US1272922A - Process for the quantitative estimation of vapors in gases. - Google Patents

Description

H. S. & M. 0. DAVIS.

PROCESS FOR THE QUANTITATIVE ESTIMATION OF VAPOIIS IN GASES. APPLICATION FILED our. 15. I9I7.

1 ,272,922. Patented July 16, 1918.

flin /waif UNITED STATES PATENT OFFICE.

HAROLD SIMMONDS DAVIS AND MARY DAVIDSON DAVIS, OF WINNIPEG, MANITOBA, CANADA.

PROCESS FOR THE QUANTITATIVE ESTIMATION OF VAPORS IN GASES.

To all whom it may concern Be it known that we, HAROLD Snnroxns DAVIS, British citizen, residing at the city of \Vinnipeg. in the county of Selkirk and Province of Manitoba, Canada, and MARY DAVIDSON DAVIS, British citizen, residing at the city of Vinnipeg, in the county of Selkirk and Province of Manitoba, Canada. have jointly invented a certain new and useful Process for the Quantitative Estimation of Vapors in Grases of which the following is a specification.

This invention relates to the method for the quantitative estimation of vapors in gases by the determination of their partial vapor pressures and has for its object to render a rapid and convenient method for the determination of such vapor pressures.

Our process is carried out in an apparatus of the form illustrated in the accom Janying drawing which represents a verticai section of the a paratus and in which Two asks I, 2 of about 300 cc. capacity are connected by a manometer tube 3. sealed into their necks. 'Into the neck of each flask is ground a glass stopper ll. Through each of the ground glass stoppers pass two tubes. One of these, 5.5. is closed at the upper end by a stopcock; Through the other, 6.6, which terminates about 1 cm.

.above the stopper, a metal rod. 7.7, passes to the bottom of the flask projecting above the stopper to a distance of about 11 cm. The upper end of this rod is screwed into a short piece of metal rod of larger diame ter, 8.8. Over this larger piece of rod and extendin down over the glass tubing projecting a ove the stopper is slipped a piece of tightly fitting rubber pressure tubing, 9.9. The rubber joints are made tight by means of vacuum grease and wire. 10.10. 10.10.

To the bottom of the metal rod a small sealed glass bulb. 11.11. is attached by means of small supports and fine copper wire. This bulb, which has a thin bottom. contains sealed up within it some of the liquid whose vapor is to be determined in the gas in question. By pushing down the rod at the proper time or by giving it a slight tap,

Specification of Letters Patent.

Application filed October 15, 1917.

Patented July 16, 1918.

Serial No. 196,720.

the bulb at the end can be broken, thus liberating the liquid it contains. The rubber tubing then draws the rod back into place.

The manometer tube may be filled with mercury or any suitable liquid and any difference in pressure in the two flasks can be read directly on a glass scale 12. \Vhen mercury is used for the manometer liquid.

1 mm. is a convenient size for the bore of the manometer tube.

It is not. necessary that the tubes 5.5 pass through the stoppers, they may be attached to the necks of the flasks or any place where. by opening the stopcocks, the pressures inside and outside the flasks can be equalized.

The actual dimensions of any of the parts of the apparatus can be varied within wide limits; but, as will be seen from what follows, in order to obtain accurate results quickly, it is essential that when the bulb of liquid is broken in the bottom of the flask its vapor should quickly penetrate all the interior of the flask; hence, local pockets in the interior surface into which the vapor would diffuse only slowly should be avoided and all connecting tubes should have a small volume compared with the total volume of the flask.

The theory of the methodis based upon the principle often called Daltons law of partial pressures. according to which the vapor pressure from a liquid is independent of the kind of gas above it. provided the gas is inert. Suppose the two closed flasks decribed above are filled with an inert gas at atmospheric pressure. If new a small sealed glass bulb containing a quantity of the same liquid is broken in each. the liquid will partially evaporate and will add its vapor pressure to the pressure already existing in the flasks: and if the temperatures of the flasks remain the same. the same additional pressure will be developed'in each so that the manometer connecting them will record no difference in pressure. Even if the temperatures of theflasks, do change no difference in pressure will be recorded until there is a relative difference in temperature between them.

