NOTES ON ANALYTICAL PROCEDURES

A Rugged Current Interrupter HAROLD SIMMONS BOOTH, Western Reserve University, Cleveland, Ohio, AND

DONALD RAY MARTIN, University of Illinois, Urbana, 111.

HE current interrupter described in this paper was developed T to supply electrical energy intermittently to an electromag- net which activates a glass spiral stirrer in a freezing point cell C (Figure 1) for determination of the freezing points of liquefied gases. As the electrical circuit is interrupted by a current inter- rupter (Figure 2), stirrer.8 rises and falls, owing to the attraction of the solenoid, M , for the glass-enclosed piece of iron, N , thus im- parting a swirling motion to the liquid in the cell (2).

When Baume (1) first devised an apparatus of this type, for determining the freezing points of liquefied gases, the electrical circuit was opened and closed by the use of a metronome carrying wires which alternately dipped into two small cups containing mercury. The metronome is unsatisfactory because its use for any length of time is limited, its wire contacts are readily fouled, and the mercury is easily spilled.

Drawn to scale in Figure 2 is a front and side view of a current interrupter now in use a t the University of Illinois which w&s de- veloped over a period of years a t Western Reserve University.

The principle involved is the mechanization of an ignition timer of a Model T Ford automobile. The essential features consist of an electric motor, M , geared by means of a worm gear, G, and a worm, W , to the drive shaft, E , of the rotor, R, of the timer, T. E is supported by two pillow blocks, H , and has the remainder of its length taken up by a commutator, C, and a concentric sleeve spacer, P. The entire unit is mounted, by means of wood screws, to a wooden base in such a manner that the motor drive shaft can be geared to E.

The electrical circuit consists of the attachment of one lead wire to the double binding post, B, which communicates by means of a brass brush to the slip ring of commutator C, which in turn connects through E with rotor R. As R revolves i t contacts the arc-shaped metal plates (solid black in Figure 2) which are connected to the four terminal posts, A , of timer T . The other lead wire connects to all four terminals if a rapid circuit inter- ruption per time interval is desired, or i t may connect to two terminals, or to one terminal if fewer interruptions are desired.

The interrupter can be made to cause any desired number of current interruptions per given time interval by changing G and IY, or by changing the motor, M , for one with the desired number of revolutions per minute. 1.f many lead wires arc desired, an- other timer may be attached a t the other end of E. This second timer can have the lead wires so attached a t points A that i t will

g i v e a d i f f e r e n t number of current in- terruptions per time

Figure 1. Freezing Point Cell

interval than the first timer is giving. The interrupters in use at Western Reserve University are of this type and in addition are enclosed in a wooden housing for protection from fumes and dirt.

A list of the parts required for making the interrupter shown i n Figure 2 is given in Table I. This interrupter produces 146 inter- ruptions per minute when only one terminal A on the timer is being used.

ALTERNATE DESIGN

Small inexpensive motors with self-contained reducing gears are on the market.

Table I. List of Parts (Wherever possible standard siie parts and material were uaed)

Letter in Number Figure 2 Required Description of Par t

M 1 Electric motor, 1/10 horsepower, 1750 r.p.m! W 1 Soft steel worm, pjtch diameter 0.625, 0.75-inch face,

0.25-inch bore, without hub G 1 Bronre worm gear, 16 pitch, 0.375-inch concave face,

sin le right-hand thread,, 12 teeth, itch diameter 0.75 incf '/I6 inch bore, 0.5-inch hub XiarneFer

E Timer'; rotor drive abaft of 8/16 inch diameter steel drill-rod, 4.75 inches long

H Pillow blocks, cut ELE cross-sectional pieces from a brsss casting as shown in Figure 2. An oil hole is drilled in top of each pillow block per endicular to 1/11 inch hole drilled to accommodate %

P 1 Concentric sleeve spacer made from 0.5-inch steel rod 1.25 inches long with '/M inch hole drilled longitu- dinally

C Commutator, slip ring made as a brass disk 0.375 inch wide from a 0.75-inch rod havine a ' / l a inch hole

1

2

1

drilled through center of diak. Brush made from a piece of sheet brass a/,? X 0.375 X

2.875 inches, cu t and bent as shown in Figure 2. Base of brush has one hole drilled with a No. 18 wire gage drill

B 1 Double binding post, American form T 1 Ignition timer (Model T Ford) D I Timer mounting made from a piece of sheet brass

a / * ? by 0.5 by 1 inch, soldered to steel cap of timer T and bent as shown in Figure 2. Base of mounting has two holes drilled with a No. 18 wire gage drill

Wooden board, 3.375 inches wide, 7.5 inches long, and 0.625 inch thick to serve as a base for T, C,, and .h!

