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ds^'10 Part Two, Meteorology and Physics of Hygiene. The Barometer,, The atmosphere exerts a pressure on the surface of the earth equal to the height of the column of air above any part of the surface multiplied by the moan density of such a column. Such a pressure may be expressed in pounds per square inch or in Millibars - which is only another way of moasuring the same pressure. Until recent years it has been customary to refer to the pressure of tho atmosphere as the Height of the Barometer, in inches or in millimetres of mercury, which means the height of a column of mercury equal in weigit to a column of air of equal cross section and reaching up to the upper limits of the atmosphere. The scientific objection to this method is that the pressure of a given column of mercury varies with its temperature, so the height of a column of mercury does not always represent tho seme pressure* A ’Bar’ is a unit of pressure independent of the properties of any liquid, such as mercury. It is based on the Centimeter-Gramme-Second system. A Dyne is the unit of force— it is the »push{ required to accellerato a mass of one gramme at the rate of one centimeter per 3econd, per second. A Bar is tho name given to a forco of one million dynos acting over an aroa of one squaro contimoter. The Millibar, or l/lOO055k>f this pressure ia the one used now for meteorological work. Mean Barometric Pressure is taken to be 1,760 mm. or 29*9 inches of mercury, or 1,013 millibars, or 14-7 lbs. per square inch. 1,000 millibarj 29*53 inches Hg. or 750*1 mm„ Standard Barometers are of two kinds, the Fortin and the Kew. In the Fortin Barometer a true scale is provided to measure the height of the column, the bottom end of the scale being represented by a datum or fiducial point to which the surface of the marcury in the cistern has to be adjusted. This adjustment should be made every time the instrument is read. In the Kew barometer the scale is contracted to allow for the lowering of the surface of the mercury in the oistem with the rising of that in the tube. No adjustment is necessary. Both instruments are, however, liable to index errors the amounts of which are stated in National Physical Laboratory certificates. ill barometer, reading? recorded for meteorological purposes have to be recorded in Millibars, or in Inches or Millimeters of mercury. If the two last named notations aro used these readings must bo reduced to thoso of a barometer at sea level and at 32°F. Millibras, of course, need no such qualifications but it must bs noted that although this is so theoretically, millibars have to be measured with a mercury barometer in practice so just tho same corrections have to bo made to roduce its readings to standard temperature and height at sea-level. Corrections for the Barometere Temperature (based on tho coefficients of expansion of mercury and brass; Ehe scales are made of brass). o 0 e.g. If a barometer reads 765 mm. at 68 F., its reading, corrected to 32 F, will work out to 762*6 mm, - a significant difference. Height above Sea Level,, Tables are available for this, as for the other corrections. The barometer drops, roughly, 1/10 inch for a rise of 100 feet. THESE W 0 CORRECTIONS ARE OF GREAT IMPORTANCE. Capilarity, or the difficulty of the convex meniscus in rising up the narrow glass tube which is unwettod* Index - (These last two can be allowed for by the calibration chart). Latitude. The force of gravity veries slightly in difforent parts of tho world. This is a very small offoct*

Transcript of ds^'10 - historicalpapers.wits.ac.za

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ds^'10Part Two,

Meteorology and Physics of Hygiene.

The Barometer,,The atmosphere exerts a pressure on the surface of the earth equal to the

height of the column of air above any part of the surface multiplied by the moan density of such a column. Such a pressure may be expressed in pounds per square inch or in Millibars - which is only another way of moasuring the same pressure.

Until recent years it has been customary to refer to the pressure of tho atmosphere as the Height of the Barometer, in inches or in millimetres of mercury, which means the height of a column of mercury equal in weigit to a column of air of equal cross section and reaching up to the upper limits of the atmosphere.The scientific objection to this method is that the pressure of a given column of mercury varies with its temperature, so the height of a column of mercury does not always represent tho seme pressure*

A ’Bar’ is a unit of pressure independent of the properties of any liquid, such as mercury. It is based on the Centimeter-Gramme-Second system. A Dyne is the unit of force— it is the »push{ required to accellerato a mass of one gramme at the rate of one centimeter per 3econd, per second. A Bar is tho name given to a forco of one million dynos acting over an aroa of one squaro contimoter. The Millibar, or l/lOO055k>f this pressure ia the one used now for meteorological work.

Mean Barometric Pressure is taken to be 1,760 mm. or 29*9 inches of mercury, or 1,013 millibars, or 14-7 lbs. per square inch.

