Preparation of Microscopic Glass Spheres

152 A N A L Y T I C A L E D I T I O N Vol. 6, No. 2

If a trace of furfural were present the turbidity had a LITERATURE CITED brownish tinge, which is characteristic of the behavior of the reagent with aldehydes. According to Gross (6), alcohols higher in the series than methanol and secondary alcohols will also form a precipitate.

TEST FOR FURFURAL Because of the volatility of furfural in steam (8) and the

danger of its being carried over in the end portions, a specific test for this aldehyde was desirable. When 6 to 8 drops of the distillate were added to 0.25 cc. of an aniline acetate solu- tion (3 cc. of freshly distilled aniline in 2 cc. of glacial acetic acid) a pink color occurred if furfural were present. The

Bates, Mullaly, and Hartley, J. Chern. SOC., 123, 401 (1923). Bergstrom, Svensk Kern. Tid., 34, 81 (1922); Chern, A h . , 17,

Davis, IND. ENG. CHEM., Anal. Ed., 1, 61 (1929). Friedrichs, Chern.-Ztg., 32, 890 (1908). Gross, Ann. fals., 18, 39 (1925). Hartley and Raikes, J . Chem. SOC., 127, 524 (1925). Jones and Amstell, Ibid., 1930, 131%. Menzies, Ibid. , 121, 2787 (1922). Meunier, Mat. grasses, 9, 4516 (1916) ; Ellis, “Synthetio Resins

Mueller, J . Pharrn. chirn., 24, 224 (1921). Scott, Cook, and Brickwedde, Bur. Standurch J . Research, 7,

1181 (1923).

and Their Plastics,” p. 218, Chemical Catalog, 1923.

935 (1931).

test‘wasfound to be sensitive to o*oool per cent Of RECEIVED October 19, 1933. Contribution 100 from the Research Labora- Mueller (10) states that the test is accurate to 0.0005 per cent. tory of Organic Chemistry, Massachusetts Institute of Technology.

Preparation of Microscopic Glass Spheres SAMUEL SKLAREW, Einson-Freeman Co., Inc., Long Island City, N. Y.

N CERTAIN physico-chemical researches, as in the study of rates of diffusion of gases and liquids and of I solids in gases or liquids, it is desirable to have per-

fect spherical particles of known size and weight. Calcula- tions are simplified since spheres are regular-shaped bodies, whose physical constants are readily determined, and will pack in a regular geometric pattern leaving interstices whose dimensions are calculable. Glass lends itself readily to the purpose. A given glass is uniform in composition. Its specific gravity and hence its weight may be determined if its size can be measured.

After a careful analysis of the problem, a procedure for the preparation of microscopic glass spheres suggested itself, I t was necessary to subject each fine particle of glass, in- sulated from every other particle, to a temperature sufficiently high to insure its becoming a free-flowing liquid. At the same time the particle had to be kept in free suspension, until i t became solid enough not to change its shape on con- tact with other bodies. Air would insulate the particles from each other, and at the same time permit them to be heated until they were free-flowing. It would keep them in suspension, if i t were moving rapidly enough, and allow them to cool to rigidity before touching anything.

APPARATUS The apparatus designed by the author utilized such mate-

rials as were available and could be constructed at the mini- mum cost and effort.

A system was constructed (A, Figure l), utilizing a wind turbine with a hollow shaft to churn the powdered glass while a powerful stream of compressed air descended the shaft and was forced to pick up the glass powder which was inclosed i n a b o t t l e having t h e turbine sealed in it. A glass tube led from the bottle to the next piece of apparatus, B, consisting of a blast lamp, the air side of which con- nected to the outlet from the b o t t l e conta in ing t h e

powdered glass. Gas from the main was fed to the other inlet of the burner. This blast lamp was placed at one end of a clay- graphite cylinder, C, 6 inches in diameter, 3 feet long, and 1 inch thick. Two blast lamps entered tangentially, facing forward at a slight angle, so that their flame would swirl and a t the same time shoot forward down the cylinder. This kept the flames from one burner impinging on the second. Gas for these two burners was supplied by interposing a blower be- tween the gas main and the burner outlets. A Y-tube supplied the necessary connections.

Following the heat chamber was the settling chamber (D, Figure a), consisting of a horizontal metal pipe 3 feet in diameter and 10 feet long, open a t both ends, fitted on the far end into a cardboard box 6 feet square, E. The box had small holes punched in the top to allow the escape of air. The bottom of the pipe and box were lined with black paper in order that the glass spheres might be discernible after they had settled. The pipe had a door fastened on the side to allow easy access, and the box was so arranged that a flap could be opened to get inside. The heat chamber exit was placed near the top of the settling chamber entrance in order that the molten glass particles might travel further before settling .

After assembling the apparatus, a run was made. The gas cocks were opened to lamps 2 and 3 and the blower started. The compressed air was turned on and the burners adjusted for maximum temperature and optimum position.