Wooden board, 7.5 incheu aquare and 0.875 inch thick, t o serve as a base for entire interruDter

1

1 .._.. . _._ . . ~ . . ~ ~ ~ ~

1

4

Flat-head steel machine screw, No. 8,32-thread, 1 inch

Round-head, steel wood screws, No. 10, 1 inch long, for long, fdr securing B and C to base

securing M to base

securing T and H to base 6 Round-head. steel wood screws, No. 8, 1 inch long, for

Figure 2. Current Interrupter

528

August, 1945 A N A L Y T I C A L E D I T I O N 599

Speedway motor No. 953 W, shaft speed 40 r.p.m., 110-volt, 60-cycle, with shaft in vertical position is suitable (manufactured by the Speedway Mfg. Co., 1834 South 52nd Ave., Cicero, Ill.). The rotor of the Ford timer may be directly attached to one end of a g/16 inch shaft 2 inches long, drilled a t the other end to slip over the shaft of the motor and fitted with a setscrew. The center part of the 9/16 inch brass extension shaft acts as the commutator surface.

The motor is fastened in a wooden housing with a hole drilled in the top for the vertical shaft. The commutator brush is mounted on the housing top and the timer's rotor above it. The timer is slipped over this and is kept from rotating by two brass straps bent in the form of an L and fastened to the opposite sides of the timer's housing. Through holes in the base of the brass

supports, screws hold the housing in place a t the corrcct distance above the top of the wooden housing. Wires from the commuta- tor's brush and from the contact3 on the timer's hou5ing lead to binding posts on the side of the woo,den housing.

Speedway motors with different shaft speeds may be obtained, so that practically any number of interruptions per minute desired may be obtained.

LITERATURE CITED

(1) Baume, G., J. chim. pkys., 9, 245-89 (1911). (2) Booth, H. S., and Martin, D. R., Chem. Rea., 33, 57-88 (1943).

Apparatus for Rapid Removal of Solvents W. F. BARTHEL AND H. L. HALLER

United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine, Beltsville, Md .

NE of the problems encountered in the preparation of puri- 0 fied pyrethrum concentrates (I) , using nitromethane as a solvent, was how to prevent .the decomposition of the pyrethrum concentrates while distilling the nitromethane. Conventional vacuum-distillation apparatus for large volumes is likely to be very bulky and unwieldy. When the residue in the still is the desired product, and this is present in the starting solution a t a low concentration, even greater trouble may be encountered.

Then, too, removal of the last traces of solvent from the con- centrates is often desirable.

It has been found that the apparatus described by Smith(@ could be modified for use under reduced pressure and that this modification was excellent for re-

W Figure 1. Diagram of Apparatus

moving medium-boiling solvents from not only pyrethrum con- centrates but other plant extracts and organic compounds.

The solution to bc evaporated is placed in the holder, 1. The stopcock, 2, regulates the flow into the boiler, 3. The boiler and the stripper, 6, are heated by means of steam passing in 14 and out 19. A bead, 4, prevents a rush of liquid through constriction 5 into 6. A trap, 8, prevents entrained liquid from passing into the condenser with the vapors. Most of the solvent is evaporated in the boiler, but the remainder is evaporated in t>he stripper so that the com- bined vapors pass into the condenser, 9, and are recovered. .4 double condenser is used because an extremely long condenser would be awkward. The solute from the stripper is collected in receiver 7, and the condensed solvent collects in receiver 10. Obviously the size of the receivers depends upon the quantity and proportions of solvent and solute. A glass rod, 18, connects the two arms of the condenser to prevent undue strain on the lower point of attachment. With liquids of high vapor pressure it is well to use an ice trap in the vacuum line from 17.

This is attached to the still a t 14 and is heated by means of coil, 12, con- nected to a variable-voltage transformer by means of leads, 13. The water level is kept constant a t 11 by recovering the steam through condenser 15. The connecting tube, 14, is large enough to permit any water from condensed steam in the still to pass back into the steam generator. The vent, 16, is necessary to prevent having a closed system; it may also be used for filling the steam generator. The coil, 12, is 240 cm. (8 feet) of KO. 22 Chrome1 A wire. I t is important to connect the coil to the power source by means of copper leads from below the water level; otherwisc, the life of the coil will be short.

In actual use thc apparatus has more than met expectations. In the preparation of pyrethrum concentrates the nitromethane solution seldom contained more than 10% of pyrethrins, yet it was possible to remove the nitromethane almost quantitatively at, the rate of 1500 ml. per hour. When solvent was removed at this rate, it was necessary to run the concentrate through a sec- ond time to remove the last traces of solvent. Little extra time is needed to make this second run. At no time has any evidence been found that the pyrethrins have been decomposed in this apparatus. When tested against houseflies, the pyrethrins pre- pared had the same potency as commercial samples of pyrethrum containing the same concentration of the active ingredients.

For liquids boiling below 70" to 80" C. the apparatus can be used without vacuum. I n this manner it can be employed for recovering alcohol and other solvents. By adjusting the pres- sure, steam flow, and rate of intake, it can be used for the rapid concentration of solutions when it is desired to retain a certain amount of solvent, ais in concentrations prior to crystallization.

The apparatus is pictured in Figure 1.

A useful part of the apparatus is the steam generator.

LITERATURE CITED

(1) Barthel, W. F., Haller, H. L., aiid LaForge. F. B., Soap and

(2) Smith, F. H., IND. ENG. CHEM., ANAL. ED., 14, 255 (1942). Sanit. Chemicals. 20, No. 7 , 121, 135 (1944).