1,000 millibarj 29*53 inches Hg. or 750*1 mm„

Standard Barometers are of two kinds, the Fortin and the Kew. In the Fortin Barometer a true scale is provided to measure the height of the column, the bottom end of the scale being represented by a datum or fiducial point to which the surface of the marcury in the cistern has to be adjusted. This adjustment should be made every time the instrument is read. In the Kew barometer the scale is contracted to allow for the lowering of the surface of the mercury in the oistem with the rising of that in the tube. No adjustment is necessary. Both instruments are, however, liable to index errors the amounts of which are stated in National Physical Laboratory certificates.

ill barometer, reading? recorded for meteorological purposes have to be recorded in Millibars, or in Inches or Millimeters of mercury. If the two last named notations aro used these readings must bo reduced to thoso of a barometer at sea level and at 32°F. Millibras, of course, need no such qualifications but it must bs noted that although this is so theoretically, millibars have to be measured with a mercury barometer in practice so just tho same corrections have to bo made to roduce its readings to standard temperature and height at sea-level.

Corrections for the Barometere

Temperature (based on tho coefficients of expansion of mercury and brass;Ehe scales are made of brass).

o 0e.g. If a barometer reads 765 mm. at 68 F., its reading, corrected to 32 F, willwork out to 762*6 mm, - a significant difference.

Height above Sea Level,,Tables are available for this, as for the other corrections. The barometer

drops, roughly, 1/10 inch for a rise of 100 feet.

THESE W 0 CORRECTIONS ARE OF GREAT IMPORTANCE.

Capilarity, or the difficulty of the convex meniscus in rising up the narrowglass tube which is unwettod*

Index - (These last two can be allowed for by the calibration chart).

Latitude. The force of gravity veries slightly in difforent parts of tho world. This is a very small offoct*

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SYNOPSIS. London School of. Hygione and Tropical Medicino.

METEOROLOGY AND THE PHYSICS OP AIR AND WATER, -----------AS related’" t'6" iflfGim ------

FIRST LECTURE.Tho studios In olomontary physics, made by tho

medical student In his earlier days, are rocalled to him to show thoir immediate bearing upon the physiological needs of man. Tho dynamic heat equilibrium which must be maintained in tho body: heat produced by motabolic processes must be disposed of by Conduction, Convection, Radiation and Evaporation.

Correlations of dry bulb tomperaturos and standards of civilisation throughout tho world, in relation to tho temperaturo found to promote tho greatest spocd of biological functions (Elsworth Huntington).

Suggestion that certain classes of disoases aro associated with a high "climatic drive" and that others aro more prevalent whore weather conditions arc more conducivo to case (C.A.Mills).

Thermometry. How outdoor temperature readings should bo taken to bo of a real meteorological value.Stevenson Screen. Maximum and Minimum Thormomotors of mercury and alcohol. Six’s Thermometer. Black Bulb Radiation Thormometor. Ground Thermometer. Fahrenheit and Centigrade scales.

Hygrometry. Introduction - the moisture present in tho air. Definitions of Absolute Humidity, Relative Humidity and Dew Point, the real significances of these torma .- How to dctcrmino these values: In tho laboratory, in tho field. The Carrier Chart and how it is constructed; the Meteorological Office Tables, and why these should only be used with the Ventilated Psychromctcr and Mason's Hygrometer, respectively.

SECOND DAY LECTURE, FOLLOWED BY TUTORIAL.Hygrometry (Continued). Examples from actual

data worked out and the expression in Absolute Humidity, Relative Humidity, Dew Point and Saturation Deficiency.(In this and subsequent tutorials following the students use all types of practical and dew point instruments and record thoir observations on the board).

The Baromotor. The significance of the Ocean of Air at the “bottom of which wo livo. How to moasuro the prossure of tho air. Experiment showing the principlo of a mercury barometer. Standard barometers: Kcw, Fortin, and their corrections. Anaeroids. The Vernier and its theory. Millibars and other barometric scalos.(Students have ample opportunities during tho tutorials following this and other lectures to loam how to take barometer readings).

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SYNOPSIS.

METEOROLOGY AND THE PHYSICS OP AIR AND WATER. AS RELATED TO HYGIENE (ContinuedV.----

THIRD DAY LECTURE.Tho olomontary laws connecting the volumo, pressure

and temperature of a 'perfect* gas.Boyle »s Law. The true significance of Absolute

Pressure and its relation to such physiological phenomena as are found in diving,

Charle--'3 Law. The true significance of Absolute Temperature, The correction of gas analysis samples in respect of Barometric Pressure and Temperature. Working of examples by the combined laws.

