract the unsaponifiable. Should the two layers not separate readily,
add a few cubic centimeters of alcohol, which will readily cause them to
separate. Draw off the watery solution from beneath and wash the ether
with water containing a few drops of sodium hydrate and run to another
dish. Pour the watery solution into the funnel again and repeat the
extraction once or twice more or until the ether shows no discoloration.
Combine the ether extractions into the funnel and wash with water until
no alkaline reaction is obtained from the wash water. Run the ether
extract to a weighed dish, evaporate and dry rapidly in a drying oven.
As some of the hydrocarbons are readily volatile at 100 degs.
Centigrade, the drying should not be carried on any longer than
necessary. The residue is then weighed and the original weight of fat
taken divided into the weight of the residue x 100 gives the percentage
unsaponifiable.
TEST FOR COLOR OF SOAP.
It is often desirable to determine the color of the finished soap by a
rapid determination before it is made into soap. It often happens,
especially with the tallows, that a dark colored sample produces a light
colored soap, whereas a bleached light colored tallow produces a soap
off shade.
To rapidly determine whether the color easily washes out of the tallow
with lye, 100 cubic centimeters of tallow are saponified in an enameled
or iron dish with 100 cubic centimeters of 21 degs. Baume soda lye and
100 cubic centimeters of denatured alcohol. Continue heating over a wire
gauze until all the alcohol is expelled and then add 50 cubic
centimeters of the 21 degs. Baume lye to grain the soap. Allow the lyes
to settle and with an inverted pipette draw off the lyes into a test
tube or bottle. Close the soap with 100 cubic centimeters of hot water
and when closed again grain with 50 cubic centimeters of the lye by just
bringing to a boil over an open flame. Again allow the lyes to settle
and put aside a sample of the lye for comparison. Repeat the process of
closing, graining and settling and take a sample of lye. If the lye is
still discolored repeat the above operations again or until the lye is
colorless. Ordinarily all the color will come out with the third lye.
The soap thus obtained contains considerable water which makes it appear
white. The soap is, therefore, dried to about 15 per cent. moisture and
examined for color. The color thus obtained is a very good criterion as
to what may be expected in the soap kettle.
By making the above analyses of fats or oils the main properties as to
their adaptability for being made into soap are determined. In some
cases, especially where adulteration or mixtures of oils are suspected,
it is necessary to further analyze same. The methods of carrying out
these analyses are fully covered by various texts on fats and oils and
we will not go into details regarding the method of procedure in
carrying these out.
TESTING OF ALKALIS USED IN SOAP MAKING.
The alkalis entering into the manufacture of soap such as caustic soda
or sodium hydroxide, caustic potash or potassium hydrate, carbonate of
soda or sodium carbonate, carbonate of potash or potassium carbonate
usually contain impurities which do not enter into combination with the
fats or fatty acids to form soap. It is out of the question to use
chemically pure alkalis in soap making, hence it is often necessary to
determine the alkalinity of an alkali. It may again be pointed out that
in saponifying a neutral fat or oil only caustic soda or potash are
efficient and the carbonate contained in these only combines to a more
or less extent with any free fatty acids contained in the oils or fats.
Caustic soda or potash or lyes made from these alkalis upon exposure to
the air are gradually converted into sodium or potassium carbonate by
the action of the carbon dioxide contained in the air. While the amount
of carbonate thus formed is not very great and is greatest upon the
surface, all lyes as well as caustic alkalis contain some carbonate.
This carbonate introduces an error in the analysis of caustic alkalis
when accuracy is required and thus in the analysis of caustic soda or
potash it is necessary to remove the carbonate when the true alkalinity
as sodium hydroxide or potassium hydroxide is desired. This may be done
by titration in alcohol which has been neutralized.
In order to determine the alkalinity of any of the above mentioned
alkalis, it is first necessary to obtain a representative sample of the
substance to be analyzed. To do this take small samples from various
portions of the package and combine them into a composite sample.
Caustic potash and soda are hygroscopic and samples should be weighed at
once or kept in a well stoppered bottle. Sodium or potassium carbonate
can be weighed more easily as they do not rapidly absorb moisture from
the air.
To weigh the caustic soda or potash place about five grams on a watch
glass on a balance and weigh as rapidly as possible. Wash into a 500
cubic centimeter volumetric flask and bring to the mark with distilled
water. Pipette off 50 cubic centimeters into a 200 cubic centimeter
beaker, dilute slightly with distilled water, add a few drops of methyl
orange indicator and titrate with normal acid. For the carbonates about
1 gram may be weighed, washed into a 400 cubic centimeter beaker,
diluted with distilled water, methyl orange indicator added and titrated
with normal acid. It is advisable to use methyl orange indicator in
these titrations as phenolphthalein is affected by the carbon dioxide
generated when an acid reacts with a carbonate and does not give the
proper end point, unless the solution is boiled to expel the carbon
dioxide. Litmus may also be used as the indicator, but here again it is
necessary to boil as carbon dioxide also affects this substance. As an
aid to the action of these common indicators the following table may be
helpful:
_Color in _Color in
_Indicator._ Acid Alkaline _Action of
Solution._ Solution._ CO_{2}._
Methyl orange Red Yellow Very slightly acid
Phenolphthalein Colorless Red Acid
Litmus Red Blue Acid
It may be further stated that methyl orange at the neutral point is
orange in color.
