I N D U S T R I A L A N D ENGINEERING CHEMISTRY
226
Calculations Feed Soluble salt in feed 462,740 X 0.0855 = 39,564 Ibs. 462,740 X 0.0892 = 41,276 Ibs. Total salt &feed Discharge Total solids in discharge 49,640 lbs. Total solution in discharge 49,640 X 3 = 148,920 lbs. Soluble salt lost in,discharge 148,920 X 0.005 = 745 Ibs. 148,920 X 0.00653 = Total salt lost in discharge 972 lbs. OverfLLw Soluble salt to evaporation and crystallization 39,564 745 = 38,819 Ibs. Total salt to evaporation and crystalllzation 41.276 972 = 40,304 lbs. Washing Ejiciency 38 819 On basis soluble salt 3~ X 100 = 98.12 per cent
--
On basis total salt
-X
100 = 97.65 per cent
The washing efficiencies cited above are admittedly not quite
VOl. 21, No. 3
so high as those that would be obtained in the standard fivethickener countercurrent decantation plant with sludge density regulation between each decantation step by means of diaphragm pumps, where washing efficiencies above 99 per cent are almost always secured. Yet a loss of a very small percentage in washing efficiency becomes of rather secondary importance when the governing factors are limited floor space and the consolidation of several washing steps in a single unit. The test results given above take on added significance when it is realized that 97.7 per cent of the soluble values are recovered in a feed of 8.4 gallons per minute by the use of about 7 gallons per minute of wash water, the entire washing taking place within a single closed tank which overflows a clear solution of a single strength to subsequent treatment and discharges a thoroughly washed waste product.
Nature and Constitution of Shellac I-Preliminary Investigation of the Action of Organic Solvents' Wm. Howlett Gardner2 and Willet F. Whitmore THESHELLAC RESEARCH BUREAUOF THE CNITED STATES SHELLAC IMPORTERS' ASSOCIATION, THe POLYTECHNIC INSTITUTE, BROOKLYN, N. Y.
H E L L A C has been
A qualitative study has been made of the solubility dye, e r y t h r o l a c c o i n , and of shellac in eighty-four organic solvents. This work odoriferous material present. known from the earliest time of recorded hip,clearly shows that the solution of shellac in these solThis soluble portion corntory, and it is difficult to devents is not simply a physical phenomena, but that posed about 7 per cent of the termine where it first became colloidal aspects are unmistakably present. Unqueslacs. They claim t o have commercially practical and in tionably there is a close connection between solubility been able to break down this and the chemical relationship between solvent and ether-soluble resin into %leucommon use. For centuries it has been found unequaled solute; and shellac seems to be most soluble in those ritic and monohydroxypalSolvents which approximate it in composition and mitic acids, C 1 5 H 2 8 ( O H ) 3 for numerous uses, but in structure. Some of the nitrogen bases are good solvents, C 0 O H a n d C15HSo (OH)spite of its great antiquity but the solvent action in this case seems to be a funcCOOH, respectively. They comparatively little is known tion of the basicity of the solvent rather than any also report the possible existof its ultimate nature and chemical relationship between the dispersed phase ence of dihydroxypalmitic constitution from the standand dispersion medium, especially since shellac is deacid, CllHZ9( 0H),C 0 0 H , point of c h e m i s t r y and physics. Although America cidedb' acidic. among the products. Gupta4 was unable to find these subhas been the largest consumer of shellac, this product has been the subject of little study stances, but reports that his extraction may not have been except by a few workers in Germany and Switzerland. The complete. He demonstrated the presence of palmitic acid in Shellac Research Bureau has therefore undertaken a study the decomposition products from some lacs. A detailed study of the resin insoluble in ether was made of its properties and constitution. This paper is the first of by Harries and Nagel.5 I n their work this resin was readily a series giving the results of this study. hydrolyzed, under the proper conditions, with 5 N aqueous Previous Investigations Dotassium hvdroxide in the cold. They isolated aleuritic From what has been published it appears that shellac is acid and another which they named shelloic acid, C ~ H W composed of 70 to 90 per cent resin admixed with other sub- (OH)2(COOH)2. Aleuritic acid they established to be hexastances. The resin apparently consists of complex linkages of decane-16, 9, lO-ol-l-acid,6 a trihydroxypalmitic acid. From a mixture of hydroxy-fatty acids containing 15 or 16 carbon the general behavior of these resin acids in forming under reduced pressure lactides resembling shellac, and their atJoms. Tschirch and his workers3 have found stick-lacs to consist method of obtaining same, they conclude that the original of a t least two distinct resins comprising 70 t o 80 per cent of shellac contained lactides of these and other yet unidentified the material, with varying mixtures of two dyes, sugars, water- resin acids.' They have also noted the curious effect that hydrogen soluble albumin, an odoriferous substance, several waxes, and also carbohydrate material derived from twigs and the chloride has upon this ether-insoluble resin,8 pointing out that body of the shellac insect, Trachardia lacca Kerr. Extrac- this reagent probably has some colloidal effect as well as tion of these stick-lacs with 10 liters of diethyl ether dissolved changing the state of aggregation of the shellac particles. one of these resins along with the small amount of yellow 1 Gupta, J . I n d i a n I n s f . Sci., 7, 142 (1924).
