EXPERIMENTS ON EMULSIONS BY
F. R. NEWMAN
The object of this investigation was: to study the nature of emulsions and to identify the phases; to prepare emulsions of benzene and similar substances in water and of water in benzene, etc., determining the proper conditions for the preparation of each type of emulsion. Except when otherwise stated, all the emulsions were made up in IOO cc bottles and a t ordinary temperature. In the early experiments the bottles were shaken by hand; but later the liquids were emulsified by shaking them violently in a shaking apparatus for periods of time varying from one minute to an hour and a half. The shaker was operated by a 1/8 H. P. induction motor and was so constructed and geared that two bottles a t a time were shaken up and down in a vertical plane at the rate of approximately 360 complete oscillations per minute. The amplitude of the oscillations was about two inches. No experiments were made to find out the best form of shaker and consequently the results obtained apply only to the apparatus used. If a small homogenizer had been available, i t is practically certain that better emulsions would have been obtained and over a wider range. Unfortunately, no such piece of apparatus is on the market. Three methods may be used for determining which of two liquids is the external phase in an emulsion: the inspection method, the indicator method, and the drop method. Determination by inspection is unreliable and unsatisfactory, especially when the liquids are the same color. It should only be relied upon in the simplest cases. Robertson1 has applied the indicator method to emulsions of olive oil and water, using the red dye, Soudan 111, which is insoluble in water but readily soluble in oils. “On sprinkling a few grains of Soudan I11 upon the surface of an emulsion of water in oil, the color spreads rapidly over the surface. If, howl
Zeit. Kolloidchemie, 7, 7 (1910).
Experiments on Emulsions
35
ever, one sprinkles the Soudan-I11 upon an emulsion of oil in water, the color remains confined to the droplets of oil with which the grains are in actual contact, since it cannot spread from them to adjacent drops throughout the intervening water.” Iodine is soluble in benzene and similar substances but insoluble in water, while methyl orange is soluble in water and insoluble in benzene. The iodine solution in benzene has a pink color while the methyl orange imparts an orangeyellow color to a water solution. Small amounts of iodine and methyl orange added to emulsions of benzene and water give a fairly satisfactory method of determining which is the external and which the internal phase. I did not find the indicator method so generally satisfactory as Robertson did and I made most use of the drop method, worked out by Mr. T. R . Briggs. This highly satisfactory method of distinguishing the phases is carried out in the following way: A small drop of an emulsion, of benzene and water for instance, is placed on a glass plate by means of a glass rod. A drop of water is placed on the drop of emulsion and the two stirred together. If the emulsified globules spread in the water, i t is an emulsion of benzene in water; but if there is no spreading, it is an emulsion of water in benzene. This result can be checked by adding a drop of benzene to a drop of emulsion and stirring as before. If the globules spread, the emulsion is one of water in benzene; but if not, we have an emulsion of benzene in water. The principle involved is that one can dilute an emulsion by adding more of the external phase. This method worked admirably in all my experiments on emulsions. It has the advantage of being a general method, applicable t o all emulsions. Two methods were tried of making emulsions of benzene in water. In the first method the whole of the benzene was added at once to the mixture of water and protective colloid, and the contents of the bottle were then shaken by hand. I n the second method the benzene was added a little a t a time, the flask being shaken vigorously after each addition.