To calculate the percentage of effective alkali from the above
titrations, it must be first pointed out that in the case of caustic
potash or soda aliquot portions are taken. This is done to reduce the
error necessarily involved by weighing, as the absorption of water is
decided. Thus we had, say, exactly 5 grams which weighed 5.05 grams by
the time it was balanced. This was dissolved in 500 cubic centimeters of
water and 50 cubic centimeters or one tenth of the amount of the
solution was taken, or in each 50 cubic centimeters there were 0.505
grams of the sample. We thus reduced the error of weighing by one tenth
provided other conditions introduce no error. In the case of the
carbonates the weight is taken directly.
One cubic centimeter of a normal acid solution is the equivalent of:
Grams.
Sodium Carbonate, Na_{2}CO_{3} 0.05305
Sodium Hydroxide, NaOH 0.04006
Sodium Oxide, Na_{2}O 0.02905
Carbonate K_{2}CO_{3} 0.06908
Potassium Hydroxide, KOH 0.05616
Potassium Oxide, K_{2}O 0.04715
Hence to arrive at the alkalinity we multiply the number of cubic
centimeters, read on the burette, by the factor opposite the terms in
which we desire to express the alkalinity, divide the weight in grams
thus obtained by the original weight taken, and multiply the result by
100, which gives the percentage of alkali in the proper terms. For
example, say, we took the 0.505 grams of caustic potash as explained
above and required 8.7 cubic centimeter normal acid to neutralize the
solution, then
8.7 x .05616 = .4886 grams KOH in sample
.4886
----- x 100 = 96.73% KOH in sample.
.505
Caustic potash often contains some caustic soda, and while it is
possible to express the results in terms of KOH, regardless of any
trouble that may be caused by this mixture in soap making, an error is
introduced in the results, not all the alkali being caustic potash. In
such cases it is advisable to consult a book on analysis as the analysis
is far more complicated than those given we will not consider it. The
presence of carbonates, as already stated, also causes an error. To
overcome this the alkali is titrated in absolute alcohol, filtering off
the insoluble carbonate. The soluble portion is caustic hydrate and may
be titrated as such. The carbonate remaining on the filter paper is
dissolved in water and titrated as carbonate.
SOAP ANALYSIS.
To obtain a sample of a cake of soap for analysis is a rather difficult
matter as the moisture content of the outer and inner layer varies
considerably. To overcome this difficulty a borer or sampler may be run
right through the cake of soap, or slices may be cut from various parts
of the cake, or the cake may be cut and run through a meat chopper
several times and mixed. A sufficient amount of a homogeneous sample
obtained by any of these methods is preserved for the entire analysis by
keeping the soap in a securely stoppered bottle.
The more important determinations of soap are moisture, free alkali, or
fatty acid, combined alkali and total fatty matter. Besides these it is
often necessary to determine insoluble matter, glycerine, unsaponifiable
matter, rosin and sugar.
MOISTURE.
The analysis of soap for moisture, at its best, is most unsatisfactory,
for by heating it is impossible to drive off all the water, and on the
other hand volatile oils driven off by heat are a part of the loss
represented as moisture.
The usual method of determining moisture is to weigh 2 to 3 grams of
finely shaved soap on a watch glass and heat in an oven at 105 degrees
C. for 2 to 3 hours. The loss in weight is represented as water,
although it is really impossible to drive off all the water in this way.
To overcome the difficulties just mentioned either the Smith or Fahrion
method may be used. Allen recommends Smith's method which is said to be
truthful to within 0.25 per cent. Fahrion's method, according to the
author, gives reliable results to within 0.5 per cent. Both are more
rapid than the above manipulation. To carry out the method of Smith, 5
to 10 grams of finely ground soap are heated over a sand bath with a
small Bunsen flame beneath it, in a large porcelain crucible. The
heating takes 20 to 30 minutes, or until no further evidence is present
of water being driven off. This may be tested by the fogging of a cold
piece of glass held over the crucible immediately upon removing the
burner. When no fog appears the soap is considered dry. Any lumps of
soap may be broken up by a small glass rod, weighed with the crucible,
and with a roughened end to more easily separate the lumps. Should the
soap burn, this can readily be detected by the odor, which, of course,
renders the analysis useless. The loss in weight is moisture.
By Fahrion's method[13], 2 to 4 grams of soap are weighed in a platinum
crucible and about three times its weight of oleic acid, which has been
heated at 120 degrees C. until all the water is driven off and preserved
from moisture, is added and reweighed. The dish is then cautiously
heated with a small flame until all the water is driven off and all the
soap is dissolved. Care must be exercised not to heat too highly or the
oleic acid will decompose. The moment the water is all driven off a
clear solution is formed, provided no fillers are present in the soap.
The dish is then cooled in a dessicator and reweighed. The loss in
weight of acid plus soap is moisture and is calculated on the weight of
soap taken. This determination takes about fifteen minutes.
FREE ALKALI OR ACID.
(_a_) _Alcoholic Method._
Test a freshly cut surface of the soap with a few drops of an alcoholic
phenolphthalein solution. If it does not turn red it may be assumed free
fat is present; should a red color appear, free alkali is present. In
any case dissolve 2 to 5 grams of soap in 100 cubic centimeters of
neutralized alcohol and heat to boiling until in solution. Filter off
the undissolved portion containing carbonate, etc., and wash with
alcohol. Add phenolphthalein to the filtrate and titrate with N/10 acid
and calculate the per cent. of free alkali as sodium or potassium
hydroxide. Should the filtrate be acid instead of alkaline, titrate with
N/10 alkali and calculate the percentage of free fatty acid as oleic
acid.
