490
T H E J O C R N A L O F IA'DCSTRIAL A R D EiVGINEERISG C H E M I S T R Y
3.0 per cent I r ) the loss on heating is negligible belonabout 900" C. 4 - B e l o ~ this temperature there may even be a slight gain in weight on heating platinum, owing t o the iron content diffusing t o the surface and oxidizing. At higher temperatures t h e presence of iron will lower the volatilization loss b y amounts depending on t h e quantity of iron present. There appears t o be no platinum made which does not contain some iron. j-The volatilization of platinum containing rhodium is less t h a n t h a t of pure platinum a t all temperatures above 900' C 6-The volatilization of platinum containing iridium is. above 900' C , very much greater t h a n t h a t of pure platinum, and increases with t h e Ir content and with temperature. 7-It appears t o make no material difference in t h e volatilization results, in t h e range 7 0 0 ° t o 1200°, what is the order of heating, ascending or descending temperatures. 8-In a n oxidizing atmosphere a t temperatures of the order of 1000' C., platinum, in t h e presence of (but not in contact with) silica, will apparently t a k e u p small quantities of this substance. 9-The loss in crucible weight due t o the solution of soluble matter in HC1, after heating, is variable, depending on t h e crucible, and may be large. This loss is relatively greater a t low t h a n at high temperatures. 1 ~ ~ 4 1of 1 t h e above losses, caused b y heating, acid treatment, and iron diffusion, apparently continue with undiminished magnitude after t h e first treatment, which is usually erratic; although, eventually, of course, t h e concentration of iron, etc., must become appreciably diminished. BUREAUOF
STANDARDS, WASHIXGTON
VARNISH ANALYSIS AND VARNISH CONTROL I-MOLECULAR WEIGHTS OF VEGETABLE OILS By MAX Y . SEATON AND G. B. SAWYER Received February 23, 1916
Modern methods of analysis a n d control have only recently been applied t o t h e products of t h e varnishmaking industry. Physical chemistry has, in particular, been t h e last branch of t h e science t o find application in this field. Although physical constants of varnishes have been determined as a matter of routine testing for a great many years, investigation has in general stopped with t h e determination of such constants as viscosity or gravity a n d t h e relation which variations of these constants bear t o variations in t h e treatment in t h e varnish kettle has b u t recently been appreciated. Considerable work in t h e determination of physical constants of varnishes and t h e causes for t h e variations in these constants has been done in this laboratory, together with much work on the chemical properties of the products produced. It is planned t o issue a series of papers covering as much of this work as is available for publication. The first paper, which follows, will deal n-ith the determination of molecular weights of t h e vegetable oils used in the varnish-
V O ~8, . NO. 6
making industry and will indicate the molecular weights of some of the resulting products. T h e literature pertaining t o the composition and reactions of the oils commonly used abounds in references t o the molecular weights of both the raw a n d the heat-treated oils. The inter-molecular changes which occur during treatment of t h e oil in varnishmaking processes are admittedly very complex. Determination of molecular weights has recently been found valuable for their study and has been widely used by various authors. I n the a t t e m p t t o apply t h e usual methods for the determination of molecular weights of substances in solution t o oils and varnishes, so many difficulties have arisen t h a t it has been necessary t o investigate t h e use of a number of solvents, until finally one was found in which consistent molecular weights could be obtained. This paper, then, will cover t h e investigation of methods for the determination of molecular weights of oil and varnish products, together with a description of a suitable and accurate method. The observed molecular weight of a vegetable oil or of a varnish mixture is in every case merely a mean or average molecular weight of the several substances which may be present. Thus, the most simple substance which will generally be investigated, linseed oil, will contain t h e glycerides of a number of different f a t t y atids together with small amounts of alcohols and traces of other substances. Under no circumstances can t h e molecular weight be looked a t as being as definite a constant as it is in case of a pure material, b u t it can, nevertheless, give much information as t o the composition a n d