36
F . R. Newrnan
I n the set of experiments now to be described, all the benzene was added a t once. Mixtures having a total volume of 40 cc were made up in 60 cc bottles, containing 5, IO, 30, 30, 40, 5 0 , 60, 70, 80, 90 and 95 percent of benzene by volume and I cc of I percent sodium oleate as protective colloid, the balance being water. These mixtures were shaken by hand for five minutes and then examined. In each case an emulsion of benzene in water was formed; but the different mixtures behaved differently on standing. With the 5 , IO, 20, 30 and 40 percent benzene mixtures an ever-increasing amount of a creamy, emulsion layer formed and rose to the top, leaving a thin, dilute suspension of drops of benzene in water as a bottom layer. With the other mixtures there were three layers formed: a clear upper layer of benzene; then a creamy, emulsion layer, decreasing in thickness with the higher benzene concentrations; and below this the thin dilute suspension of drops of benzene in water also decreasing in amount with higher concentrations of benzene. Up to 40 percent all the benzene was emulsified ; but this was not the case for 50 percent and more of benzene. The emulsions remained as described for forty-eight hours, a t the end of which time an upper layer of benzene began to appear on the 30 percent and 40 percent benzene mixtures. I n the course of a week a thin layer of benzene appeared on all the solutions, but did not seem to increase after that, contrary to Pickering’s experiments. The next experiments dealt with the effect of varying the concentration of sodium oleate. A run was made with I O cc of a I percent sodium oleate instead of I cc. Instead of using a constant amount of sodium oleate, a solution was made up of I cc of a I percent sodium oleate in 23 cc water, and the required concentrations of benzene obtained by adding this solution in suitable amounts. The 40 percent benzene mixture then had the same concentration of sodium oleate as in the first run, the more dilute benzene mixtures containing more sodium oleate and the more concentrated benzene mixtures less sodium oleate than in the first run. Still another
Experiments on Emulsions
37
run was made by adding to benzene varying amounts of a solution consisting of I O cc water plus I O cc of a I percent sodium oleate solution. The varying concentration of sodium oleate has a relatively slight effect on the break-down point, or point where the benzene layer appeared, the change always occurring between the 40 percent and 50 percent benzene mixtures. More careful measurements showed an effect due to the concentration of the soap. Using I cc I percent sodium oleate and shaking 40 cc mixtures for one minute in 60 cc bottles, the break-down point was found to be between 45 percent and 46 percent benzene by volume. With other conditions the same, but using I O cc I percent sodium oleate, the break-down point was found to lie between 46 percent and 47 percent benzene. With increasing amount of sodium oleate, the lower or water layer became more cloudy. The intermediate creamy layer in the higher benzene concentrations decreased in thickness with decreasing concentration of sodium oleate. Some experiments were made, varying the order in which the benzene, water and soap solution were mixed; but no appreciable effect was noted. One run was made at 50°, adding 5 cc of a I percent sodium oleate solution; but the temperature effect seemed to be negligible within this range. Experiments were then made to see whether the size and shape of the container had any effect. A 40 percent benzene mixture (8 cc benzene 1 2 cc of a I percent sodium oleate solution) and a 30 percent mixture (6 cc benzene 14 cc of a I percent sodium oleate solution) were placed in test-tubes and shaken by hand. The results were quite different from the preceding ones, both the 30 percent and the 40 percent mixture showing a clear, upper layer of benzene. Four 40 cc samples were now made up in 100 cc bottles as follows: I . 50 percent benzene (20 cc benzene 2 0 cc 0 . I percent soap). 2 . 50 percent benzene ( 2 0 cc benzene 2 0 cc 0 . 5 percent soap).
+
+
+ +
38
F. R. Newman
+ +
3 . 50 percent benzene (20 cc benzene 2 0 cc I percent soap). 4. 60 percent benzene (24 cc benzene 16 cc I percent soap). Nos. I and 2 showed no benzene layer and No. 4 did, these results being like those obtained with the 60 cc bottles. On the other hand there was no benzene layer with No. 3 . We thus have the 30 percent benzene mixture showing a benzene layer when shaken in test-tubes, the 50 percent mixture when shaken in 60 cc bottles and the 60 percent mixture when shaken in IOO cc bottles. Under given conditions of shaking, the appearance of the emulsion may vary markedly with the size and shape of the container. This is probably nothing more than an indirect effect due to actual differences in the degree of mixing. The narrow test-tube is clearly the least satisfactory form and a given amount of liquid can obviously be shaken more thoroughly and more easily in a IOO cc flask than in a 60 cc one. A series of runs were now made in which the benzene was added in portions and the flask shaken by hand after each addition. For convenience of reference let A denote mixtures having a creamy emulsion and a water layer below; let B denote mixtures with an upper, clear layer of benzene; and let C denote mixtures which form an apparently homogeneous emulsion with no second layer visible. To I O cc I percent sodium oleate I O cc HzO in a 60 cc flask then were added successively 14,2, I , I, I , I , and I cc benzene, the flask being shaken for one minute after each addition of benzene. The initial concentration was about 41 percent benzene and the final concentration about 51 percent benzene. All solutions belonged to type A. To 5 cc I percent soap in a 60 cc flask there were added successively, 3, 3 , 3 , 2 , 3, 5, 5, 5, 5, and I O cc benzene, the bottle being shaken for one minute after each addition. The first emulsion contained 37.5 percent benzene and was of type A ; the last contained 89.6 percent benzene and was of type C. Several other similar runs were made, varying the amount of soap used, but this seemed
+
Experiments
ovt
Emulsions
39
to have very little effect. Decreasing the time of shaking after each addition to ten seconds also had no appreciable effect. The break-down point can evidently be displaced to above 90 percent benzene, the most important factor in raising the break-down point being to add benzene in relatively small amounts a t the start. Emulsions were next made up of type B and water was added to these little by little to see if the emulsion would change to type A. This could be done in each case; but the point at which this change occurs varies with varying conditions, and seems to be a function of more than one variable. The experiments given in Table I were made in 60 cc bottles and the bottles were shaken by hand for one minute after each addition of benzene or water.
