Pure 1 % 5 % m in
W o o d S tu m p turpcn - kero kero- 5 % 5 % eral pulp. turp. tine. sene. sene. hexane, elaine. oil.
Steam d istil. . . . trace 4 .5 0 .3 1 . 0 1 . 0 1 . 0 4 .5 9 .0
R efractom eter . high high high high high 78 80
H2S O * d i s t i l.... 70 17 8 .0 10 .0 1 4 .0 1 2 .0 10.0 7
R efractom eter . 100 90 77 60 48 63 50 90
HNOv t rca tm 't. n on e 0 .5 1 .5 4 .5 3 .0 5 .0 5 .0
R efractom eter . 33 9 0 .0 low 18
R efractom eter o f the adulterant 8 8 low 25 60
T h e m ethod in detail is as follow s: 100 cc. sam ple, in a suitable flask (500 cc. Jen a K je ld a h l answers nicely), is distilled in a current of liv e steam. T h e residue and d istillate are transferred to separatory funnels and the w ater tapped off.
The distillate is returned to the flask, treated w ith 500 cc. of concentrated sulphuric acid v e ry grad
ually, shaken, and carefu lly cooled (MeCand- less’s m ethod). 25 cc. w a ter are added and the m ixture distilled w ith steam , to a to ta l of 100 cc.
W ith pure turpen tines the am ount of oil is uni
form ly 8 cc., an excess indicating adulteration.
This oil is added to th e residue from the first di
rect steam distillation.
A volum e of fum ing n itric acid, equal to three times th a t of the com bined residues, is placed in a separatory funnel and thoroughly cooled in ice water. T h e com bined oils are now added, drop b y drop, shaking carefu lly and keep in g cold.
A fter all the oil has been added, allow to rest a few m om ents and draw off the acid lay er. W ash
1Am. Ch. J.. 12, 102.
the rem aining oil once w ith fum ing n itric acid, tw ice w ith o rd in ary strong nitric acid, and fin ally several tim es w ith w ater. M easure th e volum e.
T h e refractom eter readings m ay ad van tageo u sly be m ade on the various products obtained, b u t are b y no m eans essential.
W ith pure turpentine a residuum of about 0.5 per cen t, w ill be obtained, and allow ance for this m ust a lw ays be made.
In the case of w ood turpentine 110 such residuum is obtained, or a t m ost, a m ere trace, and 110 cor
rection is necessary.
In the ab o ve series of experim ents, then, the results, a fter m aking the correction, are:
A d ded , Found, per cen t. per cent.
K erosen e a d u lteran t... 1 . 0 1 . 0 K erosene a d u lteran t... 5 .0 4 .0
E laine o i l ... 5 .0 4 .5
Mineral oil, h e a v y ... 5 .0 4 .5
H e x a n e 5 .0 2 .5
show ing th a t w ith such petroleum products as are com m ercially em ployed, the m ethod yield s alm ost q u a n tita tiv e results, irrespective of the physical constan ts thereof, or of the turpen tine em ployed.
A s little as one per cen t, is found w ith o u t an y trouble. W ith exceed in gly lig h t products — w hich are n o t used, how ever— the results w ould be low.
La b o r a t o r yo f
Ma r i n e ra n d Ho s k i n s, .
Ch i c a g o.
THE DETERMINATION OF TOTAL, FIXED AND VOLATILE ACIDS IN WINES.
By Ju l i u s Ho r t v e t. R e ceiv ed S eptem b er 21, 1908.
Considered from the standpoin t n ot on ly of the food chem ist b u t of the industrial chem ist as well, determ ination s of total, fixed and vo latile acids in w ines are am ong the m ost im p ortan t th a t are re
quired in a com plete course of analysis. T hese determ inations are necessary not o n ly for the ju d g in g of wines in accordance w ith legal standards of p u rity , b u t th ey also afford a t tim es a ve ry crucial in sigh t into conditions relating to soundness or q u a lity. A t an earlier d ate th an the la tte r p art of the la st cen tury these considerations were not so m uch em phasized, doubtless because th e y were b u t little understood.
