INDUSTRIAL AND ENGINEERING CHEMISTRY
452
7. Sulfur contained in the hydrocarbons was partially or wholly oxidized to sulfur dioxide and trioxide upon exposure in oxygen. 8. In nitrogen or hydrogen, hydrocarbons reacted with sulfur in the light. Paraffin, cycloparaffin, and aromatic hydrocarbons formed hydrogen sulfide and sulfides. Olefin and cycloolefin hydrocarbons formed hydrogen sulfide and mercaptans. 9. Addition of n-propyl disulfide resulted in color and haze formation in all of the hydrocarbons except 2-octene and cyclohexene upon exposure to light and oxygen. In nitrogen or hydrogen the disulfide caused color formation in none of the hydrocarbons except 2,2,4-trimethylpentane and cyclohexane. 10. Saturated and aromatic hydrocarbons containing n-propyl disulfide developed less peroxides when exposed to light and oxygen than the pure hydrocarbons similarly exposed. The disulfide had no effect on the peroxide numbers of unsaturated hydrocarbons. 11. In nitrogen or hydrogen all hydrocarbons to which n-propyl disulfide was added contained mercaptans due to reaction between hydrocarbons and the disulfide. 12. Comparison of the work with pure hydrocarbons and with straight-run, cracked, and blended gasolines, with and without added sulfur or n-propyl disulfide, shows that the behavior of the gasolines was such as would be expected of
VOL. 28, NO. 4
mixtures of various types of hydrocarbons. In general, pure hydrocarbons or gasolines from which sulfur and disulfides had been removed were color-stable in light. The response tos ulfur of paraffin, cycloparaffin, and aromatic hydrocarbons was similar to straight-run gasolines except that the straightrun gasoline had higher peroxide numbers in oxygen and formed mercaptans in nitrogen or hydrogen. These differences might be accounted for by the presence of unsaturates in the straight-run gasoline. The response of unsaturated hydrocarbons to sulfur was like that of cracked gasoline. The behavior of hydrocarbons containing n-propyl disulfide was similar to gasolines. The disulfide had less deleterious effect on color stability of unsaturated hydrocarbons and cracked gasoline than it did on the stability of saturated or aromatic hydrocarbons or straight-run gasoline.
Literature Cited (1) Dryer, Lowry, Morrell, and Egloff, IND. ENO. CHEM.,26, 885 (1934).
(2) (3) (4) (5)
Egloff, Morrell, Benedict, and Wirth, Ibid., 27, 323 (1935). Francis, Ibid., 18, 821 (1926). Morrell, Benedict, and Egloff, Ibid., 28, 122 (1936). Yule and Wilson, Ibid., 23, 1254 (1931).
RECEIVED October 5, 1936. Presented before the Division of Petroleum Chemistry at the 90th Meeting of the American Chemical Society, Saa Francisco, Calif , August 19 to 23, 1935.
4
,
2s
88
30
SUCROSE SOLUTIONS Influence of Pressure on Boiling Point Elevation Y
85
90
13.55 19.95
OR the purpose of more closely controlling sugar-boiling operations, boiling point elevations are widely used in estimating the degree of supersaturation. It is therefore obvious that accurate data on the boiling points of suorose solutions of various concentrations are essential. From this standpoint it is unfortunate that the boiling points of sucrose solutions as reported by various investigators have differed so greatly that considerable doubt has existed as to what values might be safely accepted. An investigation of this subject was accordingly undertaken with the object of finding answers to each of the following questions: 1. What values may be accepted as accurately representing the boiling point elevations of sucrose solutions of various concentrations?
2. To what extent, if any, are such boiling point elevations affected by the absolute pressure under which boiling takes place in vacuum pans?
In the course of this investigation a number of Iaboratory determinations were made on the boiling points of pure sucrose solutions of various concentrations a t an atmospheric pressure of 760 mm. of mercury. The results are plotted in Figure 1. The fact that boiling point elevations taken from this graph do not differ greatly from those reported by Claasen ( 2 ) is evident from Table I which compares the present determinations (reported as C. and H. data) with those of Claasen as well as with those reported by other investigators. From such results it is evident that Claasen’s values are checked closely, not only by the present determinations made a t atmospheric pressure but also by those reported by Inter-
INDUSTRIAL AND ENGINEERING CHEMISTRY
&PPRIL,1936
50
103
ABSOLUTE
PRESSURE
Zca
453 -
MM
HG
303
400
500
760
Generally it has been assumed that t h e b o i l i n g point elevation of sugar solutions is unaffected by the pressure under which boiling takes place. The facts presented in this paper i n d i c a t e that this assumption is unfounded and that supersaturation graphs based on such an assumption are in error.
