ISDCSTRIAL Ai\-D EiYGISEERIA-G CHEJIISTRY
January 15, 1930
may be left off during the neighing. If desired. tlie tube may be closed by means of a rubber policeman. Fit the other hole of the stopper with a glass tube drawn out to a capillary at the lower end and reaching nearly t o the bottom of the flask. Bend it at right angles above the stopper to make a conT-enient attachment for the purifying train, and, unless otherir ise specified, close it Tvith a rubber policeman during tlie determination. Sr.ssrax;ic
Table I SAMPLGTHEORETICAL FOLND Gram Gram Gram 0,5000 0,5000 0,5000 0.5000 0.8555 0.3302 0.5000 0,5000 0 5000 0.5000 0,6000 0.6000 0,5000 0.5000 0,3000 n ,3000
0.2200 0.2200 0 2200 0.2200 0,4482 0.1729 0.1ii-i 0.1774 0.15y2 0.1592 0 . lis9 0.li89 O.liS4 0.li54 0.1666 0.1366
0 2200 0.2202 0.2201 0,2202 0.4460 0.1726 0,liil 0.lii3 0.1593 0.1590 0.li86 0 .178.5 0.1751 0,1750 0.1566 0.1564
ERROR Grum Per cent 0 0000 0.00 n ,0002 0.10 0.0001 0.05 0,0002 0.10
n
0022 0 0003
0.0003 0 0001 0.0001 0.0002 0,0003 0.0004 0.0003 0,0004 0 0000 0 , 0002
0 . a 0,li 0,li 0.00 0.00 0.01 0.16 0.22 0.16 0.21 0.00 0.01
Tlie purification train consists of two fairly large U-tube?: the one next to tlie apparatus filled with calcium chloride and the other filled with soda lime. The air as it enters the apparatus is drawn through this purification train and is thus rendered free from carbon dioxide and dried. DETERUI~.~TIO~-~~5'1en the apparatus has been assembled as described, place about 15 cc. of dilute hydrochloric acid (1:l) in the flask. Introduce the carefully weighed sample (about 0.50 gram) in a glass thimble SO that the thimble stands upright in the acid. This t'hinible is best prepared by cutting off the loner inch of a regulation 2-dram homeo-
pathic vial and firedressing the edges. If desired, the apparatus may be weighed before the introduction of the thimble and sample and t'he two weights added to give the t'otal weight of the apparatus. After the apparatus has been carefully weighed overturn the thimble by tipping the flask. The inlet tube must he closed and the outlet' tube must be open during the reaction. K h e n the reaction has subsided attach the apparatus to the purifying train and pump and apply suction, so that the bubbles pass through the apparatus a t the rate of aliout two per second. Continue this aspiration for 15 niinutei a t this rate. Then detach the apparatus, replace the ruliber policeman, and weigh the entire apparatus. The loss iii weight is calculated as carbon dioxide. The time required for making the deterniination is ahoiit 20 minutes. The arerage raniple will he about 0.5000 gram, but wlic~n the carbon dioxide content is high 0.3000-gram samp1t.i should be used. CRmCISx-This method is very rapid and awurate! being capable of results having an error as low as 0.10 per cent or lower. It is, of course, open to .the usual objections to methods of this type, namely, that any othw substances which may be evolved as gases under the conditions obtaining during the determination vi11 be weighed and erroneously reported as carbon dioxide. Tlie method is not reconiriiended for basic carbonates or for lead carbonate. Just why these substance:;: should give difficulty is not l i n o ~ n ito tlie witers. Results
The results obtained x i t h the new method, using a number of different carbonates, are given in Table T.
Filtration Pipet for Spot Indicator Tests' Earle R. Caley PRINCETOS CSIVERSITY, PRISCETOS, S . J.
CERTAIS types of titrations wheie tlie spot indicator ItheSmethod is employed, it is desirable to withdraw froin solution being titrated liquid free from any suspended precipitate. This procedure is necessary when the color of the precipitate interferes with the spot reaction, or in cases where the precipitate reacts chemically with the outside reagent and leads to a n uncertain or false end point. A simple device for rapidly filtering small samples of turbid liquid for spot tests is shown in the figure. It is most easily constructed from a T-tube proportioned as shown. For the avoidance of capillary effects, which interfere with the operation of the instrument, glass tubing of not less than 6 mm. interiial diameter should be used. To the end of the short arni is attached a small rubber bulb, while the end of the long arni nearest the bulb is drawn out to a tip. The other end of the long arm is provided with a slight internal collar formed by holding the end momentarily in the flame. A small length of heavy-walled rubber tubing is then inserted into this end. The rubber tubing should fit the inside of the glass tube quite tightly and its upper end should be about 1 mm. from the end of the tube. As a filtering medium one or more closely fitting disks, cut from filter paper by means Received September 14 1929
spot test, the filtering end is dipped into the solution being titrated, while the rubber bulb is nianipulated b e t w e e n t h e t h u m b a n d middle finger with the forefinger closing the tip. To release the drop or two of filtered liquid thus ohtained, the instrument is inverted over the spot plate in an inclined position with the bulb uppermost. the spot plate. A device of this type can uiidoubtedly be used for other purposes than t h e o n e n i e n t i o i i e d
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