T h e first m ethods of an alysis were of such a c h aracter as one m igh t e x p ec t in the beginnings of our know ledge of ferm ented liquors as a class. T h e first know n m ethod of determ ining volatile acids
<32
consisted in distilling a measured q u a n tity of the sam ple to ab out one-third of its original volum e and titratin g the distillate. T h e results m ust o bviously have been too low . T h e n e xt step ap pears to have been in fa vo r of an indirect course of procedure w hereby the total acids w ere first titrated , then the wine evaporated off and the fixed acids titrated in the residue. F rom the difference between these titrations w as calculated the am ount of v o latile acids. V ariou s m odifications of this method cam e into use.
K isse l1 proposed evap orating th e wine w ith sand or granulated glass, then d ryin g the residue in an oven before titratin g the fixed acids.
W eigert2 evaporated 20 cc. of wine together w ith sand or pum ice or paper cu ttin gs in a sm all beaker, then heated the residue for a tim e a t io o ° C.
Nessler and B a rth 3 evaporated 20 cc. of wine and heated the residue 20 m inutes on a boiling
w ater-bath. •
In all these m ethods the aim appears to have been to lib erate the total volatile acids b y a pro- . longed heating of the e xtract. T h a t an appreciable change m ight occur in the e x tra c t constituents as a result of such treatm en t w as not a t first con
ceived. A t a later date, however, there developed grounds for the belief th a t certain of the fixed acids disappeared, in consequence of which, on titratin g the residue, there was obtained too small a result. Hence the result for volatile acids would be too high. T hese considerations fin ally resulted in the abandonm ent of. the so-called indirect m eth
ods, and it was again proposed to separate the vo la
tile from the fixed acids b y m eans of distillation and to titrate the vo latile acids in the distillate. B u t because the vo latile acids pass over only slowly and w ith difficulty, a sim ple distillation as in the determ ination of alcohol could obviously not be em ployed.
F irst K issel4 proposed a m ethod w hich w as sub
stan tially as fo llo w s:
F ifty cc. of w in e were heated to boiling w ith 20 cc. of a solution ,of phosphoric acid of specific g ra v ity 1.12, distilled from a retort on a sand-bath to 50 cc. distillate, 50 cc, of; Water added, the dis
tilla tio n continued to an additional 50. cc. distillate, and the operation repeated three, tim es until a total of 250 cc. of d istillate .w as obtained. T h is m ethod was v e ry laborious .and slow,, the
d.eternlina-. } Zeitschr. A nalyt. Chemie, 8, 416 (1869).
. ■ « Ibid.. 18, 208 (1S79). '
> Ibid.. 42, 166 (1SS3). '
. * Ibid..
8
, 416 (1869). . : ' . : ; ;.tion requiring from four to six hours’ tim e and constan t close supervision. .
W eige rt1 distilled 50 cc. of wine to e x tra c t con
sistency under reduced pressure in a brine b ath a t 109° C., added 50 cc. of w ater and again distilled.
L ater, W olff2 devised a m ethod of distillin g under dim inished pressure on a sand-bath, allow ing the w ine and fin ally w ater to pass slow ly through a funnel-tube into the flask.
N essler and B a rth 3 then cam e forw ard w ith a new m ethod in w hich it w as directed to distil 50 cc.
o f wine in a calcium chloride bath a t 1 1 9 0 C. T h e d istillation w as prolonged for a tim e a fte r the wine w as reduced to a syru p y consistency and finally a stream of carbonic oxide gas w as passed through the distilling flask.