S
1 Received September 8, 1928. Presented before the Division of Paint and Varnish Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928. This article is contribution No. 1 from the Shellac Research Bureau. 9 Research fellow. 8 Tschirch and Liidy, Hclu. Chim. Acta, 6, 994 (1923); Tschirch and Schaefer, Chem. Umschau Fettc, Oclc, Wachse, Harze, 81, 309 (1925).
Harries and Nagel, Ber., 66B,3822 (1922). Ibid., 60, 605 (1927); cf. Enderman, J . Franklin Inst., 164, 283 (1909); Bull. soc. chim., 5, 857 (1909). 7 Harries and Nagel, Chem. Umschau Fcfte, Oelc, Wachse, Harze, 31, 173 (1924); Wiss. Ver6fentlich. Siemens-Konzern, 3, 12 (1924). 8 Harries and Nagel, Kolloid-Z., 33, 247 (1923); Harries, Bcr., 668, 1048 (1923). 0
March, 1929
I S D USTRIAL AND EKGINEERING CHEMISTRY
When the hydrogen chloride was present during the purification of this resin with ether, a product was obtained which was insoluble in alcohol and, though soluble in potassium hydroxide, did not yield the usual product of hydrolysis, potassium aleuritate, with 5 N alkali. However, when this alcohol-insoluble product was dissolved in glacial acetic acid and precipitated from it with water, the resin was then soluble in alcohol but still apparently unhydrolyzed by potassium hydroxide. But when the acetic acid precipitate was dissolved in alcohol and reprecipitated from it, the resin was converted to the usual readily hydrolyzed resin. Purpose of Investigation
Since the work of other investigators has not definitely settled the question of the constitution of shellac, and has rather indicated that it is quite complex in nature, i t seemed feasible to begin this study with the behavior of shellac toward various organic solvents. Such an investigation serves a twofold purpose, for it not only promises to reveal methods of separating the various ingredients from each other, but also offers qualitative evidence as to the nature of the unknown substances. In addition, it has the practical phase of helping t o serve as a guide to the user of shellac who may from time t o time have questions arise with respect to the solubility of this commodity in organic solvents. Colloidal Aspects of Problem
I n a study of the solubility of colloidal substances such as shellac, many phenomena which would otherwise be considered abnormal can readily be explained on the assumption that these solutions are colloidal in nature. It is believed that the importance of the colloid phase of the problem cannot be too strongly emphasized. The swelling that accompanies preliminary solution with many solvents, the relative tenacity with which an occasional sample resists solution even in hot alcohol, the rapid rise in viscosity with heavy cuts (concentrated solutions of shellac), and the adhesive properties of shellac are manifestations of the colloidal nature of shellac and its solutions. In this connection it should be remembered that colloidal solutions do not necessarily show the properties of true solutions or follow the solubility rules for crystalloidal substances. The presence of traces of foreign materials and mixture with other resins may cause very marked deviations from what may be observed with fairly pure samples. This is a phase that is often overlooked in discussing the solubilities of varied substances in the preparation of lacquers. For example, what is practically a colloidal solution of shellac in water can be prepared by carefully pouring a dilute alcohol solution of shellac into a large amount of water. Yet, as everyone knows, shellac is for all practical purposes totally insoluble in water. Harries’ assumption that hydrogen chloride causes a colloidal change in the ether-insoluble resin has been mentioned, He postulates that this reagent has a coagulating effect upon t h e dispersed shellac particles, which by mutual adsorption form aggregates in such a way as to present, purely mechanically, insufficient points of attack to chemical influences acting from the outside. However, t o dismiss such a phenomenon upon the assumption of a change in degree of aggregation without experimental verification is a mistake. In doing so: sight is lost of other possible explanations and little has been added to our knowledge of the complex character of such states. The phenomena that occur in the experiments of Harries and Nagel M * can be readily explained without any assumption of change in state of aggregation. It is possible that certain groups in the micelle, or colloid particle, are -influenced by certain outside substances, such as hydrogen chloride, and by certain groups in different solvents, as glacial :acetic acid and alcohol. Under certain conditions, as McBain
