Oxygen barometer

Mantle garnets have Fe /J Fe ratios of 0.02-0.15 (Luth et al, 1990). The Fe " " content in garnet correlates with T of equilibration and Fe203 of the bulk rock (Canil and O Neill, 1996) and is also a useful oxygen barometer for garnet peridot tes (Luth et al, 1990 Gudmundsson and Wood, 1995). 

Ballhaus C., Berry R. F., and Green D. H. (1991) High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen barometer implications for the oxidation state of the upper mantle. Contrib. Mineral. Petrol. 107, 27-40. 

First however, we must examine the evidence for ancient oxygen levels from paleo-oxygen barometers in the ancient sedimentary record. 

OPAQUE MINERALS AS SENSITIVE OXYGEN BAROMETERS AND GEOTHERMO-METERS IN LUNAR BASALTS... 

Two specific examples of the application of thermodynamic methods to geological problems are considered by Wones and Dodge (biotites as monitors of granitic melts) and by El Goresy and Woermann (opaque minerals as oxygen barometers and geothermometers). These are followed by a section on the thermodynamic properties of melts. Following a review of the properties of "simple" molten salts (Kleppa) the nature and properties of silicate melts are considered by Fraser. This is followed by a chapter by Nicholls on the treatment of activities in natural silicate melts and a discussion of trace element behaviour by O Nions and Powell. 

It is readily apparent that oxygen and its compounds are used in quantities that are almost beyond comprehension. Sulfuric acid is by far the leading chemical in terms of production. This compound is used in numerous manufacturing processes both in heavy industry and in specialty preparations and consists of over 65% oxygen. Sulfuric acid is so widely used that it has been stated that the production and use of the chemical provides a barometer for gauging the status of the economy. In the sections that follow, we will explore some of the chemistry of this most important element, oxygen. 

If the barometer reads 751 mm Hg, what are the partial pressures of oxygen and nitrogen in the atmosphere ... 

Introduce into about lo cc. of oxygen free from air. The oxygen may be taken from a gas holder, or it may be prepared from the usual mixture in a test tube, since only a small volume is needed. Unclamp F and press it down upon the stopper, C clamp F again, loosen the Hofmann screw, stand a thermometer in E and allow the whole apparatus to remain undisturbed for at least ten minutes. Meanwhile, read the barometer, and write all necessary notes. Hold the top of the level tube near the eudiometer and raise or lower the level tube, until the water is at the same height in both A and F, then read the volume of oxygen in the eudiometer and the temperature of the water in E. Clamp A again in any convenient position. Record all readings as illustrated below. 

An example will make the formula more intelligible. A student actually found that a mixture of potassium chlorate and manganese dioxide yielded 2192.4 cc. of oxygen when the barometer read 757.8 mm. and the ther-... 

Ten pounds of KCIO3 is completely decomposed and the oxygen evolved collected over water at 80 F. The barometer reads 29.7 in. Hg. What weight of saturated oxygen is obtained ... 

Unfortunately, the barometer can measure only atmospheric pressure. It cannot measure the air pressure inside a bicycle tire or in an oxygen tank. You need a device that can be attached to the tire or tank. This pressure gauge must make some regular, observable response to pressure changes. If you have ever measured the pressure of an inflated bicycle tire, you re already familiar with such a device. 

Kirwan determined the densities of eight gases compared with air = i with fair accuracy, e.g. oxygen= 1-103, hydrogen = 0-0843, fixed air= 1-500, ammonia = 0-600." He gives a table of the weights in grains of 100 cu. in. at 55° F. and 29-5 in. barometer ... 

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