The insoluble portion remaining on the filter paper is washed with water
until all the carbonate is dissolved. The washings are then titrated
with N/10 sulfuric acid and expressed as sodium or potassium carbonate.
Should borates or silicates be present it is possible to express in
terms of these. If borax is present the carbon dioxide is boiled off
after neutralizing exactly to methyl orange; cool, add mannite and
phenolphthalein and titrate the boric acid with standard alkali.
(_b_) _Bosshard and Huggenberg Method._[14]
In using the alcoholic method for the determination of the free alkali
or fat in soap there is a possibility of both free fat and free alkali
being present. Upon boiling in an alcoholic solution the fat will be
saponified, thus introducing an error in the analysis. The method of
Bosshard and Huggenberg overcomes this objection. Their method is
briefly as follows:
_Reagents._
1. N/10 hydrochloric acid to standardize N/10 alcoholic sodium
hydroxide.
2. Approximately N/10 alcoholic sodium hydroxide to fix and control the
N/40 stearic acid.
3. N/40 stearic acid. Preparation: About 7.1 grams of stearic acid are
dissolved in one liter of absolute alcohol, the solution filtered, the
strength determined by titration against N/10 NaOH and then protected in
a well stoppered bottle, or better still connected directly to the
burette.
4. A 10 per cent. solution of barium chloride. Preparation: 100 grams of
barium chloride are dissolved in one liter of distilled water and
filtered. The neutrality of the solution should be proven as it must be
neutral.
5. [Greek: alpha] naptholphthalein indicator according to Sorenson.
Preparation: 0.1 gram of [Greek: alpha] naphtholphthalein is dissolved in
150 cubic centimeters of alcohol and 100 cubic centimeters of water.
For every 10 cubic centimeters of liquid use at least 12 drops of
indicator.
6. Phenolphthalein solution 1 gram to 100 cubic centimeter 96 per cent.
alcohol.
7. Solvent, 50 per cent. alcohol neutralized.
MANIPULATION.
First--Determine the strength of the N/10 alcoholic sodium hydroxide in
terms of N/10 hydrochloric acid and calculate the factor, e. g.:
10 c.c. N/10 alcoholic NaOH = 9.95 N/10 HCl}
10 c.c. N/10 alcoholic NaOH = 9.96 N/10 HCl} 9.96
The alcoholic N/10 NaOH has a factor of 0.996.
Second--Control the N/40 stearic acid with the above alkali to obtain
its factor, e. g.:
40 c.c. N/40 alcoholic stearic acid =
10.18 c.c. N/10 NaOH }
40 c.c. N/40 alcoholic stearic acid = } 10.2
10.22 c.c. N/10 NaOH }
10.2 x F N/10 NaOH (0.996) = Factor N/40 stearic acid
Therefore Factor N/40 stearic acid = 1.016.
Third--About 5 grams of soap are weighed and dissolved in 100 cubic
centimeters of 50 per cent. neutralized alcohol in a 250 cubic
centimeter Erlenmeyer flask over a water bath and connected with a
reflux condensor. When completely dissolved, which takes but a few
moments, it is cooled by allowing a stream of running water to run over
the outside of the flask.
Fourth--The soap is precipitated with 15 to 20 cubic centimeters of the
10 per cent. barium chloride solution.
Fifth--After the addition of 2 to 5 cubic centimeters of [Greek: alpha]
naphtholphthalein solution the solution is titrated with N/40 alcoholic
stearic acid. [Greek: alpha] naphtholphthalein is red with an excess of
stearic acid. To mark the color changes it is advisable to first run a
few blanks until the eye has become accustomed to the change in the
indicator in the same way. The change from green to red can then be
carefully observed.
Let us presume 5 grams of soap were taken for the analysis and 20 cubic
centimeters of N/40 stearic acid were required for the titration then to
calculate the amount of NaOH since the stearic factor is 1.016.
20 x 1.016 = 20.32 N/40 stearic acid really required.
1 cubic centimeter N/40 stearic acid = 0.02 per cent. NaOH for 5 grams
soap.
[Greek: Delta] 20.32 cubic centimeters N/40 stearic acid = 0.02 x 20.32
per cent. NaOH for 5 grams soap.
Hence the soap contains 0.4064 per cent. NaOH.
It is necessary, however, to make a correction by this method. When the
free alkali amounts to over 0.1 per cent. the correction is + 0.01, and
when the free alkali exceeds 0.4 per cent. the correction is + 0.04,
hence in the above case we multiply 0.004064 by 0.04, add this amount to
0.004064 and multiply by 100 to obtain the true percentage. Should the
alkalinity have been near 0.1 per cent. we would have multiplied by 0.01
and added this.
If carbonate is also present in the soap, another 5 grams of soap is
dissolved in 100 cubic centimeters of 50 per cent. alcohol and the
solution titrated directly after cooling with N/40 stearic acid, using
[Greek: alpha] naphtholphthalein or phenolphthalein as an indicator,
without the addition of barium chloride. From the difference of the two
titrations the alkali present as carbonate is determined.
If the decomposed soap solution is colorless with phenolphthalein, free
fatty acids are present, which may be quickly determined with alcoholic
N/10 sodium hydroxide.
