INDUSTRIAL AND ENGINEERING CHEMISTRY
478
TABLEI.
DETERMINATION OF MERCUROUS CBLORIDE AND MERCURY
HgCl Taken
HgCl Found
Error
MQ.
Mo.
Mo.
50.0 10.0 1.0
49.6
-0.4 -0.3 $0.2
9.7
1.2
H Equivalent of%gCl Taken Mg.
Hg Found Mg.
Error Mg.
42.5 8.5
42.3 8 3 0.8
-0.2 -0.2 0.0
0.8
TABLE11. ANALYSESOF MERCURY ORES Location
Total Hg
% Terlingua, Tex.
Pike County, Ark.
.
HgCl
%
60.28 0.20 11 13 0:90 e 1.83 0.14
0.21 0.02 0.13 None None 0.03
it was inserted into the tube serves as a check on the final figure obtained after expulsion of the mercury. The tube when cool is broken at the asbestos wad between the sample and the sodium carbonate. The latter is transferred to a 250-ml. beaker, put in solution in about 60 ml. of water, and made acid to litmus with nitric acid. After filtering to remove any asbestos, the chlorine is precipitated with silver nitrate and the resulting silver chloride is filtered and weighed. The quantity of mercurous chloride in the sample is computed from this figure. If the silver chloride precipitate is very small it may be necessary to arrive at its estimation by the nephelometer. The need of a bIank correction for chlorine in the sodium carbonate depends on the purity of the reagent used. The method gives excellent results on samples containing up to 50 mg. of mercurous chloride. None of the minerals found in mercury ores, including halite and sylvite, interferes
VOL. 9, NO. 10
with the determination. The rare mercury minerals, terlinguaite and eglestonite, if present, would yield chlorine and be reported along with calomel as mercurous chloride. Table I contains results of analyses of samples of pure mercurous chloride. Table I1 is made up of analytical data on mercury-bearing rocks from Terlingua, Tex., and Pike County, Ark. The samples are not representative of ore bodies a t these localities. The quantity of calomel found in these particular samples was small and was not visible under a hand lens. Calomel has been reported from Terlingua, however, in crystals up to 1 cm. in length, and is generally present in the earthy matrix of veins carrying the rarer mercury minerals (3).
Summary
A method for the determination of mercurous chloride and total mercury on the same sample is described. The mercury minerals are volatilized in a glass tube and brought into intimate contact with granulated sodium carbonate. The chlorine is fixed as sodium chloride, determined with silver nitrate, and computed to mercurous chloride. The mercury is collected on a previously weighed gold coil and weighed. Literature Cited (1) Echols, W. H., Chem. News, 44,189 (1881). (2) Eschka. 2.and. Chem.. 11.344 (1872).
(3j Hillebrand, W. F., and Sohaller] W. T.,U. S. Geol. Survey, Bull. 405,9, 159 (1909).
RECEIVED June 8,
1937. Published by permission of the Director,
U.5.
Geologioal Survey.
A Simple Fume Absorber for Kjeldahl Digestions HAROLD G. CASSIDY, Oberlin College, Oberlin, Ohio
I
N THE Kjeldahl digestion the unpleasant and corrosive
fumes which are evolved, sometimes in copious amounts, are a source of inconvenience. Many devices for disposing
of them have been developed. A common practice is to carry out the digestion in a hood, or to insert the neck of the digestion flask in a pipe leading either to an exhaust fan or to a water pump. Henwood and Garey (2) have described a flanged, porous alundum tube, closed a t the bottom, which prevents the escape of the sulfuric acid mist yet allows the free exit of steam, sulfur dioxide, and carbon dioxide formed in the process of digestion. This tube is fastened in the open end of the digestion flask (1). Under these conditions the digestion may be performed on the laboratory table. The device described below is simple and inexpensive, can be made from materials found in the laboratory, and is useful where ordinary types of fume-disposaI equipment are not available. It absorbs, completely in most cases, both sulfur dioxide and the sulfuric acid mist. The absorption tube is the most satisfactory of many which have been designed, made, and tested. It may be modified for use in other reactions which give off noxious gases-for example, organic reactions in which hydrogen chloride is evolved.
