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American Society of Heating and Ventilating Engineers Guide, 1934 Table 1. Regain of Hygroscopic Materials Moisture Content Expressed in Per Cent of Dry Weight of the Substance at Various Relative Humidities--Temperature, 75 F Classi fication Matebial Description Relative Humiditt--Peb Cent 10 20 30 40 50 60 70 80 90 Aothoeitt Cotton' Sea Island--Roving 2.5 3.7 4.6 5_5 6.6 7.9 9.5 11.5 14.1 Hartshorne Cotton American--Cloth 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10.0 14.3 Schloesing Cotton Absorbent 4.8 9.0 12.5 15.7 18.5 20.8 22.8 24.3 25.8 Fuwa Natural Textile Fibres Wool Silk Linen Australian Merino---Skein 4.7 7.0 8.9 10.8 12.8 14.9 17.2 19.9 23.4 Hartshorne . Raw Chevennes--Skein 3.2 5.5 6.9 8.0 8.9 10.2 11.9 14.3 18.8 Schloesing Table Cloth 1.9 2.9 3.6 4.3 5.1 6.1 7.0 8.4, 10.2 Atkinson Linen Dry Spun--Yarn 3.6 5.4 6.5 7.3 8.1 8.9 9.8 11.2 13.8 Sommer Jute Average of Several Grades 3.1 5.2 6.9 8.5 10.2 12.2 14.4 17.1 20.2 Storch Hemp Manila and Sisal--Rope 2.7 4.7 6.0 7.2 8.5 9.9 11.6 13.6 15.7 Fuwa Rayons Viscose Nitrocellu lose Cupramonium Average Skein Cellulose Acetate Fibre 4.0 5.7 6.8 7.9 9.2 10.8 12.4 14.2 16.0 Robertson 0.8 1.1 1.4 1.9 2.4 3.0 3.6 4.3 5.3 Robertson M. F, Newsprint Wood Pulp--24% Ash 2.1 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6 U. S. B. of S. H. M. F. Writing Wood Pulp--3% Ash 3.0 4.2 5.2 6.2 7.2 8.3 9.9 11.9 14.2 U. S. B. of S. Paper White Bond Hag--1% Ash 2.4 3.7 4.7 5.5 6.5 7.5 8.8 10.8 13.2 U. S. B. of S. Com. Ledger 75% Rag--1% Ash 3.2 4.2 5.0 5.6 6.2 6.9 8.1 10.3 13.9 U. S. B. of S. Kraft Wrapping Coniferous 3.2 4.6 5.7 6.6 7.6 8.9 10.5 12.6 14.9 U. S. B. of S. Leather Sole Oak--Tanned 5.0 8.5 1U 13.6 16.0 18.3 20.6 24.0 29.2 Phelps Catgut Racquet Strings 4.6 7.2 8.6 10.2 12.0 14.3 17.3 19.8 21.7 Fuwa Glue Misa Organic Rubber Hide Solid Tire 3.4 4.8 5.8 6.6 7.6 9.0 10.7 11.8 12.5 Fuwa 0.11 0.21 0.32 0.44 0.54 0.66 0.76 0.88 0.99 Fuwa Wood Timber (Av.) 3.0 4.4 5.9 7.6 9.3 11.3 14.0 17.5 22.0 ForestiP. Lab. Soap White 1.9 3.8 5.7 7.6 10.0 12.9 16.1 19.8 23.8 Fuwa Tobacco Cigarette 5.4 8.6 11.0. 13.3 16.0 19.5 25.0 33.5 50.0 Ford White Bread 0.5 1.7 3.1 4.5 6.2 8.5 11.1 14.5 19.0 Atkinson Crackers 2.1 2.8 3.3 3.9 5.0 6.5 8.3 10.9 14.9 Atkinson Food stuffs Macaroni Flour 5.1 7.4 8.8 10.2 11.7 13.7 16.2 19.0 22.1 Atkinson 2.6 4.1 5.3 6.5 8.0 9.9 12.4 15.4 19.1 Bailey Starch 2.2 3.8 5.2 6.4 7.4 8.3 9.2 10.6 12.7 Atkinson Selatin 0.7 1.6 2.8 3.8 4.9 6.1 7.6 9.3 11.4 Atkinson Asbestos Fibre Finely Div. 0.16 0.24 0.26 0.32 0.41 6.51 0.62 0.73 0.84 Fuwa Silica Gel. 5.7 9.8 12.7 15.2 17.2 18.8 20.2 21.5 22.6 Fuwa Inorganic Domestic Coke Materials Activated Charcoal Steam Activated 0.20 0.40 0.61 0.81 1.03 1.24 1.46 1.67 1.89 jelvig 7.1 14.3 22.8 26.2 28.3 29.2 30.0 31.1 32.7 Fuwa Sulphuric Acid HtSOt 33.0 41.0 47.5 52.5 57.0 61.5 67.0 73.5 82.5 Vlason 48 Chapter 3--Industrial Air Conditioning foodstuffs. Where the physical properties of the product affect value, the question of moisture is of special importance. With increase in moisture content, hygroscopic materials ordinarily become softer and more pliable. Economy of manufacturing, therefore, requires that the moisture content be maintained at a percentage most favorable to rapid and satisfactory manipulation and to a minimum loss of material through breakage. A constant condition is desirable in order that high speed machinery may be adjusted permanently for the desired production with a minimum loss from delays, wastage of raw material and defective product. In the processing of hygroscopic materials, it is usually necessary to secure a final moisture content suitable for the goods as shipped. Where the goods are sold by weight it is proper that they contain a normal or standard moisture content. Air conditioning is important in certain branches of the chemical industry in controlling the temperature of reaction and facilitating or retarding evaporation. The control of moisture content of air supplied to blast furnaces in the manufacture of pig iron also has proved advantageous. The moisture content of an hygroscopic material at any time depends upon the nature of the material and upon the temperature and especially the relative humidity of the air to which it has been exposed. Not only do different materials acquire different percentages of moisture after prolonged exposure to a given atmosphere, but the rate of absorption or drying out varies with the nature of the material, its thickness and density. Table 1 shows the regain or hygroscopic moisture content of several organic and inorganic materials when in equilibrium at a dry-bulb tem perature of 75 F and various relative humidities. The effect of relative humidity on regain of hygroscopic substances is clearly indicated. The effect of temperature is comparatively unimportant. In the case of cotton, for instance, an increase in temperature of 10 deg has the same effect on regain as a decrease in relative humidity of one per cent. Changes in temperature do, however, affect the rate of absorption or drying. Sudden changes in temperature cause temporary fluctuations in regain even when the relative humidity remains stationary. Conditioning and Drying Exposure of hygroscopic materials to an atmosphere of controlled humidity and temperature for the purpose of establishing a specified moisture condition in. the material is called conditioning. Where the desired final moisture content is relatively low, the term drying is usually x used. In any case, control of relative humidity, temperature, air velocity and length of exposure are all of more or less importance. The conditioning treatment may be undertaken in a special -enclosure (conditioning room) or it may be accomplished in the same room and at the same time as some regular manufacturing process. For instance, in the weaving of textiles a high relative humidity is commonly employed to keep the yarn strong and pliable, thus assisting in the weaving process and at the same time leaving the product in a satisfactory condition of regain for commercial reasons. As a rule, commercial regain standards are specified percentages which by test have been found equivalent to a so-called standard atmosphere to 49