INSOLUBLE MATTER.
The insoluble matter in soap may consist of organic or inorganic
substances. Among the organic substances which are usually present in
soap are oat meal, bran, sawdust, etc., while among the common inorganic
or mineral compounds are pumice, silex, clay, talc, zinc oxide,
infusorial earth, sand or other material used as fillers.
To determine insoluble matter, 5 grams of soap are dissolved in 75 cubic
centimeters of hot water. The solution is filtered through a weighed
gooch crucible or filter paper. The residue remaining on the filter is
washed with hot water until all the soap is removed, is then dried to
constant weight at 105 degrees C. and weighed. From the difference in
weight of the gooch or filter paper and the dried residue remaining
thereon after filtering and drying, the total percentage of insoluble
matter may easily be calculated. By igniting the residue and reweighing
the amount of insoluble mineral matter can be readily determined.
STARCH AND GELATINE.
Should starch or gelatine be present in soap it is necessary to extract
5 grams of the soap with 100 cubic centimeters of 95 per cent.
neutralized alcohol in a Soxhlet extractor until the residue on the
extraction thimble is in a powder form. If necessary the apparatus
should be disconnected and any lumps crushed, as these may contain soap.
The residue remaining on the thimble consists of all substances present
in soap, insoluble in alcohol. This is dried and weighed so that any
percentage of impurities not actually determined can be found by
difference. Starch and gelatine are separated from carbonate, sulfate
and borate by dissolving the latter out through a filter with cold
water. The starch and gelatine thus remaining can be determined by
known methods, starch by the method of direct hydrolysis[15] and
gelatine by Kjeldahling and calculating the corresponding amount of
gelatine from the percentage of nitrogen (17.9%) therein.[16]
TOTAL FATTY AND RESIN ACIDS.
To the filtrate from the insoluble matter add 40 cubic centimeters of
half normal sulfuric acid, all the acid being added at once. Boil, stir
thoroughly for some minutes and keep warm on a water bath until the
fatty acids have collected as a clear layer on the surface. Cool by
placing the beaker in ice and syphon off the acid water through a
filter. Should the fatty acids not readily congeal a weighed amount of
dried bleached bees-wax or stearic acid may be added to the hot mixture.
This fuses with the hot mass and forms a firm cake of fatty acids upon
cooling. Without removing the fatty acids from the beaker, add about 300
cubic centimeters of hot water, cool, syphon off the water through the
same filter used before and wash again. Repeat washing, cooling and
syphoning processes until the wash water is no longer acid. When this
stage is reached, dissolve any fatty acid which may have remained on the
filter with hot 95 per cent. alcohol into the beaker containing the
fatty acids. Evaporate the alcohol and dry the beaker to constant weight
over a water bath. The fatty acids thus obtained represent the combined
fatty acids, uncombined fat and hydrocarbons.
DETERMINATION OF ROSIN.
If resin acids are present, this may be determined by the
Liebermann-Storch reaction. To carry out this test shake 2 cubic
centimeters of the fatty acids with 5 cubic centimeters of acetic
anhydride; warm slightly; cool; draw off the anhydride and add 1:1
sulfuric acid. A violet color, which is not permanent, indicates the
presence of rosin in the soap. The cholesterol in linseed or fish oil,
which of course may be present in the soap, also give this reaction.
Should resin acids be present, these may be separated by the Twitchell
method, which depends upon the difference in the behavior of the fatty
and resin acids when converted into their ethyl esters through the
action of hydrochloric acid. This may be carried out as follows:
Three grams of the dried mixed acids are dissolved in 25 cubic
centimeters of absolute alcohol in a 100 cubic centimeter stoppered
flask; the flask placed in cold water and shaken. To this cooled
solution 25 cubic centimeters of absolute alcohol saturated with dry
hydrochloric acid is added. The flask is shaken occasionally and the
action allowed to continue for twenty minutes, then 10 grams of dry
granular zinc chloride are added, the flask shaken and again allowed to
stand for twenty minutes. The contents of the flask are then poured into
200 cubic centimeters of water in a 500 cubic centimeter beaker and the
flask rinsed out with alcohol. A small strip of zinc is placed in the
beaker and the alcohol evaporated. The beaker is then cooled and
transferred to a separatory funnel, washing out the beaker with 50 cubic
centimeters of gasoline (boiling below 80 degrees C.) and extracting by
shaking the funnel well. Draw off the acid solution after allowing to
separate and wash the gasoline with water until free from hydrochloric
acid. Draw off the gasoline solution and evaporate the gasoline.
Dissolve the residue in neutral alcohol and titrate with standard alkali
using phenolphthalein as an indicator. One cubic centimeter of normal
alkali equals 0.346 grams of rosin. The rosin may be gravimetrically
determined by washing the gasoline extract with water, it not being
necessary to wash absolutely free from acid, then adding 0.5 gram of
potassium hydroxide and 5 cubic centimeters of alcohol in 50 cubic
centimeters of water. Upon shaking the resin acids are rapidly
saponified and extracted by the dilute alkaline solution as rosin soaps,
while the ethyl esters remain in solution in the gasoline. Draw off the
soap solution, wash the gasoline solution again with dilute alkali and
unite the alkaline solutions. Decompose the alkaline soap solution with
an excess of hydrochloric acid and weigh the resin acids liberated as in
the determination of total fatty acids.
