Atmosphere humid

Cyanoacrylate adhesives (Super-Glues) are materials which rapidly polymerize at room temperature. The standard monomer for a cyanoacrylate adhesive is ethyl 2-cyanoacrylate [7085-85-0], which readily undergoes anionic polymerization. Very rapid cure of these materials has made them widely used in the electronics industry for speaker magnet mounting, as weU as for wire tacking and other apphcations requiring rapid assembly. Anionic polymerization of a cyanoacrylate adhesive is normally initiated by water. Therefore, atmospheric humidity or the surface moisture content must be at a certain level for polymerization to take place. These adhesives are not cross-linked as are the surface-activated acryhcs. Rather, the cyanoacrylate material is a thermoplastic, and thus, the adhesives typically have poor temperature resistance. 

The use of black cyanide as a fumigant and rodenticide makes use of the atmospheric humidity action that Hberates hydrogen cyanide gas. It can only be used effectively ia confined spaces where hydrogen cyanide builds up to lethal concentrations for the particular appHcation. Black cyanide is also used ia limited quantities ia the production of pmssiates or ferrocyanides (see Iron compounds). 

For measurement of atmospheric humidities the sling psychrom-eter is widely used. This is composed of a wet- and dry-bulb thermometer mounted in a sling which is whirled manually to give the desired gas velocity across the bulb. In the Assmann psychrometer the air is drawn past the bulbs by a motor-driven fan. 

For low-temperature drying, dehumidification of the drying air may be required when atmospheric humidities are excessively hi. ... 

The phosphate coating itself is not protective unless sealed with a protective coating of primer. Sealing is therefore carried out by applying a coat of primer within 12 hours of phosphating, if the atmosphere is dry, or immediately if it is humid. Otherwise the atmospheric humidity may react with the surface and form a film of rust (i.e. ferric oxide (Fe20,))-... 

The Si—X linkages react with water to form a Si—O—Si linkage with the liberation of HX. Typical catalysts include diaryl alkyl tin acylates. Such a curing reaction may be brought about by atmospheric humidity and such rubbers are... 

Theoretically, this system offers the advantages of the thermal cure systems that include fast cure and low temperature processing. However, these systems are sensitive to atmospheric humidity and the possible toxicity of the catalyst may represent an issue. 

Ripening seeds, except where they are enclosed in fleshy fruit, lose water until their water content is in equilibrium with atmospheric humidity and at this stage they contain 5-20% water. The water contents of some seeds can be reduced still further with no adverse effects on viability, rather this can enhance their survival in the dried state (Roberts, 1973). The longevity of seeds in this anhydrobiotic state can be prodigious, lasting for several hundred years (Priestley Posthumus, 1982). 

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

Rainfall is an important criterion of climatic suitability, but precise requirements cannot be stated since its distribution pattern, atmospheric humidity, temperature, and altitude all affect plant requirements. If drainage is adequate, there does not seem to be an upper limit since tea is grown successfully in some parts of Sri Lanka where rainfall exceeds 500cm/yr.19 Long periods of drought are harmful, but are mitigated to some extent by high atmospheric humidity and lower temperatures. 

Some aspects of temperature limitations have already been discussed with regard to cold sensitivity. Mean monthly temperature maxima over 30°C usually result in such low atmospheric humidity that normal growth is impeded. 

As another criterion of purity, the amino acid content of heparins should be determined. This is usually performed by ion-exchange88 or liquid89 chromatographic analysis of hydrolyzates. Reasonably pure heparin preparations contain < 1% of total amino acids, mostly L-serine and glycine. Heparin preparations should also be analyzed for residual solvents, and analytical (as well as biological) data be expressed on a dry basis. (Heparins equilibrated with atmospheric humidity contain up to 15%, or even more, of water.) Unless volatile materials are completely removed or accounted for, elemental analyses of heparin are meaningless. 

It is known that pesticide aerosols, formed when the pesticide steam settles on surfaces of miniscule droplets of water, are much more toxic than the steam form of the same pesticide. This circumstance turned out to be extremely important. Table 2.2 gives an idea of how dangerous pesticides are to humans when we ignore the role of factors such as atmospheric humidity. Data from... 

FIGURE 23 Hydration layer in obsidian. When obsidian is broken into two or more pieces, new surfaces are created. As a new surface is exposed to the environment, water (from atmospheric humidity, rain, or the ground) penetrates the surface gradually, the water diffuses into the bulk and forms hydrated obsidian, that is, obsidian containing water. With time, the thickness of the hydration layer, as such a layer is known, gradually increases the rate of increase is affected by such factors as the vapor pressure of the water in the atmosphere, the environmental temperature, and the composition of the surrounding environment as well as of the obsidian. If the hydration layer reaches a thickness of 0.5 microns or more, it becomes discernible under a microscope, the thickness can be measured, and the age of the surface calculated. The microphotograph shows an hydration layer on obsidian. 

Karp, C. (1983), Calculating atmospheric humidity, Stud. Conserv. 28, 24-28. 

Mixtures with sulfur are unstable, and may ignite some hours after preparation, depending on the state of subdivision and atmospheric humidity [1], Selenium reacts violently with aqueous solutions of the oxidant [2],... 

A flow stream produced from boiling water appears white in color. Similar to cloud in the sky, condensed water vapor shows a white color in the atmosphere. Humid air leads to condensation when nucleating materials are present in the atmosphere, producing a white-colored fog. However, condensed water vapor and fog appear as black smoke when the background is brighter than the foreground. 

It was also found that the coal-dust in the presence of which explosives were tested, varied in ignitability to achieve comparable results therefore coal-dust from the same seam of the same mine must be used. If the same explosive is always used, the ignitability of coal-dust in a given mine may be tested to determine to what extent work in the mine is dangerous. It is obvious that changes of atmospheric humidity also affect the results. 

Atmospheric humidity has a deleterious effect on the stability of powder. Storm [54] reports that a good nitrocellulose powder, which withstood heating at a temperature of 65.5°C for 400 days without marked decomposition, showed evident decomposition in 175 days when stored at the same temperature in an atmosphere saturated with water vapour. Powder which passed the first test subsequently withstood heating for 5 hr at a temperature of 135°C without explosion, whereas powder from the second test exploded at the same temperature after 10 min. 

Because atmospheric humidity must be avoided, the reaction flask is isolated from the atmosphere with drying tubes. Moreover, since the solvent is rarely perfectly anhydrous and will contain traces of water due to its hygroscopic nature, its water content must be measured prior to the determination. The equivalence point of the titration reaction is detected by an electrical method instead of a visual method. The current intensity that passes between two platinum electrodes inserted in the reaction medium is measured (see Fig. 19.10). The reagent, which is a mixture of sulphur dioxide, iodine and a base, is characterised by the number of mg of water that can be neutralised by 1 cm3 of this reagent. This is referred to as the equivalent mass concentration of water, or the titre T of the reagent. 

---