.- - _ - _ __ _ - -
T o 5 cc
_____
I
TABLEI percent sodium oleate solution
Add 8 cc benzene 2 cc water Add 12 cc benzene I cc water Add 13 cc benzene I cc water I cc water I cc water Add 2 0 cc benzene I cc water I cc water I cc water
__
I
1
61.5 percent 53.3 70.6 66.6 72.2
68.4 65 .o 61.9 80.0 76.9 74.1 71.4
-~
I ‘ I
._ -
B A B A B
l
BB
I
A B
When I cc I percent sodium oleate and 4 cc water were taken and 1 2 cc benzene added, the emulsion was still of the B type after the addition of 8 cc water (48. o percent benzene) and only changed to the A type on adding I O cc water (44.4y0 benzene). Decreasing the soap concentration seems to change the break-down point under these conditions from about 67 percent benzene to about 45 percent benzene. Several runs were now made in IOO cc bottles. This permitted more efficient shaking and gave rise to very different results. The efficiency of emulsification was increased
40
F. R. Newwan
and also the stability of the emulsions. The final emulsions were perfectly homogeneous (type C) and showed no tendency to separate into layers in the course of several months. As has been found by others, it is best to begin with a small amount of the liquid to be emulsified; after some emulsion is formed it is possible and apparently desirable to.make additions at increasing rates. The flasks were shaken for one minute after each addition. To 2 cc 5 percent sodium oleate solution there were added successively, 2 , 2 , 4, 6, 6, 8, 8, 8, and IO cc benzene giving a homogeneous emulsion of benzene in water, and containing 96.4 percent benzene by volume. To 2 cc 5 percent sodium oleate solution there were added successively, 4, 4, 8, 12, 12, and 16 cc benzene, giving a homogeneous emulsion containing 9 6 . 6 percent benzene. To 2 cc 5 percent sodium oleate solution there were added successively, 4, 8, 16, and 24 cc benzene giving a homogeneous emulsion containing 96.3 percent benzene. To 2 cc 5 percent sodium oleate solution there were added successively, 4, IO, and 40 cc benzene, giving a homogeneous emulsion containing 9 6 . 4 percent benzene. The stiffness of these emulsions increased with increasing rapidity of addition of benzene, the last being the stiffest. The last portions of benzene are emulsified more rapidly than the first portions. Since better results were obtained in a IOO cc flask than in a 60 cc flask, one run was made in a 250 cc flask. The results exceeded all expectations, the emulsion being the stiffest one obtained. To 2 cc 5 percent sodium oleate solution there were added successively, 5, IO, 15, 2 0 , 2 0 , 20, 2 0 , 30, and 50 cc benzene, giving a homogeneous emulsion containing 99. o percent benzene by volume. We have here 190 cc benzene emulsified in 2 cc of a 5 percent soap solution. To put i t another way, the emulsion consists of 99 volume percent of benzene and I volume percent of water, with 0 . 0 5 g sodium oleate as emulsifying agent. I n other words, 99 cc benzene and I cc water can be converted into a stiff jelly by a little over 0 . 0 5 percent by weight of sodium oleate. This is not
Experinaeizts on Emulsions
41
quite as good as Pickering’s famous jelly,l which consisted of 99 percent kerosene by volume and one percent of a one percent soap solution; but it is of the same order. Using a 5 percent solution of hard soap instead of sodium oleate, a 99 percent benzene emulsion was obtained, shaking by hand. To 2 cc 5 percent hard soap solution there were added successiyely, 5, IO, 15, 20, 2 0 , 20, 2 0 , 3 0 , and 50 cc benzene. The resulting homogeneous emulsion was even stiffer than that obtained with sodium oleate alone; but it did not stand up so well. In the course of four or five days, this emulsion cracked, disintegrating gradually until there were merely flocculent masses suspended in clear benzene. On the other hand, the emulsion made with, sodium oleate was quite unchanged at the end of six weeks. This may give a clue to a discrepancy between Pickering’s results and mine. Pickering’ says that once de-emulsification has started, it progresses at an increasing rate.” This has not been my experience; and it is quite possible that Pickering’s conclusions are not general ones, but apply merely to the particular emulsifying agent that he was using-a potash soap. Since the character of the emulsions varied so markedly with the degree of shaking, all subsequent experiments were done with the power shaker previously referred to. The effect of prolonged shaking was then tested, the conditions of each experiment being: I cc 5 percent sodium oleate solution; final volume of solution, 40 cc; benzene added in portions; total time of shaking, 90 minutes. The details are given in Table 11. The emulsions containing 10-70 percent benzene were all of the A type with a continuously-increasing amount of creamy emulsion at the top and a continuously-decreasing layer at the bottom, consisting of a thin dilute suspension of drops of benzene in water. There was no break-down point and no emulsions of type B with a clear layer of benzene a t the top. When the concentration of benzene reached eighty I‘
Pickering: Jour. Chem. SOC.,91,2002 (1907).