According to Lewkowitsch, the results obtained by the volumetric method
which assumes a combining weight of 346 for resin acids, are very likely
to be high. On the other hand those obtained by the gravimetric method
are too low.
Leiste and Stiepel[17] have devised a simpler method for the
determination of rosin. They make use of the fact that the resin acids
as sodium soaps are soluble in acetone and particularly acetone
containing two per cent. water, while the fatty acid soaps are soluble
in this solvent to the extent of only about 2 per cent. First of all it
is necessary to show that the sample to be analyzed contains a mixture
of resin and fatty acids. This may be done by the Liebermann-Storch
reaction already described. Glycerine interferes with the method. Two
grams of fatty acids or 3 grams of soap are weighed in a nickel crucible
and dissolved in 15-20 cubic centimeters of alcohol. The solution is
then neutralized with alcoholic sodium hydroxide, using phenolphthalein
as an indicator. The mass is concentrated by heat over an asbestos plate
until a slight film forms over it. Then about 10 grams of sharp,
granular, ignited sand are stirred in by means of a spatula, the alcohol
further evaporated, the mixture being constantly stirred and then
thoroughly dried in a drying oven. The solvent for the cooled mass is
acetone containing 2 per cent. water. It is obtained from acetone dried
by ignited sodium sulfate and adding 2 per cent. water by volume. One
hundred cubic centimeters of this solvent are sufficient for extracting
the above. The extraction of the rosin soap is conducted by adding 10
cubic centimeters of acetone eight times, rubbing the mass thoroughly
with a spatula and decanting. The decanted portions are combined in a
beaker and the suspended fatty soaps allowed to separate. The mixture is
then filtered into a previously weighed flask and washed several times
with the acetone remaining. The solution of rosin soap should show no
separation of solid matter after having evaporated to half the volume
and allowing to cool. If a separation should occur another filtration
and the slightest possible washing is necessary. To complete the
analysis, the acetone is completely evaporated and the mass dried to
constant weight in a drying oven. The weight found gives the weight of
the rosin soap. In conducting the determination, it is important to dry
the mixture of soap and sand thoroughly. In dealing with potash soaps it
is necessary to separate the fatty acids from these and use them as
acetone dissolves too great a quantity of a potash soap.
TOTAL ALKALI.
In the filtrate remaining after having washed the fatty acids in the
determination of total fatty and resin acids all the alkali present as
soap, as carbonate and as hydroxide remains in solution as sulfate. Upon
titrating this solution with half normal alkali the difference between
the half normal acid used in decomposing the soap and alkali used in
titrating the excess of acid gives the amount of total alkali in the
soap. By deducting the amount of free alkali present as carbonate or
hydroxide previously found the amount of combined alkali in the soap may
be calculated.
To quickly determine total alkali in soap a weighed portion of the soap
may be ignited to a white ash and the ash titrated for alkalinity using
methyl orange as an indicator.
UNSAPONIFIED MATTER.
Dissolve 5 grams of soap in 50 cubic centimeters of 50 per cent.
alcohol. Should any free fatty acids be present neutralize them with
standard alkali. Wash into a separatory funnel with 50 per cent. alcohol
and extract with 100 cubic centimeters of gasoline, boiling at 50
degrees to 60 degrees C. Wash the gasoline with water, draw off the
watery layer. Run the gasoline into a weighed dish, evaporate the
alcohol, dry and weigh the residue as unsaponified matter. The residue
contains any hydrocarbon oils or fats not converted into soap.
SILICA AND SILICATES.
The insoluble silicates, sand, etc., are present in the ignited residue
in the determination of insoluble matter. Sodium silicate, extensively
used as a filler, however, will only show itself in forming a pasty
liquid. Where it is desired to determine sodium silicate, 10 grams of
soap are ashed by ignition, hydrochloric acid added to the ash in excess
and evaporated to dryness. More hydrochloric acid is then added and the
mass is again evaporated until dry; then cooled; moistened with
hydrochloric acid; dissolved in water; filtered; washed; the filtrate
evaporated to dryness and again taken up with hydrochloric acid and
water; filtered and washed. The precipitates are then combined and
ignited. Silicon dioxide (SiO_{2}) is thus formed, which can be
calculated to sodium silicate (Na_{2}Si_{4}O_{9}). Should other metals
than alkali metals be suspected present the filtrate from the silica
determinations should be examined.
GLYCERINE IN SOAP.
To determine the amount of glycerine contained in soap dissolve 25 grams
in hot water, add a slight excess of sulfuric acid and keep hot until
the fatty acids form as a clear layer on top. Cool the mass and remove
the fatty acids. Filter the acid solution into a 25 cubic centimeter
graduated flask; bring to the mark with water and determine the
glycerine by the bichromate method as described under glycerine
analysis.
When sugar is present the bichromate would be reduced by the sugar,
hence this method is not applicable. In this case remove the fatty acids
as before, neutralize an aliquot portion with milk of lime, evaporate to
10 cubic centimeters, add 2 grams of sand and milk of lime containing
about 2 grams of calcium hydroxide and evaporate almost to dryness.
Treat the moist residue with 5 cubic centimeters of 96 per cent.
alcohol, rub the whole mass into a paste, then constantly stirring, heat
on a water bath and decant into a 250 cubic centimeter graduated flask.
