Part 10 (1/2)

In the thermo-electric pyrometer of Le Chatelier, the wires used are platinum and a 10 per cent alloy of platinum and rhodium, enclosed in porcelain tubes to protect theases The couple with its protecting tubes is called an ”eleths to suit conditions

It is not necessary for accuracy to expose the whole length of the element to the temperature to be measured, as the electromotive force depends only upon the te tube and that of the cold end of the elealvanoth of the wires leading to it simply alter the resistance of the circuit, for which allowance es of the there of tes, and the ease hich observations can be taken Its disadvantages are high first cost and, in so Points of Metals--The approximate temperature of a furnace or fluecertainpoints are known The more co points differ by 100 to 200 degrees Fahrenheit, and by using these in order, the te points of some two of them This method lacks accuracy, but it suffices for deters are satisfactory

The approxi points of certain metals that iven in Table 8

Radiation Pyrometers--These are similar to thermo-electric pyroiven out by the hot body fall on a concave ht to a focus at a point at which is placed the junction of a thers are obtained from an indicator similar to that used with thermo-electric pyrometers

Optical Pyrometers--Of the optical pyrometers the Wanner is perhaps the most reliable The principle on which this instruht eht, in this case a two-volt osmium lamp

The lamp is placed at one end of an optical tube, while at the other an eyepiece is provided and a scale A battery of cells furnishes the current for the laht appears, divided into distinct halves of different intensities

Adjustmentis then taken from the scale The temperatures are obtained fros For standardizing the osmium la the optical tube

TABLE 8

APPROXIMATE MELTING POINTS OF METALS[8]

+-----------------+------------------+ | Metal | Terees Fahrenheit| +-----------------+------------------+ |Wrought Iron | 2737 | |Pig Iron (gray) | 2190-2327 | |Cast Iron (white)| 2075 | |Steel | 2460-2550 | |Steel (cast) | 2500 | |Copper | 1981 | |Zinc | 786 | |Antimony | 1166 | |Lead | 621 | |Bismuth | 498 | |Tin | 449 | |Platinum | 3191 | |Gold | 1946 | |Silver | 1762 | |Aluminum | 1216 | +-----------------+------------------+

Deterht--As a furtherapproximately the temperature of a furnace, Table 9, compiled by Messrs White & Taylor, iven temperature is approximately the same for all kinds of combustibles under similar conditions

TABLE 9

CHARACTER OF EMITTED LIGHT AND CORRESPONDING APPROXIMATE TEMPERATURE[9]

+--------------------------------------+-----------+ | Character of Erees | | | Fahrenheit| +--------------------------------------+-----------+ |Dark red, blood red, low red | 1050 | |Dark cherry red | 1175 | |Cherry, full red | 1375 | |Light cherry, bright cherry, light red| 1550 | |Orange | 1650 | |Light orange | 1725 | |Yellow | 1825 | |Light yellow | 1975 | |White | 2200 | +--------------------------------------+-----------+

THE THEORY OF STEAM MAKING

[Extracts froe H Babcock, at Cornell University, 1887[10]]

The chemical compound known as H_{2}O exists in three states or conditions--ice, water and steam; the only difference between these states or conditions is in the presence or absence of a quantity of energy exhibited partly in the form of heat and partly in molecular activity, which, for want of a better name, we are accustomed to call ”latent heat”; and to transform it from one state to another we have only to supply or extract heat For instance, if we take a quantity of ice, say one pound, at absolute zero[11] and supply heat, the first effect is to raise its terees above the starting point Here it stops groares from ice to water, and e have added sufficient heat to have rees hotter or a terees Fahrenheit's thermometer, it has all become water, at the sae, narees by Fahrenheit's scale Let us still continue to add heat, and it will noarh at a slower rate--that is, it now takes about double the quantity of heat to raise the pound one degree that it did before--until it reaches a terees absolute (assu that we are at the level of the sea) Here we find another critical point However much more heat we may apply, the water, as water, at that pressure, cannot be heated any hotter, but changes on the addition of heat to steah to have raised the terees by Fahrenheit's ther for the ed since it became water), that it has all become stearees, at which the water began to change Thus over four-fifths of the heat which has been added to the water has disappeared, or become insensible in the steam to any of our instruments

It follows that if we could reduce steam at atmospheric pressure to water, without loss of heat, the heat stored within it would cause the water to be red hot; and if we could further change it to a solid, like ice, without loss of heat, the solid would be white hot, or hotter thanassumed, of course, that the specific heat of the water and ice remain nor point

After steam has been forain at a much faster ratio to the quantity of heat added, which ratio also varies according as we maintain a constant pressure or a constant volume; and I am not aware that any other critical point exists where this will cease to be the fact until we arrive at that very high temperature, known as the point of dissociation, at which it becoases