Hoar frost

Creation is wonderful. We admire Nature s work first - from simple things such as the hoar frost that settled overnight on the red maples, to the most intricate creation, repeated thousands of times each day, a human infant brought to term and born [1],... 

Solid Snow, haU, ice, snow pellets, frost pellets, hoar frost, rime Liquid Rain, drizzle, fog deposition... 

The vap. press, curve of solid iodine is indicated by PO, Fig. 16 that of liquid iodine by 00 and the effect of press, on the m.p. of iodine by ON. At the triple point 0 these curves meet. Fig. 18 shows a similar curve for water. The curve PO thus represents the sublimation curve or hoar-frost line OC. the boiling or vaporization curve, i.e. the effect of press, on the b.p. of the liquid. The same phenomenon occurs with water, iodine, etc., and the principle involved is the same as indicated in the law represented by Clapeyron-Clausius equations with respect to the lowering of the m.p. by an increase of press. Consequently, if the vap. press, of iodine be less than that of th,e triple point, the solid does not melt, but rather sublimes directly without melting at the triple point at 114-15° (89 8 mm.) and A. von Richter at 116 1° (90 mm.). According to R. W. Wood, if the condensation of iodine vapour occurs above —60°, a black granular deposit is formed, but below that temp, a deep red film is produced. 

Nitrogen is used to blanket the reaction and the raw materials to stop the absorption of moisture and to prevent oxidation of the product. The dew point of a gas is the temperature at which the water vapor present in the gas saturates the gas and begins to condense. Dew points of below 0°C are sometimes called the hoar-frost point. Industrial-grade nitrogen gas normally is dry enough for use. 

Crystallization from a vapor, which occurs naturally, e.g., in the formation of hoar frost, is employed in sublimation processes and for the condensation of water vapor during freeze-drying. 

A small plant is fixed in position with a wire in such a way that it just remains standing. It is then placed in the glass flask, the bottom of which is covered by 10 g of benzoic acid. A suitable watchglass is placed over the flask (a small porcelain dish can also be used) and the Erlenmeyer flask with its contents heated on the wire net with a small flame. After a short time white hoar frost is seen to be formed on the plant. 

Benzoic acid, known since the 17th century as a sublimation product of gum benzoin, sublimes at 100 °C and is deposited on the surface of the plant as a molecular vapor slight cooling thus leads to the formation of the white hoar frost crystals . 

The specific volumes and the latent heats are generally quite different from the three changes of state, and therefore the slopes of the three curves at the triple point are also different. The difference in the slopes of the tangents of the solid-vapour (hoar frost line), and the liquid-vapour (steam line) curves of water (Fig. 39) is... 

Hence calculate the difference in the slope of the hoar frost and steam lines for water at the triple point. Latent heat of water = 80 L12 = 80 x 42,700 T = 273, v3 - v2 = 209,400 c.c. Substitute these values on the right-hand side of the last equation. Ansr. 0-059. 

Hence, in certain arctic regions, water is always, or nearly always, solid. Even in that state, however, and at all temperatures below 212 , it is always slowly assuming the gaseous form. It is in this way that watery vapour is constantly nsing into the atmosphere from the surface of the sea, of lakes, of rivers, and of the soil which watery vapour, being again condensed into the liquid form, falls back on the earth in the shape of rain or dew, or if frozen, as snow, hail, and hoar-frost. 

And it came to pass, that at even the quails came up, and covered the camp and in the morning the dew lay round about the host. And when the dew that lay was gone up, behold, upon the face of the wilderness there lay a small round thing, as small as the hoar frost on the ground. And when the children of Israel saw it, they said one to another. It is manna for they wist not what it was. And Moses said unto them. This is the bread which the Lord hath given you to eat. 

Condensation of water vapor occurs when the dew point is undershot onto cooler surfaces resulting in a subsequent diffusion process in the direction of the surface (that is dry deposition, similar to surface removal of other molecules than H2O, but these are ad- or absorbed onto the surface - only water can condense into liquid in the earth s climate system). When the temperature is above 0°C, liquid drops (not film) are formed on the surface - most likely on condensation or crystallization centers - and we call it dew. If r < 0 °C, water vapor is transferred into ice on the surface frost) in different sizes and forms, mostly depending on temperature and wind on trees, filigreed ice needles and structures are formed hoar frost). 

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