S h o rtly afterw ards, in 1883, L indem ann4 de
scribed a m ethod of drivin g ou t the vo latile acids b y steam , and this m ethod form s the basis of the official m ethods w hich for some years have been prescribed in E urope and in A m erica. In its es
sential details, the present official m ethod6 is as follow s:
F ifty cc. of wine are distilled in a curren t of steam , in the m eantim e heating the flask containing the sam ple until the liquid boils and regulating the flam e so th a t the volum e rem ains constant.
T w o hundred cc. of d istillate are collected and titrated w ith tenth-norm al sodium hydroxide, using phenolphthalein as an indicator.
Chem ists w ho h ave had considerable experience w ith this m ethod m ust h ave noticed th a t it often happens th a t d istillates collected beyond 200 cc.
show a m ore or less strong acid reaction. T h is is the case especially w ith certain red wines, n o tab ly B urgundys, P orts and Clarets and w ines of the Sautern e typ e. In fact, as the accom p an yin g tab le shows, it seldom if ever occurs th a t the first 200 cc. d istillate contains, even to a fair a p p ro x i
m ation, the total volatile acids. In some instances it is seen th a t b y carryin g the d istillation beyond 200 cc. the error is ve ry considerable. F or exam ple, follow ing closely the official m ethod and collecting 400 cc. of distillate, there are shown the follow ing rates of increase in the to ta l vo latile acids: in a B u rgu nd y, ap p roxim ately 14 per cen t.; in tw o sam ples of P ort, resp ectively 13 and 14 per cen t.;
in a Claret, 13 per cen t.; and in a w h ite wine, 9 per
" 1 Zeitschr. A n alyl.2Chemic, 18, 208 (1879).
. ; f R e pert. A nalyt. Cliemiet 1, 213 (1883).
3 Zeitschr. Anolyi. Chemie, 22, 166 (1883), 1 * Ibid.] 22, 516 ( 1 8 8 3 ) . ...
» B ull. 107, U . S . D ept. A g r.. p . 86. .i i
T H E J O U R N A L O F 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 . 33
cent. T h ere occur indeed wines in w hich the com e too large, an insufficient am ount of volatile volatile acids appear never to becom e com pletely acids w ill pass over; if the d istillation be too rapid exhausted, in which, in fact, the d istillate fails to and th e volum e of the wine be perm itted to dim inish appear perm an ently n eutral even a fter very pro- too m uch, there m ay occur an overheatin g and the longed distilling. T h is phenom enon m ay be at- am ount of vo latile acids w ill be too great. F in ally, tributed n o t so m uch to acids of difficult v o la tility in order to obtain a fa irly acceptable concordance as to a possible decom position of the e x tra c t con- in results, th e distillation m ust be w atched from stituents under the influence of prolonged heating beginning to end w ith the greatest care,
b y the d irect action of the flam e w hich the official I t has also been recognized th a t the agreem ent directions require should be m aintained below the in results obtained b y se venal distillations on a given flask containing the sam ple. I t w ould seem, sam ple fails to reach as high a degree as ough t to be therefore, th a t 300 cc., or a t m ost 400 cc., of dis- expected, even in ap p roxim ately e x a c t determ ina-tillate should contain p rac tica lly all of the vo latile tions. W hen the distillation s are carried ou t to acids, and th a t it m ay n o t be necessary or p ractical 400 cc., or even until the van ish in g p oint of a cid ity to prolong th e distillation until the la st portions of is fa irly reached, the results often fail to agree w ithin the d istillate are neutral. T h e results obtained on reasonable lim its. A difference in the results of the the sixteen sam ples of wine included in the foregoing titratio n s am ounting to from 0.3 to 0.5 cc. of the
Vo l a t i l e Ac i d s i n Wi n e s.
(R esu lts a ccordin g to present official m eth od .) D istillates.
R esu lts in term s o f cc . N / l N a O H required to neutralize Per cent.
/--- '---—» a cid in
F irst S econ d T h ird F ou rth F ifth First F irst First T ota l first „
S am ple.1 100 cc . 100 cc . 100 cc. 100 c c . 100 cc . 200 c c . 300 cc. 400 cc . 500 cc . 300 cc.
