Extraction Pipet for Spot Test Analysis. Jack K. Carlton, Louisiana State University, Baton Rouge, La.
Framingham, Mass.) will very readily dkolve many precipitates encountered in gravimetric work.
to apply extraction techniques to spot test analysis Iandandsimple preserve the essence of the spot test method, a small device was needed, in which the component liquids
NaOOCCH CH2COOSa ~ N - C H , C H ~ - - P \ \CH2COONa '/ (1) NaOOCCH/
N ORDER
could be thoroughly mixed and allowed to separate as rapidly as possible. A dropper pipet, with a few modifications, satisfied these requirements.
A hot 0.1 molar solution of the dry salt was found to be effeotive in dissolving the precipitates listed below. (A reliable private source has indicated that this material will dissolve practically any insoluble metallic compound, except sulfides and ferricyanides.) Aluminum oxide Barium sulfate Calcium oxalate Calcium phosphate Cupric hydcoxide Lead carbonak Lead iodate Lead oxalate Magnesium ammonium phos9hPt.: Magnesium carbonate Magnesium sulfate
The pipet consists of a capillary tip 6 cm..lop 7 nim. in outside diameter and 1.8 mm. in insif; diameter; a bulb blown )just above the capillary tip, 4 cm. long, 1.15 cm. in outside diameter, and about 2- to 3-ml. capacity; an upper stem 5 cm. long, 7 mm. in outside diameter, and 5 mm. in inside diameter; and a rubber bulb of 10-ml. capacity. The over-all length of the pipet is approximately 15 cm. None of these dimensions is critical. When low boiling liquids such as ether, chloroform, carbon tetrachloride, and carbon disulfide are used as extractants, a capillary of about 0.7- or O.&mm. bore is recommended. Mixing is accom lished by drawlng the liquids into the pipet a n 8 then expelling them, repeating the rocedure several times, quickly. By using a rufber bulb of considerably greater ca acity than that of the pipet, a large quantity o f air is drawn into the pipet after the liquids have been drawn up, and the bubbling of this air through the two liqmd layers provides a very efficient mixing of the two layers. Care should be exercised in using the pipet to avoid the loss of the liquids being mixed. When the liquids are drawn into the pipet the pressure of the fingers on the rubber bulb should be released slowly, so that when the air begins to bubble through, the liquids will not spatter into the rubber bulb or on the sides of the upper stem, to which droplets might adhere and consequently be lost. On expulsion, pressure should be applied to the rubber bulb slowly to avoid spattering when the air begins to bubble through the liquids which have been passed into a small beaker. The use of extraction techniques in spot test analysis offers a means of separating an ion from its interferences which might prove valuable in a manner similar to the use of masking agents. West and Carlton [(ANAL.CHEM.,22, 1055 (1950)l use such an extraction in separating gold from the platinum metals. For such work the extraction pipet described should find useful application. The author wishes to express his appreciation for financial assistance given him under a contract with the Office of Naval Research.
Cleaning Sintered-Glass Filtration Crucibles. W. M. Budde and S. J. Potempa, Loyola University, Chicago, Ill. N MANY
cases the collection of inorganic precipitates on sin-
1tered-glass crucibles is more oonvenient than using filter paper or asbestos mats. However, sintered-glsss crucibles tend to
It is generally thought that the substance dissolves precipitates [Schwarzenbach and Ackermann, Helv. Chem. Acta, 31, 1029 (1948)l by a complex formation (II),as shown for barium sulfate. NaOOCCHz-NrCHz-C
(1)
+ BaSO,
I
".
ck,
//o b
/
Even thoroughly dried precipitates can be easily removed from the pores of sintered-glass filtration crucibles when a hot 0.1 molar solution of the tetrasodium salt ef ethylenediamine tetraacetic acid is drawn through the funnel by means of suction, or when the clogged crucible is placed in a vessel filled with a hot 0.1 molar solution. In most cmes the sintered-glass plate ia completely freed of precipitate in a matter of seconds. A definite airvantage of this method over using hot acids is that the tetrasodium salt is almost completely nontoxic, does not cause burns if brought into contact with the akin, is inexpensive, and can be used as a water-softening agent for general laboratory cleaning. Sintered-glass crucibles which have been used to filter permanganate solutions soon accumulate a film of difficultly removable manganese dioxide. This can be removed by pouring cold dilute solutiow of sodium bisul6te and sulfuric acid alternately through the crucible while gentle suction is applied. This method works better on a fresh precipitate than on one that has been allowed to dry.
become clogged after a certain afnount of use, and in many cases the precipitate is difficult to remove-for example, barium sulfate. The present work has shown that the tetrasodium salt of ethylenediamine tetraacetic acid (I) (available under the trade qame Versene at low cost from the Bersworth Chemical Company, 1072
