ANALYTICAL CHEMISTRY
536
r
I ,
Ji
I
END VIEW
FRONT VIEW
Figure 1.
1-1
Calculator for Selecting Sample Weights
vealed no method of selecting a swinple size which is a function of the carbon and hydrogen composition of the given compound and also takes into account maintenance of the lpad dioxidewater-carbon dioxide equilibrium. A calculator (Figure 1) w?s designed, therefore, to meet these requirements. It can quickly indicate the optimum sample size for an accurate and preciw determination of both elements.
The author wishes to thank Walter
L. Save11 and Paul D. Sternglanz for their kind cooperation. LITERATURE C l T E D
(1) Bmedetti-Pichler, A. A,, IND.Ex(-. CHEX..ANAL. ED., 11, 226 (1934,. (2) Grant, J., “Quantitative Organic Microanalysis,” 4th English ed.. p. 59, Philadelphia, Blakiston C‘O., 1945. (3) Niederl, J. B., and Niederl, V., “111cromethods of Quantitative Organic .inalysis,” 2nd ed., p. 43, NeaYork. John Wiley & Sons, 1946.
(4) S i d e r l , J. B., Siederl, V., Xagel, R. H., and Benedetti-Pichle:. -1.A , , TND. ENG.CHEM.,-4~~1,. ED.,11, 412 (1939). ( 5 ) Ogg, C. L., Willits, C. 0.. Ricciuti, Constantine, and Conneliy. J. A , , A N A L . CHEM.,23, 914 (1951). (6) Steyermark, A,, “Quantitative Organic Microanalysis,” p. 107, Philadelphia, Blakiston Co., 1951. (7) Wagner, H., Nilikrochemie w r . Icf ikrochim. Acta, 36/37, 636 (1961). (8) Wuraschniitt, E.. C’hem.Z t g . , 74,420 (,1950).
OPERATION
The three top rows of the calculator are a unit used in connection with the determination of carbon, while the lower three are used for the determination of hydrogen. Each unit has a diding square with a window. The use of the calculator in finding a suitable sample pize may best be illustrated by examples. Consider first a compound R hich theoretically contains 23.15% carbon and 14.43% hydrogen. The upper sliding square is set a t 23, the number nearest to the theoretical carbon content. I n the window appear the figures 5.9 and 24, representing sample weights R hich would yield approximately 5 and 20 mg. of carbon dioxide, respectively. (The range 5 to 20 mg. of carbon dioxide is cnonsidered suitable for carbon determinations,) Then the l o ~ e sliding r square is set a t 14, the number nearest to the theoretical hydrogen content. In the window appear the figures 2.0 :tiid 8.0, representing the sample weights which would yield approximately 2.5 and 10 mg. of water, respectively. (The range 2.5 to 10 mg. of water is considered suitable for hydrogen determinations.) It is evident that the two ranges, 5.9 to 24 and 2.0 to 8.0, overlap. To find the optimum range of sample sizes, the largest and smallest of the four figures are rejected. The optimum range is thus 5.9 to 8.0 nig. A sample of 7 f 1 mg. should accordingly be weighed. For some compounds, the t F o ranges indicated by the calculator do not overlap. The sample size, however, may be figured in the manner described above, The weight of carbon dioxide and water obtained would, of course, be outside the 5- to 20-mg. and 2.5- to 10-mg. ranges arbitrarily chosen for the calculator. A compound which contains 76.95% carbon and 2.10% hydrogen aerves to illustrate this case. The two sample size ranges are found t o be 1.8 to 7.1 mg. and 14 to 56 mg. A sample of 10 to 11 mg. is thus indicated. In designing the calculator, it mas assumed that the percentage of carbon and hydrogen in most compounds is 11 to 89% and 1 to 25%, respectively. Several sample weights printed on the instrument exceed the semimicro scale; several others are of the range 1 to 2 mg. In the process of selecting the optimum sample, however, these figures will always be rejected, as illustrated in the second example. The smallest optimum sample which can be indicated by the proper use of the instrument is 3 mg. I n this case the calculator would be set for a compound whose theoretical composition is about 75% carbon and 25% hydrogen. The analyst may wish to construct a calculator with different carbon dioxide and water ranges. If the present ranges are doubled, i t is apparent that the optimum sample weights indicated will also be doubled If the instrument is scaled downward, due regard must be given to the dependence of the sample size on the preciqion of the balance to be uwd (1, 4 ) .
C. It. Parks, Research Laboratory, The Goodyear Tire & Rubber Co., Akron, Ohio.
Cold Extractor.
the extraction of some solid materials, it is often desirable F to run the extraction a t room temperature or below. Cold extractors have been described for the extraction of such mateOR
rials as rubber (a), shellac ( I ) , and plant materials (S), but are rather cumbersome and difficult to assemble. The extractor described here is of the Soxhlet tvpe using standard ground-glase equipment available in most chemical laboratories. It can be used for the cold extraction of almost any solid material except \\here the extract is thermallj unstable and is to be saved or analyzed. In the usual Soxhlebtype e\tractor available commerciallj the extractor proper ,is in direct contact with the extraction flash containing the heated liquid. In addition, the vapors from the exF tracting liquid are in contact with the material being extracted, so that the material is always a t an elevated temperature. I n this extractor, the heat transfer from the extraction flask. 8, to the extractor, B, was reduced to a minimum by connecting the extraction flask to the siphon tube, C, by means of an adaptor, D,and a short piece of pure gum tubing, E. Hot vapors that may come in contact with the sample were eliminated by using an efficient condenser of the Friedrichs type, F , the condensate being near the temperature of the water in the condenser before coming in contact with the sample. The tip of the condenser was placed 2 to 3 inches down in the extractor to keep evaporation a t a minimum. Heat loss from the vapor tube, G, leading up t o the condenser m-as reduced by using asbestos tape or heated resistance Fire.
LJ
LITERATVRE CITED
(1) Gardner, W. H., and Harris, H. J., IND. ENQ.CHEM.,ANAL.ED., 6, 401 (1934). (2) Lindsly, C. H.. Ibid., 8, 180 (1936). (3) Gchechter. >I, S , , and Haller. H. L., Ibid., 13, 482 (1941).