1 C laret 6 .3 0 2 .1 0 0 .6 0 0 .3 0 0 .1 5 8 .4 0 9 .0 0 9 .3 0 9 .4 5 9 5 .2
2 Z in fa n d el 5 .8 0 1 .7 0 0 .5 0 0 .2 5 0 .1 5 7 .5 0 8 .0 0 8 .2 5 8 .4 0 9 5 .2
3 B u rg u n d y 9 .2 5 3 .6 5 1 .2 5 0 .5 5 0 .2 0 1 2 .9 0 14.1 5 1 4 .7 0 1 4 .9 0 9 5 .0
4 S h erry 4 .6 5 1 .5 5 0 .5 0 0 .2 5 0 .1 0 6 .2 0 6 .7 0 6 .9 5 7 .0 5 9 3 .6
5 S h erry 5 .6 0 2 .2 0 1 .1 0 0 .7 0 0 .3 0 7 .8 0 8 .9 0 9 .6 0 9 .9 0 9 0 .0
6 P o r t 10.7 0 3 .4 5 1 .2 5 0 .6 5 0 .2 5 14.15 1 5 .4 0 16.05 1 6 .3 0 9 4 .7
7 P o r t 5 .4 5 2 .0 0 0 .7 0 0 .3 5 0 .1 5 7 .4 5 8 .1 5 8 .5 0 8 .6 5 9 4 .2
8 M u sca t 2 .7 5 1 .0 0 0 .4 0 0 .2 5 0 .1 0 3 .7 5 4 .1 5 4 .4 0 4 .5 0 9 2 .2
9 H o c k 2 .8 5 0 .9 0 0 .5 0 0 .2 5 0 .1 0 3 .7 5 4 .2 5 4 .5 0 4 .6 0 9 2 .4
10 W h ite w in e ... 4 .4 5 1 .4 5 0 .8 0 0 .4 5 0 .1 5 5 .9 0 6 .7 0 7 .1 5 7 .3 0 9 1 .7 11 W h ite w in e ... 6 .9 0 2 .2 5 0 .5 0 0 .3 5 0 .2 0 9 .1 5 9 .6 5 1 0 .0 0 1 0 .2 0 9 4 .6 12 P o r t . . ... 2 .1 5 . 0 .8 0 0 .3 5 0 .2 0 0 .0 0 2 .9 5 3 .3 0 3 .5 0 3 .5 0 9 4 .3 13 S h erry... 5 .9 0 2 .4 0 0 .8 5 0 .4 5 0 .1 5 8 .3 0 9 .1 5 9 .6 0 9 .7 5 9 3 .8 14 C laret... 7 .6 5 2 .6 5 0 .9 5 0 .4 0 0 .1 5 1 0 .3 0 11.25 11.65 1 1 .8 0 9 5 .7
15 A n g elica ... 4 .7 0 1 .6 5 0 .6 0 0 .3 0 0 .1 0 6 .3 5 6 .9 5 7 .2 5 7 .3 5 9 4 .5
16 P o r t ... 4 .1 0 1 .9 5 0 .7 5 0 .3 5 0 .1 5 6 .0 5 6 .8 0 7 .1 5 7 .3 0 9 3 .1
table show th a t in o n ly fou r cases did the fifth 100 stand ard alk ali has often been noted, and the cc. of d istillate require as m uch as 0.2 cc. of tenth- differences are com m only fa r greater a t the close of normal alkali to n eutralize; hence, for p ractical the 200 cc. period, am ounting to 0.6 or o.S cc. in purposes it m ay be assum ed th a t the van ish in g several instances. •
point of the vo latile acids occurs w hen 500 cc. of B riefly, then, the objections to the present official distillate h ave passed over. On this basis, the m ethod are :
results obtained show th a t the proportion of volatile (1) T h e m ethod is com plicated, requiring rather acids collected in th e first 300 cc. of d istillate elab orate ap p aratu s and tiresom e supervision, ranges from 90.0 to 95.7 per cen t., only fou r sam ples (2) T h e prolonged heating of the w ine b y the showing a proportion sligh tly greater than 95 per d irect action of the flam e doubtless affects in some cent. . Thus, éven in th e present official m ethod, m anner the constitu tion of th e acid ingredients, if the entire ap p aratu s be of fixed dim ensions and (3) T h e results do n o t to a sufficient ex ten t relations in addition to th e other conditions ex- represent th e-total vo latile acids,
presslv stipulated, a large p a rt of th e fundam ental . (4) T h e results are n o t reason ab ly concordant error is still retained even b y -c a rry in g the distilla- in the hands of different persons or even in the tion to. 300 cc. ; I f t h e , d istillation be conducted hands of a single in d iv id u a l.. , , . slowly and the volum e of the w in e perm itted ,to be- O w in g to these considerations, variou s chem ists
1 Samples 1 to 11 furnished b x California, W in e . A ssociation, 1906; sam ples 12 t o 16 obtained from various, sources. . ...