227
has postulated for colloidal soap particles, 9 active particles of shellac may be arranged as radiating balls resembling eels tied together by their tails, with the active groups a t the outside extremities; while inactive particles may have some parallel arrangement, where groups within the inactive particle neutralize the sensitivity of each other to outside attack by their parallel arrangement. A purely chemical theory may also be advanced to account for the insolubility after contact with hydrogen chloride. Since hydrogen chloride has a dehydrating effect in promoting the splitting off of water between carboxyl (COOH) and hydroxyl (OH) groups which are present in the shellac molecule, it is not unreasonable to suppose that this may occur in one or between two or more molecules with the production of lactones or lactides or both. Some reverse process, inaugurated by the acetic acid and then the alcohol, would be required to account for the conversion of this inactive resin to the form that is readily hydrolyzed. A small amount of hydrochloric acid is always necessary to flocculate the resin when alcohol solutions are precipitated with water. In the course of the present work an effect apparently similar to that reported with hydrogen chloride in ether took place when an alcohol solution of purified shellac was poured into water containing too great a concentration of hydrochloric acid. I n this manner a product which was insoluble, not only in alcohol, but also in cold glacial acetic acid and 85 per cent formic acid was obtained. Solution could only be affected when these last solvents were hot, but proper flocculation upon dilution with water, as Harries and Kagel report, was not obtained. Precipitation of shellac from alcohol solutions cannot be effected by hydrogen chloride gas. Even the addition of hydrogen chloride to an alcohol solution to which ether or benzene has been added as diluent will not precipitate the gum, unless actual precipitation has already been initiated by the diluent. I n the case of benzene, addition of hydrogen chloride, decreasing the solubility of benzene in alcohol, will give a two-liquid-layer system. From the color of the benzene layer apparently a small amount of shellac is distri buted in this benzene-alcohol equilibrium layer. Important as the colloidal phase of the problem may be, one must constantly keep the chemical aspects in mind. That shellac undoubtedly contains free carboxyl groups irrespective of the other complex linkage, whether of the lactide type or not, is evidenced by its high acid value in alcohol solution. From the high hydroxyl-carboxyl ratios of the resin acids reported, we may expect free hydroxyl groups as well, if shellac is composed of lactide linkages of hydroxy-fatty acids. Harries and Nagel obtained 30 per cent of aleuritic acid from their purified resin. This acid contains three hydroxyl groups to one carboxyl. The other resin acids all contain at least one hydroxyl to a carboxyl group. I n lactide formation a hydroxyl and carboxyl group of one molecule react, respectively, with the carboxyl and hydroxyl of another, with the elimination of water; hence from such evidence as the above we can deduce that there are probably free hydroxyl as well as carboxyl groups present in the shellac particle. It is not surprising, therefore, to find, from the accompanying table, that the best solvents are the alcohols and anhydrous acids. Method of Study
I n determining solubilities shown in accompanying table, about 0.5 to 1 gram each of three representative grades of shellac (stick-lac, T. N. grade, and dry bleached samples) were treated with 15 t o 20 cc. of solvent, shaken a t intervals for 48 hours, and qualitative observations of their solubilities recorded. 9
McBain, J . A m . Chem. Soc.. 60, 1636 (1928).
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
228
T a b l e I-Solubility
No.
FORMULA
SOLVENT
ps:r:
VOl. 21, No. 3
of Shellac in Various Organic Solvents
SOLUBILITY kick-lac T. N. Bleached
No.
stick-lac T. N. Bleached
c. 1 Methyl alcohol CHiOH *2 Ethyl alcohol (anhydrous) CzHsOH 3 Ethyl alcohol,
c.
