JOURNAL OF CHEMICAL EDUCATION
500
aetonished when I observed that this oil had been transformed into a fatty crystalline ivory-white solid, which when analyzed was found to contain about 0.2 per cent selenium. Thus the selenium appears to act as a catalyst. I am not in the position to determine the composition of this substance and would welcome possible guidance from the readers of THIS JOURNAL. Cottonseed and corn oils when treated in the same manner did not solidify upon standing.
ample, the emulsifier has reduced the work required, violent agitation consequently being unnecessary. An example of an O/W emulsion as presented in the last paragraph of the article (containing a small amount, 0.5 per cent emulsifier, when the work must be supplied mechanically) is also of interest in comparison with the above formula. When it is desirable to use only a minute quantity of emulsifier a formula such as 20 ml. of water, 0.5 g. of Dreft (or 0.5 ml. of Tween 80), and 80 ml. of oil may be employed. With a small amount of emulsifier a Waring Blendor, homogenizer, or colloid mill must be employed. F o r W/O Emulsions
To the Editor:
Mineral oil (Nujol) or petrolatum.. . . . . . . ,100 ml. Span 80 emulsifier.. . . . . . . . . . . . . . . . . . . . . . 15 ml. Tween 80 emulsifier.. . . . . . . . . . . . . . . . . . 1 ml. Water.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ZOO ml.
We have noted with interest the article "Oil and water emulsions: a lecture demonstration" by Sister M. Ignatia (J. CHEM.EDIJC., 28, 112 1951). I t apTo 100 ml. of oil or petrolatum in a 400-ml. beaker pears to the writer that the clarity of the demonstra- add 15 ml. of Span 80 and 1 ml. of Tween 80. Stir by tion might be improved in the following manner: hand with a spatula until the emulsifiers are uniformly I n the demonstration cited a single formulation is dispersed in the oil. Add water in increments, stirring used to prepare both O/W and W/O emulsions, the throughly after each addition. The emulsion will intype of emulsion depending upon the method of prepa- crease in viscosity as the amount of water is increased ration. It is possible that a mistaken conclusion and at 2200 ml. of water, the emulsion has a heavy might he drawn to the effect that the method and order "body." However, it will not invert, and if water of mixing determine the nature of the product. The addition is carried beyond "saturation" of the W/O type of emulsion usually depends more upon the hydro- emulsion, the emulsion will break. To obtain a good phile-lipophile balance of the emulsifier rather than commercial W/O emulsion, the product obtained after on the method of mixing the ingredients. the addition of the 200 ml. of water should be passed Use of the Waring Blendor in the preparation of through a homogenizer. these emulsions is inadvisable because it is possible We believe that the above tests will present a more to instill the belief that such violent agitation is neces- accurate demonstration of the action of emulsifiers. sary in preparing a satisfactory emulsion. We suggest the following formulations for such a demonstration: F o r O/W Emulsions Mineraloil (Nnjd). . . . . . . . . . . . . . . . . . . . .,100 ml. Span1 40 emulsifier (molten). ............. 8 ml. Tween' 40 emulsifier.. ................... 8 ml. . ml. Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2M)
To 100 ml. of oil in a 400-ml. beaker add 8 ml. of molten Span 40 and 8 ml. of Tween 40. Warm the oil and emulsifiers t o 50°C. Stir by hand with a spatula until the emulsifiers are uniformly dispersed in the oil. Add water in small increments, stirring thoroughly after each addition. As the water is added, the emulsion (W/O at first) will become thicker and after about 80100 ml. of water have been added, the maximum viscosity will be achieved. Further addition will cause a sudden reduction of viscosity. At this point, the emulsion has inverted to the O/W type. The balance of the 200 ml. of water may be added rapidly. Preparation by this "inversion" technique usually produces a finer particle size and a more stable O/W emulsion than by adding the oil to the water. To obtain good inversion the emulsifier must be properly balanced. I n this ex-
' Reg., U. S. Pat. Off.
To the Editor:
The article entitled "As I knew Michael Faraday" by James R. Irving which appeared in the June issue of the JOURNAL OF CHEMICAL EDUCATIOX brings to mind a Faraday letter which I donated to the Library of the Chemists' Club, New York City, a short while ago. This is addressed to H. Hopwood, Esq., and reads as follows: R. Institubion June 17 Sir I have not time to go into your objection to the atomic theory. It would require a view of what we know of chemical affinity but you will find the difficulty referred to in m o ~ accounts t of the atomio theory especially in the earlier accounts. I do not myself adopt the term atomic theory or atom. I do not know what an atom is. The theory of definite proportionals seems to me consistent and being the expression of a multitude of facts is as relates to these facts, quite true. Whether it be or be not universal is of little consequence to the multitude of useful cases in whioh it does apply. The hypothetical views which under the term atomic bheory
