LIQUID AhIMOSIA AS A LYOPHILIC DISPERSIOY hIEDIUM
B Y ROBERT TAFT
The properties of colloidal systems in non-aqueous dispersion media have not been examined extensively or systematically. Even systematic qualitative information upon the nature of substances which will disperse in a given liquid are meager and scattered. Since a study of the solvent properties of liquid ammonia a t the hands of Cady, Franklin, Kraus, and their students has enlarged considerably the general theory of solutions, it seems not unlikely that a study of colloidal systems in this solvent would enable additions to be made to the general theory of colloidal behavior. With this object in view, the writer began several years ago a review of the existing literature upon this subject, together with a few preliminary observations on the qualitative dispersabilities of the more common colloidal substances, the results of which have already been published.’ The present paper extends the qualitative observations over a very considerably wider field. The experimental procedure was to place 0 .I gram of test substance in a pyrex tube 1 5 mm. in diameter and some 43 centimeters long. To these tubes were added approximately I O cc. of anhydrous ammonia, care being taken to prevent absorption of water in the process of transfer. The tubes were then sealed before the blast’lamp and replaced in a bath of liquid ammonia. After 48 hours, with occasional agitation, a t this temperature (-33 ,5”C) they were removed, examined for evidence of dispersion and swelling and allowed to come to room temperature. After standing a t room temperature for 24 hours they were again examined to determine if any change in solubility or dispersion had taken place a t the higher temperature. By observing the tubes as they were warming slight changes in behavior could be detected by the appearance of opalescence. I n many cases, the tubes were recooled with liquid ammonia and observations of their behavior upon cooling likewise made. If changes in opalescence occurrpd q o n heating or cooling but the major portion of the material remained unchanged the observations were reported as “slight dispersion” or “slight increase”. The extent of such dispersion in any case probably does not exceed 1 / 4 of the amount added-that is dispersion in all likelihood is less than 1/4 of one per cent. \There dispersion appeared greater, the results are reported as “considerable dispersion” and likely in such cases the system is approximately concentrated to a maximum of I / Z of one per cent. In a few cases, dispersion is complete. In general the observations a t room temperature are recorded as compared to their behavicr at the boiling point of liquid ammonia; thus if the dispersion Presented before the Kansas Academy of Science April 15. 1527. Published in Trans. Kansas Acad, Sci.. 32, 38-41, (1929).
LIQUID AMMONIA AS DIBPERSIOS MEDIUM
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a t the boiling point (bp) of ammonia is “slight” and that recorded in the third column states “greater” it indicates that dispersion is greater at room temperature than a t the boiling point of ammonia. The materials in most cases have been obtained from reliable manufacturers-the majority were obtained from either Eastman Kodak Co. or the Digestive Ferments Co. The writer is indebted to Dr. E. L. Tague of the Kansas State Agriculture College for a supply of zein and of gliadin, and to the Hercules Powder Co. for furnishing supplies of the nitro-cottons employed here and in other researches now in progress. Carbohydrates and Related Substances Behavior at bp, “a
Substance
Corn starch Potato starch Dextrin Cellulose triacetate Cellulose acetate Inulin Glycogen Filter paper Cotton Agar Cellulose nitrates Guncotton (Nz12.84%) X2 1 2 7 G 1 7 see. Kz 1 2 7 3-20 ~ see. Xz 11.44% 3 - 2 0 sec. Xz 1 1 . 6 4 7 ~43 see. S 2 11.107~ 58 sec. 5 2 unknown 7 0 see. SZunknown 18 sec. S2 unknown 4-20 sec.
Behavior a t Room Temp.
Slight Slight Considerable Sone Considerable Complete Complete Slightly swollen Slightly swollen None
Less than a t bp Less than at bp Complete dispersion Slight Complete dispersion Slight residue Insol. Same Same Kone
Considerable Considerable Considerable Complete Considerable Considerable Considerable Considerable Considerable
Complete dispersion Complete dispersion Complete dispersion Complete dispersion Complete dispersion Complete dispersion Complete dispersion Complete dispersion Complete dispersion
Proteins and Related Compounds Substance
Egg albumin Hemoglobin Sodium caseinate Blood fibrin Blood serum Chitin Blood albumin Nucleinic acid Zein
Behavior at bp, XHs
Swollen Slight Very slight Swollen h-one Slight swelling Xone Considerable Complete
Behavior at Room Temp.
