VOL IV. No. 8.

Hygiene.

BY ALFRED CARPENTER, M.D., M.R.C.P. (LOND.),
Chairman of the Council of the Sanitary Institute.
AIR : ITS HYGIENIC PROPERTIES.
(Continued.)

Ozone is oxygen in a condensed state; it is always present in the fresh air, but is absent in the close air of rooms, and not always found out of doors in large towns, and but seldom in great cities. It may be found on one side of a town on one day, and absent in the same place on the next, simply because the wind has changed to the opposite quarter. We do not know how it is formed in nature. It may be evolved by electric action, or oxygen, set free by various agencies may take the form of ozone when first eliminated. It has a peculiar smell. It is able to set iodine free from potassium iodide, by which its presence may be recognised with certain limitations. The smell which is observed when an electric machine is worked is that of ozone. It is half as heavy again as oxygen; that is, 2 vols. of ozone form 3 vols. of oxygen. It is an important agent in all sanitary operations; probably produced by motion, and set free by growing plants, and by other chemical actions, it assists to diminish the incidence of disease-producing agencies. It seizes upon the so-called albumenoid ammonia compounds, oxidizes them, and renders them comparatively harmless. It is found near to the surface of the sea, probably in some way connected with the physical changes which are always going on at the surface of the water, when that water is in constant movement. Its presence in the air on one side of a great city and its absence in the other, arises from its being used up in oxidizing the organic matters which have been discharged into the air by the decomposition of dead matter in the city. Thus ozone is never found where such decomposition is going on, when that is in excess of the quantity of ozone produced. Its production is associated with many of the processes which are in vogue for the purification of the atmosphere. It may be simply oxygen in an electrified form, intimately associated with the molecular state of the gas, but chemists are not thoroughly agreed as to its nature. Those who wish for more information upon this agent

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and its associations should study Dr. Cornelius Fox's important work on Ozone and Antozone, which gives a complete account of the 'when, where, why, and how is Ozone observed in the atmosphere.'

Chemical Examination of the Air.-The presence of O is easily shown by the eudiometer, as is explained in every work upon elementary chemistry. N is found when P has been burnt in a receiver containing a measured quantity of air, and so placed over water that the fumes of the P,O, which result from the union of the O with the P will be absorbed by the liquid. Onefifth of the original volume disappears, and N remains with the minute quantity of CO, which is always present in the air. The presence of CO, is shown by passing a measured volume of air through a solution of lime or baryta water. The volume of air being known, and the quantity of carbonate of lime or baryta which has formed in the solution being ascertained, the percentage of CO, in the air experimented on will be easily worked out, but the process is very delicate and requires close attention to minute detail. The watery vapour varies with the temperature; a purely dry air is seldom met with ; a cubic foot of air may have from one grain up to 10 grains of water diffused through it. The watery vapour may be collected by passing a given quantity of air through calcium chloride. The increase of weight of the latter after the operation will give the amount of watery vapour.

NH, is collected by drawing the air by means of an aspirator through wash-bottles containing a measured quantity of water which is perfectly free from NH3 and by then determining the free and albumenoid NH2 by Wanklyn's method. This process should be studied by all who are engaged in sanitary work. It is set out in full in Water Analysis,' by J. A. Wanklyn, to which I must refer the reader, as space prevents me giving all the details.

Ozone is indicated by test papers which have been dipped in solution of KI and starch. The paper should be exposed for a definite time, if possible, with exclusion of light. The quantity of ozone is said to be made out by observing the depth of blue colour produced and comparing it with a scale which has been previously assessed at its value. The conclusion may be erroneous, as nitrous acid (NO3) will affect the test paper when present to the extent of the volume of the air, and a minute portion of the

of

iodine set free never acts upon the starch, as it is immediately volatilized or oxidized. These agencies can, however, be averaged and allowed for.