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FIGURE 1. DETAIL OF APPARATUS

T h e h e a t chamber was warmed t o whi te h e a t . The wind turbine was then s e t i n mot ion a n d ad- justed to maximum speed. The gas was turned on in bu rne r 1, a n d t h e com- pressed air released down the hollow turbine shaft. The air supp ly was care- fully adjusted so that little glass powder was picked up and carried into the heat chamber.

By va ry ing t h e speed of the turbine and the air pressure down the shaft, it was possible to control

March 15, 1934 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 153

the amount of glass passing through the heat chamber and also the speed as it was carried along by the wind stream.

The apparatus was run in half-hour periods and the glass spheres were collected from the black paper lining where they had settled. The larger balls were, of course, nearer the heat chamber, while the smaller were a t the farther end of the box. Some were even on the sides and top inside of the box, where they had floated on the air stream.

Examination under the microscope gave the size range from 0.01 to 0.00001 inch. There were about 95 per cent per- fect spheres, about 4 per cent egg-shaped particles, and about 1 per cent deformed particles among the larger sizes. The percentage of perfect spheres increased in the finer sizes, until the very smallest were all perfectly spherical in shape. From any given section of the settling chamber the particle size varied very little. A re-run of the larger sizes would probably bring the percentage of perfect spheres nearer 100.

USES OF SPHERES

Aside from the uses mentioned above, the following have been suggested :

1. In the preparation of porous plugs or filters for use in a study of such problems as (a) the recovery of petroleum from underground sand deposits by displacement with water, aqueous solutions, gases, etc. (1); (b) diffusion of gases in long columns where major eddy currents could be prevented

I \ w .+’

/ BLACK PAPER

LlNiNG

FIGURE 2. SETTLING UNIT

and longer heat chamber would lengthen the time of heating and permit incompletely converted particles to be converted to spheres. The wind turbine mixer and the glass-air jet could be redesigned for greater efficiency. Continued ex- perimentation would determine the optimum conditions and apparatus.

PHOTOGRAPHIC DATA

The illustrations for this article were made on Press 2000 plates, triple emulsion, the exposures running from 15 to 30 seconds with a 60-watt source of light brought to a focus with

a plane mirror and a subs t age con- denser. The plates were deieloped under red light in Eastman D11 con- trast developer for 7 minutes, fixed, and washed. The pos i t ives were printed on Azo paper with D72 de- veloper.

Because of t h e inadequacy of photographic apparatus and technic, it was impossible to photomicrograph the very small particles, some of which were a small fraction of the size of that shown in Figure 3.

ACKNOWLEDGMENT The apparatus was collected and the

experiments were done in the labora- 1 Partial conversion. Poor conversion from 2, Diffractlon pattern Conclusive evidence of tory at Nichols Chemistry Building at

g r o h d to spherical glass takes place when the spherical shape of particle. Diffraction pattern particles are shot a t too high speed through heat and outer edge are both perfectly circular under New York University, where the re- chamber. Close examination will reveal very tiny the microscope. This particle presented a beauti- search was done under the direction of particles in close contact with spheres. These ful display of colored rings, unreproducible in particles are not round and seem to adhere through . Close examination will reveal two H. J. Masson, t o whom t h e a u t h o r

feels greatly indebted. electrical charge. They can be removed by care- f%%%i and possibly a third in the dark band. ful manipulation with a glass hair under the mi- (5418 diameters. Original 0.00066 cm.)

The author is especially indebted croscope. (1323 diameters)

FIGURE 3. PHOTOMICROGRAPHS OF GLASS SPHERES to Arthur Liebers for assistance in editing this article, to C. C. Clark for

the loan of apparatus which made possible the illustrations, and to Robert Irving Langer for the sketches of the apparatus.

LITERATURE CITED

by a packing of uniformly small spheres; ( c ) the filtration of liquids, destructive to ordinary filtering media; (d ) filtration problems where filter cakes of material having a known uni- form size are desired, etc.

In studies of sedimentation phenomena such as rate of settling, settling equilibria, Brownian movement, etc., or where uniformly sized spherical particles would be an ad- junct to lecture demonstration or instruction.

3. In studies of certain adsorption phenomena where large surfaces of known value are desired. 4. studies of fluid flow where stab]e suspensions of

solid spherical particles having a different index of refraction from the fluid under consideration would permit fluid move- ment to be observed, etc.

currents were eliminated, no trouble should be entertained in obtaining a size separation of particles by settling. A wider

2. (1) Bur. Mines, Circ. 6737, 27 (1933).

RH~CEIVED August 2,1933.

FLEXIBLE GLASS. A flexible form of plate glass, produced by a secret process in one of the largest glass factories in Great Britain, is claimed to be meeting with considerable success, ac- cording to a report made public by the commerce Department.

The new glass is flexible to a remarkable degree, and capable of withstanding enormous pressure. In a recent demonstration,

narrow boards. Pressure was then applied, causing the glass to curve, but upon removal of the pressure the glass resumed its normal straightness.

With a large enough settling chamber so arranged that eddy a Plate of the glass measuring 3 feet in length was raised on two