F . R. Newman
42
Total volume, 40 cc; of shaking, 90 minutes
i
Water, 35 cc -_
Benzene per cent
IO
in cc added
1
___
I
TABLEI1 cc 5 percent sodium oleate; total time
I
Benzene per cent added in cc
Minutes shaken
1
Water, 31 cc Minutes shaken
20
i
Benzene 30 per cent
j
added in cc
1 1
2 2
,
27
cc
Minutes shaken
1
I
I 5 5 ; : IO
'I
Water, Ig cc
1
I
Minutes shaken
I 1
I I
1
5 5
I
2 2 I
I
Io Io
30
i
Water, 23 cc Benzene 40 per cent added in cc
I
Water,
1
IO IO IO IO
water, 15 cc minutes shaken
50 in cc
in cc
2
I5
5 IO
2
2 IO
2
2
IO IO
2
Water, Benzene
70 per cent
11
1 1
added in cc
1
3
I
I
cc
I
1
Minutes shaken
1
, I
Water, 7 cc Benzene 80 per cent added in cc
Minutes shaken
10 IO IO IO
IO IO
IO
IO
IO IO
Ib IO
20
20
IO IO
Experiments on Emulsions
43
percent, the lower liquid layer disappeared and we had a homogeneous emulsion of type C. Further runs were made, starting with 5 cc 5 percent sodium oleate and with I O cc 5 percent sodium oleate. About the only difference to be observed is that the watery lower layer is more opaque the higher the concentration of sodium oleate. I t was not possible to obtain homogeneous emulsions with 70 percent benzene or less, even by shaking them every few days, though this did decrease the lower liquid layer somewhat. I n an attempt to obtain homogeneous emulsions with lower benzene content, I started with I O cc of a 97 percent solution, adding successively, 2 , 2 , 2 , and 2 cc water, shaking for ten minutes after each addition. The final mixture (54 percent benzene) did not remain homogeneous but separated into two layers. To I O cc of a 97 percent emulsion I added successively, 3 , 3 , 3 , and 3 cc water, shaking for ten minutes after each addition. This mixture (44.4 percent benzene) separated into three layers (type B). To I O cc of a 97 percent emulsion I added I O cc of a 5 percent sodium oleate solution in I cc lots, shaking for I O minutes after each addition. This mixture (48.5 percent benzene) separated into two layers (type A). A few experiments were next made to see how the maximum amount of benzene in a homogeneous emulsion varied with varying concentrations of sodium oleate. To I cc 5 percent sodium oleate solution there were added successively, I , I , 2 , 3 , 5, 3, 5, IO, IO, 2 0 , 30, 25, and I O cc benzene. The last addition was too much, the excess of benzene separating while the emulsified mass remained apparently unchanged. We thus have a homogeneous emulsion a t 99. I percent and an inhomogeneous one at 99.2 percent benzene by volume. To I cc I percent sodium oleate solution there were added successively, I , I , I , 2 , 3, IO, IO, IO, and 20 cc benzene. Free benzene appeared on the last addition, the emulsion being homogeneous a t 97.6 percent benzene and inhomogeneous at 98.4 percent benzene. Cutting down the amount of sodium oleate to two-fifths apparently decreases the permissible ben-
'
F . R. Newman
44
zene content about one percent. In this last experiment we have 0 . 0 2 g sodium oleate converting about 98 cc benzene and 2 cc water into a jelly. I n emulsions of type A with a lower, watery layer, this lower layer is a homogeneous emulsion containing very little benzene. It seemed desirable, therefore, to learn something about its composition and to prepare such a watery emulsion, if possible, without any of the creamy emulsion being present. In the following experiments, Table 111, I started with 5 cc 5 percent sodium oleate solution and added varying amounts of water and benzene, the total volume being kept at 40 cc:
TABLE I11 Total volume, 40 cc; 5 cc Water --__-__
1
Benzene cc
j
Benzene11 Percent
percent sodium oleate solution Water cc
I
Benzene cc
~
Benzene Percent -
Experiments on Emulsions
45
surface, forming a creamy upper layer. The emulsion will consist apparently of this layer alone when the water layer is present only in the pores. People have calculated that spherical globules will touch when they occupy 74 percent1 of the total volume. One might reasonably expect some dripping until a somewhat higher concentration is reached, and the limiting value of about 80 percent benzene by volunie, as shown by my experiments, is about what one might have expected. With more efficient emulsifying nothing of this sort will take place and we shall have a continuous series of homogeneous emulsions, which will be very fluid a t the low benzene concentrations and which will become more viscous with increasing benzene concentration. M y own work with the power shaker shows that the appearance of an upper benzene layer, a t any rate, a t concentrations below 98 percent