KO change A-o change S o change
KOchange ?;o change S o change KO change S o change KO change
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ROBERT TAFT
Proteins and Related Compounds (Continued) Substance
Proteose peptone Glutenin Casein iodide Edestin Silver proteinate Casein Gliadin Human skin Pepsin Bacto-peptone Silver nucleinate Rennin Ptyalin Sodium nucleinate Glue Gelatin (ash-free) Lecithin Silk
Behavior at bp, a”
Considerable Slight Yery slight Sone Slight Slight Considerable Swollen Slight Considerable Kone; “mclts” Considerable Slight Very slight Slight Slight Slight Slight swelling
Behavior at Room Temp.
So So So No
change change change change S o change 30 change Very much less than at bp Same Less than at bp Less than at bp Xone Somewhat more Same Same Same Same Increased over bp Slight disintegration
Gums and Resins Substance
Behavior at bp, “1
Gamboge
Considerable
Styrene Bakelite
Slightly Swollen Swollen-slight dispersion Slightly swollen Slightly swollen Slightly swollen Considerable Slight Sone Kone Slight Sone Purple sol-slight Considerable Sone
Indian gum Cherry gum Rosin Ammoniac gum Mastic Dammar resin Zanzibar copal Gum myrrha Amber Shellac Benzoin gum Redmanol resin Raw rubber Rubber latex Vulcanized rubber Crepe rubber
_l;onp
Sone Sviollen Slightly swollen
Behavior a t Room Temp.
More than at bp, orange sol. No change Greater dispersion residue black KOchange Slight dispersion Slight dispersion Less than a t bp KO change Yery slight dispersion Swollen X o change Xone Greater than at bp Greater than at bp Slight swelling Considerable dispersion Sone Sone Increased swelling Increased swelling
LIQUID AMMOXIA AS DISPERSION MEDIUM
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Gums and Resins (Continued) Substance
Behavior a t bp, a"
Vulcalock (rubber cement) None Elemi resin Sone Gum arabic Very slight dispersion Japan wax Sone Storax resin Slight Gum tragacanth Slight Carnuba wax None Gutta percha Slight swelling
Behavior at Room Temp.
Kone Kone Less than at bp None Greater than a t bp Less than at bp Slight S o change
Dyes Substance
Behavior at bp, a"
Aniline Blue 2B
Brownish red sol considerable residue Beneopurpurin roB Blood red sol-considerable residue Night Blue Dark red sol-large residue Bengal Indigo Brown sol-large residue Alizarol Black 3G Wine colored sol., slight residue Sulfur Black G extra Dark green sol, considerable residue Alizarol Brown R B Brown-red sol. residue 1/2 of original Congo Red Dark red, large residue
Behavior at Room Temp.
Amber sol-dispersion greater Little change Solution colorless, brown deposit Brown opaque sol, large residue Brown opaque sol, dispersion greater Greenish black sol., considerable residue Brown opaque sol., dispersion greater Little change
Soaps Substance
Sodium oleate Zinc stearate Lead stearate Barium stearate Calcium oleate Barium oleate Calcium stearate Silver stearate Ferrous stearate Alonoethanolamine palmitate Triethanolamine palmitate
Behavior at bp, NHs
None None None Slight None None ?jone Sone h-one ;l;one ?ITone
Behavior at Room Temp.
Sone Sone h-one S o change Slight Slight None Slight Sone Sone Sone
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ROBERT TAFT
Miscellaneous Substances Substance
Behavior a t bp, NHI
Bentonite Gelocol Saponin Collargol Diastase malt Cholic acid Pectin hquagel 11. Tannic acid Sodium silicate, cryst. Sodium silicate, dry com. Acheson graphite Cupric ferrocyanide Prussian blue Zinc oxide (Kadox) Lanolin Trilaurin
None None Slight None Slight None Slight Sone Brilliant red sol., little residue Slight None Xone Colorless liquid; green residue Slight Kone None Slight
Behavior at Room Temp.
None Xone Slightly greater None Less than a t bp None hTo change lTone Brown sol-little residue Less None Sone So change Greater Kone Kone Less
Carbohydrates and Related Compounds
It appears that ammonia at its boiling point is a good solvent for cellulose acetate, dextrin, inulin, glycogen, and the nitro-cottons. The dispersibility (or solubility) increases with rising temperature for cellulose acetate, the nitrocottons and dextrin. On the other hand there is a very marked decrease in the case of glycogen. The process in the case of glycogen is reversible, that is cooling to the boiling point of ammonia redissolves the glycogen and rewarming again precipitates it. This reversal was repeated several times with no apparent effect on the glycogen. The process of solution is reversible also in the case of dextrin, Le., a slight precipitate appears on cooling to the boiling point of ammonia after standing at room temperature. In the case of t,he cellulose acetate and triacetate the process is irreversible. After standing for several days a t room temperature the entire system containing the cellulose acetate jelled. Slight gel formation was noticed a t the same time in the case of the triacetate. These gels did not appear when cooled to the boiling point of liquid ammonia for several days. The process of solution in the case of the nitrocottons is also not reversible with temperature, Le., a precipitate does not reappear when recooled to the boiling point of ammonia. I n fact there is evidence of chemical change as the solutions become progressively darker in color (brown) with age. The rate of solution of these substances is a function evidently of both their nitrogen content (listed in the table as ‘;C of S ) and their viscosity (the trade iiscosities of these samples are given in seconds in the table).
