SEPTEMBER 15, 1940 TABLE 111. Excess
IiI
Time
'c
.win.
0
TR.4h'SPARENCIES O F KESSLERIZED AiVHOXIUM
CHLORIDE SOLUTION (0.05 milligram equivalents per liter) -Mole of HOII per Equivalent of Hg 3 0 7 10
4
0.(j5rJ'
0.652"
O.64Ya
32 64
0.642 0.630 0.743" 0,047 0.632
0.840 0.631
0.636 0.629
0.857" 0.643 0.637 0.661 0.643 0.635 0.852 0.679 0 659
0.655a 0.640 0.631
4
32 64 10
ANALYTIC.4L EDIT10 \
4 32 64
0 930" 0.711 0.673
0.659 0.63s 0,627
+ -
15
0.645" 0,635 0.628
0.647 0.636 0.631
0.649 0.638 0.027 0.653 0,639 0 633
0.633 0.640 0.633 0.651 0.837 0.629 0.649
0.672 0.63!1 0.637 0,629 0.624 0.632 0.647 0.843 0.7.52 0.978 0 913 20 4 0.641 0.63i 0.684 0.643 32 0.970 0.628 0.632 0.657 0.634 64 0.964 .kt these concentrations of IC1 and IiOH a red precipitate of IlgIi foriiis i n 1 hour or less; hence t h r a r are not suitable concentrations t o USP for a Srssler's reagent. 13
4
32 64
0.975 0.830 O.ilCl
0.775
+
0.641
These d a t a show very strikingly the slowing up of the color formation by increasing amount's of excess potassium iodide; and they show hon- increasing concentrations of potassium hydroxide overcome the effect of the potasdium iodide and speed u p the color formation. These effects are st,illmore noticeable when tlie concentration of the ammonia is lower, a i d are less noticeable a t higher concentrations. The dept'h of color developed a t tlie eiid of 1 hour is remarkably uniform, except for those cases in which the reaction is much slower antl full color ha. evidently not developed in 1 honr. It is erident froin these results t h a t about 5 per cent excess of pot,assiuni iodide is needed to prevent the formation of a red precipitate when Sessler's reagent is diluted, unless excessive concentrations of potassium hydroxide are usetl. -4further increase in the ainount of potassium iodide noticealdy s l o ~ wup the color formation, especially with low con-
317
centrations of ammonia. The effect of increasing the coiicentration of potassium hydroxide is t o speed up the d e v e l o p nient of color antl to decrease the amount of excess potassium iodide required to prevent the formation of the mercuric iodide precipitate. The aut'hor, after taking all factors into consideration recommends tlie following formula for the preparation of a satisfactory Sessler'a reagent : The reagent should hare 10 moles of potassium hydroxide for each equivalent of niercuric ion in solution with 5 per cent excess of potassium iodide over and above that called for by the hypothetical compound potassium mercuric iodide. Furthermore, it should stand several days before being used, to permit any precipitate to settle out. There is no necessity of using any such involved methods of preparation as those given by Treadwell and Hall (j)Koch , and Mcllleekin (3),and Fuchs (2). Rather, it is recommended that 45.5 grams of mercuric iodide aiid 34.9 grams of potassium iodide be dissolved in as little xvater as is needed, 112 grams of potassium hydroxide (140 ml. of an almost saturated solution, sp. gr. _ - 1.538) added, and the n-hole diluted to 1 liter. This
yoo
solution is 0.2 S with respect to the merr'ury content. In the Sessler test, 5 nil. of this reagent, to 100 ml. of final volume are used, aiid the color comparisons with th? rtandards are made 30 minutes after. mixing. Sessler's reagent prepared according to t'his forinula has been usetl in this laboratory for srl-era1 years with completely sat,isfactory iwults a t all times.
Literature Cited Dunningham, 8.C., J . Chem. Soc., 105, 3 6 S - i 9 (1914). (2) Fuchs, H.J., 2. physiol. C'hcm.. 223, 144-6 (1934). (3) Koch and M c I l e o k i n . J . A m . ('hem. Soc., 46, 2066 (1924). (4) IIellor, J. TI-., "Comprehensive Treatise of Inorganic and Theoretical Chemistry", Vol. I V , p. 933, K e r n York, Longmans Green and Co., 1923. ( 5 ) Treadwell, F. P., and Hall, W. T., "Analytical Chemistry", Vol. I, p. 91, S e w York, John Wiley & Pons, 1937.
(1)
PAPER 412, r n i r e i s i t r of California, C'ollpge of A w i c u l t u r e
Preparing Asbestos for Filtering Mats BEN L. K l S P I N Bureau of Agricultural Chemistry and Engineering, U. S. D e p a r t m e n t of .iipricultnrc*. K a s h i n g t o n , D. C.
T
HE preparation of asbestos for use in Gooch crucibles
by hand shredding has aln-ays been one of the less pleasant of the chemist's tasks. Asbestos prepared b y means of the simple a p p a r a h s devised in this laboratory for niechariically performing t h a t job has been used during: the last 6 months in graviiiietric deterniinations of barium sulfate, cuprous oxide, crude fiber, etc., antl has been found very satisfactory. The construction of the apparatus is shown by the diagram. ,4 widemouthed, square glass jar, 1, of about 2-quart capacity is covered by a piece of moderately heavy cloth, 2 (ordinary laboratory towel material is suitable). A glass tube, 3, passes through a small hole in the cloth and is held in position by tvio tightly fitting rubber stoppers, 4, 5 , one placed above and the
&her below the cloth. The stoppers are pressed together to hold the cloth firmly bet,ween them. The tube should be placed near one corner of the jar arid extend approximately halfway to the bottom. The outer eiid of t,he tube is connected to a compressed air line. To operate, cut the asbestoa to roughly 0.5-inch length-, place a 0.25-inch layer of this material in the bottom of the j u , securely fasten the cloth cover, and gradually admit the compressed air. When the correct rate of flon is attained, the asbestos is lifted by the air currents and swirled violently in what appears to be a miniature tornado. In about 5 minutes the asbestos becomes fluffy and half fills the jar. The finished product is removed and the operations are repeated until the desired quantity of prepared asbesto:: is obtained. If the air is admitted too rapidly the asbestos tends t,o rise and accumulate at the top of the jar. When this occurs, turn off the air, tap the cover to dislodge the asbestos, and again start the air. The apparatus slioiild be used in a hood with a rtrong draft, since its operation produces a fine asbestos dust that is extremely irritating. FOOD Hc.earch
Division ContrihutirJn Xo. 499.
