By Augustus H . Gill and Henry S. Simms
Ma s s a c h u s e t t s In s t i t u t s or Tb c h n o l o o y, Ca m b r i d g e, Ma s s a c h u s e t t s
A lthough m uch work has been done on perfecting the m ethods for identifying oils, little a tte n tio n has been paid to reducing th e q u a n tity required for a n a l
ysis. Occasionally, as in ex tractin g oils from leath er, th e oil chem ist is called upon to id en tify a q u a n tity of oil so sm all in a m o u n t as to h an d icap him in ob
taining accu rate results. T he purpose of th is paper is to show th a t an accu rate proxim ate analysis m ay be m ade upon an oil w hen only a few drops are av ail
able, an d w ith an accuracy com parable to th a t of th e usual m ethods.
F o r th e p resen t work a tte n tio n has been focused on four oils, selected because of th e ir widely differing properties. T hese were olive, lard , cottonseed, and raw linseed. I t is safe to assum e th a t these oils represent in th e ir properties all classes of saponifiable oils. A ny a d a p ta tio n of th e general te sts which would apply to th e m -would ap p ly equally well to others.
T he te s ts to which m ost a tte n tio n was given were th e iodine num ber, saponification value, a n d specific gravity.
A P P A R A T U S
T he a p p a ra tu s used in ob tain in g th e iodine n u m bers an d saponification values is show n in Figs. 1 to 7.
Fig. 1 rep resen ts th e o rd in ary titra tio n a p p a ra tu s on a sm all scale. T h e b o ttle was a lite r b o ttle an d
1 Received January 21, 1921.
th e b u re t was an o rd in ary b u re t-p ip e t of 10-cc. cap acity . F o r th is purpose one 30 cm. long was selected. A ball or bead valve was used. I t was of course neces
sary th a t th e drops falling from th e nozzle tip be as sm all as possible. To th is end th e tip was so draw n
o u t th a t th e o u tle t wras on th e side of th e tip a b o u t half w ay down, th e lower half being a fine glass rod dow n which th e solution would ru n a n d fall off in fine drops. (T he sam e effect m ay be produced w ith a finely p o in ted tu b e sm eared w ith a lay er of grease.) A p p aratu s of th is description w as used for th e sodium th io su lfate in th e iodine n u m b er d eterm in atio n s
548 TI 1 E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 13, No. 6 a n d for th e sta n d a rd hydrochloric acid in th e saponi
fication value determ inations.
Figs. 2 an d 3 show th e arran g em en t for filling th e p ip et used for th e iodine solution, th e p otassium iodide solution, an d th e alcoholic po tash solution. T he capaci
ties of these pipets were 3 cc., 1 .5 cc., and 2 .5 cc., respectively. T hey were blown for th is p articu lar w ork w ith unusually fine stem s. T hey were fitted in to stoppers of th e respective reag en t bottles, to gether w ith a fine capillary tu b e, as shown. On blowing th ro u g h th e capillary tu b e th e p ip et was filled w ith th e reagent. I t was raised (Fig. 3), allowed to d rain to th e m ark on th e stem , and em ptied in the usual m anner. W ith a very fine stem m ed p ip et small q u an tities of liquids m ay be h a n dled w ith negligible error. W ith th e arran g em en t described above, such liquids as iodine solution m ay be handled w ith o u t danger of b re a th ing th e fumes, and alcoholic potash solution m ay be handled w ithout danger of serious contam ination.
I t m ight be advisable in th is la t
te r case to seal a b u lb of lime in the m outh tu b e to absorb th e carbon dioxide in th e b re a th . T his was not done b y th e au th o rs, and no tro u b le resulted from this, since blanks were ru n w ith each d eterm ination.
Fig. 4 shows th e syringe pipet devised by th e au th o rs to m easure th e chloroform in th e iodine nu m ber determ inations. I t was blown and ground to fit th e b o ttle, an d was calibrated to deliver 1 cc. of chloro
form .
Fig. 5 shows th e d ropper used to deliver tw o large drops of starch solution in th e iodine n u m b er d e te r
m inations. A sim ilar d ropper used for phenolplithalein would deliver one sm all drop.
Tw enty-five-cc. E rlenm eyer flasks w ith sm all funnels m ade from glass tu b in g , as shown in Fig. 6, were used in o btaining th e saponification
F io . 8—Gr a v i t o m e t e r values
Iodine num bers were determ ined in 25-cc. glass- stoppered weighing bottles, as shown in Fig. 7. A stirrer was used to stir th e solution while titra tin g . T his proved to be very necessary in keeping th e solu
tion mixed during th e titra tio n .
T he a p p a ra tu s used in determ ining th e specific g ravities will be discussed la te r (Fig. 8).