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Proteins and Related Compounds Dispersion of these substances in liquid ammonia is not marked save in the cases of zein, gliadin, nucleinic acid, proteose peptone, and bactopeptone. I n the case of gliadin the process was reversible, i.e. recooling to the boiling point of ammonia after standing for several days a t room temperature caused nearly complete resolution; warming again caused precipitation. It was also noticed in the case of this substance that the solid phase at room temperature became blue (robin's egg blue), the blue color disappearing after several days. Similar phenomena (i.e., the blue coloration) were noticed in the case of blood serum and blood albumin. Gums and Resins Liquid ammonia apparently is a poor solvent for this class of substances. Gamboge, ammoniac gum, and benzoin gum show the most marked solubility. Of these gamboge was possibly the greatest. I t is of interest to note that Bakelite and Redmanol are affected by liquid ammonia. Dyes All of the dyes showed some solubility, altho in no case was it complete for the amounts of solute and solvent tried. The most striking case is that of night blue which forms a red solution a t the boiling point of ammonia, and either reacts with ammonia or is completely insoluble a t the higher temperature.
Soaps Apparently liquid ammonia does not have the ability to disperse soaps of either the alkali metals or of the heavy metals, the two ethanol amine soaps are likewise non-dispersible in the solvent. Commercial soaps are likewise non-dispersible.' Miscellaneous Substances Xone of these show any marked dispersibility save tannic acid. This is an interesting case as the solution is a bright blood red at the boiling point of liquid ammonia, the color becoming much duller as the temperature rises. The color at the lower temperature was so striking that a second specimen was tried, to make sure that no other substance save tannic had found its way into the tube. Discussion Liquid ammonia does not have marked dispersing ability for the majority of proteins or soaps. Doubtless here, as in the case of other solvents, suitable peptizing agents or methods could be found for a number of additional substances in the above list. The use of acidic or alkaline reagents in liquid ammonia could be tried, etc. On the other hand the cases where dispersion Taft: Trans. Kansas Acad. Si,32, 38 (1929)
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ROBERT TAFT
does occur, particularly in the case of cellulose esters,’ should be well worth studying in further detail and we are a t present engaged in the study of such systems, as well as of zein and gliadin. In addition, attention is directed toward the possibility of using this solvent as a means of purification or separation in those cases where dispersion (or solution) does occur. Incidently the table given above forms a fairly extensive list of substances most of which produce lyophilic systems in other liquids. Of course but little evidence has been produced that these substances are present in liquid ammonia as lyophilic substances, or for that matter as even being colloidal. In the case of cellulose nitrate and cellulose acetate, however, extremely viscous solutions can be produced with no evidence of a limiting solubility or dispersibility. This high viscosity and the gel formation noted in the case of cellulose acetate makes it, seem probable that we are dealing with lyophilic sols in these cases. I n this connection the cases of glycogen and of inulin are of interest and have been investigated by several workers. Reihler and Kestle2 determined the molecular weight of inulin in this solvent by the vapor pressure method and combining their results with those of Schmid and Becker3 who had determined the molecular weight in this solvent by the cryoscopic method found values ranging from 2 7 0 to 375. This would appear to make inulin a disacharride of the formula CI~HZOOM. The determinations were all made a t the boiling point of ammonia or lower. Schmid, Ludwig and Pietsch4 determined the molecular weight of glycogen by the freezing point method obtaining values rangipg from 131 to 197. Schmid and Zacherlj have determined the electrical conductances of both inulin and glycogen in liquid ammonia and conclude as the electrical conductance of liquid ammonia is changed neither by the presence or the concentration of these substances that they do not undergo molecular change when dissolved in liquid ammonia. The rather abrupt change in solubility of glycogen noted in the writer’s observations above would tend to confirm the fact that glycogen was present as a molecular solution rather than a colloidal dispersion. Cases of definite solubility are rarely, if ever, connected with the colloidal state. Before concluding this discussion a consideration of the claims of Ostwald6 with respect to solutions of sodium and of other alkali metals and of sulfur in liquid ammonia seems advisable. Ostwald suggested that systems of alkali metals and ammonia were colloidal chiefly upon the similarity of color (blue) of solutions of these metals in liquid ammonia to the metallic sols of the same metals which had been For example Highfield (Trans. Faraday SOC.,22, 73 (1926) ) states that “no material is known which is a solvent for nitrocellulose and which like water or benzene contains an overwhelming preponderance of polar or of non-polar groups.” Liquid ammonia is very distinctly polar in character and disperses cellulose nitrate readily. I n fact sols containing over 40% of nitro cotton have been prepared in this laboratory. a Ber., 59, 1159 (1926). Ber., 58, 1868 (1925). Monatsheft, 49, 118 (1928). Monatsheft, 53 and 54, 498 (1929). 6 Kolloidchem. Beihefte, 2, 437 (1910-11).
