Vol. 2 , To. 3 - 250 A ATAL Y TICAL EDI TIOAV

Carbon Dioxide Generator for Combustion Analysis in the Estimation of Nitrogen’

Edgar J. Pothz

UNIVERSITY OF TEXAS. AuSTIS, T E X .

N AN investigation of the bases occurring in kerosene stock from California petroleum, microcombustion analysis is indispensable because of the limited amount of material

usually available. One important essential in the estima- tion of nitrogen by this method is carbon dixoide containing only a negligible admixture of air. Two types of carbon di- oxide generators described in this paper, provided a highly sensitive microbalance is employed, enable one to make a nitrogen determination on a 3- to 6-mg. sample in 20 minutes with a mean error of less than 0.1 per cent.

marble is employed. The objection to this type of generator, to quote from Pregl, is ‘hem- generators hold large amounts of air, not only on the inner surfaces of the glass. but also ab- sorbed in the rubber stoppers, and this is only liberated after being exposed for days to an atmosphere of carbon dioxide.” d form of generator has recently been described by Marck ( I ) . but it does not overcome the difficulties encountered with the ordinary Kipp apparatus.

Of the two generators described herein, in Type I the gas is stored over mercury, and in Type 11, over water. Apart

from the cost of the mercury, Type I is preferable because of the simpler manipulation required. The advantages of these apparatus, the construc- tion of which requires no great skill in glass blow- ing, are as follows: (1) After P charge of bicar- bonate has been introduced, only 10 to 15 minutes are required to eliminate the air; (2) a single charge of bicarbonate has a production capacity of sufficient gas for a large number of analyses; (3) in about 5 minutes a stored supply of practically pure carbon dioxide under pressure and sufficient for five to ten nitrogen determinations can be generated; (4) the carbon dioxide is prepared before the analysis is started, so that the op- erator can devote his entire attention to the com- bustion; ( 5 ) the flow of gas can be regulated a t will; (6) since the gas is stored under pressure, over mercury or de-aerated water, and in a closed system devoid of rubber connections, its puri ty i s maintained i n d e f i - ni tely.

Operation of Type I Generator

With 4 (made from a Pyrex tube) charged with sodium bicarbon- ate so as to leave a small channel a t the upper surface, and G (500-cc. flask) f i 11 e d

with mercury to stopcock J , ex- haust the system with a n oil L pump throughH, stopcock J being closed. Apply a gentle heat to d with a luminous Bunsen burner, and pump the system for 10 min- utes, while heating F (500-ce. flask) to expel gases occluded on its inner surface. Next allow air to enter through J so as to fill F with mercury to its junc- tion with the delivery tube. It is important then to generate enough carbon dioxide to fill

I

C a r b o n Dioxide G e n e r a t o r (Dimensions in mm.)

I n the Pregl microcombustion method of estimating nitro- gen an important factor is pure carbon dioxide. One source of carbon dioxide is sodium bicarbonate. There are, however, several objections to the ordinary procedure: (1) The bi- carbonate tube is refilled for each determination and must be swept free of air; (2) the flow of gas cannot be readily regu- lated with great exactness; (3) the process requires very close supervision, and analyses are frequently vitiated by failure to observe some necessary precaution.

Pregl (2) recommends as a source of carbon dioxide a Kipp generator in which the action of hydrochloric acid on

1 Received March 12, 1930. This paper is the outgrowth of an investiga- tion on “The Kitrogen Compounds in Petroleum,” listed as Projert 20 of American Petroleum Insti tute Research. Financial assistance in this work has been received from a research fund of the American Petroleum Insti tute donated by John D. Rockefeller. This fund is being administered by the institute with the cooperation of the Central Petroleum Committee of the National Research Council.

2 American Petroleum Institute Fel!ow.

F aDDroximatelv half full. With I I J &en test for the purity of the gas by connecting the sys- tem through H with a n azometer Deta i l of S a f e t y Trap

M a n o m e t e r

July 15, 1930 I S D U S T R I A L A 5 D ESGIA'EERI*VG CHEMISTRY 251

filled with 50 per cent potassiuni hydroxide solution. Should this test give a n unsatisfactory result, repeat the process just described taking care not to allow air to enter through H. I t is advisable to have a plug of cotton a t the lower end of B. The functions of D, a capillary manometer, and E , a mercury bubble trap, are self-evident. To obviate a possible intake of air through H , maintain at all times a pressure in F aboye atmospheric. Since A must be heated whenerer carbon dioxide is generated any clamps supporting it should be cushioned with asbestos. K h e n the 1)icarbonate is to be renewed, break the connection at a point ahow side arm R.