benzene, is merely the result of insufficient emulsification. When a homogeneous 95 percent benzene emulsion was frozen and thawed, the emulsion cracked and the change was apparently irreversible, for the emulsion could not be restored by shaking. The cracking of the emulsion is due to the rupturing of the soap films around the globules. The irreversibility is probably only apparent, and due to the coagulated sodium oleate not redissolving readily in water. No emulsions of water in benzene were obtained with sodium oleate as emulsifying agent. Some experiments were also made with other lyophile colloids, such as haemoglobin, lacmoid, pepsin, peptone, dextrin, etc. These all gave emulsions of benzene in water and seemed not to bring out anything new. Before going on with experiments to prepare emulsions of water in benzene I decided to try some experiments with olive oil and water, because Robertson2 had apparently obtained emulsions of water in oil as well as of oil in water by adding caustic soda. In the first run, Table IV, I cc of 2 . 5 N NaOH was added in each case and varying amounts Wa. Ostwald: Zeit. Kolloidchemie, 6 , 108;7, 64 (1910). Zeit. Kolloidchernie, 7, 7 ( 1 9 1 0 ) .
F . R. Newvnan
46
TABLEIV Total volume, 50 cc;
I
cc
2.5
N NaOH;
time of shaking,
IO
minutes Oil per cent
1
0 il cc
49 48 46 45 44 25
1i
Water cc
I
-
Oil
Water cc
20
39 44 46.5 47.5 48,5
I I
3
1
74 24
11
IN
3 I
-
-
of oil and water, the total volume being always 50 cc. The flasks held IOO cc and the mixtures were shaken for I O minutes in the power shaker. The mixture containing 0 . 5 percent oil was a fluid emulsion of oil in water and the one percent mixture showed traces only of a creamy emulsion. Mixtures containing 3-50 percent oil were of the type called A, with an increasing amount of a creamy emulsion of oil in water. At 88 percent and 90 percent oil we have a homogeneous creamy emulsion of oil in water. At 92 percent we apparently get four layers, a narrow yellow upper layer which has the appearance of being a foam of air in oil; a yellow almost clear liquid, which is what Robertson called an emulsion of water in oil; the creamy emulsion of oil in water; and the thin emulsion of oil in water which forms the lower layer in the emulsions containing 3-50 percent oil. This layer has disappeared entirely in the 96 percent emulsion and the creamy emulsion disappears in the 98 percent mixture, leaving only the foam and the so-called emulsion of water in ail. Further experiments convinced me that we get no emulsions of water in oil with caustic soda as emulsifying agent. What Robertson thought was an emulsion of water in oil is merely a cracked emulsion in which the appearance of the oil is changed by the presence of solid sodium oleate, etc. When pure oil is shaken with solid sodium oleate, we get about the same appearance. Robertson’s test with Soudan I11 proves nothing because it is not denied that oil is the external phase. It is merely denied
Experiments on Emulsions
47
that we have here an emulsion a t all, in the sense of a coated drop of one liquid suspended in another liquid. Another run was made with I cc 0 . 5 N NaOH. The general result was the same; but the 94 percent mixture formed a homogeneous creamy emulsion instead of the 88-90 percent mixtures, and there were three layers (type B) in the 90 percent and the 96 percent mixtures. With 3 cc 5 percent sodium oleate the homogeneous, creamy emulsions contained 80-86 percent oil. With 5 cc 5 percent hard soap the results were identical with those obtained with sodium oleate except that the homogeneous emulsions were a little stiffer and that there was more foaming with the lower oil concentrations. Starting with 2 cc olive oil and 2 cc 5 percent sodium oleate, it was possible to get homogeneous emulsions varying from 76 percent oil up to 96.8 percent oil by adding oil, portions at a time and at different rates. Starting with I cc oil and I cc 5 percent sodium oleate, a homogeneous emulsion was obtained containing 99.3 percent oil. Heating mixtures before shaking seemed to have no effect other than to increase the amount of foaming. If I were arranging the emulsifiers in the order of efficiency, I should put hard soap first, then sodium oleate, with sodium hydroxide last. Having shown that no water in oil emulsions are formed with hard soap, sodium oleate, or caustic soda, I came back to the problem of'emulsifying water in benzene. To obtain emulsions of benzene in water, protective colloids were used which were soluble in water only. Consequently, it was necessary to use colloids which were soluble in benzene and insoluble in water, if one wished to emulsify water in benzene. Some of the colloids tried were: crude rubber ( 0 . 2 percent sol.); paraffin ( 2 percent); rosin (5 gram per 100 cc); sulphur (concentrated sol.) ; solutions of various resins : lard; butter; oleic acid. I n nearly every case it was evident that there was a tendency to form emulsions of water in benzene; but the emulsions were very instable and cracked soon, so that something better had to be found. Soaps of magnesium, zinc, nickel, and calcium were pre-