LIQUID AMMONIA AS DISPERSION MEDIUM
2799
prepared by Svedberg in organic liquids a t low temperatures; in addition the swelling phenomena produced by these metals in the presence of ammonia gas was compared to the swelling of gels, etc. I n dilute solutions, Kraus’ and his students have determined the molecular weight of sodium and have found it to be approximately 23, Le., sodium is atomatically dispersed. Ostwald st,ates that probably the concentrated solutions are colloidal; but these solutions are not blue but copper-red2 and one of his arguments thus loses its force. A simple calculation also renders it entirely unlikely that the concentrated solutions are of colloidal character. A particle of sodium I m p diameter (certainly near the lower limit of colloidal size) would contain 14 atoms of sodium, assuming that the particles were spherical and that the density of the particles was I (density of sodium is 0.97 a t zoo C). On the basis of a molecular weight of 3 2 2 , ( 1 4 X 2 3 ) , the mol fraction of a solution saturated with respect to sodium3 a t -33.5’ C is 0.013. On the basis of Raoult’s law, assuming that the law can be applied to a solution with a mol fraction of 0.013, such a solution would have a vapor pressure depression of I O mm. The actual depression observed4 is 360 mm, which would make it appear that sodium present in these concentrated solutions is certainly below the lower limit of colloidal size. Again the well defined solubility of these metals in liquid ammonia would militate against the argument for the colloidal existence of these metals in this solvent. Further Kraus5 has shown that the electrical conductivity of these systems is to be compared to metals rather than to those of electrolytic solutions. As far as the writer is aware there is no colloidal system which has an electrical conductivity even equal to that of 6he best conductors of the second class. All in all it would seem that Ostwald’s suggest,ion for the colloidal existence of these metals in liquid ammonia is ent,irely unwarranted on the basis of existing data. In the case of sulfur the evidence is not quite so clear. Ostwald again bases his claims on the varying colors of sulfur solutions as evidence of their colloidality. Friedrichs6 states with regard to sulfur in liquid ammonia “This solution has more the appearance of a colloidal solution than a homogeneous phase.’’ He subjected the solution to ultramicroscopic examination with negative results and also stated that it gave no Tyndall cone upon illumination and as a result concluded that sulfur in liquid ammonia forms a true solution. Bergstrom’ has summarized the work of previous investigations upon this topic and has contributed evidence t o the view that, sulfur is acted upon by “‘The Properties of Electrically Conducting Systems,” Chapter XIV (1922). See also the excellent review by Johnson and Fernelius: J. Chem. Ed., 6,20, 35 (1929). Cf. the color illustrations of Johnson and Fernelius: J. Chem. Ed., 7, 985 (1930). 3Computed from the data of Kraus, Carney and Johnson: J. Am. Chem. SOL, 49, 2206 (1927) who give the composition of a saturated solution of sodium in ammonia a t this temperature as 24.5 grams of sodium per loo grams of ammonia. ‘ Kraus, Carney and Johnson: 1. c. 5 1. c. 3. Am. Chem. Soc., 35, 1872 (1913). ‘ J. Am. Chem. SOC.,48, 2319 (1926).
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ROBERTTAFT
liquid ammonia, forming compounds of sulfur and nitrogen, sulfur and hydrogen, etc. The topic is still under investigation in Bergstrom’s laboratory. In a private communication to the author Bergstrom states: “I have never inclined to the view that a solution of sulfur in ammonia is entirely colloidal in character, though there may well be some colloidal material present.” The rate of diffusion of a liquid ammonia solution of sulfur thru a suitable gel has been carried out in this laboratory. This will further be described in a forthcoming paper but the evidence from this source points to the fact that a considerable amount (if not all) the material is present in true solution. summary
The qualitative dispersiblities of over one hundred colloidal materials in liquid ammonia have been examined. This liquid forms an excellent dispersion media for certain starches, cellulose esters, dyes of high molecular weight, and a few proteins. It does not disperse gums or resins, most proteins and soaps. 2. The views of Ostwald upon the colloidal character of liquid ammonia solutions of alkali metals and of sulfur are not supported by our present experimental knowledge of these solutions. I.
University of Kansas, Laurence.