properties of t h e material investigated. The literature in which most complete record of molecular weight determinations in this field appears refers t o the mechanism of the polymerization reactions both of linseed and China wood oils. I n this connection Maquenne,' Lewkowitsch:2 Genthe,3 Morell,^ Normann,5 and others, have reported determinations using t h e boiling point method in ether and in benzol, and t h e freezing point method in benzol and glacial acetic acid. I n general, results of previous investigators show a comparatively wide variation in t h e ralues obtained. Some difference is naturally to be expected on account of t h e different sources and accordingly different composition of the oils studied, b u t t h e values reported differ too widely for t h e difficulty t o be ascribed t o this source. There is a dearth of information as t o t h e exact details of the methods used, so t h a t in most cases critical examination is impossible. Of extreme interest, however, is t h e observation of Kormann,5 who shows t h a t varying values are obtained in different concentrations of solution. Normann obtained these results in an investigation of t h e molecular weight of raw and polymerized oils a n d although 1 2
3 4 5
Compl. rend., 1902, 686-6248, "Chem. Tech. and Oils, Fats and \\'axes," Val. 111, pp. 98-100. Z . angew. Chem. 19 (1906), 2098. Tvans. Chem. Soc. London, 101 (1912), 2082-2089. Chem.-Ztg., 1907, 188.
June, 1916
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
he details in full t h e results of his experiments he does not suggest a remedy for t h e trouble indicated. As far as t h e literature available t o t h e writers indicates, his observation is t h e only one of this t y p e which has been reported on such molecular weight work. I n a number of cases various authors have reported molecular weights of t h e acids prepared b y saponification of t h e oils. It is probable t h a t such a device has been used, owing t o t h e greater solubility of t h e acids in most solvents, a n d also t o t h e fact t h a t b y t h e use of t h e acids, solvents of t h e t y p e of glacial acetic acid are made available. Such solvents cannot be used on t h e original oils on account of low solubility. I n many instances where t h e molecular weights of t h e acids are obtained, simple molecular weights are not obtained. Morrell,' for example, shows t h a t t h e molecular weight of oleic acid in benzol is double t h e simple molecular weight, which latter however is obtained in' glacial acetic acid. An examination of t h e literature shows t h a t there appears t o be a conflict of evidence as t o whether t h e molecular weights of oil-acids paralleled those of t h e oils from which t h e y are prepared; i. e . , whether in polymerized oils t h e molecular weight of t h e f a t t y acid increases in t h e same ratio as t h a t of t h e oil. Until this question can be cleared u p , methods dealing with t h e molecular weights of t h e acids must be considered as useful only when no satisfactory methods for determination of t h e molecular weights of t h e oils themselves are available. The determinations on t h e acids necessitate, in addition, lengthy saponification, separating a n d drying processes a n d from t h e standpoint of speed of working are not a t t r a c tive. I n t h e determinations a t t e m p t e d in this laboratory, t h e freezing point method using benzol as a solvent was first tried. The method is attractive on account of its rapidity and sharpness of freezing point. Benzol is a good solvent for most oils a n d polymerized oils and might be expected t o give satisfactory results. The apparatus used was t h e familiar freezing point apparatus. I n all determinations benzol of a boiling point range of less t h a n one-tenth degree was used. I n Table I are given t h e results obtained on a number of substances b y use of this method. I t is seen at once t h a t t h e molecular weight of t h e oils in solution varies widely with t h e concentration. Especially in t h e case of polymerized oils t h e variations are very great. The determinations on oil acids indicate t h a t t h e method does not give correct results even on these substances. When the acids are obtained from raw linseed oil t h e molecular weight remains approximately constant over a wide variation of concentration, t h e value obtained being about double t h e simple molecular weight, but when t h e acids are obtained by saponifying a n d acidifying a polymerized oil a constant molecular weight cannot be obtained, t h e variations becoming more pronounced as polymerization increases. 1
J Soc Chem. Ind., 34, 105.