Graham's Law of Gas Diffusion and its importance in problems of disinfection.

Meteorolop̂ r. Variations of atmospheric pressure. Cyclones and Anticyclones. (Students are shown a working model to explain the complex movements of the winds in a moving cyclonic depression).

Terms used In Meteorology, Synoptic Charts and Daily Weather Reports - how they are made and how to interpret them. Admiral Fitzroy?s Weather Rules. The Beaufort Scale, as used by the Admiralty. ’’Rain Fronts" and their formation over the British Isles, Clouds, their appearance and names. Fogs and Mists, how and when they are formed#

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ATMOSPHERIC POLLUTION.I. PROPERTIES OF SMOKE AM) DUST-CLOUDS.

1. Large volume occupied by small amount of solid matter.2. Large surface aroa exposed by finoly divided mattor,3. Groat chamical activity,4. Proportion of particles oloctrioolly charged.5* Groat stability of fine dust-clouds.

■ or TM-- .II. SMOKE POLLUTION.

Charcoal, coke and anthracite are over 90$ carbon and do not cause smoke. Bituminous coals have 20$ to 40$ volatile mattor. incamploto combustion allows emission of solid oarbon or soot, w

Example:- Methane. CH^ + Og “ C + SHgO.Ordinary constituents of smoke are carbon, tar, ash, steam, sulphur and grit,

t

Cauaos of smokei-1. Cooling of gases before combustion is complete.2. Insufficient supply of air for combustion.3. Bad stoking. Fuel should be supplied frequently and in small amounts.Domostic fires cause greater part of smoke in town atmospheres and practicably

all the tar which gives to the 3moke its adhesive properties.Effects of smoke;- '1. Economic loss:- waste of fuel; cost of cleansing; damago to buildings

and vegetation; additional illumination (loss of light due to smoke in New York averaged 30$ at 8.30 a.m. and 16$ at 1.30 p.m. Loss in I*eds is about 40$).

2. Effects on Health.Loss of sunshine. Increase of respiratory diseases in foggy weather. Measuremant of Smoke Pollution.1. Deposition measured by standard deposit gauge.2, Suspended""impurities measured by dust filter or some kind of dust counter.

III. INDUSTRIAL DUSTS.Dusts and their effects (after Collis).

( Viable (Pathogenio and non-pathogonic (Infectious ( ( microbes and moulds (Diieasos,

Organic (( Dead (Protoins..................... Asthma(Carbohydrate ,.•••••••.•••«.. Harmloss

( Insoluble (Large particles.............. Bronchitis( (5 microns and less*.......... pneumonia

Inorganic (( (Lead and toxio motals........ General poisoning( (Silica.. ............... Silicosis and 1aber-( Soluble (Some s i l i c a t e s , ...•••••. ABbostosis^culosis.( (Calcium compounds.,,,...Harmless

A rocont investigation suggests that silioa aots as a general body poison.Estimation of PustB.

' Various methods permit ofj-(a) Particulste counts, with or without size distribution,(b) Estimations as milligrsms per cu, metre of air.

Provention of dust hazard.1 Proper exhaust arrangements.

Wet drilling.Control of blasting.Dust traps. ,Wearing of respirators.

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JL<*ndon School of Hygiene and Department of Industrial Physiology. Tropical Medicine.

HEATING AND VENTILATION

Instruments for Measuring Warmth: Scales of Warmth: Comfort Standards:

If the warmth of an environment is to be completely specified, the temperature, humidity and velocity of the air, and the temperature of the surrounding surfaces (walls, etc.) must he taken into account. Certain instruments and scales of warmth allow for the effects of combinations of these factors.I. THE KATA THERMOMETER.

The standard instrument has a cooling range of from 100°F. to 95°P. Factor divided by cooling time gives the cooling power. which is a measure of the rate of heat loss (milli-calories) per sq. cm. of the bulb area per second. The kata may be used as a dry-bulb or as a wet-bulb instrument. The dry kata cooling power is influenced by radiation and convection, and the wet kata cooling power is also influenced by evaporation. At ordinary temperatures the dry kata is the more important, but at high temperatures the wet kata becomes of increasing importance. A high temperature kata which cools from 130°- 125°F. has been devised for use in very warm environments.

From the dry kata cooling power and the air temperature, the air velocity can be readily calculated. In the presence of much radiant heat a silvered kata should bo used for this purpose.