34
h ave proposed the abandonm ent of the direct m ethod of determ ining vo latile acids in favor of an d n d irect course of procedure. A fte r a prolonged exam in ation of the relative m erits of these general m ethods, W in d isch 1 proposes the follow ing:
T w en ty-fiv e cc. of wine are titrated in the usual m anner for total acids, using litm us or litm us paper as indicator. A n oth er 25 cc. portion is then evaporated on a w ater-bath in a porcelain dish to 3 to 5 cc., the residue .dissolved in ab o u t 25 cc. of h ot w ater, the liquor again evap orated to 3 to 5 cc., the residue again dissolved in ab o u t 25 cc. of hot w ater, and the liquor evap orated a third tim e to 3 to 5 cc. F in ally, the residue is dissolved in hot w ater and the fixed acids titrated , using litm us as an indicator. T h e difference betw een the results of these titratio n s represents the vo latile acids.
G uerin2 has devised a m ethod w hich contem plates gettin g rid of coloring m atter. T h e determ ination is m ade as follow s:
Ten cc. of wine (previously boiled a few minutes under a reflux condenser) are treated w ith 5 cc. of a ten per cent, solution of m ercuric acetate, filtered from the precipitate and washed w ith cold w ater until the filtrate and washings equal 300 cc. T h e colorless liquid is treated w ith 10 cc. of a tw en ty per cent, solution of sodium -potassium tartrate and titrated w ith fourth-norm al potassium h y droxide, using phenolphthalein as an indicator.
A b lank determ ination is m ade w ith w ater in place of wine, using the sam e q uantities of reagents and titratin g as before. T h e difference betw een the results corresponds to the total acids. A nother 10 cc. portion is evaporated gen tly on a w ater-bath to a thin sy ru p y consistency, m ixed w ith a little hot w ater and evaporated again. T h e residue is tak en up w ith boiling w ater, cooled and clarified, and the fixed acids titrated and determ ined as in the m ethod for total acids. T h e difference betw een th is result and th a t obtained for total acids cor
respond to the am ount of v o latile acids.
R oos and M estrezat3 heat 20 cc. of wine under reduced pressure on a w ater-bath and distil off the vo latile con stituents until the contents of the flask have been reduced to 2 to 3 cc. T w e n ty cc. of w a ter are then run in and the distillation continued, under reduced pressure, until th e volum e is reduced to 5 to 6 cc. A second addition of 20 cc. of w ater is m ade and th e volum e fin ally reduced to ab out
1 Ztitschr. fu r UnUrsuchuno der Nahrungs und GenussmiiUl, 9, 70 (1905).
* J ou r. Pharm . C hcm ie, 25, 4 9 1 -2 (1907).
* B ull. A ssoc. Chim . Suer., 25, 4 1 -9 (1907).
io cc. T h e fixed acids are titrated in the residue, using tenth-norm al sodium h ydroxide togeth er w ith phenolphthalein as an indicator.