30
40
50
national Critical Tables and by Kahlenberg. It is believed therefore that Claasen's values, which incidentally are those most widely used by the sugar industry, may be accepted, for all practical purposes, as being sufficiently representative of the boiling point elevations of sucrose solutions a t atmospheric pressure. However, although it was believed that the accuracy of the Claasen values was established by the foregoing comparison, it was found that the supersaturation coefficients calculated by such values did not give a true picture of conditions in actual sugar-boiling operations. In actual practice it was found that the Claasen values indicated neither the correct concentration as established with a vacuum pan refractometer, nor the correct saturation point as determined by a microscopic study of grain formation. The investigator who observed these discrepancies suggested that the boiling point elevation of sucrose solutions might be appreciably influenced by variations in the absolute pressure under which boiling takes place and that Claasen's values might be strictly accurate only when boiling is conducted under atmospheric pressure-a condition not encountered in practical sugar boiling. Such a possibility was a bit revolutionary in that it appears to have been generally assumed by practically all writers on sugar technology that the boiling point elevation of a. sugar solution is unaffected by the pressure under which boiling takes place. To note how firmly this belief has been held,
.... ..
..
ao
Washburn and Read Formula (10) From data included in this reference, it is possible to derive the following formula for estimating the boiling point elevation a t any pressure, P (mm. of mercury), when the boiling point elevation at an atmospheric pressure of 760 mm. of mercury is known: B. P. E. a t P
= [l.OO - (760 -
P ) X 0.00021 B. P.E. a t 760 mm.
For example, since the B. P. E. for an 80 per cent sucrose solution is 9.3' C. a t 760 mm., the B. P. E. for this solution a t an absolute pressure of 76 mm. may be calculated in the following manner:
-
Boiling Point Elevation, C . Kahlen- GerFreutPerJorI. C. T. Claaaen berg lach re1 man den C. & H.a.. (6) (8) (8) (6) (4) (9) (7) 1.0 1.0 30 0.70 0.7 0.6 0.95 0.6 1.5 1.10 1.5 1.1 40 1.45 1.05 1.45 2.0 1.9 i:s 1.90 1.8 2.0 2.00 50 2.14 2.5 2.5 2.50 2.3 2.4 2.50 55 2.62 3.0 3:0 3.1 3.4 3.25 3.0 3.20 60 3.23 4.7 4.8 4.5 4.20 3.9 4.2 4.10 3.8 65 6.5 5.3 5.55 6.5 6.3 70 5.5 5.1 5.40 9.2 7.0 8 . 8 9.2 7.4 7.2 75 7.3 7.15 12.0 12.6 .. 10.3 14.8 80 9.4 9.65 17.1 20.3 13.0 14.5 85 13.55 .. 29.2 19.6 27.0 22.6 90 19.95 a Values based on C. and H. determinations appear to average about 0.3: C. higher than those reported by Claasen. The came of thia small but rather consistent difference has not yet been ascertained.
..
WATER
one need merely glance through the literature on this subject and find statements to the effect that the boiling point elevation of sugar solutions is in no way affected by the pressure, and that the same set of boiling point elevations is valid for all pressures. In view of such indications, a study of this phase of the subject was also undertaken. The presumption that boiling point elevations of sugar solutions are constant for all pressures was found to be more or less contradictory to certain physico-chemical laws. As a matter of fact, such boiling point elevations appear to be appreciably influenced by the pressures under which boiling takes place, and the magnitude of this effect may be readily estimated by several means to be discussed.
POINTELEVATIONS FOR PURESUCROSE TABLEI. BOILING SOLUTIONS AS REPORTED BY VARIOUS IWESTIGATORS Concn. of Soh., % Solids
no
- 'C 70
60
BOILING POINT OF
B. P. E. for 80' Brix solution a t 76 mm. = [1.00 (760 - 76) X 0.0002]9.3° C. = (1.00 - 0.137) 9.3' C. = 0.863 X 9.3' C. = 8.02' C .
Duhring's Principle (3) Duhring's principle states that where Ts and Ts' are the boiling points of a solution a t two absolute pressures, and Tw and Tw' are the boiling points of water a t those same pressures, the boiling points are then connected by the following approximate formula: T s - Ts' = K , a constant
TW - Tw'
INDUSTRIAL AND ENGINEERING CHEMISTRY
454
VOL. 28, NO. 4
Using each of the above methods, the boiling point elevations for sugar solutions containing from 50 to 90 per cent sucrose have been calculated for the various absolute pressures. In general, the results obtained by the several methods of calculation have agreed as well as could be expected in view of the fact that each of the methods has been extended to cover a much greater range of pressures than that for which it was originally derived. The rather consistent agreement obtained by the various methods is illustrated by Table 11.