64.57
S
78.4
S
S
4
10 11 12 13
15 16 17 *18 *19 ‘20 21 22 23 24 25 *26 Ethylene glycol ethyl ether CzHsOCzHrOH 134.8 *27 Ethylene glycol hutvl ether C J H ~ O C Z H ~ O H1 7 0 . 6 28 Etbylkne ch6rohydrin ClCzHpOH 128 *29 Acetate of ethylene glycol ethyl ether (commercial) .... 30 Acetate of ethylene glycol ethyl ether (disCzHsOC2H4tilled) OOCCHi 154 31 Ethylene diCHCOOCzHr. 186-7 acetate OOCCHi 32 Diethylene gly189b col methyl ether *33 Diethylene glycol ethyl ether CzHsOCzH4OCzH40H 186 *34 Diethylene glycol butyl ether C~HPOCZHPOCZHdOH 222 .~ 35 Propylene’glycol methyl CHIOCH(CH~)119-13Ob ether (mixture) CHzOH 36 Propylene glycol ethyl ether CtHsOCH(CH3 (mixture) CH20H 125-1366 Common solvents for nitrocellulose VS = Very rapidly dissolved S = Soluble FS = Fairly soluble
S
S
S
S
S S S
S S
S S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
FS S
FS
FS
S
S
ss
ss
ss
FS
ss
ss
S
S
S
S
S
S
FS
FS
FS
S I
S I
S I
FS
FS
S
I
I
I
S
S
S
S
S
S
S
S
S
S
..
..
FS
FS
ss
I
I
I
..
ss ..
S
S
S
S
S
S
~
*=
S
S
S S
S
8 9
S
S
S
5 6 7
14
SOLUBILITY
FORMULA B~~~~
SOLVENT
S
S
S
S
S
S
S
S
S
SS
= Slightly soluble
I = Insoluble SW = Swells
Note-Samples were prepared by 0. M. Olsen, of Wm. Zinsser & Co., from composites of the January, 1928, shipments. Stick-lac is the raw shellac. consisting of the shell-like crust from twigs, gathered shortly after the swarming of the young insects from this shell, and has not been treated or processed in any way. T. N. (truly native) is a grade of native refined shellac. It constitutes 50 per cent of the shipments of shellac to the United States. I n preparation the raw lac has been soaked in water, ground, and wrung through cloth bags while heated in front of an open fire. The molten lac is drawn into sheets, which on cooling are broken into flakes, the product of the market. Dry bleached shellac is orange shellac (T. N.) that has been dissolved in hot aqueous solution of borax or soda and treated with chlorine gas or a similar bleaching agent. It is then precipitated with acid and dried.
I n all cases, as a means of confirmation, clear solutions were diluted with ether, benzene, or water to precipitate the shellac, or evaporated to dryness. In this table “soluble” is taken to indicate apparent complete solution of the resin; “fairly
*37 38 39 40 41 42
Acetic acid (glacial) Formic acid, 85% Propionic acid Butyric acid Palmitic acid Lactic acid
CHCOOH
118.1
HCOOH CzHsCOOH C3H:COOH CisHnCOOH CHaCH(0H)COOH
100.47~ S 140.7 S 162.3 S I 119d FS
43 Ethyl acetate C2HsOOCCHi (pure) 44 Ethyl acetate, 85% 45 n-Butyl acetate CaHoOOCCHi (pure) 46 %Butyl acetate, *47 *48 *49 *50 *5l 52 53 54 ”5 *56
Q
As given by varied autho;ities
b Approximate c
S
FS I
FS
I
I
I
FS
FS
I
I
I
148
FS I
ss
ss
137
I
I
I
I
1
125.8
I
I
I
290.4
I
I
I
340 222,2 186.1 208c 56.48
I I
CHCOCzHs 79.60 CzHsOOCH2COC H3 181 (CHzCOCHz), 166.7 184.40 CsHsNHz
67 o-Nitraniline in ethyl acetate NOzCsHaNHz 68 d-Phenylene diamine in ethj acetate 69 Diethyl ether 70 Acetaldehyde 71 Butaldehyde 72 Acetaldol 73 Benzene 74 Toluene 75 Xylene 76 Petroleum ether 77 Bromobenzene CaHsBr 78 Nitrobenzene CeHsNOz 79 Amvl chloride CsHiiCl 80 Eth>lene dichloride CzHrCh 81 Cyclochlorohexanes C6HiiCL 82 Chloroform CHCh 83 Carbon tetrachloride CClr 84 Carbon disulfide CS?
