I N D U S T R I A L A N D ENGINEERING CHEMISTRY
1268
Dixon, Bradshaw, and Campbell, J. Chem. Soc., 106, 2027 (1914). Dixon, Harwood, and Higgins, Trans. Faraday Soc., 22, 267 (1926). Duchene, Compt. rend., 186, 220 (1928). Egerton. Nature, 119, 259 (1927). Egerton and Gates, J . Inst. Petroleum Tech., 13, 244 (1927). Fenning, Rept. Mem. Aeronautic Research Committee, No. 979 (1925); Engineering, 121, 180 (1926). (12) Hunn and Brown, IND. ENG.CHEM.,20, 1032 (1928). (13) Mason and Wheeler, J. Chem. Soc., 126, 1868 (1924). (14) Maxwell and Wheeler, Ibid., 2069 (1927).
(6) (7) (8) (9) (10) (11)
Vol. 21, No. 12
(15) Maxwell and Wheeler, J . Znst Peiroleum Tech., 14, 175 (1928); IND. ENG.CHEM.,20, 1041 (1928). (16) Morgan, J. Chem. SOL.,116, 94 (1919). (17) Morgan, Phil. Mag., I71 3, 1161 (1927); Automotive Enq., 16, 27 (1925). (18) Paterson and Campbell, Proc. Phys. Soc., 1919, 177. (19) Petavel, Phil. Mag., 3, 461 (1902). (20) Pignot, J . usines gaz, 60, 293 (1926). (21) Podbielniak, Oil Gas J., 27, No. 35, 38 (1929). (22) Taffanel and LeFloch, Compt. rend., 166, 1544 (1913); 167, 469 (1913). (23) Woodbury, Lewis, and Canby, J . SOL.Automoiioe Eng., 8, 209 (1921).
Effect of Hydrogen-Ion Concentration in the Dyeing of Cherries’ R. N. Jeffrey and W. V. Cruess FRUITPRODVCTS LABORATORY, UNIVERSITY
HREE dyes, Ponceau 3R, Amaranth, and Erythrosine, are commonly used in the coloring of maraschino style cherries. Erythrosine only is used in coloring cherries that are added to canned mixed fruits to be used for making salad because it does not “bleed” and does not discolor the other fruits. Difficulty in obtaining rapid and uniform penetration of the cherries by the Erythrosine, however, is encountered during the dyeing process. I n some cases also the color imparted by Erythrosine has “bled” and stained the fruits to which the cherries were added. Preliminary experiments in the Fruit Products Laboratory indicated that hydrogen-ion concentration is of great importance in dyeing cherries with Erythrosine and in fixing the color. To establish more definitely the effect of this factor the experiments reported in this paper were conducted. Amaranth, Ponceau 3R, and Erythrosine were compared quantitatively with respect to their rates of “bleeding”-i. e., rates of dissolving from cherries prepared according to standard commercial procedure. The cherries had previously been dyed in solutions of 0.1 per cent of each color in canesugar sirups. Pitted imported Italian cherries, containing as received 1600 mg. of sulfur dioxide per kg. (1600 p. p. m.), were used in these experiments. To determine the comparative rates of “bleeding,” the cherries were allowed to stand for 48 hours in distilled water and also in cane-sugar sirup of 20” Brix containing 0.5 per cent citric acid. The color in the liquid was determined by use of a Klett colorimeter and standard dye solutions. The Erythrosine gave up 0.59 part per million to distilled water and 0.10 part per million to the sirup; the Amaranth 29.1 and 12.2 parts per million; and the Ponceau 3R, 28 and 13 parts per million. Successive leachings in water and sirup dissolved much more of Amaranth and Ponceau 3R than of Erythrosine. Varying the pH value of the leaching medium had no noticeable effect on the leachability of Ponceau 3R and Amaranth. Both leached very rapidly a t all pH values used. At pH values in the distinctly acid range (4 or lower) the solubility of Erythrosine decreased markedly. Many organic and inorganic mordants were also used with the three dyes, but without effect in fixing the color in the fruit. The effect of pH value of the medium on dissolving Erythrosine from cherries is shown in Table I. The data in Table I show that leaching of the Erythrosine was rapid a t pH 6.7, appreciable a t pH 4.7, and very slight a t pH 3.5 and lower. As the Erythrosine was found to respond to the reaction of the medium, further study was made on the effect of pH value on its rate and evenness of penetration into the cherries, on its
T
1 Received
August 16, 1929.