Repeat the washing with 5 cubic centimeters of alcohol five or six
times, each time pouring the washings into the flask; cool the flask to
room temperature and fill to the mark with 96 per cent. alcohol, agitate
the flask until well mixed and filter through a dry filter paper. Take
200 cubic centimeters of the nitrate and evaporate to a syrupy
consistency over a safety water bath. Wash the liquor into a stoppered
flask with 20 cubic centimeters of absolute alcohol, add 30 cubic
centimeters of absolute ether 10 cubic centimeters at a time, shaking
well after each addition and let stand until clear. Pour off the
solution through a filter into a weighed dish and wash out the flask
with a mixture of three parts absolute ether and two parts absolute
alcohol. Evaporate to a syrup, dry for one hour at the temperature of
boiling water, weigh, ignite and weigh again. The loss is glycerine.
This multiplied by 5/4 gives the total loss for the aliquot portion
taken. The glycerine may also be determined by the acetin or bichromate
methods after driving off the alcohol and ether if so desired.
SUGAR IN SOAP.
To determine sugar in soap, usually present in transparent soaps,
decompose a soap solution of 5 grams of soap dissolved in 100 cubic
centimeters of hot water with an excess of hydrochloric acid and
separate the fatty acids as usual. Filter the acid solution into a
graduated flask and make up to the mark. Take an aliquot containing
approximately 1 per cent. of reducing sugar and determine the amount of
sugar by the Soxhlet method.[18]
GLYCERINE ANALYSIS.
The methods of analyzing glycerine varied so greatly due to the fact
that glycerine contained impurities which acted so much like glycerine
as to introduce serious errors in the determinations of crude glycerine.
This led to the appointment of committees in the United States and
Europe to investigate the methods of glycerine analysis. An
international committee met after their investigations and decided the
acetin method should control the buying and selling of glycerine, but
the more convenient bichromate method in a standardized form might be
used in factory control and other technical purposes. The following are
the methods of analysis and sampling as suggested by the international
committee:
SAMPLING.
The most satisfactory method available for sampling crude glycerine
liable to contain suspended matter, or which is liable to deposit salt
on settling, is to have the glycerine sampled by a mutually approved
sampler as soon as possible after it is filled into drums, but in any
case before any separation of salt has taken place. In such cases he
shall sample with a sectional sampler (see appendix) then seal the
drums, brand them with a number for identification, and keep a record of
the brand number. The presence of any visible salt or other suspended
matter is to be noted by the sampler, and a report of the same made in
his certificate, together with the temperature of the glycerine. Each
drum must be sampled. Glycerine which has deposited salt or other solid
matter cannot be accurately sampled from the drums, but an approximate
sample can be obtained by means of the sectional sampler, which will
allow a complete vertical section of the glycerine to be taken including
any deposit.
ANALYSIS.
1. _Determination of Free Caustic Alkali._--Put 20 grams of the sample
into a 100 cc. flask, dilute with approximately 50 cc. of freshly boiled
distilled water, add an excess of neutral barium chloride solution, 1
cc. of phenolphthalein solution, make up to the mark and mix. Allow the
precipitate to settle, draw off 50 cc. of the clear liquid and titrate
with normal acid (_N_/1). Calculate the percentage of Na_{2}O existing
as caustic alkali.
2. _Determination of Ash and Total Alkalinity._--Weigh 2 to 5 grams of
the sample in a platinum dish, burn off the glycerine over a luminous
Argand burner or other source of heat,[19] giving a low temperature, to
avoid volatilization and the formation of sulphides. When the mass is
charred to the point that water will not be colored by soluble organic
matter, lixiviate with hot distilled water, filter, wash and ignite the
residue in the platinum dish. Return the filtrate and washings to the
dish, evaporate the water, and carefully ignite without fusion. Weigh
the ash.
Dissolve the ash in distilled water and titrate total alkalinity, using
as indicator methyl orange cold or litmus boiling.
3. _Determination of Alkali Present as Carbonate._--Take 10 grams of the
sample, dilute with 50 cc. distilled water, add sufficient _N_/1 acid to
neutralize the total alkali found at (2), boil under a reflux condenser
for 15 to 20 minutes, wash down the condenser tube with distilled water,
free from carbon dioxide, and then titrate back with _N_/1 NaOH, using
phenolphthalein as indicator. Calculate the percentage of Na_{2}O.
Deduct the Na_{2}O found in (1). The difference is the percentage of
Na_{2}O existing as carbonate.
4. _Alkali Combined with Organic Acids._--The sum of the percentages of
Na_{2}O found at (1) and (3) deducted from the percentage found at (2)
is a measure of the Na_{2}O or other alkali combined with organic acids.
5. _Determination of Acidity._--Take 10 grams of the sample, dilute with
50 cc. distilled water free from carbon dioxide, and titrate with _N_/1
NaOH and phenolphthalein. Express in terms of Na_{2}O required to
neutralize 100 grams.
6. _Determination of Total Residue at 160deg. C._--For this determination
the crude glycerine should be slightly alkaline with Na_{2}CO_{3} not
exceeding 0.2 per cent. Na_{2}O, in order to prevent loss of organic
acids. To avoid the formation of polyglycerols this alkalinity must not
be exceeded.