F . R. Newman
48
pared by precipitating these oleates from a solution of sodium oleate. These soaps were dissolved in benzene and were then used as protective colloids. These colloids give promise of good results. It was soon seen that the magnesium oleate was the most satisfactory and consequently nothing more than preliminary experiments were made with the others. Starting with a mixture containing 20 percent water and 5 cc of a concentrated solution of magnesium oleate in benzene, it was possible to prepare an emulsion of water in benzene. On adding water to this little by little, the water content could be run up to 80 percent before the emulsion cracked. The emulsions are homogeneous only between 75 per cent and 80 percent water. At lower concentrations two liquid layers were formed just as in the case of the sodium oleate emulsions of benzene in water. The homogeneous emulsions were moderately stable, standing up for several days without cracking. It was next discovered that the addition of a small amount of sodium oleate solution made the emulsion of water in benzene much more stable. Within certain limits there was no tendency to form emulsions of benzene in water. The data in Table V show that the change to emulsions of benzene
TABLE V Total volume, 40 cc; 5 cc conc. Mg oleate in benzene; 15 cc benzene; percentage water, 50; time of shaking, I O minutes -
-
__
-.
__
19 cc
18 cc 17 cc 19 cc I8 cc 16 cc 14 cc I O cc
_____--
__
Sodium oleate
Water
1 1
cc z cc 4 cc 6 cc I O cc 1
'
, 1
percent)
3 cc
, ~
cc
.
(I
percent) (5 percent) (5 percent) (5 percent) (5 percent) (5 percent)
I_--__-
___.
Type of emulsion
z cc ( I percent)
I
,
__
(I
I I
Water in benzene Water in benzene Water in benzene Water in benzene Water in benzene Water in benzene Benzene in water Benzene in water
in water occurs only when 6 cc of 5 percent sodium oleate solution have been added. These 50 percent emulsions formed
Experiments on Emulsions
two liquid layers a t once; but there was no apparent further change after standing five weeks. A number of experiments were made to see how high the water content could be brought in a homogeneous emulsion. I started with 5 cc conc. magnesium oleate I cc 5 percent sodium oleate 4 cc water. This was shaken vigorously and water was added in 2 cc lots until 50 cc had been added. This gave a stiff, homogeneous emulsion, containing about 92 percent water by volume. This emulsion stood up for two weeks before it cracked. The same original mixture was taken and water added in 2 cc lots as before; but I cc 5 percent sodium oleate was added after each I O cc water. The resulting 92 percent emulsion was the most stable one obtained with a high water content. At the end of two months, it was apparently unchanged. This run was repeated in a 250 cc flask instead of a IOO cc bottle and water was added until the emulsion cracked. A homogeneous emulsion was obtained containing 96 percent water. These emulsions with high water content are quite instable, as a rule, and conditions have to be kept just right if one wishes to prepare a satisfactory emulsion. On the other hand, there is a good deal more latitude about the homogeneous emulsions containing about 75 percent water. A very satisfactory one can be made starting with 5 cc conc. magnesium oleate 5 cc benzene 9 cc water I cc I percent sodium oleate, and adding 2 0 cc water in 2 cc lots. This emulsion is practically as stiff as those of higher concentration. After standing for eight weeks, there was no apparent change in this emulsion. To show the general applicability of the method, some runs were made on the emulsification of water in carbon bisulphide. To 5 cc 2 percent magnesium oleate in carbon bisulphide 5 cc I percent sodium oleate in water there were added 25 cc 0.01percent sodium oleate solution in I cc lots and then 25 cc 0.01percent sodium oleate in 2 cc lots. This gave a homogeneous emulsion of water in carbon bisulphide, containing 92 percent water by volume. In another run I started with 5 cc 2 percent magnesium oleate in benzene
+
+
.