O ther investigators h ave proposed variou s m odi
fications of a m ethod of carryin g o ut the volatile acids b y m eans of a curren t of steam .
C u rtel1 heats 25 cc. of w ine and 25 cc. of w ater in a sm all flask on a w ater-bath, in the m eantine passing steam through the liquor. T h e fixed acids are titrated in th e residue.
R o b in 2 proceeds in the follow ing m anner: T h e app aratus consists of a 60 cc. ord inary round flask and a 250 cc. E rlenm eyer flask, the la tte r of w hich is provided w ith a stopper in w hich is fitted a funnel togeth er w ith a d eliv ery tub e w hich leads to near the bottom of the sm aller flask. T en cc.
of wine are introduced into the sm aller flask, the w ater in the E rlenm eyer heated to boiling and the steam passed through the w ine from 40 to 45 m inutes, in the m eantim e heatin g the sm aller flask gen tly b y m eans of a sm all flam e. T h e E rlen m eyer is then raised until the d elivery tub e does not dip into the wine, the tu b e rinsed off w ith w ater, the liquor transferred to a beaker and the fixed acids titrated .
In these m ethods the to ta l acids are titra te d in a separate, portion of the sam ple and the vo latile acids determ ined b y difference.
Sellier3 has described a sim ple ap p aratu s w hich consists of a sm all w ide-neck flask in to w hich is fitted a cylindrical-shaped flask. In the bottom of the latter flask is a sm all opening leading inw ard through a siphon-shaped tub e ben t b a ck upon itself and term inating a t a p o in t close to the bottom . In m aking the determ ination, 50 to 60 cc. of dis
tilled w ater are placed in the larger flask, the sm aller flask fitted into the w ide neck b y m eans of a section of rubber tubing, 10 cc. of w ine run in and the w ater heated to boiling. T h e steam passing through the wine carries o u t the vo latile acids, in the m eantim e causing no appreciable change in the volum e of the wine liquor. W hen the w a ter is reduced to ab o u t 5 cc. the flam e is rem oved and as the app aratus cools the rem aining liq uor is draw n into the larger flask. T h e inner flask is rinsed ou t w ith a little h ot w ater, the tw o flasks disconnected, the liquor cooled and the fixed acids titrated .
T h is m ethod has been em ployed in th is lab orato ry in the analysis of a num ber of sam ples of w ine and in the in vestigation of a dozen or m ore of the com m on
* A nnal. Chim . A n a lyt., S, 361 (1901).
2 J o u r. P h a rm . C hlm .% 1 9 , 5 3 1 -3 (1904).
* An nul. Chim . A n alyt., 5, 414 (1901).
T H E J O U R N A L O F 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 . 35
varieties of fru it juices, and has proven satisfactory not on ly from the standpoin t of convenience in m anipulation b u t on accoun t of the fa c t th a t the results appear to be reliable and concordant. I t has been considered, how ever, th a t the vo latile acids are n o t collected b u t are allow ed to dissipate into the air; hence it has occurred th a t w hile there is here afforded a sim ple, satisfacto ry m eans of separating the vo latile from the fixed acids, it m ight also be desirable to condense the vapors and titra te the vo latile acids in the distillate. B y joining a condenser to the flask containing the sam ple there is provided an apparatus w hereby m ay be
determined in one operation both the vo latile and fixed acids on the sam e portion of wine.
’* T he apparatus, as now con structed, consists of a 3 o o c c . spherical, flat-bottom ed flask provided w ith an elongated w ide neck. In to the neck of this flask is fitted a 75 cc. cylin drical-shaped flask pro
’* T he apparatus, as now con structed, consists of a 3 o o c c . spherical, flat-bottom ed flask provided w ith an elongated w ide neck. In to the neck of this flask is fitted a 75 cc. cylin drical-shaped flask pro