TABLE11. BOILINQPOINTELEVATION OF SUCROSE SOLUTIONS AT 76 MM. ABSOLUTEPRESSURE B. P. E. -B. P. E. a t 76 Mm. Estimated by:-Conon. at Washburn Diihring Badger of Soln. 760 Mm. formula formula formula Average % ' solids C. O c. a a 60 2.90 2.51 1.7 2.41 2.2 65 3.85 3.32 2.7 3.20 3.1 70 5.10 4.40 3.9 4.25 4.2 75 6.85 5.91 5.7 5.69 5.8 so 9.30 8.02 8.10 7.9 8.0 85 13.30 11.48 12.10 11.1 11.5 90 19.6 16.91 18.4 16.3 17.20
c.
I I25 ABSOLUTE
IS0
c.
'
I PRESSURE
-
100 MM
HG
From the work presented by Perman and Saunders (9) on the vapor pressures of sucrose solutions of various concentrations, it has been found that K is approximately equal to 1.022. Application of Diihring's principle to calculation of the boiling point of an 80 per cent sucrose solution a t an absolute pressure of 76 mm. may be made in the following manner: 109.3 - 2. = 1.022 = 109.3 - x 100
c.
- 46.1 - x = 55.1
53.9
109.3
x = 54.2" C. = b. p. of an 80" Brix sucrose solution a t 76
mm. pressure
At 76 mm. pressure, water boils a t 46.1" C.; therefore the B. P. E. of the 80" Brix solution a t 76 mm. will be 54.2" C. 46.1" C. or 8.1" C .
Badger and Shepard ( I ) Badger and Shepard report some studies on the boiling points of salt solutions a t various pressures. While the properties of salt solutions are very different from those of sugar solutions, there is nevertheless sufficient similarity to warrant a general comparison. For instance, in Badger's data it is shown that the B. P. E. of a 36 per cent salt solution is reduced from 7.55" C. a t 760 mm. pressure to 6.4" C. a t 100 mm. pressure (Badger gives no data for boiling points below 100 mm. pressure). If it is assumed that the B. P. E. of sugar solutions will be reduced proportionally to that of the salt solutions reported by Badger, the B. P. E. of an 80 per cent sucrose solution a t 100 mm. pressure would be (6.4/7.55) X 9.3" C. = 7.91' C., which obviously agrees fairly well with the values calculated by more conventional methods. ' Summary Comparative results given by various methods of calculating the boiling point elevation of an 80 per cent sucrose solution boiling a t an absolute pressure of 76 mm. are: By Washburn formula By Diihring formula By analogy with Badger d a t a on salt solutions
-
8.02' C . 8.10 7.9
The average B. P. E. for an' 80" Brix solution a t 76 mm. pressure is approximately 8.0" C . , as compared to 9.3" C. a t 760 mm. pressure.
The entire set of values for the pressures mentioned above has been plotted on Figure 2, a Duhring graph in which the water boiling points and the sugar solution boiling points are coordinates. The advantage of plotting on this type of graph is that such results may be represented by substantially straight lines. Figure 2 shows only the boiling point elevations of pure sucrose solutions, but the boiling point of impure sugar solutions may be calculated in a similar manner.
Conclusions The conclusions arrived a t as a result of this study are briefly as follows: 1. The boiling point elevations of pure sucrose solutions as reported by Claasen are accurate only when boiling is conducted under substantially atmospheric pressure of 760 mm. 2. The assumption that the boiling point elevation is unaffected by the pressure under which boiling takes place is unjustified. As a matter of fact, the boiling point elevations of sucrose solutions boiling under an absolute pressure equivalent to 76 mm. mercury are about 13 per cent lower than at atmospheric pressure. The direction of this error is such that supersaturation coefficients calculated on the basis of previously available data have apparently been somewhat too low.
APRIL, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
The supersaturation charts of Figure 3 bring out more clearly the importance of this point. The dotted lines show the supersaturations calculated on the assumption that the boiling point elevations are not affected by the absolute pressure. The solid lines show supersaturation values calculated on what appears to be the more logical assumption that boiling point elevations are affected by absolute pressure in the manner covered by the foregoing discussion. The important point indicated by these results is that supersaturation coefficients calculated on the apparently unjustified assumption that Claasen’s values are also valid a t the reduced pressures prevailing in a vacuum pan are all about 0.1 too low. For instance, Claasen’s data would indicate that a sugar solution boiling a t 58.4” C. under an absolute pressure of 100 mm. mercury would merely be saturated. As a matter of fact, however, this solution would have a supersaturation of about 1.1a condition which has repeatedly been verified by other means. By making the necessary corrections for absolute pressure a series of constant supersaturation lines as shown in Figure 4 has been obtained. The supersaturation values determined with the aid of this graph have been found to represent accurately the conditions encountered in actual sugar-boiling practice.