Microscopical Examination of Air.-There are a great number of materials found suspended in the air, organic as well as inorganic. The observations which have been recently made out connected with the magnificent sunsets of 1883 will be a case in point, for it seems to be established beyond refutation that the minute dust from volcanic action reaching the upper regions of the air, continue to circulate round the earth for long periods before the whole is again deposited upon its surface. These particles allow of refraction, and so produce the colours which have been so manifest at eventide. The matters suspended in the air may be collected by arranging a small funnel with a microscopical slide below its point, which has been moistened with glycerine. The end of the funnel must be with the slip of glass enclosed in an airtight chamber, such as is provided by Pouchet's aeroscope; from this a small glass tube passes out and is connected with an aspirator; as the water runs away, the air impinges on the slide, any solid particles which it may contain are arrested by the glycerine, or the air may be drawn through pure distilled water and the resulting deposit examined after it has settled. The collected inorganic particles are found to be particles of silica, calcium salts, and iron oxides. If the water is slowly evaporated, chlorides are found, especially if the specimen has been collected near the sea. A large number of living cells and the debris of dead creatures are sometimes arrested. Ehrenberg collected more than 200 forms of rhizopods, tardigrades, and anguillulæ, micrococci, bacteria, spores of fungi, varying with the season of the year; pollen from flowers, starch grains, dried cells of all kinds, such as those of pus and mucus, epidermic scales both animal and vegetable. It has been shown how very minute particles are made visible by a ray of light passing through a dark room, as any one may see for himself. The suspended matters which are found in enclosed spaces are indicative of the actions which are taking place in those spaces. The dust from the ward of a hospital contains just those particles which we might expect to find there-germs which will propagate disease if carried to a favourable site. It is probable that cattle diseases, such as pleuro-pneumonia and foot-and-mouth disease, are spread in this way, whilst small pox, scarlatina, and measles, may owe their diffusion to a similar source; and erysipelas may be spread from case to case by currents of air, carrying with them the spores which are able to create the disease.

Some of these spores may be dried and retained as dust for long periods; when moistened with water they revive and are able to propagate their species or set up the disease anew. The air of mines, workshops, and factories are seen to contain particles sufficiently numerous to set up diseases in the lungs, etc., of the work people employed, whilst in some occupations, such as woolsorters, disease so often arises that it becomes recognised by the name of the occupation of the persons attacked. Bacilli of various kinds are cultivated in the raw material which is being worked into a manufactured article, and the hands employed may suffer seriously from the effects of the cacozyme.

Sewer air may propagate disease by carrying the germs and discharging them by ventilators into the

open street, to the possible injury of the passengers. When sewers smell, there is a fault somewhere, which should be rectified by a removal of its cause, not, as is too often the case, simply by closing the opening from which the smell comes. The air of vaults may be shown to contain injurious particles, and organic matter has been arrested in air from marshes which is supposed to be the cause of intermittent fever. It is certain that microscopical examination of air will, in the future, be a necessary part of the work of a disease preventer.

THE REMOVAL OF WASTE AND IMPURITIES.

The waste which arises from the mere act of living, the impurities which necessarily follow from that act, and which must be incessantly removed, are some of the most difficult problems of sanitary work in great towns. The impurities consist of defilements of the air which have to be reduced to the lowest amount by natural ventilation if possible, and if natural ventilation is not equal to the work, then by artificial means. They also consist of the natural refuse from sinks, baths, and closets, and are intimately associated with the formation of drains and sewers, as well as of traps and means for ventilating the same. The removal of such impurity invites a question as to the transit of sewage by the dry method or by water carriage. It entails a consideration also of sewer gas and septic organisms generally, as well as the use of antiseptics, deodorisers, and disinfectants. We will consider each of these under its separate heading.

Ventilation. The means whereby air is set in motion may be considered under two heads. 1. Natural. 2. Artificial.

Natural Ventilation. This is promoted by changes in temperature and moisture; by the winds; and by the law which causes the diffusion of gases through space. The changes in temperature and moisture are such as arise from the unequal weight of the air when heated by the sun's rays or chilled by cold blasts from distant regions. Tables are given in scientific works by which calculations are made as to velocities produced by dif ference of temperature, and rules are laid down for making the calculations. In ordinary cases the difference in pressure cannot be obtained by direct observation, but must be gathered by finding out the difference of temperature of the outer and inner air of the room under consideration. A formula is given by Prof. de Chaumont, which is as follows: The height from the aperture at which air enters to that from which it escapes multiplied by the difference of temperature between the outside and inside and divided by 491.' This will give the actual movement produced by unequal weight of air. The 491 indicates the fraction which is called the co-efficient of the expansion of gases. If Fahrenheit is the thermometer employed, it should be remembered that the volume of a gas expands times for every degree of risen temperature, or if the Centigrade is used.

