JANUARY 15,1936 ANALYTICAL EDITION 27

fifty or more tests yielding similar data. plot of the data given in this paper.

Estimation of Ash-Softening Temperature from Chemical Composition

A rapid but approximate estimation of the softening tem- perature Of a Coal ash O r a mixture of coal ashes (as in blending) may be made from the chemical analysis of the ash as follows:

Determine the percentage of alumina on a basis of silica plus alumina equals 100.

From Figure 1 find the melting point of a silica-alumina mixture corresponding to the percentage of alumina found under 1 above.

Determine the percentage of basis (oxides of iron, calcium, magnesium, and the alkalies).

Figure 2 shows a 4. From Figure 3 determine the softening temperature lowering due to these bases.

5. From the figure found under item 2, subtract the lowering due to basis found under item 4 and obtain the softening tem- perature to be expected.

Literature Cited (1) Bowen and Grieg, J. Am. Ceram. Xoc., 7, 238-54 (1924). (2) Fieldner, Hall, and Feild, Bur. Mines Bull. 129, 53-63 (1918). (3) Haslam and Russell, “Fuels and Their Combustion,” p. 379,

New York, McGraw-Hill Book Co., 1926. (4) Marson and Cobb, Gas J., 171, 30-46 (1925). (5) Nicholls, P., Selvig, W. A., and Ricketts, E. B., Bur. Mines Bull.

1.

2. 364, 24 (1932).

RECEIVED April 19, 1935. Preeenterl before the Division of Gas and Fuel Chemistry at the 89th Meeting of the American Cheaical Society, New York, N. Y., April 22 to 26, 1935.

3.

An Inexpensive Ball Mill LAURENCE L. QUILL,’ University of Illinois, Urbana, 111.

N SOME chemical laboratories a ball mill is a very useful I and much needed piece of apparatus, although i tmaynot be used as continuously as in a ceramics or other laboratory where large quantities of powdered materials are required. The most satisfactory ball mill in such laboratories should not occupy too much floor space, should be adaptable for use with ball mill jars or other containers of various sizes, and should be fairly inexpensive, simple, efficient, compact, and, if necessary, portable, The ball mill shown in the figure was designed and constructed to meet these requirements. A ball mill involving the same principle has been described by Furnstal (1) .

The principle of the device is simple, there being two rollers on which cylindrical objects may be placed. The rollers are made from 90-cm. (%foot) lengths of 7.5-om. (3-inch) pipe, the ends of which are plugged. A piece of steel rod is inserted in the center of each plug to serve as the bearing axle. Ordinary brass bearing supports for holding the Babbitt metal, having a grease cup on top for lubrication, are used. The rear roller is connected through a speed reducer (20 to 1 ratio) and an ordinary V-belt to a motor, and is thus the “power” roller, while the front roller is free to rotate as it will. To increase the traction between the rollers and the racks for the jars and to quiet the operation of the mill, a piece of automobile inner tube is slipped over each roller. There is ordinarily suf- ficient traction between the objects and the rolls so that it is not necessary to connect the rollers by a belt. However, when small bottles about 5 cm. (2 inches) in diameter are used for preparing mixtures; traction is secured by placing a short length of pipe of about the same diameter on the rollers.

(Longer rolls can be used.)

1 Present address: Department of Chemistry, The Ohio State University, Columbus, Ohio.

In the figure, the support for the rollers is shown as pieces of I- beam, about 40 cm. (2 feet) long. If I-beam is not available, pieces of timber, railroad rail, or other material may be used. A series of holes is drilled in the upper surface of each I-beam. Each of the two bearings for the “idler” has two pins pro- jecting from its lower surfaces. It is therefore possible to regulate the distance between the rollers by placing the pins in the proper set of holes, and to use containers of various sizes on the same machine. The rolls are close together when small jars are used; for larger jars, the distance between the rollers is increased.

The racks for holding the ball jars also can be made from in- expensive and easily obtainable materials. The rings for the racks are made from pipe of suitable diameter. For the small jars shown, 15-cm. (6-inch) pipe is used, and for the large ones, 30-cm. (12-inch) pipe. (The small jars hold about 1 liter, the large ones, 6.5 liters.) The rings for the large jars are at- tached to each other by two pieces of T-iron which also act as supports for the metal straps holding the jar in the rack. The rings for the small jars are held in place by stri s of 1.3-cm. (0.5-inch) strap iron. One end of the small racf is partially closed by a cross of the strap iron. The jars are held in these small racks by a screw passing through a small bar of steel, which also holds the cover of the jar in place. When the bar is placed crosswise against one of the rings, the screw may be turned down against the cover of the jar, and the jar against the cross closing the other end of the rack, thus holding both the jar and the cover in their proper places.

Since for different sized containers there is an optimum speed for obtaining the best grinding results, this particular mill is driven by a direct current motor, the speed of which can be varied by a rheostat.

This particular set-up can also be used for producing uniform mixtures such as those used in ceramics, paints, etc. The materials can be put in a bottle or other suitable con- tainer and subjected to the rolling process in exactly the same manner as the ball mill jars are used.

The ball jars used for this mill were purchased from the Ceramics Department, University of Illinois. The actual construction of the machine was done by Arthur E. Wood, mechanician for the Chemistry Department, who also de- serves credit for his many valuable suggestions. The cost of materials, which included three small and two large jars, was about forty-five dollars.

Literature Cited (1) Furnstal, A. H., IND. ENG. CHEW, Anal. Ed., 7, 342 (1935).

RECEIVED November 16, 1935.