Ten grams of the sample are put into a 100 cc. flask, diluted with water
and the calculated quantity of _N_/1 HCl or Na_{2}CO_{3} added to give
the required degree of alkalinity. The flask is filled to 100 cc., the
contents mixed, and 10 cc. measured into a weighed Petrie or similar
dish 2.5 in. in diameter and 0.5 in. deep, which should have a flat
bottom. In the case of crude glycerine abnormally high in organic
residue a smaller amount should be taken, so that the weight of the
organic residue does not materially exceed 30 to 40 milligrams.
The dish is placed on a water bath (the top of the 160deg. oven acts
equally well) until most of the water has evaporated. From this point
the evaporation is effected in the oven. Satisfactory results are
obtained in an oven[20] measuring 12 ins. cube, having an iron plate
0.75 in. thick lying on the bottom to distribute the heat. Strips of
asbestos millboard are placed on a shelf half way up the oven. On these
strips the dish containing the glycerine is placed.
If the temperature of the oven has been adjusted to 160deg. C. with the
door closed, a temperature of 130deg. to 140deg. can be readily maintained
with the door partially open, and the glycerine, or most of it, should
be evaporated off at this temperature. When only a slight vapor is seen
to come off, the dish is removed and allowed to cool.
An addition of 0.5 to 1.0 cc. of water is made, and by a rotary motion
the residue brought wholly or nearly into solution. The dish is then
allowed to remain on a water bath or top of the oven until the excess
water has evaporated and the residue is in such a condition that on
returning to the oven at 160deg. C. it will not spurt. The time taken up to
this point cannot be given definitely, nor is it important. Usually two
or three hours are required. From this point, however, the schedule of
time must be strictly adhered to. The dish is allowed to remain in the
oven, the temperature of which is carefully maintained at 160deg. C. for
one hour, when it is removed, cooled, the residue treated with water,
and the water evaporated as before. The residue is then subjected to a
second baking of one hour, after which the dish is allowed to cool in a
desiccator over sulphuric acid and weighed. The treatment with water,
etc., is repeated until a constant loss of 1 to 1.5 mg. per hour is
obtained.
In the case of acid glycerine a correction must be made for the alkali
added 1 cc. _N_/1 alkali represents an addition of 0.03 gram. In the
case of alkaline crudes a correction should be made for the acid added.
Deduct the increase in weight due to the conversion of the NaOH and
Na_{2}CO_{3} to NaCl. The corrected weight multiplied by 100 gives the
percentage of _total residue at 160deg. C._
This residue is taken for the determination of the non-volatile
acetylizable impurities (see acetin method).
7. _Organic residue._--Subtract the ash from the total residue at 160deg.
C. Report as organic residue at 160deg. C. (it should be noted that
alkaline salts of fatty acids are converted to carbonates on ignition
and that the CO_{3} thus derived is not included in the organic
residue).
ACETIN PROCESS FOR THE DETERMINATION OF GLYCEROL.
This process is the one agreed upon at a conference of delegates from
the British, French, German and American committees, and has been
confirmed by each of the above committees as giving results nearer to
the truth than the bichromate method on crudes in general. It is the
process to be used (if applicable) whenever only one method is employed.
On pure glycerines the results are identical with those obtained by the
bichromate process. For the application of this method the crude
glycerine should not contain over 60 per cent. water.
REAGENTS REQUIRED.
(_A_) _Best Acetic Anhydride._--This should be carefully selected. A
good sample must not require more than 0.1 cc. normal NaOH for
saponification of the impurities when a blank is run on 7.5 cc. Only a
slight color should develop during digestion of the blank.
The anhydride may be tested for strength by the following method: Into a
weighed stoppered vessel, containing 10 to 20 cc. of water, run about 2
cc. of the anhydride, replace the stopper and weigh. Let stand with
occasional shaking, for several hours, to permit the hydrolysis of all
the anhydride; then dilute to about 200 cc., add phenolphthalein and
titrate with _N_/1 NaOH. This gives the total acidity due to free acetic
acid and acid formed from the anhydride. It is worthy of note that in
the presence of much free anhydride a compound is formed with
phenolphthalein, soluble in alkali and acetic acid, but insoluble in
neutral solutions. If a turbidity is noticed toward the end of the
neutralization it is an indication that the anhydride is incompletely
hydrolyzed and inasmuch as the indicator is withdrawn from the solution,
results may be incorrect.
Into a stoppered weighing bottle containing a known weight of recently
distilled aniline (from 10 to 20 cc.) measure about 2 cc. of the sample,
stopper, mix, cool and weigh. Wash the contents into about 200 cc. of
cold water, and titrate the acidity as before. This yields the acidity
due to the original, preformed, acetic acid plus one-half the acid due
to anhydride (the other half having formed acetanilide); subtract the
second result from the first (both calculated to 100 grams) and double
the result, obtaining the cc. _N_/1 NaOH per 100 grams of the sample. 1
cc. _N_/NaOH equals 0.0510 anhydride.
(_B_) _Pure Fused Sodium Acetate._--The purchased salt is again
completely fused in a platinum, silica or nickel dish, avoiding
charring, powdered quickly and kept in a stoppered bottle or desiccator.
It is most important that the sodium acetate be anhydrous.
(_C_) _A Solution of Caustic Soda for Neutralizing, of about N_/1
_Strength, Free from Carbonate._--This can be readily made by dissolving
pure sodium hydroxide in its own weight of water (preferably water free
from carbon dioxide) and allowing to settle until clear, or filtering
through an asbestos or paper filter. The clear solution is diluted with
water free from carbon dioxide to the strength required.