T he general size of th e a p p a ra tu s used m ay be seen by com paring th e h an d in Fig. 3 w ith th e a p p a ra tu s in Figs, 1 to 7.
Q U A N T IT IE S U S E D
T he qu an tities of reagents were, in general, one- te n th those usually required for th e sam e tests. I t would be possible, w ith o u t d o ubt, to o b tain good re-, suits w ith still sm aller q u an tities. T his, however,
seems unnecessary. M ore d ilute reag en ts would be required, and th is would involve m any difficulties, aside from th e tro u b le of p reparing th e reagents. T he ra te of ad d itio n of iodine to th e oil would have to be studied w ith th e new stre n g th of iodine solution.
D ifficulty m ight be encountered in saponifying some oils in m ore dilute alcoholic p otash solution.
T he reagents used by th e a u th o rs were those cus
to m arily used for saponification and iodine num ber d eterm in atio n s (H anus m ethod), except th a t th e s ta n d ard hydrochloric acid was 0 .1 N ra th e r th a n 0 .5 N.
Sim ilarly, th e th io su lfate solution m ight be diluted from 0 .1 N to 0 .0 5 N , if desired. However, th e resu lts ob tain ed by th e a u th o rs could be reproduced m ore easily th a n could results obtain ed w ith m ore dilute solutions. F u rth erm o re, it is d oubtful if it would be desirable to o b tain th e saponification value w ith less th a n an o rd in ary drop of oil or to find th e iodine n um ber on less th a n 11 mg. (a sm all drop of oil).
I t was found th a t th e sam ples of oil could be reduced to considerably below on e-ten th th e norm al q u a n tity , while still using th e sam e q u an tities of reagents. In th e case of th e iodine num ber, th e q u a n tity was re duced to 11 mg., which is one-fourteenth to one- tw en ty -sev en th of th e usual sam ple.
E ven b e tte r results were ob tain ed w ith th e saponifica
tion value, for here th e w eight was reduced to less th a n 25 mg. w ith o u t prev en tin g accu rate results. This is one-fortieth to one-eightieth of th e usual am ount.
I t is n o t to be expected th a t th e oil a n aly st would be called upon to m ake an analysis w ith such sm all sa m ples on any b u t rare occasions. On such occasions he would find it a sim ple m a tte r to m ake such an a n a l
ysis if th e size of his a p p a ra tu s and th e q u an tities of his reag en ts were all reduced by th e sam e facto r—
one-tenth.
M E T H O D O F W E IG H IN G
T he m ethod of weighing used th ro u g h o u t th is work was th e single-swing m ethod of P a u l.1 T he principle involved is th a t of ta k in g a single scale reading as th e po in ter m akes its first swing. T he pans are so a d ju ste d th a t when th e pans are released th e p o in ter will swing to th e rig h t. T he distance to w hich it swings is observed, and th e p an release is throw n off.
This can be done very quickly. T he balance which was used w orked so well by th is m ethod th a t its ac
curacy could be relied upon w ith o u t repeating th e swing, th o u g h it was alw ays checked up by a second reading ta k e n in th e sam e w ay. F or convenience, th e scale was so num bered th a t th e m ark th ree spaces to th e rig h t of th e center was zero. Scale divisions to th e rig h t of th is were positive, while those to th e left were negative.
T he w eight on the p o in ter arm was so ad ju ste d th a t a swing of one scale division was equal to a difference in w eight of 1 mg. T he balance was so ad ju sted th a t when th ere were no w eights or equal w eights on b o th pans th e p o in ter would swing to th e rig h t as far as th e zero m ark on releasing th e pans.
T hus, in adding th e w eights in m aking a weighing, th e pans are released when each w eight is added ju s t
> J . A m . Chem Soc , 11 (1 9 1 9 ), 1151.
Ju n e , 1921 T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 549 long enough to see w hich way th e p o in ter s ta rts to
•swing, and, w hen w eights hav e been added to th e n e a r
e s t 10 mg., a reading is ta k e n of th e distance which th e po in ter swings. If, for instance, it swings to the + 2 m ark, one knows th a t th e object weighs 2 .0 mg. m ore th a n th e w eights on th e pan. Accordingly, th e rid er is placed on th e 2 .0 mg. m ark and an o th er reading is ta k e n , which should be exactly zero.
T his m ethod gave entire satisfaction, being n o t only quick b u t accurate.
D ATA FO R OILS B Y U S U A L L A R G E R -S C A L E M ETH O DS
Before going in to the m icroanalysis of th e oils which h ad been selected it was necessary to determ ine first th e properties of these oils b y th e usual m ethods a n d w ith th e usual am ounts. T his was done w ith
■care, a sufficient n u m b er of d eterm in atio n s being run in each case to w a rra n t reliance on th e resu lts ob
tain ed .
