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T H E J O U R N A L OF I N D U S T H A L A N D EIVGINEERTNG CHEIWISTRY
of t h e orifice used, t h e effusion pressure a n d t h e confining medium. T h e effect of different effusion pressures with t h e same orifice a n d different gases is shown in Fig. 2 , where R is t h e ratio of t h e apparent specific gravity t o t h e t r u e specific gravity a n d t h e effusion pressure r is expressed as t h e ratio of t h e atmospheric pressure t o t h e total effusion pressure. Different orifices give curves for t h e same gas which are similar in form b u t have different values for t h e apparent specific gravity. This is shown b y t h e curves in Fig. 3 for six different orifices when using methane. The results may be summarized as follows: I n general, t h e deviations are greatest a t t h e lowest effusion pressures (highest values of I ) a n d a low effusion pressure should be avoided; but it is not true that t h e higher t h e effusion Pressure t h e more nearly correct will be t h e there may be a pressure a t which a certain orifice will give correct results (i. e . , correct ratio t o air) with a certain gas, there is no pressure a t which i t will give correct results with all gases. The combination of factors which produces such a low result in t h e case of carbon dioxide or methane produces just t h e opposite effect with hydrogen. Decreasing t h e diameter of t h e orifice or increasing t h e thickness of t h e orifice plate tends t o give a lower apparent specific gravity with methane or carbon dioxide; t h e same changes give a higher result with hydrogen, as previously explained. Examination of t h e results obtained with 30 orifices shows t h a t orifices of t h e following characteristics give t h e most satisfactory results: t h e orifice should be round a n d smooth, with all burr a n d ragged edges carefully removed. For apparatus using a mean effusion pressure ratio of 0 . 9 0 (with mercury as a confining liquid) a n orifice 0 . 1 j mm. t o 0.30 m m . in diameter in a plate 0.05 mm. or less in thickness should prove satisfactory. For apparatus using a mean effusion pressure ratio of 0 . 9 9 (with water as a confining liquid) a n orifice 0.18 mm. t o 0.30 mm. in diameter in a plate 0.04 mm. or less in thickness may be used. These limits are merely given as a guide t o aid in constructing suitable orifices, as such orifices do not necessarily give accurate results, although they can probably be relied on t o within a few per cent. Mercury and water have bee-, t h e tn.0 confining mediums most widely used in effusion apparatus. When using water, t h e gas must be measured saturated with water vapor; a n d under these circumstances, erratic results are often produced b y condensation of water vapor in t h e orifice. This trouble is eliminated by t h e use of mercury. Lower effusion pressures are usually obtained with water; b u t t h e pressure should not be allowed t o fall below 2 in. of water in a n y case, even at t h e end of t h e test. T h e effusion method, although not adapted to securing absolute results, should prove well adapted for control work or other uses where only relative values are desired. It is suggested t h a t t h e apparatus be calibrated for use with a gas of t h e character under test. The method will give results accurate t o I
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or 2 per cent when properly carried out and a somewhat greater precision can be secured b y t h e calibration recommended. Suitable forms of apparatus, operating directions a n d precautions as well as other details will be found in t h e Bureau of Standards, Technologic Paper No. 94. . op
WASHINGTON, D. C.
A SIMPLE IMPROVISED APPARATUS FOR HYDROGEN SULFIDE PRECIPITATION UNDER PRESSURE By AUBREYVAII. FULLER Received April 20, 1 9 1 i
The ordinary method of conducting hydrogen suifide precipitations b y allowing t h e gas t o bubble through t h e solution is a t Once time-consuming, wasteful, a n d uncleanly from both chemical and hygienic standpoints. In order to obviate these objections attending the customary practice, the has constructed the apparatus pictured, joo cc. Kipp generator is provided with a two-holed rubber stopper which carries a one-way stopcock, B , and a small-bore glass t u b e about 3 feet long which terminates a t its upper end in t h e reservoir bulb C, of about I O O cc. capacity a n d whose lower end extends several inches below t h e acid level. T h e gas outlet is fitted with a rubber stopper carrying a two-way stopcock, A . The operation of t h e device is as follows: t h e flask in which t h e precipitation is t o be conducted is closed with a rubber stopper carrying two glass tubes, one of which is provided with a short length of rubber tubing a n d spring pinchcock, t h e other being connected Of rubber tubing to the gas wash-bott1e by (not shown). is Opened and the gas passed through the Cock flask in order t o sweep out t h e air, t h e pinchcock of having been removed' The gas is then shut o f f , t h e pinchcock replaced, and t h e two-way cock A is opened t o t h e air t h e acid level rises almost to the tubulature, when t h e cock is turned SO as t o connect t h e flask with t h e generator, and cock B is closed. T h e acid level is t h u s caused to sink in t h e reservoir of t h e generator proper and t o rise in t h e t u b e as shown in t h e figure. When through using t h e generator, the is Opened in O r d e r t o the cock the apparatus is and is allowed t o remain open
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of
It is evident t h a t with an effective pressure column I meter height a n d employing I : 3 hydrochloric
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