45 EO
Although the boiling point elevations reported by Claasen are valid when boiling is conducted at an atmospheric pressure of 760 mm., it is believed that they cannot be used for a highly accurate control in practical sugar-boiling operations unless a suitable correction is made for the reduced absolute pressure prevailing in a vacuum pan.
Literature Cited (1) Badger and Shepard, Trans. Am. Inst. Chem. Engrs., 13, 166 (1920). (2) Claasen, Versinzsitschrift, 1904, 1161. (3) Duhring, “ N e w Grundgesitae der rationellen Physik und Chemie,” Leipzig, 1878. (4) Freutzel, Spencer, Handbook of Cane Sugar Manufacture, 6th ed., p. 453, New York, John Wiley & Sons, 1917. (5) Gerlach, 2. Ver. deut. Zucker-Ind., 13, 283 (1863). (6) International Critical Tables, Vol. 111, p. 328, New York, McGraw-Hill Book Co., 1926. (7) Jordan, “Confectionery Problems,” 1st ed., p. 252, Chicago, National Confectioners Assoc., 1930. (8) Kahlenberg, J. Phys. Chem., 5, 339 (1901). (9) Perman, E. P., and Saunders, H. L., Trans. Faraday Soc.. 1923. (10) Washburn and Read, J. Am. C h m . Soc., 41, 738 (1919). RECEIVED October 22, 1935. Presented before the Division of Sugar Chemistry at the 90th Meeting of the American Chemical Society, San Francisao, Calif., August 19 t o 23. 1935.
Spray Residue on Apples R. H. ROBINSON Oregon Agricultural Experiment Station,Corvallis, Ore.
T
HE removal of spray residues by a chemical washing process is now considered a regular adjunct to the several phases of the apple and pear industry ( 3 ) . Washing of fruit is necessary in order to meet a tolerance limit for lead and arsenic spray residues established by Federal Health Officials. At present the tolerance permitted for lead is 0.018 grain, as lead (Pb), and for arsenic is 0.01 grain, as arsenous oxide (Asnos), per pound of fruit (4). The codling moth, or more correctly, the larva of the codling moth, is the insect or worm that infests apples and pears and causes wormy fruit. In order to control this pest, several applications of lead arsenate or other arsenical are required during the growing season. As a consequence, appreciable amounts of the poisonous residues remain on the fruit a t harvest time. During the past few years, codling moth infestations have increased steadily. In some parts of the country ordinary spraying methods do not give satisfactory control. Consequently, heavier spray applications with the use of mixtures such as combinations of lead arsenate with soap, fish or petroleum oils, or certain special emulsions are required in order to deposit a heavy protective film of poison on the fruit. Accordingly, it has become more difficult to clean the heavily sprayed apples below the prevailing tolerances. Solvents in Common Use Hydrochloric acid and sodium silicate (KazO, 19.5 per cent; SiOz, 30.5 per cent) are the two major solvents used for the removal of spray residues. Each of these solvents is particularly effective for cleaning certain lots of varieties of apples, depending upon the sprays applied and the condition
Supplementary Solvents for Its Removal of the fruit a t the time of washing. [Neither of these solvents, however, is sufficiently effective for cleaning heavily sprayed apples, especially when the residue has become imbedded in natural-wax or petroleum-oil spray deposits. Heating of the solvent to a point where danger of injury to the fruit may r e s u l t h a s aided but has not Heavily sprayed been e f f e c t i v e for the waxy apples that f r u i t m o s t difficult to cannot be cleaned by clean. T h e t y p e of f r u i t t h e u s u a l hydrowasher to use is imporchloric a c i d or sotant. During the past dium silicate solvent year an efficient doubletreatment m a y b e process machine was perwashed effectively in fected that has been a material aid in cleaning a c i d supplemented bad lots of apples. This with petroleum oil. machine is depicted in Wetting or degumFigure 1 with a detailed ming agents properly diagram to indicate the used in combination manner of conveyance of the fruit t h r o u g h the with hydrochloric machine. The machine acid increase the solconsists of two sections vent action of the that permit the use of a acid on spray residifferent washing solvent due. in each s e c t i o n . For