O il, Specific G ra v ity S aponification Iodine
15° C. V alue N u m b er
L a rd ... 0 .9 3 2 195.1 0 0 .9 O live... 0 .9 1 8 193 .9 8 4 .2
C o tto n see d 0 .9 2 2 1 9 5 .0 11 0 .3
L in seed ... 0 .9 3 4 191 .4 17 3 .8 E F F E C T OF E X T R A C T IO N ON OILS
I t was highly im p o rta n t to know w ith certa in ty w h eth er or n o t an y change is b ro u g h t a b o u t in th e properties of an oil w hen it is ex tracted w ith an o r
ganic solvent, such as gasoline or ether, and subse
quently freed from th a t solvent b y ev ap o ratio n . If th e solvent were able to affect th e iodine num ber, for instance, of an oil, th e p ractical application of m icro
chemical m ethods for identifying oils would be se
riously handicapped. If th e an aly st has a sm all sam ple of le ath er from w hich he can e x tra c t only a few drops of oil, he can identify th a t oil b y m icrochem ical m ethods only if he is certain th a t th ere is no change in its properties as a resu lt of th e ex traction.
T his was te ste d w ith th e four oils by th e following m ethod: A few drops of th e oils were poured in to an E rlenm eyer flask an d dissolved in eth er or gasoline.
The solvent was th e n ev ap o rated off in a c u rren t of
■air in th e case of th e n ondrying oils, an d of carbon dioxide in th e case of th e drying oils. W hen th e oil h ad been dried to a co n sta n t w eight, sam ples were rem oved b y m eans of a stirrin g rod, th e w eight of th e sam ples being determ ined by difference. B oth th e iodine num ber an d saponification value were determ ined on
■each oil.
T he resu lts of th e iodine n u m b er d eterm in atio n s are given below.
I?rom F ro m Original
O n , G asoline E th e r V alue
L a r d ... 6 0 .8 6 0 .7 6 0 .9 O live... 8 4 .0 8 3 .2 S 4 .2
C o tto n see d 11 0 .6 111 .0 110.3
L in se e d ... 1 7 3 .0 172 .0 173.8
The saponification values agreed w ith th e tru e values w ithin th e lim its of error of th e d eterm ination.
F rom th e above results it m ay be seen th a t th ere need be no d o u b t in th e m ind of th e a n a ly st as to th e possibility of error as a resu lt of chem ical action d u r
ing th e extraction, provided, of course, th a t th e p re
caution is ta k e n in th e case of drying oils to ev ap o rate off th e solvent in an in e rt atm osphere, such as car
bon dioxide or illum inating gas.
T he gentle h eat of a w ater b a th m ay be used to aid th e drying if th is seems advisable. T he a u th o rs used a w ater b a th consisting of tw o tin pans of 2- or 3-qt.
capacity, 26 cm. in d iam eter b y a b o u t 8 cm. deep.
One of these was filled a th ird full of w ater an d placed on a trip o d over a burner. T he o th er p an floated on th e w ater in th e first. Flasks co n tain in g solutions to be ev ap o rated could be placed in th e u p p er p an and receive a co n sta n t an d even heat.
D E T E R M IN A T IO N OF I O D IN E N U M B E R
T h e a p p a ra tu s has already been described. In general, th e m ethod is th e sam e as th a t com m only used for th e H an u s m ethod. T he q u a n titie s of th e reag en ts were reduced to o ne-tenth th e usual am ounts.
T he sam ples were reduced to 11 mg.
A few gram s of oil were poured in to a sm all beaker.
A sh o rt stirrin g ro d was placed in th e b eaker and th e w eight o b tain ed to th e fo u rth decim al place. A drop of oil was allowed to ru n from th e rod in to th e weighing b o ttle, and th e b eaker w as weighed again.
T he second sam ple was rem oved and th e beaker was w eighed th e th ird tim e. T h e difference betw een tw o weighings gives th e w eight of th a t sam ple. Six sam ples an d tw o blanks were usually ru n a t a tim e.
T he oil w as dissolved in 1 cc. of chloroform deliv
ered from th e syringe pipet.
A fter all (or nearly all) of th e sam ples h ad been weighed o u t, 3 cc. of iodine solution were delivered from th e p ip et (Figs. 2 an d 3) in to th e first sam ple. Five m inutes la te r iodine was added to th e second sam ple, an d in like m anner all th e sam ples were tre a te d a t 5-min. in terv als. A fter each sam ple h ad been acted upon b y th e iodine solution for exactly 15 m in., 1. 5 cc.
of potassium iodide solution were added from a pipet, an d im m ediately titr a te d w ith 0 .1 N N a2S203 solu
tion.