49 1
I n every case a lowering of t h e molecular weight with increase in concentration is observed. This is rather surprising as t h e reverse result might perhaps be expected. It is known, for example, t h a t solutions of polymerized oils in many solvents show all of t h e characteristics of colloidal solutions. I n such TABLEI-MOLECULAR WEIGATS
B Y FREEZING POINT METHODS BENZOLSOLVENTNITEOBBNZOL SOLVENT P e r cent Mol. P e r cent Mol. Substance Concentration Wt. Concentration Wt. Naphthalene.. . . . . . . . . . . . . . . . . . 0.80 126 0.61 130 1 .93 125 1.38 129 (true molecular weight = 128) 0.54 200 Bq"t~~e'~~~~;la;.wejght.=.iilj. 1.41 222 2.28 223 2.29 224 .... ... 2.78 223 Raw Linseed oil,,, , , , , , , , , , , , o,593 930 1.37 825 1.32 890 3.48 845 895 2.46 874 7.09 3.46 864 9.75 905 5.55 803 .... ... 8.45 740 .... ...
.
Raw China Wood Oi.
y:;:
iy;
io.oo 1.5 3.5 6.5 10.0 19.5 12.2
765 728 760 740 715 590 1290 1025 890 500 490 480 580 555 520 7 80 755 690
.
' ' ' ' ' ' '
Polymerized Wood Oil..
'.
........
heated 45 at 4500 F. 32 1 2 . 10 Oil AcidsfromRefinedLinseedOil 8.6 17.2 19.3 Oil Acids from Refined Linseed Oil 15.1 heated 1 hour a t 600' F. 22.3 33.0 Oil Acids from Refined Linseed Oil 6 . 3 heated 3 hours a t 600° F. 13.5 31.0
....
... ...
.... ....
....
... ... ...
.... ....
...
....
....
.
I
.
...
.... .... .... ... .... ... .... ... solutions a n d in solutions in which association of t h e solute occurs molecular weight rises as concentration is increased. A lowering such a s is indicated in Table I is generally ascribed t o combination between t h e solvent a n d t h e solute, a n d until some better explanation appears this must be accepted as t h e cause of t h e phenomenon noted here. It is possible t h a t association does play some p a r t in t h e changes observed, although it is apparently overbalanced in this case by t h e influence of combination. Solvents which generally possess markedly different associating powers from benzol might be expected t o give interesting results. Benzol is generally accepted as a n associating solvent ; nitrobenzol behaves as a neutral solvent a n d chloroform as a dissociating solvent in ordinary molecular weight determinations. T h e two latter materials were therefore chosen for further investigation. Determinations of molecular weight by the freezing point method using nitrobenzol as t h e solvent were made in t h e ordinary apparatus a n d although slight difficulty was found with excessive undercooling fairly accurate results could be obtained. Some of t h e observations in this solvent appear in Table I . In this case t h e characteristics usually ascribed t o association in solution appear, t h a t is! increase of molecular weight with increase in concentration. It is interesting t o note, however, t h a t benzoic acid increases in exactly t h e same ratio in this solvent as it did in benzol, while t h e behavior of linseed oil is exactly t h e opposite. Boiling point determinations were made b y suspending t h e boiling point tube in a Dewar buib t o insure insulation from external temperature changes, and heating t h e solvent t o boiling b y means of a n
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 ENGIIVEERING C H E M I S T R Y
492
immersed coil of wire heated electrically. This method has been widely applied recently a n d has been found t o give results comparable with those obtained in the older style boiling point apparatus. TABLE 11-MOLECULAR WEIGHTS BY BOILINGPOINTMETHODS CHLOROFORM SOLVENT BENZOLSOLVENT % Mol. % Mol. Naphthalene(o).
..
Benzoic Acid(b)
...
Alkali Refined Linseed Oil.. . . . . .
Raw Linseed Oil. . .
Polymerized Linseed Oil.. . . . . . .
Conc. 0.8 2.7
Wt. 129 133
0.2 0.63 1.75 5.70
211 222 228 220
Benzoic Acid@)., . , . .