The Absorption Tube
EASK
/
IN FIQURE 1. FUME ABSORBERIN POSITIOX NECKOF KJELDAHL FLASK
A test tube (preferably, though not necessarily, of Pyrex) is chosen of the largest size which easily slips into the neck of the Kjeldahl flask to be used. The tube is heated at 8 point somewhat above the rounded end and the wall is pushed inwards and upwards to form an invagination,or deep depression. This is most easily done with a stout wire flattened a little at the end. The wire is held in the depression until the glass sets, then it is given a sharp twist: The flattened portion acts as a lever and shatters the glass at the upper point of the invagination, leaving a hole
OCTOBER 15, 1937
ANALYTICAL EDITION
in the position shown (fume inlet). The tube is ready for use as soon as it has cooled. The tube is first filled with glass beads or glass wool to a point somewhat above the fume inlet. The glass beads or wool support a column of loosely packed soda lime or other suitable absorbent. A wad of cotton may be placed above this. The filled tube is fitted tightly into the neck of the Kjeldahl flask by means of a collar of folded filter paper, as suggested by Henwood and Garey (1). The tube must not project down too far into the neck of the flask; otherwise spray may collect on it. Before beginning the digestion, the cotton wad is removed and the soda lime moistened with a little distilled water. The wad may then be replaced. The charge in one tube may last for several digestions. The filling and fitting of the tube require only a few minutes. This type of absorber has been used with Kjeldahl flasks of 100- to 500-cc. capacity and with a variety of digestions, including feeds, sugars, and pure organic compounds. It has shown itself satisfactory, enabling the digestions to be carried out in the open room without inconvenience. Occasionally a small amount of sulfuric acid mist has escaped from the tube at the beginning of a digestion, but this has always ceased after a few minutes. Because of the shape of the opening, any spray which spat-
479
ters u p onto the bottom of the tube may readily be washed off the rounded end with the stream from a wash bottle, and any small condensate which forms inside the tube will collect safely inside the rounded end.
Summary A test tube, perforated near the bottom, is filled with moist soda lime or other suitable absorbent, the perforation being first shielded with glass beads or glass wool, and is then tightly fastened into the neck of the Kjeldahl flask by means of a collar of folded filter paper. This device absorbs and prevents the escape of practically all irritating fumes during the digestion, and thus permits it to be carried out in the open room without inconvenience. It may be modified for use in other reactions which evolve unpleasant fumes.
Literature Cited (1) Henwood, A,, and Garey, R. M., S. Franklin Inst., 221, 531-8 (1936). (2) Henwood, A.,and Garey, R. M., Science, 76, 524 (1932). RECIDIVSD J U ~ Y9,1937
A Self-Filling Pycnometer G, F. HENNION University of Notre Dame, Notre Dame, Ind.
T
HE pipet type of pycnometer is widely used for the determination of densities, particularly of organic liquids, but has the serious inconvenience that filling requires suction. As this is frequently accomplished orally, obnoxious vapors may be drawn into the mouth. Precise adjustment of the liquid volume is also frequently troublesome. By making a few minor changes in construction, pycnometers have been made in this laboratory which are entirely self-filling and extremely easy to adjust. Figure 1 illustrates one of these. The dimensions are somewhat variable except for the capillary tip, A, and tube D. The pycnometer is used as follows: Hold with thumb and second finger at oint F , place index finger over opening G, and dip capillary tip beneath the surface of the liquid whose density is t o be determined, contained in a small crucible or beaker. Remove pressure at G . The pycnometer fills automatically, owing to capillary rise of liquid at A and overflow at B. When the liquid reaches the calibration mark, apply pressure at G and withdraw A from the liquid. Wipe the capillary tip, rock the pycnometer gently to withdraw the li uid from A B , suspend in a balance, and weigh. desired, the pycnometer may be filled beyond the calibration mark and suspended in a constant-temperature bath maintained at the desired temperature. Excess liquid may be subsequently withdrawn at A in the usual manner. The capillary section at A B must extend beyond both sides of bend B . Too fine a capillary causes very slow filling. A 2ml. pycnometer used by the author fills with water in 18 seconds at 25" C. If tube D has an internal diameter greater than 2 mm. the descending column of liquid tends to break, causing air bubbles. Naturally the pycnometer must be cleaned and dried before use. The presence of a small slug of liquid at E prevents liquid rise at A .
B
1
2 mm. i.d.
If
A number of these pycnometers have been constructed by the author, with volumes varying from 0.75 t o 10 ml., and have been used with organic liquids of various densities and surface tensions. The pycnometers are readily constructed from selected pipets and are calibrated without difficulty in
FIOURE1. SELF-FILLINO PYCNOMETER the usual manner. A fine wire, connected a t C and F, serves for suspending the pycnometer in the balance. RECEIVED August 13, 1937.