OF
CALIFORNIA, BERKELEY, CALIF.
fixation in the fruit, and on precipitation of the dye from water solution. I n one experiment there was added to a series of tubes of 0.1 per cent Erythrosine solution from 0.1 to 1.0 per cent citric acid in intervals of 0.1 per cent and from 0 to 0.1 per cent citric acid in intervals of 0.01 per cent acid. In another series rather concentrated solutions of the dye and acid were mixed to cause precipitation of the dye and were then diluted to the desired acidities. Attempts to determine the pH values of these dye solutions were not very successful because of coating of the dye on the hydrogen electrode and colorimetric pH determinations were out of the question. It is probable that the dye, being a sodium salt of a weak acid, affected the pH values t o an important degree, particularly a t low acidities. Equilibrium in the two series was reached very slowly, more than two months being required. Although the results obtained were chiefly qualitative, it was found that precipitation of the dye was complete a t pH 3 or lower and no precipitation occurred a t pH 7, with gradation in the degree of precipitation from pH 3 to 7. Evidently the sodium salt of the dye is soluble, while the free acid (undissociated Erythrosine) is practically insoluble. Table I-Effect
of pH Value on Amount of Erythrosine Dissolved from Cherries
1
CITRIC
SAMPLE ACID
ADDED
FINALPH OF SOLN.
Grams per
1
100 cc. 0
3 4
0.1 0.2 0.3 0.4
R
0 5
2 5
6.7 4.7 03 5 , 4 . 8 3.5 a2.6,3.4 ”2.4.3.8
I
ERYTHROSINE IN SOLUTION Cherries heated to looo C. and allowed to stand 36 hours
Cherries not heated, allowed t o stand 36 hours
P. p . m.
P. 9 . m.
33.7 7.7 7.7 0.15 0.05 0.04
27.6 3.75 0.15 0.13 0.05 0.04
The higher pH values in samples 3, 5, and 6 varied with the method used for leaching the SO2 from the cherries. Those of higher pH value had been soaked in hot water for rather a long petiod; those of lower pH value had been boiled a short time in water before coloring. a
I n a second experiment cherries were heated in water solution of Erythrosine solutions of the dye to which 0, 0.05, 0.15, 0.25, 0.35, 0.45, and 1 per cent of sodium bicarbonate was added. The pH values were 4.5, 6.3, 6.7, 7.5, 7.5, 7.6, and 8.0, determined after heating. Penetration of the dye was much more rapid and uniform in the alkaline solutions. The solutions containing the sodium bicarbonate penetrated the cherries much more rapidly than the plain water solution, although the high pH values caused the Erythrosine to be bluish red instead of its normal “pink-red.” Acidification
December, 1929
IYDUSTRIAL AND EAYGINEERISG CHEMISTRY
of the sodium bicarbonate treated specimens, however, caused the return of the normal color. Cherries leached with running hot water to remove sulfur dioxide were found to be considerably higher in pH value than those boiled repeatedly in water when both had reached less than 25 p, p. m. of sulfur dioxide, the pH values being 4.5 and 3.0. Other things being equal, Erythrosine should penetrate cherries leached with running hot water more rapidly than it does cherries boiled repeatedly in water. Additional experiments proved the efficacy of the sodium bicarbonate solution of the Erythrosine for dyeing the cherries and the desirability of acidifying the sirup after dyeing in order to fix the color. Comparison of various concentrations of Erythr osineshowed that a 0.1 per cent solution gave as good results as more concentrated solutions. Applying the results of these experiments to the practical
1269
preparation of maraschino style cherries showed that rapid dyeing of the cherries is accomplished by adding Erythrosine in dilute (0.3-0.1 per cent) sodium bicarbonate solution and that practically complete fixation of the color is then obtained by adding a dilute citric acid solution (approximately 0.5 per cent). Summary
The pH value of the cherries and that of the solutions used in the dyeing of cherries with Erythrosine greatly affect the evenness and rapidity of dyeing and the fixation or the bleeding of the color in dyed cherries. Ponceau 3R and Amaranth are not appreciably affected by the pH value and bleed rapidly a t all the pH values used in the experiments here reported. It is recommended that Erythrosine be applied in dilute sodium bicarbonate solution of approximately pH 7.5 and be fixed by dilute citric acid or other permissible fruit acid a t approximately pH 3.0-3.5.