Now suppose that one of the flasks had contained a certain pressure of vapor of the same composition as the liquid in the sealed bulb, nd that this pressure was less than the saturation pressure at that temperature. 'hcn the small bulb of liquid was broken in this flask, thr liquid would not add all its vapor pri -Lure to the pressure already in the flash for part of that pressure wa already due to its vapor. It could add only the pressure. required to bring its vapor pres sure up to saturation; and since the total saturation pressure was added to the inert gas in the other tlaslt. the manometer con net-tin."- the two would register a pro. 'ure equal to the pre-smRe Ml' this particular va por in the original gas.

Each of the sealed bulbs must contain considerably more liquid than it is required to saturate, at. thattemperature, the atmos phere in the flask into which it, is broken with the vapor in question.

Two important points should be noticed hereThe partial pressure of any particular vapor in a sample of gas is independent; of the temperature of the gas. provided that the total pressure on the. gas remains constant while the volume can change with the temperature and provided the vapor remains always unsaturated and obeys the simple gas laws.

Second. The difference in pressure devel oped between the two flasks, one of which contains inert gas and vapor and the other inert gas free from vapor, will vary as the absolute temperature. provided the relative temperatures of the flasks remain the same. .that is, for practical purposes the ditien ence in pressures is independent of the temperature.

An apparatus constructed on this principle will therefore measure a definite quantity, the pressure of any particular vapor in the gas at a definite gas pressure.

An actual determination of the pressure of a vapor in any particular gas is carried out in the following way ()ne of the flasks is filled bv displacement with the gas and the other with pure air con'tair none of the vapor. When the temper. arcs of the gases in the flasks have become the same, the stopcocks on both sides are opened to bring the gases to atmospheric pressure, after which they are closed. Next the small sealed glass bulbs containing liquid of the same composition as the vapor are broken by pushing on the metal rods and the apparatus is allowed to stand with occasional shakin until the manometer levels cease changing. In the case of the determination of the amount 01' benzene vapor in a gas the time required to reach equilibrium was 5-10 minutes for flasks of 140 cc.

capacity and 10-15 minutes lor those of 340 cc. capacity.

Ttgreater accurate is required he deter nnnation may be carried out with t t appa ratus sulnnerged in a thermostat and (on rection should be made for the change in volume in the flasks due to the movement oi the manometer liquid. For erdinauv work this is quite unnecessary.

The differential pressure which develops between the two flasks is equal to the origiual partial pressure of the vapor in the gas. when the total pressure on the gas is equal to the ati'nospherie pressure at the time of the experiment. This can be reduced to standard m'nu'litions in the following way.

Let P be the atlnospherie pressure at the time of the experiment.

Let lo be normal atmospheric pres ure 76 cm. of mercury.

Let X be the differential pressure developed between the flasks.

Then

is independent of the temperature provided every,component of the gas remains unsaturated.

In a similar way the total of the partial pressures of two or more vapors may be reduced to its value for a total standard pressure on the gas.

However, though this partial pressure of a vapor is independent of the temperature. the actual weight of the vapor contained in unit volume of the gas depends on the temperature. For one vapor this may be calculated from the partial pressure in the following way on the assumption that the va- 110 por gives the same partial pressure as it; would if it were a true gas at that temperature and molecular concentration ;If M is the gram molecular weight of the vapor,

The process for the quantitative esti1nation of a vapor in a gas which consists in that required to saturate with the va or, at 10 filling to the same pressure two similar that temperature, the flask in whio it is asks connected by a manometer, the one broken, and of calculating the original conwith the gas to be analyzed, the other with centration of the vapor in the gas from the an inert gas free from the vapor-in quesdifferential ressure which develops between tion and of breaking inside each flask a, the two fies s.

sealed. glass bulb, which bulb contains a liquid of the same com osition as the vapor HAROLD SIMMONDS DAVIS.

to be estimatedin a arger quentity than MARY DAVIDSON DAVIS.

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