49
+
+
+
+
+
F. R. Newman
50
5 cc I percent sodium oleate in water to which were added 24 cc water in I cc lots and 46 cc water in 2 cc lots, while I cc I percent sodium oleate was added after each I O cc water. The resulting emulsion contained 9 4 . 3 percent water and stood up for three days before cracking. Increasing the relative concentration of sodium oleate must eventually change the type of the emulsion from water in carbon bisulphide to carbon bisulphide in water. This point was tested with a 50 per cent water emulsion which forms two layers, Table VI. The change comes when the ratio of sodium oleate to magnesium oleate rises about to unity.
TABLEVI Total volume, 40 cc; 5 cc 2 percent magnesium oleate in CS2; 15 cc carbon bisulphide; percentage water, 5 0 ; time of shaking, IO minutes Water
19 cc I8 cc 17 cc 16 cc 1 5 cc 14 cc I O cc 5 cc
---_____-~ -
I
Sodium oleate
cc ( I percent) cc ( I percent) 3 cc ( I percent) 4 cc ( I percent) 5 cc ( I percent) 6 cc ( I percent) IO cc ( I percent) 15 cc ( I percent) 2 2
Type of emulsion
Water in carbon bisulphide Water ‘in carbon bisulphide Water in carbon bisulphide Water in carbon bisulphide Water in carbon bisulphide Water in carbon bisulphide Carbon bisulphide in water Carbon bisulphide in water
Some experiments with carbon bisulphide and water were also made with nickel oleate, calcium oleate, barium oleate, paraffin, spermacetin and guncotton as emulsifying agents. Though it was possible to prepare emulsions of water in carbon bisulphide, none of them were stable. Egg albumin was dissolved in a solution of caustic soda and precipitated by means of salts of zinc, aluminum, copper, magnesium, and calcium. The several precipitates were filtered and dried; but were found to be insoluble in carbon bisulphide and hence useless as emulsifiers. A few experiments were made on paints to determine the nature of the emulsion. A mixed white paint; labeled “ Eastlake Household Paint” was bought a t a local store and
Experiments on Emzllsions
51
also a sample of “white lead,” labelled “Genuine White Lead” and made by the Empire Works. Raw linseed oil was obtained from the University paint shop. The drop test showed that oil was the external phase in the mixed paint. To 2 2 cc mixed paint in a bottle there were added 70 cc water in 5 cc lots, the bottle being shaken after each addition of water. A homogeneous emulsion of water in oil was formed which did not differ materially in consistency from the original paint. This emulsion contained 71 5 percent water plus the undetermined amount of water in the original paint. Ten grams of the “white lead” were now mixed with I O cc linseed oil and 7 0 cc water added in I O cc lots. An emulsion of 87 5 percent water in 1 2 . 5 percent oil was formed; but it cracked at the end of two days. These experiments were conclusive as to the formation of an emulsion of water in oil; but they left the question of emulsifying agent open. A qualitative test of the “white lead” showed the presence of lead, zinc, barium, and calcium; and of carbonates, sulphates, and silicates or silica. About 5 grams of each of the substances, zinc oxide, basic lead carbonate, lime, calcium carbonate, barium sulphate, lead sulphate, and silica were shaken up with 2 5 cc raw linseed oil and 25 cc water. Homogeneous emulsions were obtained in all cases; they seemed to be most stable with zinc oxide and least stable with silica. The differences were not great, however, and the experiments did not seem to bring out anything that was not known before. Since it was not at all clear why these substances should behave so much alike, or why they should give water in oil emulsions, it seemed well to try oil and water alone. A thick homogeneous emulsion of water in oil was obtained by shaking together 2 0 cc raw linseed oil and 2 0 cc water. This emulsion stood up indefinitely. On testing the linseed oil for rosin with the Liebermann-Storch” test and the sulphuric acid color test, positive results were obtained by each method. The rosin is undoubtedly the emulsifying agent, both with the oil and in the case of mixed paints. Though Pickeringl -~~ __
_____ Jour Chem. SOC.,91,2008 (1907)
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F . R. Newvnan