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Another rule may also be remembered with advantage, viz., that air rushes into a vacuum with a velocity which a heavy body would acquire in falling from a height of five miles, viz., 1,304 feet per second. The velocity in feet per second of falling bodies is equal to nearly eight times the square root of the height through which they have fallen, and fluids pass through an orifice in a partition with a velocity which is equal to that which a body attains in falling through a height

equal to the difference in depth of the air on the two sides of the partition. This is called the Rule of Montgolfier. The causes of movement are constantly acting with every change of temperature, and it is added to by the alteration in moisture which such changes bring about. There are losses of power produced by friction and angles, but these are not great except in cases when the openings are too minute to be of much service. The most powerful ventilating agent is the wind; its agency must be considered in all plans for ventilating a given place. The pressure of the wind equals three-quarters of an ounce on each square foot when the air moves at the rate of three miles per hour; 2 ozs. at five miles; 4 ozs. at seven miles; 8 ozs. at 10 miles; and 1 lb. when the air travels at the rate of fourteen miles per hour. This power of the wind is but too often forgotten in artificial systems of ventilation. It can be always more or less trusted to, if there is room for open windows and simple ventilating apertures. These openings allow the changes of temperature and moisture (which must arise when a number of people occupy a room) to come into play. The great difficulty is to arrange the openings so that a draught may not impinge upon some of the occupants, the result of which is but too generally an outcry on their part for the opening to be closed. Windows should always be placed at opposite sides of the room. They should reach to the ceiling, and open both top and bottom. The top sash may be made to open inwards, so that the draught may be towards the ceiling in the first instance; a wire gauze may cover the space which is left at the lower part when the sash is raised, provided care be taken that the gauze be kept clean. Various kinds of ventilators are provided, such as glass louvres, movable sheets of glass with perforated mouldings. Tobin's tubes, by which air is brought from pure sources and delivered in the room at suitable places, pierced conical bricks, etc., etc. It is necessary to consider-1st. The inlets for fresh air. 2nd. The exits for used-up air; and 3rd. the number of people who are likely to occupy the room or building. (To be continued.)

The New Class-Subject, 'Elementary Science.'

(What to teach, and how to teach it.)

BY RICHARD BALCHIN.

THE work for Standard V., as set forth in the code, is as follows: (a) Animal or plant life; (b) the chemical and physical principles involved in one of the chief industries of England, among which agriculture may be reckoned; (c) the physical and mechanical principles involved in the construction of the commoner instruments, and of the simpler forms of industrial machinery.

This syllabus is extremely vague-probably intentionally so in order to allow the teacher a wide freedom of choice. As a matter of fact, however, we require no further explanation of the general intention of the Department beyond that given in the instructions to prepare a progressive course of lessons adapted to cultivate habits of exact observation, statement, and reasoning.'

It will, of course, be necessary for the teacher to arrange a syllabus of about sixty lessons and submit it to H.M. Inspector. A reading book on 'Elementary Science' is required for Standard V.; and the scheme of lessons will necessarily be based upon the contents of that book. I will assume that No. 3 of 'Hughes' Science Readers' is used. From page 1 to page 60 treats of the following subjects:-The three states of matter; the physical properties peculiar to each state; simple machines; heat. Here is ample material for a year's work. A course of sixty lessons may easily be arranged from this bare outline. As a fact, this part of the reader exactly embraces the work for the first stage 'Mechanics' as given in the 'Fourth Schedule' of the code; and if I were taking 'Mechanics' as a specific subject, I should certainly use this book as the 'General Reader' for Standard V. A complete syllabus of lessons on this division of the book appears in volume I. page 223 of this magazine; hence, I need not repeat here what I then gave with considerable detail.

From page 86 to page 174 of the class-book we have material for another and distinct course of lessons. The subject is 'Elementary Chemistry.' Hence the teacher who uses this book has a choice of two subjects to serve as the basis of his lessons on Elementary Science for Standard V. He may confine his attention to the first part of the book and take 'Natural Philosophy,' or he may devote the time to Elementary Chemistry. I will assume the latter course is adopted. The following is therefore a syllabus of lessons in Elementary Science' as a classsubject for Standard V., based upon the contents of the latter part of 'Hughes' Science Reader,' No. 3.

LESSONS I. to IV.

Elements and compounds; composition of chalk and red oxide of mercury.

LESSONS V. and VI.

Difference between a chemical compound and a mechanical mixture. Composition of water and of air.

LESSONS VII. to X.

Analysis and synthesis. Analysis of red oxide of mercury; of chalk; and of water. The combination of oxygen and iron; of carbon dioxide and lime; and of the fumes of hydrochloric acid and ammonia.