(6)
Refined Linseed Oil
0.87 2.00 3.00 4.6 6.0 7.4 9.3
1.3 2.9 4.3 5.75 7.2 9.3
,
.
1400 865 TOO
655 580 472
(d)
s45 IO0 625 605 512
Oil Acid from 1,inseed Oil. .... . . . . . . . . .
Conc. 0.9 3.9 8.0 1 .5 3.2 5.5
Wt. 135 137 135 240 252 240
1.1 2.5 4.7 8.0 10.9 14.8
2980 2780 1042 860 765 682
1.9 4.6 7.0 9.8 12.4
544 540 485 474 460
1.8 3.6 5.5 7.9 9.8
yt. .
((1) True Mol. Boiling Point 0.01 BoilinR Point 0 . 0 7 O .
iYaphthalene(a). . , .
(e) 3380 1800 1192 960 = 128. ( b ) True Mol. Wt. = 122. ( d ) Lowered Boiling Point 0.033'.
(c) Lowered ( e ) Lowered
T h e results of determinations in chloroform b y this method (see Table 11) indicate lowering of molecular weight with increase in concentration, although benzoic acid still behaves as though associated. The variations are even greater in chloroform t h a n in t h e other solvents previously tried. The remarkable lowering of the boiling point which has been observed b y Firth and Myers' appears here when low concentrations are used. I n one instance. for example, it has as high a \-alue as 0.07'. T h a t this phenomenon occurs explains t o some extent t h e abnormally high molecular weights observed in low concentrations. Csing benzol as a solvent. different results as 'regards association might be expected a t boiling temperature from those observed a t freezing temperature. Accordingly, determinations were made by t h e boiling point method in benzol. Here again (see Table 11) molecular weight varies widely with concentration and t h e results cannot be accepted as satisfactory. I t should be noted t h a t t h e value.of t h e constant used in calculating the results was somewhat in error as is shown b y t h e high molecular weight of naphthalene observed. It is seen f r o m the preceding results t h a t all t h e methods so f a r tried have given unsatisfactory results. I n the search for a solvent which would gire normal molecular weights, stearic acid was suggested. Stearic acid has been recommended b y Biltz,2 who finds it a satisfactory solvent for many determinations. It is especially desirable in an investigation of t h e molecular weights of oils as it possesses remarkable solvent powers for t h e highly polymerized and highly oxidized oils mrhich are but sparingly soluble in other solvents. I t was accordingly tried as a solvent in the usual freezing point method. I t developed a t once t h a t the ordinary apparatus 1
3
Chenz. SOL. Trans.. 105, 2887-2892. Z . p h s s i k . Chem., 19, 385.
v01. 8 , NO. 6
is not suitable as the stearic acid tends t o crawl u p t h e side of the tube and u p the stirrer, giving considerable trouble. Such difficulty was readily remedied, however, b y covering with asbestos paper a piece of brass tubing of such size as t o fit over t h e t o p of t h e freezing point tube, a n d winding on a resistance coil of nichrome wire. By passage of a suitable current t h e tubing was maintained a t about 60" C. By the use of this simple heater t h e top of the freezing point t u b e remains clean and free from acid throughout many determinations. Stearic acid of commercial purity, preferably t h e triple pressed grade: will be found suitable for t h e determinations. T h e melting point is not quite as sharp as in the case of benzol, but it is sharp enough t o give concordant results as the d a t a quoted later will show. I t is necessary first t o dry the acid b y heating it for some time below 100' C. in a n oven or on a steam-heated hot plate. The acid thus dried does not readily absorb moisture from t h e air a n d can be filled directly into t h e freezing point tube. The constant of t h e acid used was found t o be 4 2 . j, a figure in concordance with the results reported b y Bi1tz.l Table I11 indicates t h e results of the determinations of molecular weights of a large number of substances b y this method. I n this method no uniTABLEIII-hfOLECULAR
