The Use of Filter Pa Ier Disks with Gooch and Porous-Type Crucib es in Routine Filtrations J. M. FULTZ, Froehling & Robertson, Inc., Richmond, Va.
T
loosened with the aid of a spatula, it can be brushed out with a camel's-hair balance brush.
HE acute shortage of Gooch-grade asbestos fiber has made it necessary for all laboratories to devise means for conserving their diminishing supply, or to turn to other leas satisfactory means of quantitative filtration. The following procedure has proved of value 3s a time-saver and as a means of conserving asbestos fiber, especially when routine filtrations of precipitates such as barium sulfate or magnesium pyrophosphate are in order.
The procedure with modifications has been applied with equal satisfaction in the use of the porous-type filtering crucible and the time saved in cleaning has been considerable. In using this type of crucible the filter paper disk (24mm. in diameter for 30-ml. crucibles) is inserted just before filtering and, as with the Gooch crucible, the precipitate is removed mechanically just after weighing. The crucible is then reweighed and ready for reuse. The succesa of the use of the filter paper disks seem to be brought about by the following action during ignition within the crucible. The paper prevents adherence of the ignited precipitate to the asbestos mat or to the filtering medium of the poroustype crucible by the expulsion of the volatile organic matter during the combustion. It also prevents the clogging of the asbestos mat or the filtering medium by the material being filtered. The procedure can be used for any ignited precipitate, whether it be capable of removal by solution or not. The removal of moat filtered mlids by solution L time-consuming, and doubtful BB to completenesa. The method described provides a crucible, weighed and ready for another filtration in very short order, with no impairment to the filter mat by occlusions.
Where a limited supply of asbestos is still available, a Gooch crucible is made up in the ordinary manner, ignited, cooled, and weighed. Just before filtering, a filter paper disk (24 mm: in diameter for 30-ml. crucibles is placed on the mat in the crucible and washed once with distiled water to secure it as firm1 as osaible against the mat. [Carl Schleicher & Schuell %.Is 895-Eashlesa filter mats have proved very satisfactory for the use described.] The filtration i? then carried out in the usual manner, and the crucible IS igmted, cooled, and weighed. Immediately after weighing, the precipitate is removed mechanically, and the crucible is reweighed and thus is immediately ready for reuse. To remove the recipitate, the crucible is inverted and gently tapped. Most o t t h e nonadhering precipitate will drop out, since the filter aper disk prevents the adherence of the recipitate to the %Iter mat, whether it be asbestos, fritted g L , or porcelain. Should any precipitate adhere, after I t is gently
KO.
!
Electric Heating Unit GABOR B. LEVY, Schenley Research Institute, Lawrenceburg, Ind.
I
T IS frequently necasssry to provide apparatus with a bath containing boiling water in order to maintain a temperature of approximakly 100' C. In order to heat up and maintain the liquid a t the boiling point, an electric heater can be used to advantage. Since it is rather difficult, at present, to procure suitable heaters, the construction of a heating unit in the laboratory may often become imperative. A s i m p l e electrical heater can be assembled from readily available materiab by using the liquid of the bath aa resistance. In such heaters, the rate of boiling is controlled by the quantity of electrolyte present, the dimensions and distance of the electrodes, and the voltage apRlied. If available, a variable resistance or variable transformer may therefore be included in the circuit to facilitate control of the rate of heating. A heater can be o p e r a t e d satisfactorily, however, without the use of either of these devices. In this c a s , the exact concentration of the electrolyte for the desired rate of heating has to be determined empirically. On this basis a heating unit was assembled as follows:
Two spectroscopic carbon rods, a, of &mm. diameter and 150-mm. length are immersed in the bath and rigidly fixed at a distance of approximate1 10 mm. by means of a glass holder, as shown in the figure. The holder is made by b e n e g a g l m rod of 3-mm. diameter mto proper shape. The carbon rods are passed through laea tubes which are inserted into tBe cover, c, of the water bath. The leada of the 110volt alternating current line are forced to the carbon rode by means of spiral springs d. Approxlmateiy 0.01 N sodium chloride solution is used as the electrolyte solution. The water bath itself ie a closed system, provided with a reflux condenser.
f,
166
In an apparatus for the a d y e i a of butadiene ( 1 ) a heating unit of the above description has bean substituted and in ,use for several months. The main advantagea are ita small space requirement and the fact that it can be aesembled in little time and without the UBB of critical materiab.
(1)
Literature Cited Tropsch, H.,and Mattox, W. J.. IND. ENG.CH~Y.,~ A L E.D.,8, 104 (1934).
767