LESSONS X. and XI.

The chemistry of air. Experiment with the belljar and phosphorus.

LESSONS XII. and XIII. Oxygen its preparation and properties. LESSONS XIV. and XV. Hydrogen: its preparation and properties.

LESSONS XVI. and XVII.

The chemistry of water. Analysis by (a) heat; (b) electricity; (c) sodium.

LESSONS XIX. to XXII.

Chief compounds of oxygen. (a) Oxide of iron; (b) oxide of mercury; (c) carbon dioxide; (d) nitrous oxide, etc.

It will at once be seen that the above syllabus, besides being adapted for the class-subject 'Elementary Science' for Standard V., is also arranged to suit the requirements of the first stage of the specific subject'Chemistry.' In the Fourth Schedule of the code we find the following outline given as indicating the work of the first stage of this specific subject:— Elementary and compound matter. Illustrations of combination and decomposition in such bodies as hydrochloric acid, water, oxide of mercury, and rust of iron.' The 'Science Reader' (Hughes') so exactly embraces this official syllabus that, as I intend taking 'Chemistry' as a specific subject next year, I shall certainly use this book as the 'general' reader for Standard V.

Perhaps it may be well I should here mention that my arrangement of Elementary Science' as a classsubject in Standards I. to IV. inclusive is intended to lead up to the specific subjects in Standards V. to VII.; and that 'Chemistry' and 'Mechanics' are the two specifics I have chosen. This year, however, being with me a ten-months' year, and my school quite a new school, I am not taking any specific subjects at all. And I should strongly advise all teachers opening new schools to follow my plan in this respect; for if, while the school is only partly full, and there are comparatively few boys in the upper standards, these subjects are begun, the work is thrown into considerable confusion in future years. I would,

of course, from the very day of the opening of the school, start an interesting and attractive series of object lessons, not for examination purposes, but merely to make the school a popular one in the neighbourhood.

There is one point in connection with this subject of chemistry that I ought to explain. The nomenclature of the science, as well as the manner of stating the chemical formulæ, are at present in an unsettled state. This is, of course, inevitable in the case of such a progressive science as chemistry, where fresh discoveries are continually being made, involving the modification of old statements and the adoption of an altered formula. The symbols, however, remain the For instance, the symbols H, O, N and Ca stand respectively for hydrogen, oxygen, nitrogen, and calcium. Shall I, for water' and 'ammonia,' write H2O and H,N, placing the electro-positive element first (as being the one which appears at the negative pole during electrical analysis), or shall I use as formulæ for these binary compounds OH, and NH3, as I find Dr. Frankland does in his 'Lecture Notes for Chemical Students'? And with respect to the nomenclature. Shall I, in the case of the compounds CO, CO2, and H,CO,, use the terms carbonic oxide, carbonic anhydride, and carbonic acid? or shall I call the first oxide of carbon, and the second carbon dioxide and carbonic acid indifferently? Shall I call chalk calcic carbonate, or carbonate of lime? the compound expressed by the formula K2SO, which term shall I use? Sulphate of potash, or sulphate of potassium, or dipotassic sulphate, or potassium sulphate ?

For

It is quite evident that before I begin to teach even little boys the most elementary chemistry, I must settle what nomenclature to use, and what system of formulation to adopt. My difficulty is just this. I must assume that some at least of my boys will pursue the subject further when they leave school. Well, what will they then think of me and my teaching if they find to their cost that most of what I have told them they have to unlearn before going any further? They will perhaps conclude that I had far better have taught them nothing. And yet I cannot possibly be continually referring to the same substance under three or four different names, nor every time I use a formula show that there are very good reasons why it should be written in two or three other ways.

I have decided in these notes to use the ordinary names and the most commonly received formulæ, except in cases where such are positively erroneous. For instance, I shall use the term 'oxide of iron' in preference to 'ferric oxide,' and adopt the formula H2O (water) rather than OH,. I shall, however, call CÓ, carbon dioxide, and not carbonic acid, for the simple reason that it is not an acid at all with the H20 abstracted, there being in CO, no hydrogen for a metal to displace; it is, in fact, an anhydride.

I feel there is no injustice done to the boys by the adoption of these terms, because my lessons will deal only with the most common every-day substances, to which common every-day names will always be given. If I were teaching a class of adults, the case would be quite different. Then most assuredly I should follow Dr. Frankland's system, and as certainly, Dr. Aveling's method of teaching.

(To be continued.)