Ah objection to the kata as an index of comfort is that because of its small size it is very susceptible to convection effects and consequently makes a proportionately less allowance for radiation.II. THE EUPATHE0SC0PE AND EQUIVALENT TEMPERATURE.

The eupatheoscope is a hollow, blackened, copper cylinder 22 ins, high and 7% ins. in diameter, which is heated electrically.Its surface temperature is kept nearly constant at 75°F., which is the average surface temperature of the clothed human body in calm air at 65 F. A coil carrying a portion of the heating current is wound round the bulb of a thermometer, the stem of which lies on the outside of the cylinder. The temperature of this thermometer thus depends on the heat input, and gives an index of the combined effects of air temperature, air movement and radiation* .The , / readings are given on a scale of equivalent temperature,(

Definition: The equivalent temperature of an environment is that’ temperature of a uniform enclosure (i.e. air and walls at same temperature) with still air, in which a sizable black body (i.e. a body of a size of the same order as that of the human body) would lose heat at the same rate as in that environment. The scale does not extend beyond 75°F.Thus, for example, whenever the instrument reads 65°F. it is losing heat at the same rate as in a still air enclosure at 65°F,

The equivalent temperature can be estimated by using special kata thermometers, one silvered and one blackened, called oupatheometers, or from globe thermometer readings,(see be low)',

III. EFFECTIVE TEMPERATUHE. ^ ̂ ̂A scale widely used in the U.S.A. Measures effects of

temperature, humidity and movement of the air, but neglects radiation. Defined as "that temperature of saturated, motionless air whioh would produce the same sensation of coolness as that produced by the combination of temporature, humidity and air motion under observation'. Neglect of radiation effects is a serious drawback.

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IV. GLOBE THERMOMETER,A blackened, hollow coppor sphere, 6 ins. in diameter

containing on ordinary thermometer with its bulb at the centre of tho sphcro. Its temporature depends entirely on the environment, and lies betwoon the temperature of the air and tho mean temporature of the surroundings (walls, etc.).

Prom the air temperature and air velocity, plus the reading of tho globe thermometer, one can estimate (a) the moan temporature of the surroundings, or the mean intensity of radiation, and (b) the equivalent temperature.V. COMFORT STANDARDS.

In appropriate circumstancos any of these measures will bo a good index of tho sonsation of warmth, but equivalent temporature is tho most generally applicable.

In ordinary rooms, where there is little air movomont, the globe thermometer reading is a good index - even with much radiant heat. Provided there are no appreciable radiation effects, tho effective temperature scale can be used.

Where there is little air movement and no strong radiation (e.g. in rooms heated by hot water pipes) the air temperature itself is a good enough guido.

It has been shown that under English summer conditions dry kata readings of 3 or under are associated with complaints of overheating and 'airlessness1 whilst with dry kata cooling powers of 4 up to 7 there will be few complaints. Where it is not possible to reduce the air temperature of enclosures owing to manufacturing processes, the kata cooling power or the equivalent temperature or the effective temperature, and the comfort of tho occupants, can bo improvod by suitably stirring tho air to prevent stagnation.

In this country under winter conditions, for persons who are ordinarily clothed and only slightly active tho most comfortable warmth is an equivalent temperature of 62°F. In the appropriate conditions, this degree of warmth is given by a globe thermometer reading, or an air temperature of 65°F., or an effective temperature of 61°F., or a dry kata cooling power of 6. Acclimatisation to cooler or warmer conditions materially influence individual reactions to warmth conditions.VI. REFERENCES.

(a) On Kata thermometer:-Sill, ¥ ,R ,'c'. Spoc • Repts . 32, 52 and 73.Bedford and Warner (1933): J. Hyg. vol.33, p.330.Angus (1936): J, Inst. Heat & Vent. Eng. (In Press).

(b) On Equivalent Temperature:-Dufton (1932 ): Building Research Board Tech* Paper No.13

H (1933): J. Hyg. vol.33, pp.349 and 474,Bedford and Warner (1934): J. Hyg. vol. 34, p.458.

(c) On Effective Tomperature:-Yaglou (1926):"J. Industrial Hyg. vol. 8, p.5.

(d) On Globe Thermometer:-Vernon (1932): J. Industrial Hyg. vol.14, p,95.Bedford and Warner (1934): J. Hyg. vol. 34, p.458.

(e) On Comfort Standards:*-" Vernon, Bedford

and Warner(1926): Industrial Fatigue Res. BoardReport No, 35.

Bedford (1036): Industrial Health Res. Board Report(In Press)•

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No.