WEIGHTS BY STEARIC ACID METIiOD Per cent Molecular Substance Concentration Weight 3.2 126 Naphthalene., . , , , , , , . , , . , , , . . , , , , , . , . . . (true molecular weight 128) 9.1 127.5 120 2.2 Benzoic Acid, . , . , . , , , , , , . , , , , , . , , . . . . . . . . . (true molecular weight 122) 6.1 121 10.8 123.1 3.8 740 Raw Linseed Oil.. . . . . . . . . . 7.4 735 (chemically refined) 10.2 760 735 Refined Linseed O i l . , , , . , . . . . . . , , . . . . . . . . . . . 4.3 770 I . , heated t o 600' F. 11.8 765 1000 4.1 Refined Linseed O i l . , , . , . , . , , , , . . . . . , . . . , , . . 8.4 1000 heated 1 br. a t 600' F. 12.0 1020 3.84 1250 Refined Linseed Oil., . . . , , , , , , , , , , . . . . . . , . , 7.5 1220 heated 2 hrs. a t 600' F. 1240 18.8 1510 6.2 Refined Linseed Oil , , . . . . . . . . . . . , . . . , . . , , . heated 3 hrs. a t 600' F. 11.3 1500 17.1 1530 274 Acids from Refined Linseed Oii. . , . . , , , , . , , , , 5.3 14.0 300 19.0 316 5.9 310 Acids from Refined Linseed Oil 10.0 325 heated 1 hr. a t 600' F. 21.8 342 5.1 335 Acids from Refined Linseed O i l . . . . . . . . . , . , . . heated 3 hrs. a t 600' F. 12.1 354 19.2 380 7 . 0 840 Raw China Wood O i l . . , , . , . . . . . . , , , . . , . . , . , 13.5 825 28.2 855 6.5 1700 Polymerized China Wood Oil 14.8 1760 heated 45 mins. a t 450' F. 21.1 1740 Soya Bean O i l , . . , , , . , , , , , , . , . . , , , , , , , . , , , , 5 . 6 719 8.1 735 10.2 750 1250 Polymerized Soya Bean Oil. , . , . , . , , , . . . . . . , , 1230 315.0 0.0 heated 2 hrs. a t 600' F. 282 W . G. Rosin .... , , . . . . , , . . . . . , . , . . . . . , . . . . . 288 5 . 95 6
.
.
.
form variation of molecular weight with concentration is shown. I n t h e determination of t h e molecular weights of oil acids slight variation does appear, it is true, but this is not as pronounced as in t h e case of molecular weights of oils in other solvents. I t should also be noted in this connection t h a t t h e molec1LOC.
cil
June, 1916
T H E J O R iV A L 0 F I N D C S T RI 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
ular weights of t h e acids obtained are fairly close t o t h e simple molecular weight as calculated from t h e combining numbers. With t h e possible exception noted, t h e n , t h e method can be applied t o routine determinations without t h e necessity of laboriously plotting curves showing t h e concentration effect for each oil used. Owing t o t h e great solubility in stearic acid of t h e various oils likely t o be encountered, t h e method is widely applicable a n d , in fact, there will be b u t very few oils found t h a t cannot be dissolved completely in t h e quantities required for a determination. The method is simple a n d easy t o operate. No correction for loss of solvent b y evaporationtneed be applied. The solvent is non-hydroscopic a n d t h e precautions which must be taken with nitrobenzol a n d , t o some extent, with benzol, can therefore be omitted. Some difficulties with t h e method have, of course, developed during its investigation in this laboratory; these in general, however, admit of satisfactory solution. For example, t o obtain concordant results i t is necessary t o keep t h e b a t h in which t h e freezing point t u b e is immersed a t approximately 40' C. Variation of more t h a n one degree in t h e temperature of t h e b a t h will cause slight variation in t h e observed freezing point. If a n automatically regulated thermostat is available t h a t factor will cause no trouble. I t is necessary t o stir somewhat more vigorously t h a n when benzol is used, in order t o prevent undue supercooling. Under no circumstances are t h e observed freezing points sharper t h a n one one-hundredth of a degree. On this account t h e accuracy OP t h e method is not as great as t h e freezing point method in benzol b u t i t compares very favorably with a n y of t h e boiling point methods. The method as outlined clears u p a number of difficulties which have been found with t h e determinations of molecular weights of oils a n d varnishes in t h e past a n d opens up t h e field for further investigations 