A Six-Atmosphere Mercury Manometer WALTERSCHOLLAND R. 0. E. DAVIS Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
I
N MEASURING vapor pressures over solutions of urea and liquid ammonia, a simple mercury manometer capable of measuring pressures u p to six atmospheres was constructed. A method for reading the manometer was provided by the use of a periscopic arrangement consisting of a sliding unit, with a light, a mirror, and a reading glass, mounted to reflect the image of the mercury meniscus downward to another mirror conveniently placed for o b s e r v a t i o n s . The assembled manometer is shown in perspective in Figure 1. The wooden post 13 em. square, as shown at the end section, was made up of five 2-cm. white pine boards. A beam of this c o n s t r u c t i o n was found to be free from warping and had very little bending movement. The Pyrex U was made of tubing 6 mm. outside diameter and 4 mm. inside diameter and the two parallel arms were so spaced as to be close to the scale, mounted b e t w e e n them. The scale was made up from selected wooden meter sticks carefully jointed so as to eliminate, as far as possible, any large corrections. The scale was compared with a Bureau of StandFIGURE 1 ards c a l i b r a t e d steel tape, For convenience in reading, a paper scale was prepared from millimeter coordinate paper, by printing the total millimeters in a horizontal position a t each centimeter of length. The paper scale was shellacked to 2.5-cm. wooden strips and mounted to the right of the mercury U. The strips should be boiled in paraffin to prevent warping.
A track in the form of a T channel, for the accommodation of the slide units Band C, was mounted to the right of the manometer. The track was made by assembling several brass strips: first the base plate (50 X 3 mm.), attached to the beam with screws, and then the spacers (14 X 7 mm.) and face plates (19 x 3 mm.) attached to this by machine screws at frequent intervals to prevent bending the slides. The unit C, a steel piece 17 cm. long, carried a slotted arm to which was attached the lower mirror, and was provided with a thumb screw for locking it in position. The unit B was a slotted steel piece 38 cm. long and provided for mounting the second mirror at 180" to the first and 45" to the plane of the supporting beam. On this unit also was attached a 25-watt bulb blackened so as to illuminate the manometer and scale only and placed just above the mirror. Below the mirror was a 12.5-cm. reading glass adjusted to the focal length, about 15 cm. from the mirror. To the upper and lower ends of unit B were attached the ends of a length of picture wire used in moving the unit. The picture wire passed over four brass pulleys a t the top and bottom, and opposite each other, on the front and back faces of the beam. The wire made several turns on a brass drum, shown at D, which when turned supplied sufficient friction for moving the unit B in any desired direction. To the drum was attached a ratchet and a wooden hand-hold mounted on the end of the axis. The ratchet held B at any desired position. The manometer and attachments were mounted on the wooden beam before raising to the vertical position and adding the mercury. To the top of the U a t A was attached, by means of a metal joint ( 1 ) supported by a clamp, a copper tube through which the gas pressure to be measured was applied. The other side of the U connected to a trap, not shown in the figure, for mercury inadvertently forced out of this arm. Three thermometers, placed at equal intervals along the side of the mercury U, were used for making the necessary temperature corrections. The manometer as constructed had an accuracy of 1 2 mm. a t 5 atmospheres pressure.
LITERATURE CITED (1) McKelvey and Taylor, J.Am. Chem. SOC.,42, 1364 (1920). RECEIVED December 19, 1934.
Preparation of Sintered Glass Filters PAUL L. KIRK,Division of Biochemistry, University of California Medical School, Berkeley, Calif.
I
S MANY cases in which sintered glass filters' are highly useful, very fine grades and carefully standardized porosities are not necessary. If, in addition to this, the diameter of disk need not exceed about 15 mm., i t has been found very easy to make such filters directly in the flame of an air-gas blast lamp. Various investigators are making such filters for their own use as aerators and for other simple requirements, b u t it seems desirable t h a t the method be recorded in the literature. The chief field of use of such filters in this laboratory has been in the form of filter sticks similar to those described by Kirk (1). This apparatus is made by blowing on one end of a t hick-walled capillary tube a small thin-walled bulb which is filled with ground glass, mounting the tube in a stirring motor in a vertical position with the bulb down, and rotating the tube in a moderate air-gas blast burner flame for about 10 minutes. If the flame is properly adjusted, the ground glass will sinter through without fusing the bulb walls. The 1 Manufacture of sintered glass filters is covered by patents held by Schott & Gem, in the United States by Patent No. 1,620,815.
glass should scarcely be red during the heating. After cooling, the end of the bulb is ground away, preferably on a slowspeed silicon carbide wheel, until the sintered disk is of proper thickness. For making larger diameters of filter, the process is essentially the same, except that the tuhe is of the correct size for the filter desired. Instead of having a bulb on the end it is simply pulled off in a flame until it is roughly squared across the end, leaving the walls thin, after which the powdered glass is poured in and sintered as described, followed b y grinding off the end. For larger filters the heat must be a little more intense. Either Pyrex brand chemical or soda glass may be used, though the former yields the better results. The glass powder may be of any size desired, but not finer than about 200-mesh. For aeratow, coarse filters, and the like, 100mesh is satisfactory, though finer may be used. The filter sticks are most satisfactorily used with asbestos as described by Miller and Kirk (S), and are of the greatest utility when so employed. Another valuable application is in the filtration
133
'