ATMOSPHERIC CONDITIONS AND THE INDUSTRIAL WORKER.

I. THEORIES OF VENTILATION.Old Theories:- 111 effects of crowded rooms said to bo duo to

(a) Excossivo amount of C0S, or(b) Presence of organic pbiaon exhaled from body.

Modern Physical theory.Such ill effects can be traced to physical factors; warm, moist,,

stagnant air.

II. FACTORS INFLUENCING THERMAL COMFORTt-Subjective factors.

1. Hoat-balance of tho body (hoat-production and hoat-loss).2. Skin temperature.3. Clothing.4. Susceptibility to radiant heat?

Environmental factors.. £ £ * * * - <1. Air temperature )8. Air velocity ) Convection.3. Temperature of surrounding surfaces - radiation..4. Air humidity - ovaporation.5. Ionisation.

III. T̂KTHQDS OF ASSESSING ENVIRONMENTAL FACTORS.1, Measurement of single factors,.

(a) M r temperature and humidity - by hygrometer,(b) Air velocity - conveniently measured by means of Kata thermometer..(c) Radiation by moans of radiation thermopile, or by use of ordinary

and silvered Kata thermometers,(d) Ionisation — by some form of ion-counter,

2. single measures of combinations of environmental conditions,(a) Kata thermometer, dry and wet.(b) "Effective” temperature scale,(c) Eupatheoscopo - "equivalent" tomporaturo,

IV. EFFECTS OF THERMAL CONDITIONS ON EFFICIENCY.Many investigations have shown that working capacity is diminished at high

temperatures, and in work which needs much manual dexterity, tho level of perfor­mance falls if the subject is unduly cold. Mass statistics from various indus­tries show a diminished output in hot weather,

V. ACCIDENTS AND THERMAL CONDITIONS,— Q In munition works the accident frequency was loast at a tcmporaturo of 65

to 69°F, Colder or warmer conditions led to more frequent accidents. In mines also, accidents woro found to bo more numorous in tho hotter soams,

VI. SICKNESS AND ATMOSPHERIC CONDITIONS.Various investigations have shown that absenteeism on account of sickness is

related tp- atmospheric conditions,

f rVarious reports of the Industrial Health Research Board and of the Medical

Research Council,Various papors in tho Journal of Industrial Hygiono,

v Valuablo summaries of papors on this subject are to bo found in tho Bullotin of Hygiene, and in the Abstracts section of the Journal of Industrial Hygiene,

REFERENCES.

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APPLIED PHYSIOLOGY L.S.H. and T,M«

Nutrition: SALTS: VITAMINS WATER.

SALTS. The following inorganic constituents must "bo present in the diet.Sodium phosphorusPotassium ChlorineCalcium SulphurMagnesium Iodine Iron

Most of th6se elements are automatically supplied in any average mixed diet associated with the Protein and Carbohydrate Foodstuffs in milk, fruit and vegetables.

VITAMINS.

Vitamin A:

Normal growth, life, reproduction and resistance to disease can only be maintained if the following Accessory Food Factors or Vitamins are present in the diet.

Connected with Growth and Resistance to infection, present in:- Cod Liver Oil, Liver and Dairy produce.

Vitamin D: Anti-rachitic factor. Normal growth and calcifioation of bone. Present in:- Cod Liver Oil, Liver and Dairy Produce. Irradiated Ergosterol: Sunlight.

Vitamin B: Bx. Antineuritic Factor. Deficiency related to beri-beri.Ba. Deficiency related to pellagra.Both Bx and b 2 are necessary for growth, present in:- Yeasts, Germ of Cereals, Fresh Meat and Dairy Produce.

Vitamin Ci Antiscorbutic factor. Present in:- Orange and Lemon juice, Fresh Meat, Fruit and Vegetables. Germinated Seeds.

Vitamin E: Related to normal reproduction. Present in:- Butter, Oil from Wheat Germ, Lettuce Leaves,

WATER, Water is an essential requirement of the body. It is the----- medium in which the chemical reactions occurring inside the

body take place* It renders food soluble; it helps in temperature regulation, in maintaining the viscosity of the blood constant, etc.

Water balance sheet for sedentary worker.Inoomo Output

Drink 1,450 cc. Urine 1,500 cc.Food 800 cc. skin 600 cc.Oxidation 350 cc. Lungs 400 cc.

Faecos 100 cc.

8,600 cc. 2,600 cc.

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Collection Number: AD843

XUMA, A.B., Papers

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