Vapor Pressures and Other Physical Constants of Methylamine and Methylamine Solutions' W. A. Felsing and A. R. Thomas UNIVERSITY O F TEXAS, AUSTIN, TEXAS
The vapor pressures of methylamine have been deH E introduction of reheats of evaporation of liquid termined from - 8 0 " to -10" C. and combined with frigerating units i n t o m e t h y l a m i n e f r o m vapor the data of Berthoud to obtain a general relation from home refrigerators has pressure data, are included. -90' to 156.90" C. (critical point). been exceedingly rapid in reThe use of methylamine as The densities of liquid methylamine have been dea refrigerant does not seem to cent years. Most of t h e s e termined from -80" to 20' C. units use as the refrigerating be accompanied by great danThe total pressures of methylamine solutions have ger in case of leakage, etc. fluid some of the more easily been measured for concentrations 1.67, 7.64, 13.39, Frankel (7) d i s c u s s e s t h e condensable gases, such as 22.86, 36.12, and 48.60 mol per cent. The partial presphysiological effect. Monosulfur dioxide, butane, methyl sures have been measured for a number of dilute soluchloride and ammonia. A m e t h y l a m i n e irritates the tions. comprehensive list of possible mucous membranes, and its The total heats of solution have been measured; the fluids for refrigerating units is odor is similar t o that of study of the change of this heat with the concentration ammonia. T h e c r a m p i n g given by Taylor (19). The of solution formed will be studied in detail. two systems in common use effect of ammonia is lessened The heats of evaporation have been calculated. by the substitution of methylare the compression and the groups for hydrogen. Metha b s o r u t i o n t v u e s . Both types utilize as the cooling principle the heat absorption when ylamine causes a slight depression of the blood pressure, but the liquid fluid evaporates. The two types differ, however, it does not alter the rate of breathing. The hematolytic in the method of causing rapid evaporation and in the method action of methylamine is due to the hydroxyl ions produced. of again liquefying the gaseous fluid. In the compression units Frankel concludes with the statement that methylamine is the fluid is liquefied by mechanical compression iind cooling much less poisonous than ammonia. The irritating odor of (generally air-cooling); in the absorption units the gaseous methylamine would seemingly call attention to a leak before fluid is absorbed by a solid or liquid absorbent during the any serious physiological action could take place. cooling portion of the cycle, and is then boiled out or driven Existing Data out by heating the solution or absorbent. The various types of apparatus employing the absorption principle a1e discussed Berthoud (1) measured the vapor pressures of methylby Keyes ( I S ) . amine from -7.55' t o Sl56.9' C. (critical point). The The fluid usually employed in the absorption units is International Critical Tables cite Berthoud's data a t even ammonia. With certain materials of construction and some temperatures, using smoothed-out values. The probable absorbents, however, this fluid has some disadvantages. accuracy of the data is stated t o be 5 in the last figure given, Monomethylamine, CH3.NH9, has often been suggested as a the pressures being listed in atmospheres; this means an possible substitute for ammonia in such cases. Since rela- accuracy for the first nine determinations to within 38 mm., tively few data on the physical properties of this substance and for the others to within 380 mm. Several authors (8, exist in the literature, it was thought profitable to determine 1 2 , 16) give values for the boiling point under different barothe vapor pressures and densities of liquid nitthylamine metric pressures. The International Critical Tables cite a and the total and partial pressures of methylamine solutions value identical with that of Olsen. a t different concentrations and temperatures. A few preVery few density values are available. Hoffman ( l a ) , liminary measurements of the heat of solution of methyl- Hodgeman and Lange (11), and the International Critical amine vapor in water, together with the calculation of the Tables cite values a t differing temperatures. Received August 7, 1929 The data on the partial pressures of methylamine out
T
\