S
FS I FS
FS
128.39 202
CsHsNH(CH3
S
S S
....
....
CHCOCaHs
S
77.1;
125.1
85% n-Am;l acetate CsHuOOCCH3 Isobutyl propionate CrH900CCzHs Diethyl carbonate Diethyl phthalate Dibutyl phthalate Methyl salicylate Ethyl oxalate Ethyl sulfate Acetone Mesityl oxide
57 Acetophenone 58 Ethyl methyl ketone 59 Ethyl acetoacetone 60 Cyclohexanes 61 Aniline 62 Monomethylaniline 63 Monoethylaniline 64 Dimethylaniline 65 Diethylaniline 66 Pyridine
S
I I S S
I
I
1
ss
..
I FS
..
I
FS
FS
FS
FS
FS
FS
FS
ss
ss
ss
S
S
I
ss
S S
FS
FS
198.8
FS
206 192.5 215.0
ss I I
I’ I
I I
115.50
VS
vs
vs
... .
ss
..
..
FS
ss S
ss
I
I
I’ I I I I I sw I
I ‘sw
....
34.97 20.8 73-4
,...
79.70 110.70 142,6
....
156.15 210.85 106.6
ss S ss I I I
I
I I
I I
sw
sw
..
..
S
sw sw I sw ss s w I
I I
I
sw
I
sw
.... 61.20
I I
sw i ‘sw i ‘SW
76,74 46.2
I I
83-4.5
I
I I
I
I I
sw
12 mm. Decomposes a t this temperature
d At a
For pure formic acid
soluble” either very slow peptization or solution, or any appreciable partial solution; “slightly soluble,” a slight or partial solubility or sol formation; “insoluble,” no apparent solution of the gum. No attempt has been made to determine solubility in a quantitative manner, because it was believed that uncontrolled variations that occasionally occur with different samples and apparent variations from effects of one constituent upon another did not warrant such a t this time, in view of the yet incomplete knowledge of shellac. Further work on solvents and a study of the nature of these solutions is projected. For similar reasons only the relative solubility of the resin has been considered, since suitable methods for the separation of the various substances from each other have still to be developed. However, since the red dye, laccaic
hfarch, 1929
INDUSTRIAL A N D ENGIiVEERISG C H E X I S T R Y
acid, imparts a distinct red color to those solutions in which it is dissolved, its general behavior will be mentioned. Discussion of Results
From what has been said of the possible chemical structure of shellac, a careful study of the table will show that there exists a parallelism between what are commonly considered the general rules of solubilityI0 as pertaining to crystalloids and the solubility of shellac. Solvents for shellac may be divided into four groups: those containing hydroxyl groups, those with carboxyl groups, some of the ketones, and the basic amines. The best solvents from a commercial point of view are the alcohols and other liquids having alcoholic groups. This includes many of the newer lacquer solvents, solvents which dissolve both shellac and nitrocellulose. Most of the other shellac solvents of this group can be used as diluents in lacquer formulas. We find that most of the solvents containing a hydroxyl group will dissolve shellac whether or not other groups are present. This group of shellac solvents may be called the alcohol group. It would include the esters of the hydroxy acids, like ethyl lactate and ethyl oxybutyrate, and the glycols and their monoether derivatives. We find also that the length and complexity of the carbon chain of the alcohol has an influence upon the solvent action of such alcohols, as dimethylethyl carbinol, geraniol, and citronellol. The two polyhydroxy1 liquids, ethylene glycol and glycerol, are not solvents for shellac, although pure propylene glycol, 1, 2-hydroxypropane, is an excellent solvent. However, we would expect the first two substances to resemble water more closely than alcohols, since they contain two or three hydroxyl groups in close proximity in a comparatively small molecule. It is interesting to find that, like water, they dissolve the red dye, laccaic acid, present in stick-lac. I n all the other solvents studied the laccaic acid and resin showed similar solubilities. The resemblance to water should be lost by the substitution of an alkyl group for the hydrogen of one of the hydroxyl groups of ethylene glycol. We find all the monoalkyl ethers of ethylene glycol to be solvents for shellac. When both hydroxyls have been substituted, the alcohol properties are lost, and we find that pure ethylene glycol diacetate and the acetate of ethylene glycol ethyl ether are not solvents. The influence of the length of carbon chain on the solubility in any one class is clearly illustrated by the solubility of shellac in the fatty acid series. I n this series the rate of solution is the greatest with those solvents of lower molecular weight. A slight decrease in solubility in butyric acid was observed, while shellac was found to be insoluble in palmitic acid. The length of the carbon chain of the palmitic acid entirely negates the effect of the carboxyl and causes the substance to act as a hydrocarbon, a type of solvent in which shellac is insoluble. The low solubility in lactic acid, an alpha-hydroxy acid, may be due to the position of the hydroxy group. The hydroxy groups in aleuritic acid are in the theta, iota, and omicron positions. Several of the ketones dissolve shellac. The complexity of the molecular structure in this group apparently has a very marked effect. KOketone groups have been reported present in shellac. Hydrocarbons and substituted hydrocarbons that do not contain hydroxyl, carboxyl, carbonyl, or amino groups generally do not dissolve shellac. This group of solvents includes the esters, a group of nitrocellulose solvents used in lacquer manufacture. However, when a small amount of alcohol or fatty acid is present in the ester, a fair solvent for shellac is obtained. This is illustrated by the commercial 85 per cent 10
1923.