I n each operation of storing a supply of gas in F , carbon di- oxide is trapped before the mercury seal in the generator d , arid, as the contents of d cool this carbon dioxide is re-ab- sorbed, producing a partial vacuum in this part of the system. Sliould a pinhole leak be overlooked in the construction of the apparatus, t h i s allowing an intake of air. this is easily detected by a drop in the mercury column of the manometer. Ob- viously a leak on the other side of E would not allow a n en- trance of air before detection, because the gas in F is under pressure.

Type I1 Generator

C is of use in filling and emptying A.

The construction of the apparatus is the same as for Type I, except' that G of Type I is replaced by K (3-liter flask) and L (safety trap). By varying the amount of mercury intro-

duced into L , it can be regulated to give any maximum pres- sure in K up to 300 mm.

Temporarily connect H to a T-shaped, three-way stopcock, the perpendicular arm of which is filled with and extends into de-aerated water. After charging A with sodium bicarbonate and filling E and L with the proper amounts of mercury, flame the entire generator system and pump with an oil pump for at least 15 minutes to remove occluded air from the inner surfaces of the glass. It is necessary to evacuate L partially and close JI during the pumping of generator &ern. X o w allow ap- proximately 550 cc. of deaerated water to run in. Close H and then generate carbon dioxide until it bubbles through L when 31 is open. so as not to suck air back into the storage systems. If the stored gas gives a satisfactory test for purity, the generator is ready for use. Obviously, if the occluded air in K is thoroughly swept' out, the water seal between K and F can be dispensed with.

Caution should be exercised in opening

. Acknowledgment

The author takes this opportunity to express his apprecia- tion for the many valuable suggestions and criticism offered by J. R. Bailey, director of Project' 20.

Literature Cited (1) Alarck, Bi tL SOC. chim., [41 46, 559 (1929). (2) Pregl, "Quantitative Organic Xlicroanalysis," translated by Fyleman,

p. 79, Churchill, 1924.

S A previous paper (30) there was d e s c r i b e d a I procedure for the deter-

mination of sulfide sulfur in stibnite by evolution of hy- drogen sulfide, this being re- ceived in ammoniacal cad- m i u m s o l u t i o n and deter- mined iodometrically.

.Vole--Von Bacho ( I ) reported low results by a similar procedure attr ibuting the error t o loss of hy- drogen sulfide, during decomposi- tion of the cadmium sulfide, because of either volatilization or air oxida- tion The loss may be explained by the fact t h a t the cadmium sul- fide was treated with hydrochloric acid before the iodine solution was added.

Evaluation of Stibnite' 11-Determination of Antimony

Wallace M. McNabb and E. C. Wagner

UKIVERSITY OF PENKSYLVAKIA, PHILADELPHIA, P A

The titrations of trivalent antimony by bromate, iodine, or permanganate, under properly adjusted conditions, yield practically identical results. In presence of ferrous iron the titration of trivalent

antimony with iodine, in a solution buffered with bicarbonate, is affected by a negative error.

A method for determination of iron present as im- purity in stibnite is described.

The Frankford Arsenal method for determination of antimony in stibnite was found to yield results about 0.5 per cent too low, apparently owing to loss of antimony by volatilization.

The evolution procedure has been extended to in- clude both the iodometric determination of sulfide sulfur and the titration of antimony with permanga- nate. The analysis for both constituents is made on a single sample, and is rapid, easily executed, and ac- curate.

The present paper gives a n account of the extension of the procedure to include the determination of antimony, both elements being determined volumetrically and in the same sample.

Volumetric Methods for Determination of Antimony

Methods which involve reduction of pentavalent to tri- valent antimony include Weller's application of Bunsen's evolution method (40), a similar method (36) in which iodine is liberated from hydriodic acid by pentavalent antimony in the cold, with titration with thiosulfate in either case,

Received January 31, 1930.

and reduction by t i t a n o u s chloride (24), the end point being located potentiometri- cally.

M e t h o d s in which triva- lent antimony is oxidized to the pentavalent condition in- clude most prominently the titrations with iodine (32), with permanganate (19), and with bromate (35). Willard and Young (42 ) applied their ceric sulfate method to the determination of antimony, t h e aT7eraged results being very close to the theoretical. Knop (21) titrated antimony with standard dichromate, with diphenylamine as in-

ternal indicator, and Fleyscher ( I O ) -deteknined the end point electrometrically. Jungmichl and Hack1 ( I @ , and also McMillan and Easton (29), titrated with dichloramine-T. Kakosono and Inoko (33) modified the bromate method by titrating in presence of potassium bromide. h4anchot and Oberhauser (98) described an excess method using stand- ard bromine and arsenite solutions. Iodate titrations have been proposed by Jamieson (17) and by Lang (25) . Winkler (49) revived the method of Gooch, and Bertiaux (3) titrated antimony with permanganate using methyl orange as internal indicator.

Accuracy studies of several methods for determination