04 this t y p e . I t has been found i n this laboratory, for example, t h a t determinations of molecular weights are of great importance i n varnish control work a n d of even greater value in varnish analysis, for in many cases t h e t r e a t m e n t of a n oil or varnish will be more accurately represented b y its molecular weight t h a n b y a n y other of t h e common constants. For such application it is, of course, necessary t o have a t hand methods for determining t h e .molecular weight of t h e various substances which make u p t h e mixture of which t h e mean molecular weight has been determined b y t h e methods indicated. The process of determining such individual molecular weights in substances as simple as oils a n d polymerized oils is comparatively easy a n d will be outlined in full in a subsequent paper on polymerized linseed oil. Much greater difficulties arise when t h e molecular weight of t h e oil portion of a rosinChina wood oil varnish needs t o be determined, b u t considerable progress has been made in t h e development of satisfactory methods. This mill also be reported on later.
493
SUMMARY
T h e question of t h e determinations of molecular weights of oils, treated oils a n d varnishes has been outlined a n d t h e value of such investigations brought out. T h e most usual solvents used in molecular weight determinations have been investigated a n d their inadaptability t o t h e present problem pointed out. A method for determinations of molecular weights of these products b y use of stearic acid as a solvent has been outlined a n d t h e conditions surrounding its use developed. Determinations by this method have been made on a large number of oil and varnish products. T h e applicability a n d value of such a method have been indicated. The writers wish t o acknowledge their indebtedness t o Dr. W.R. Veazey, Case School of Applied Science, Cleveland, Ohio, for advice a n d suggestions. RESEARCH LABORATORIBS. THE 4 R C O CLEVELAXD. OHIO
COMPANY
GlLSONITE AND GRAHAMITE: THE RESULT OF THE METAMORPHISM OF PETROLEUM UNDER A PARTICULAR ENVIRONMENT By CLIFFORD RICHARDSON Received December 29, 1915
Gilsonite a n d grahamite are t w o forms of solid native bitumen which are not widely distributed in nature, gilsonite being t h e rarer, a n d are t h e result of metamorphism of petroleum under a particular environment. They are found in fissure veins which approach t h e vertical a n d afford conditions which are favorable for t h e metamorphosis of petroleum into those materials. This change has gone on, under a varying time factor, t o a n extent t h a t has resulted in substances presenting various degrees of condensation, from one which floim slowly in t h e sun, as in t h e case of t h e softest gilsonite, t o one of t h e hardness of t h e brittlest grahamite, which does not melt even a t high temperatures. Between these extremes is t o be found materials of varying consistency, b o t h in t h e gilsonite a n d grahamite series, showing t h a t these bitumens are t h e products of metamorphism, t o a varying extent. under t h e environment t o which t h e y have been subjected, of some more or less liquid bitumen. T h e indication of these changes or metamorphism is t o be explained in t h e gradual decrease, as t h e metamorphism goes on, of t h e hydrocarbons a n d their derivatives which are soluble in naphtha, from t h e amount present in t h e softest gilsonite t o t h a t found in t h e hardest grahamite, with a corresponding increase in t h e residual coke which t h e y yield on ignition. The following d a t a €or typical gilsonites a n d grahamites demonstrate this very plainly. T h e gradual decrease from t h e softer t o t h e harder form in t h e percentage of bitumen soluble in n a p h t h a a n d increase in t h e yield of residual coke is striking. At t h e same time there is a corresponding increase, as t h e metamorphism increases in degree, i n the melting point a n d in t h e specific gravity. These results