Kamm, "Qualitative Organic Chemistry," p . 9, John Wiley and Sons,
229
ethyl acetate and butyl acetate shown in the table. Lacquer solvents usually consist of blends and many contain alcohol as one of their formula ingredients. In the hydrocarbon group, as previously pointed out, we find diethyl ether dissolving a small percentage of the resin. Chloroform and ethylene chloride cause shellac to swell; when hot, chloroform will extract a portion of the resin. In the group of basic solvents of the amino type, pyridine has a strikingly rapid action. Solution in these solvents probably involves some chemical reaction between the shellac and solvent. With aniline, substitution of one of the hydrogens of the amino group causes a marked decrease in the solvent action. Disubstituted anilines are inert. This group of shellac solvents is of little commercial value, because of the objectionable odor and lack of suitable stability of these liquids. Within the varied groups of shellac solvents just presented, it would appear that, for solvents in the same class, there is an optimum oxygen carbon ratio for ideal solubility, and that when the ratio falls below this optimum or rises higher than another limit, solubility no longer occurs. This is illustrated by the fatty acid series, and by the two members of the glycol series, ethylene and propylene glycols. Conclusion
Reviewing the data to procure some idea of the constitution of shellac, we perceive that unquestionably the best solvents for this substance are the alcohols, organic acids, and ketones. Since a substance is most soluble in those solvents which are most closely related to it structurally,11 this information indicates that hydroxyl, carboxyl, and carbonyl groups are present in shellac; and although shellac is a colloid, and such generalizations are only strictly true for crystalloids, it seems very likely that they apply in this case. The data would also indicate that one of the two adjacent hydroxyl groups in aleuritic acid, hexadecane-16, 9, 10-01-1-acid grouping is involved in some other grouping such as that of a lactide group, from the insolubility of shellac in ethylene glycol and glycerol. Bleached shellac in general behaves toward organic solvents in a manner similar to the other grades. Its relative inertness toward the inert chlorinated solvents may indicate little, if any, appreciable chlorination of the resin during bleaching. Swelling in some of the inert solvents, with a slight tendency to dissolve in ethylene glycol, may be construed as indicating that partial hydrolysis has taken place during bleaching where sodium hypochlorite has been used as bleaching agent. The lack of solubility of shellac in most solvents other than those few groups in which it has been shown to be soluble and the apparent tendency to give colloid solutions even in these solvents indicate the complexity of the molecular aggregation in the solid state and a probably high molecular weight for shellac. Although we are not justified in applying rules of solubility that are known t o be true for crystalloidal substances t o colloidal substances, like shellac, nevertheless, as a result of this work, it seems that factors which determine solubility in cases of crystalloids may be possible factors in determining the dissolving power or peptizing action of solvents for shellac. This may prove to be an interesting field in connecting the solubility of crystalloids with those of colloids. Acknowledgment
The authors wish to express appreciation to John C. Olsen, of the Shellac Research Bureau, and to the Chemists' Committee of the Shellac Association, whose interest and assistance made this work possible. 11 For a discussion of this rule when applied to nitrocellulose and varied gums in lacquer solvents, see Brown, IXD.ENG.CHEM.,20, 183 (1928).
