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20 Tae Marine REVIEW "TABLE II. , TEMPERATURES AND PRESSURES OF SATURATED AIR. . ; Proportions of Air and Steam by Weight. i ib oven a ie ae . s Air 0-75. Air 1:0, poi | Bitten | seta | steamia | Simmio. | Stamio Inches. Degrees F, Degrees F. Degrees F. Degrees F. Degrees F. 29 (9:5 75 71 67°5 64:5 28 101:5 96:5 924 88°8 85:3 i 27 115 110 105°6 101-7 98°6 26 126 120-2 1155 LS 108-3 25 134 128-4 123°5 119:2 116:2 24 141 135:°2 130°3 125:8 1223 and differ only in the proportion of the constituents. It is true that what is termed air may not have exactly the same composition of atmospheric air, but this is a point of little conse- quence in the present investigation. Table I.--There is, as is well known, a definite temperature corre- sponding to any pressure of saturated steam. This is given by Table I, a column representing vacuum expressed as inches of mercury being added to the usual columns expressing abso- lute pressure and temperature. But there is also a definite and lower tem- perature corresponding to every proportion of air to steam in satur- ated air at every pressure. Table II--This table gives the vacuum and corresponding tempera- ture of airless steam and also of three proportions of air to steam, which are merely chosen to exemplify the principle. It will be seen from these tables and from diagram II that for a given vacuum the fall in temperature of the gaseous mixture which passes through a condenser and on to the air pump changes with the ratio of air to steam in a per- fectly definite manner; and this prop- erty, which has not hitherto received the recognition it deserves, has an important bearing on all investiga- tions on this subject. Diagram I.--I have found this dia- gram of great service in dealing with condenser and air pump problems, and a brief explanation regarding it, and also Table III, which expresses the 'same results in tabular form, may be of interest. The first column in the ta- ble is one of temperatures, and the sec- ond column gives the pressure of water vapor corresponding to these 'temperatures. This relation between the presssure and the temperature of 'steam has already been given in Table iL, and. is, of course, well known. iets & 'Important to note "hat, "if is mixed with another the total pressure is the sum of the presssures of the several constituents, the pressure of each of which may be termed the partial pressure. The partial pressure of the water vapor is dependent only on the temperature; it is unaffected water vapor gas. OF. gases, by the presence of the other gas or gases. The third and fourth columns refer to a vacuum of 24 in. of mercury when the barometer is at 30 in, the corresponding absolute pressure being 2.95 Ibs. per square inch. If air sat. urated with water vapor is at a tem- perature of, say, 50 degrees Fahr., and if its total pressure is 2.95 Ibs., then, as the partial pressure of water va- por at this temperature is 0.17 Ib., the partial pressure of the air must be the difference between these figures, i. e., 2.95 -- 0.17 = 2.78 lbs. per square inch, as given at the top of the third column of the table. The volume of air is, as is well known, dependent upon its temperature and pressure, and can be readily calculated if these data are given. The fourth of the table gives the volume of 1 Ib. of saturated air. This has been calculated from the partial pressure of the air; the volume of the water vapor which occupies the space coincidentally with the air does not affect the result. The DIAGRAM I. VOLUME OF 1 LB. OF "AIR WHICH Is SATURATED WITH WATER VAPOUR At VARIOUS TEMPERATURES AND VACUA. 3000 "2800 2600 2400 2200 2000 '1800 1600 1400 1200 VoLuME IN Cusic Feet. ' _1000 : 8 290-7" 29" 28-5" 28" Inches or Mercury (Saruratep Stream). 27"