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V O L U M E 2 2 , NO. 2, F E B R U A R Y 1 9 5 0 A graphite funnel of the same material, split lengthwise to avoid electrical pickiup by the induction coil, is inserted into the end of the crucible. Graphite powder of 200-mesh or less was prepared from the rod with a file. The quartz tube is filled approximately one third full of graphite powder, the crucible is floated in the powder, and after the top of crucible is covered with a small watch glass, additional graphite owder is added up to the top of the funnel. Every effort should e made to avoid packing the powder about the crucible. 4 loosely packed assembly results in maximum heat insulation and optimum conditions for out-gassing without danger of lifting the powder from the assembly. The watch glass is removed and any graphite powder within the crucible is blown out, by inserting a small glass tube connected with a rubber hose to a low-pressure air line. The removal of this graphitepowderisimportant,in that the powder in the crucible never reaches the temperature of the crucible during out-gassing and therefore will result in high blanks. Furthermore, the powder will cause a very rapid evolution of gas, which induces undue sputtering of the molten metal. The furnace is cooled with a high-velocity air stream which is directed uniformly about the walls of the furnace by means of a glass funnel of special design. The air is supplied from a highspeed Breuer Tornado blower which is regulated to the proper s eed with a Variac. The elimination of water cooling simplifies tge construction and manipulation and reduces the size of the furnace. This reduction of the outside dimensions of the furnace results in the use of a smaller induction coil, arid thus provides
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more efficient heating. The General Electric 5-kw. output unit, which operates a t a frequency of approximately 625 kilocycles, will provide ample power. In general, the out-gassing of the crucible is carried out for 2 hours at 2400" C. After this treatment the temperature is lowered to 1650" C.; the amount of oxygen evolved as carbon monoxide in 30 minutes is equivalent to less than 0.0002~ooxygen per gram of sample. This furnace has been in constant use for about 2 years and many determinations have been made on iron, molybdenum-iron alloys, copper, germanium, and nickel. It has been applied to the heating in high vacuum of materials a t 2400O C. for continuous periods of 6 hours. The design of the all-glass furnace, providing a high vacuum envelope with full vision, and the suspension of the quartz tube assembly in vacuum eliminate massive metal heads, quartz to metal or glass joints, rubber or lead gaskets, various cements for attaching dissimilar materials, radiation shields, ceramic supports, and water cooling. LITERATURE CITED
(1) Jordan and Eckman, Bur. Standards, Sci. Paper 514 ( 1 9 2 5 ) . (2) Oberhoffer and Schenck, Stahl u . Eisen, 47, 1526 (1927). RECEIVED September 20, 1949.
Device for Filtering and Precise Dispensing of Solutions in Closed Systems SAM ROTHMAN, National Bureau of Standards, Washington, D . C.
HE use of equipment that assures the complete absence of Tall forms of foreign matter, such as dust particles, requires special techniques. This is especially true in the high polymer field when light scattering and viscosity measurements are made. A simple device has been constructed for filtering, n-eighing, and transferring solutions to measuring equipment with a minimum
loss of solvent and exposure to the atmosphere. are readily available and simple to adapt.
,ill the parts
The device consists of two units, a sintered-glass filter of required porosity and a weight buret. The all-glass filter is constructed as shown in Figure 1. A pressure bulb with valves is placed between a and b in order to exert pressure on the liquid in the filter bottle, thereby accelerating filtration. I n order t o eliminate the possibility of liquid being drawn into the tube a t b, a ring seal c, is constructed above the exit tube, d. The outer part of a standard-taper ground joint is attached a t e . The weight buret is modified as shown in Figure 2. The inner part of the standard-taper ground joint a t e (Figure 1) is attached to the buret at f. This feature permits filtration directly into the buret. A cap, g, closes the top of the buret. The outer part of a standard-taper ground joint, h, is ring-sealed to the exit tube. In order t o prevent loss of li uid while the weighings are performed, the tip of the exit t u l e is equipped with a small ground-glass cap, i, held in place by wirej. Evaporation which may occur a t the stopcock can be minimized by using a well-ground unit plus a grease not soluble in the solvent used. Sager ( 1 ) developed tetraethylene citrate for use with aromatic hydrocarbons. The measuring equipment is fitted with the inner part of the standard-taper ground joint a t h. When liquids are pipetted from one vessel to another, the chief sources of foreign matter are material clinging to the inner and outer surfaces of the pipet and material drawn into the liquid from the atmosphere. The proper use of the weight buret will permit the transfer of known amounts of liquids with less contamination than results from the use of pipets. The solution can be prepared in the usual manner, and poured directly into the filter bottle, and stopper a put in pIace. If desirable, the stopper may be covered with tin foil to avoid possible contamination or the unit can be replaced by a standard-taper glass joint. With the filter unit and buret connected, the filtered liquid will enter the buret more rapidly if pressure is exerted with the rubber bulb. The buret is then removed, capped, and weighed before liquid is transferred to the measuring equipment.
d
Figure 1.
Sintered-Glass Filter
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/--
~i~~~~ 2. fied Weight Buret
LITERATURE CITED (1) Sager, T. P., ISD.ENG.CHEM.,ANAL.ED.,4, 388 (1932). RECEIVED April 16, 1949.