(_D_) _N_/1 _Caustic Soda Free from Carbonate._--Prepared as above and
carefully standardized. Some caustic soda solutions show a marked
diminution in strength after being boiled; such solutions should be
rejected.
(_E_) _N_/1 _Acid._--Carefully standardized.
(_F_) _Phenolphthalein Solution._--0.5 per cent. phenolphthalein in
alcohol and neutralized.
THE METHOD.
In a narrow-mouthed flask (preferably round-bottomed), capacity about
120 cc., which has been thoroughly cleaned and dried, weigh accurately
and as rapidly as possible 1.25 to 1.5 grams of the glycerine. A Grethan
or Lunge pipette will be found convenient. Add about 3 grams of the
anhydrous sodium acetate, then 7.5 cc. of the acetic anhydride, and
connect the flask with an upright Liebig condenser. For convenience the
inner tube of this condenser should not be over 50 cm. long and 9 to 10
mm. inside diameter. The flask is connected to the condenser by either a
ground glass joint (preferably) or a rubber stopper. If a rubber stopper
is used it should have had a preliminary treatment with hot acetic
anhydride vapor.
Heat the contents and keep just boiling for one hour, taking precautions
to prevent the salts drying on the sides of the flask.
Allow the flask to cool somewhat, and through the condenser tube add 50
cc. of distilled water free from carbon dioxide at a temperature of
about 80deg. C., taking care that the flask is not loosened from the
condenser. The object of cooling is to avoid any sudden rush of vapors
from the flask on adding water, and to avoid breaking the flask. Time is
saved by adding the water before the contents of the flask solidify, but
the contents may be allowed to solidify and the test proceeded with the
next day without detriment, bearing in mind that the anhydride in excess
is much more effectively hydrolyzed in hot than in cold water. The
contents of the flask may be warmed to, but must not exceed, 80deg. C.,
until the solution is complete, except a few dark flocks representing
organic impurities in the crude. By giving the flask a rotary motion,
solution is more quickly effected.
Cool the flask and contents without loosening from the condenser. When
quite cold wash down the inside of the condenser tube, detach the flask,
wash off the stopper or ground glass connection into the flask, and
filter the contents through an acid-washed filter into a Jena glass
flask of about 1 litre capacity. Wash thoroughly with cold distilled
water free from carbon dioxide. Add 2 cc. of phenolphthalein solution
(_F_), then run in caustic soda solution (_C_) or (_D_) until a faint
pinkish yellow color appears throughout the solution. This
neutralization must be done most carefully; the alkali should be run
down the sides of the flask, the contents of which are kept rapidly
swirling with occasional agitation or change of motion until the
solution is nearly neutralized, as indicated by the slower disappearance
of the color developed locally by the alkali running into the mixture.
When this point is reached the sides of the flask are washed down with
carbon dioxide-free water and the alkali subsequently added drop by
drop, mixing after each drop until the desired tint is obtained.
Now run in from a burette 50 cc. or a calculated excess of _N_/1 NaOH
(_D_) and note carefully the exact amount. Boil gently for 15 minutes,
the flask being fitted with a glass tube acting as a partial condenser.
Cool as quickly as possible and titrate the excess of NaOH with _N_/1
acid (_E_) until the pinkish yellow or chosen end-point color just
remains.[21] A further addition of the indicator at this point will
cause an increase of the pink color; this must be neglected, and the
first end-point taken.
From the _N_/1 NaOH consumed calculate the percentage of glycerol
(including acetylizable impurities) after making the correction for the
blank test described below.
1 cc. _N_/1 NaOH = 0.03069 gram glycerol.
The coefficient of expansion for normal solutions is 0.00033 per cc.
for each degree centigrade. A correction should be made on this account
if necessary.
_Blank Test._--As the acetic anhydride and sodium acetate may contain
impurities which affect the result, it is necessary to make a blank
test, using the same quantities of acetic anhydride, sodium acetate and
water as in the analysis. It is not necessary to filter the solution of
the melt in this case, but sufficient time must be allowed for the
hydrolysis of the anhydride before proceeding with the neutralization.
After neutralization it is not necessary to add more than 10 cc. of the
_N_/1 alkali (_D_), as this represents the excess usually present after
the saponification of the average soap lye crude. In determining the
acid equivalent of the _N_/1 NaOH, however, the entire amount taken in
the analysis, 50 cc., should be titrated after dilution with 300 cc.
water free from carbon dioxide and without boiling.
_Determination of the Glycerol Value of the Acetylizable
Impurities._--The total residue at 160deg. C. is dissolved in 1 or 2 cc. of
water, washed into the acetylizing flask and evaporated to dryness. Then
add anhydrous sodium acetate and acetic anhydride in the usual amounts
and proceed as described in the regular analysis. After correcting for
the blank, calculate the result to glycerol.
WAYS OF CALCULATING ACTUAL GLYCEROL CONTENT.
(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 160deg. 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 as glycerol. 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.
BICHROMATE PROCESS FOR GLYCEROL DETERMINATION. REAGENTS REQUIRED.
(_A_) _Pure potassium bichromate_ powdered and dried in air free from
dust or organic vapors, at 110deg. to 120deg. 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 15.5deg. 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 of _N_/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. solution of 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.
THE METHOD.
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 160deg. C.
NOTES.
(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.
SAMPLING CRUDE GLYCERINE.
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 the drum. 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
which has 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 x 10 x
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.