Test for Sediment in Fuel Oil by Extraction B. E. JACKSON Dominion Luboratory, Department of ScientiJic & Industrial Research, Wellington, N . Z . A method of overcoming the difficulty caused by water clogging the thimble has been devised which allows the extraction to be completed without interruption for drying the thimble in an oven. It is based on the fact that water and benzene (the extraction solvent) distill azeotropically but separate into two phases on condensation. A small addition is made to the apparatus in the form of a cup which is hung on the bottom loop of the condenser (Figure 1). Any water which is distilled out of the thimble condenses with the benzene on the condenser and forms a second liquid phase which eventually colleck in the cup, displacing the benzene with which it is normally 6lled. Glass cups which have been made at the Dominion Laboratory are conical in shape, approximately 20 mm. in diameter and 25 mm. deep, and hold 3 ml. A glass hook fused on the rim at one side is so shaped that when hung on the condenser the cup hangs with its rim reasonably level. When the water cup is used some other means of suspending the extraction thimble than that shown in the standard method must be emplo ed. A satisfactory suspension consists of two stiff platinum or dchrome wires hung from wire eyelets soldered to the top plate of the condenser. The lower ends of the wires are bent up slightly and are passed through the holes i - ;he thimble. In use, any water in the oil contained in the thimble is fairly readily distilled out and soon collects in the water cup. If the cup becomes full of water, it is a simple matter to empty it after cooling the apparatus slightly.
Figure 1. Extraction Apparatub
FOOTNOTE to method D 473-48 of the American Society
A for Testiag Materials (method 211.58-1948 of the American Standards Association) reads:
ACKNOWLEDGMENT
When testing oils having high water content, difficulty due to clogging of the thimble with moisture may be overcome by interrupting the extraction when this occurs and drying the thimble in an oven before proceeding further with the extraction.
The author wishes to thank the director of the Dominion Laboratory for granting permission to publish this note. RECEIVED October 24, 1949
Protective Colloids in the Volumetric Determination of Chloride Ion ROBERT F. STALZER, EDITH STAPF DILLON, AND W. C. VOSBURGH Duke University, Durham, N . C .
sults by this method were found too high by about 9 parts in 1OOO. The dichlorofluorescein end point is much improved by a protective colloid. In comparative titrations with the four colloids the volume of silver nitrate solution required was 1 to 2 parts in lo00 less with dextrin and agar agar than with gelatin and gum arabic. Shortly before the end point in the presence of a protective colloid the color changes from a green fluorescence to a milky tan. The end point was taken as the first change from tan to pink. A very small excess of silver nitrate beyond this point changes the color to bright red. When gum arabic waa used in titrat,ions with the standardized solutions, excellent agreement with the calculated end point was obtained. For example, several 24.98m1. portions of 0.1OOO N potassium chloride solution to which were added 45 ml. of water, 5 ml. of 1% gum arabic solution, and 0.8 ml. of 0.1% dichlorofluorescein solution required 24.97 +; 0.01 ml. of 0.1000 N silver nitrate solution. Variation of the volume of 0.1OOO N potassium chloride from 10 ml. to 45 ml. with the same total volume made no difference in the precision and accuracy, nor did inclusion of 1.2 grams of calcium nitrate. I t is best to keep the pH above 4. In comparisons of the standardized solutions by the Volhard method, the silver nitrate required varied from good agreement with the dichlorofluorescein method to 2 to 4 parte in 1OOO too
HE use of protective colloids in titrations involving the preT cipitation of silver halides has been found advantageous by Schneider ( 4 ) in silver iodide titrations and by Lottermoser and Lorenz (2) in the Mohr method for chlorides, but has not been tested as thoroughly as is desirable. Kolthoff and Stenger ( 1 ) state that a protective colloid aids in the detection of the end point with adsorption indicators. Pierce and Haenisch (5)state that dextrin is often used in chloride titrations to prevent coagulation. Standard solutions of silver nitrate and potassium chloride were prepared by direct weighing of the purified salts and the concentrations were checked gravimetrically; the agreement was within 1 part in 1OOO. As protective colloids, gum arabic, gelatin, dextrin, and agar agar were tried. A 1% solution of each was prepared and 5 ml. in a total volume of 100 ml. gave good results. In the hlohr method a11 four colloids retarded coagulation of the silver chloride and made the end point much easier to detect than in their absence. Gum arabic and gelatin gave slightly more consistent results than the other two. Gelatin gave some trouble from frothing, leaving gum arabic aa first choice. When the two standardized solutions were compared by the Mohr method with gum arabic as protective colloid, 24.96 ml. of 0.1000 N potassium chloride solution required 25.18 * 0.02 ml. of 0.1OOO N silver nitrate solution in three titrations. Thus, the re952
