ANALYTICAL EDITIOK
FEBRUARY 15, 1940
123
An automatic electric microfurnace is described in which two samples may be ashed in a stream of oxygen either simultaneously or individually. I n order that the weight of the ash may not be too small, the analytical samples employed are larger than those customarily used even in semimicroprocedure but much smaller than those used in the macroprocedure. The saving of time resulting from this automatic modified microprocedure is considerable when compared to that required by the macromethod, even using the muffle furnace which allows the ashing of many samples at one time.
-Acknowledgment The authors wish to acknowledge the assistance of TT, L. Hattcin in the design and construction of the automatic ashing furnace.
FIG~JR 3E
method: however. when the total elapsed time is considered the macromethod'is about five times as long as the micromethod. Table Iv shows the comparison of time necessary for analysis tiy the two methods.
Summary Data are presented to contrast the usual macroprocedure regard to precision and modified microscheme With speed.
Literature Cited (1I ;ilher, H. K., .lfikrochemie, 18, 95 ( I 935). ( a ) Coombs, H,I , , Biochem, J , , 21, 404 ( 1 ~ 2 ~ ) . (31 Hallett, L. T.. ISD. ESG.CHEW,Anal. Ed., 10, 101-3 (1938). (1) Roth. H., "Quantitative Organic Analysis of Fritz Pregl", by E. B. Daw, p. 136, Philadelphia. P. Blakiston's Son & Co., 1937. PRESEYTED before the Division of lMicroohemistry a t the 98th Meeting of the American Chemical Society, Boston, hlais.
Modification of Rauscher's Method for Determining Mercury ANTHONY SHUKIS, JR., AND RALPH C. TALLMAN Schieffelin & Co., New York, N. Y.
R
AUSCHER'S method ( 1 ) for the determination of mercury by reduction of its compounds with mono- or diethanolamine is generally satisfactory. However, certain difficulties have been encountered in its application as originally described which may be obviated by the modifications outlined belon-. The changes do not apply to the gravimetric determination. The principal source of error in the original method seems to be that,, despite all precautions, tiny particles of mercury tend to remain on the surface of the amine after reduction, held there presumably by surface tension. They are drawn off during the siphoning process anti never become part of the main globule of mercury. The difficulty can be overcome in the folloning manner: The sampie is weighed directly into a tared centrifuge tube of 15-ml. capacity, and the digestion and ail subsequent manipulations are carried out therein instead of in a Pyrex test tube as provided for by Rauscher. At the end of the digestion period, the tube and its contents are centrifuged for 5 minutes at about 2800 r. p. m. In t h i s n-ay, all the floating particles become combined viith the main globule in the bottom of the tube. The supernatant liquid is then sucked off, water is added t o wash the globule of mercury, and the tube and contents are centrifuged again. The washing operation may be repeated as many times as desired. Solution of the mercury and its determination by titration are carried out in general as indicated in the original method. In
order to complete the reaction in the same centrifuge tube, hobever, 0.1 to 0.2 N thiocyanate solution is used to avoid the large volume necessitated by the -maker solutions uwd by Rauscher. Accuracy In titration is achieved by the use of a microburet graduated in 0.02 ml. Samples for analysis x-eighing 100 to 200 mg. Ti-ere found the most satisfactory, the exact amount taken depending on the quantity of mercury believed to be present. Immersion of the lower part of the tube in an oil bath heated to 170" to 180" C. during digestion was more satisfactory than direct heating with a burner, since bumping and spattering are avoided in this way. A 15-minute digestion period ensures more complete reduction of the mercury compound than the %minute period originally prescribed. With the modifications above described, the method has given results entirely comparable with those reported by Rauscher in his original paper, over a wide variety of compounds. It remains a simple, short, accurate, and reliable general method of determining mercury. At the same time, sources of error are minimized by ensuring complete recovery of all mercury through centrifuging, and b y avoiding any loss in transfer.
Literature Cited (1)
Rauscher, ISD. E m . C H E x . , dnal. Ed.. 10, 331 (1938).