T h e above m ethod allows 5 m in. for each titra tio n . I t is essential th a t th e tim e of reactio n be exactly 15 m in., as th e iodine n u m b er will be high or low, accord
ing as th e actio n is allowed to continue m ore or less th a n th is tim e.
D uring th e titra tio n th e solution can n o t be mixed b y p u ttin g th e cover on and shaking, as th is is sure to cause a loss. T he mixing can be done very satisfac
to rily b y th e stirrer show n in Fig. 7. W ith th is stirrer th e s ta n d a rd solution m ay be ru n in fairly rap id ly rig h t up to th e p o in t where th e starch is added w ith
o u t danger of ru n n in g p a st th e end-point.
t h e b e a d v a l v e— A nother p recau tio n has to do w ith th e use of th e bead v alve of th e b u ret. I t is custo m ary w hen using one of these to pinch th e bead betw een th e fleshy surfaces of th e th u m b an d fore
finger, th u s producing a w rinkle in th e tu b in g th ro u g h w hich th e solution m ay pass. T his in v ariab ly pro
duces an error which, while it m ay be negligible in o rd i
n a ry work, is a serious m a tte r when an error of 0.01 cc. is n o t allow able. T he surface of th e th u m b presses no t only on th e tu b in g around th e bead b u t also on th e tu b in g above an d below th e bead. On rem oving th e pressure of th e th u m b th e tu b in g resum es its norm al shape an d a bubble of air is draw n up in to th e tip . T h is would be perm issible if th e bubble
550 T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 13, No. 6 were th e sam e size in all cases, b u t its size depends
upon th e m anner in which th e th u m b is rem oved, an d it m ay b e large or n o t form a t all, according to th e am o u n t of pressure on th e tu b in g below th e bead a fte r th e flow h ad ceased.
In ste a d of pressing w ith th e fleshy surfaces of th e th u m b and forefinger, one should press on one side w ith th e end of th e th u m b n ail and on th e o th er side w ith th e end of th e forefinger n ear th e nail. In th is w ay no air is draw n up an d th e flow m ay be so easily regulated th a t no drops of solution are allowed to re
m ain on th e tip.
r e a d i n g t h e b u r e t— In an alytical laboratories
various devices are used to aid in read in g burets.
Am ong these are th e use of p ap er (usually black paper) w rapped aro u n d th e b u re t an d fastened w ith a pin;
th e telescope w’hich is fastened to th e b u re t an d slides up an d dow n on it; an d th e use of b u rets hav in g a blue line flashed on th e side opposite th e scale.
T he experience of th e w riters is th a t these m ethods are all cum bersom e, inconvenient, slow, an d n o t so accu rate as m ight som etim es be desired. Accord
ingly a different m ethod, which has none of these faults, was ad o p ted . A pocket m irror was placed ag ain st th e back of th e b u re t a t th e level of th e m eniscus and sw ung around so th a t th e observer was looking d irectly in to it. B y raising or low ering his head u n til th e scale g rad u atio n nearest th e m eniscus was in line w ith its im age in th e m irror he was sure th a t th ere could be no error th ro u g h parallax. W ith o u t m oving his h ead , th e observer th e n sw ung th e m irror around (keeping it in co n tact w ith th e b u re t all th e while) u n til th e im age of th e lig h t from th e window could be seen in such a position as to m ake th e m eniscus very clearly defined. T he observer m u st be facing in a direction n eith er to w ard nor directly aw ay from th e window.
T his can be done very quickly, and one can read w ith rem ark ab le accuracy, w ith o u t ta k in g an y more tim e th a n would be required to get a n approxim ate reading w ith o u t any appliance.
T he tip of th e b u re t was of th e ty p e described above.
E ven in th is w ay it was difficult to get drops sm aller th a n one-sixtieth cc. Since th e required accuracy did n o t perm it an error of 0 .0 1 cc., th is caused an o th er diffi
c u lty which was overcom e b y tran sferrin g , n ear th e end-point, half a drop a t a tim e from th e tip to th e solution by m eans of th e stirrin g rod.
M ore accu rate results were obtain ed , how ever, by th e use of a tip having a longer glass th re a d on th e end w hich dipped in to th e solution. In th is wray drops were n o t form ed a t all, b u t th e sta n d a rd solution could ru n o u t in q u an tities m uch sm aller th a n a drop.
M ore accu rate results were obtain ed , how ever, by th e use of a tip having a longer glass th re a d on th e end w hich dipped in to th e solution. In th is wray drops were n o t form ed a t all, b u t th e sta n d a rd solution could ru n o u t in q u an tities m uch sm aller th a n a drop.