has shown that emulsions can be made with insoluble ernulsifiers, his experiments showed that the substances he used gave rise to emulsions of kerosene in water and not to emulsion of water in kerosene. Since rosin would naturally give rise to an emulsion of water in oil, the assumption of rosin as the emulsifying agent clears up the theoretical difficulties. The general results of this paper are as follows: (I) A satisfactory general method has been devised for determining which phase is the external one in an emulsion. (2 j When benzene and water are emulsified by means of sodium oleate, the water is always the external phase. (3) It was possible to obtain homogeneous emulsions containing up to 0 . 5 per cent benzene by volume, and from about 80 percent up to 99 percent benzene. Intermediate emulsions separated into a creamy upper layer and a watery lower layer. (4) The failure to obtain a continuous series of homogeneous emulsions of continuously varying properties is due to the experimental difficulty in making the drops of benzene so small that the Brownian movements will keep the drops distributed uniformly through the water. The larger drops rise and pack together. ( 5 ) With my shaking machine, homogeneous emulsions with high concentrations of the liquid forming the internal phase, could be obtained only by adding that liquid gradually. ( 6 ) It is possible to make a stiff jelly out of 99 cc benzene, I cc water, and about 0.05 gram sodium oleate. This jelly did not change perceptibly in six weeks. (7) It is possible to make a stiff jelly out of 99 cc benzene, I cc water, and about 0.05 gram hard soap; but this jelly cracked inside of a week. (8) It is possible to make a stiff jelly out of 98 cc benzene, z cc water, and about 0 . 0 2 gram sodium oleate. Cutting down the amount of sodium oleate to two-fifths, decreases the maximum volume percentage of benzene from 99 to 98. (9) No emulsions of water in oil are formed when olive oil and water are shaken with soap, with sodium oleate, or
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with caustic soda. What Robertson thought was an emulsion of water in oil was merely sodium oleate or the sodium salt of other fatty acids suspended in oil. ( I O ) It is possible to make a stiff emulsion out of 97 percent olive oil, 3 cc water, and about 0.I 5 gram sodium oleate. (11) Magnesium oleate is the best emulsifying agent yet tried for making an emulsion of water in benzene. The emulsions are much more stable if a little sodium oleate is also present. (12) Depending on the relative amounts of magnesium oleate and sodium oleate we get emulsions of water in benzene or of benzene in water. (13) Using proper proportions of magnesium oleate and sodium oleate, it was possible to make an emulsion of water in benzene containing 96 percent water by volume. (14) With my shaking machine, homogeneous emulsions of water in benzene could be obtained between the approximate limits of 75 percent and 96 percent water by volume. These limits have no theoretical significance and would be changed by more perfect emulsification. (15) With perfect emulsification it is probable that there would be a marked increase in viscosity at or near the point where the internal phase constitutes 74 percent by volume of the emulsion because the globules would begin to be deformed by contact as the concentration increased above this value. (16) Using proper proportions of magnesium oleate and sodium oleate, it was possible to make an emulsion of water in carbon bisulphide containing over 94 percent water by volume. This emulsion cracked at the end of three days. (17) I n mixed paints, water is the internal phase and oil the external one. By shaking a commercial white lead together with raw linseed oil and water, a water in oil emulsion was obtained containing 87.5 percent water and I 2 . 5 percent oil by volume. This emulsion cracked a t the end of two days. ( I S ) On shaking raw linseed oil and water together, an emulsion of oil in water was obtained. Rosin proved to be the
F . R. Newman
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emulsifying agent and this is undoubtedly the usual emulsifying agent in the case of mixed paints. (19) The pigments themselves cannot usually be the emulsifying agent in the case of mixed paints because Pickering’s work on insoluble emulsifiers shows that most pigments would tend to produce emulsions of oil in water in so far as they had any emulsifying action. ( 2 0 ) Whether one liquid is emulsified in a second or the second in the first depends on the nature of the emulsifier. A hydrophile colloid will tend to make water the external phase and a hydrophobe colloid will tend to make water the internal phase. (21) In order to be a good emulsifying agent, a hydrophile or a hydrophobe colloid must be able to form a suitably coherent film round the internal phase. It is consequently not possible to obtain an emulsion starting with any colloid. ( 2 2 ) There is no necessary connection between the initial stiffness of the emulsion and its permanency. In a permanent emulsion the film round the globules of the emulsified phase must not age much. ( 2 3 ) When an emulsion of benzene, water, and sodium oleate was frozen, the emulsion cracked. When thawed and shaken, the mixture did not emulsify again. This is undoubtedly due t o the fact that the sodium oleate did not redissolve readily in the water under the conditions of the experiment. This work was suggested by Professor Bancroft and was carried out under the supervision of Mr. T. R. Briggs. Cornell Unizlersity June, 1912
