50 per cent. of the gas registered by the meter, and the gas bill will be twice as high as it should be. Suppose, now, that you have ten common, 4-foot lava-tip burners in the house, that each one is in use, on an average, 3 hours every night, that the gas pressure is 2 inches, that all the burners run full blast, and that the cost of the gas is $2 per thousand cubic feet. The quantity consumed at the end of a month will be about

Number Consump- Days

of X tion in X burners cu. ft. 10 X

8.46

Hours

in X burning month each night

X 30 X

3

= 7,614 cu.ft.

he explains where and how the waste of gas (and consequent loss of money) takes place. He also states what should be done to prevent further loss, and very sensibly suggests that a pressure regulator be placed on the gas pipe near the meter so that the gas pressure throughout the building may be automatically regulated to that point best adapted for economical combustion. He also suggests that you remove the old burners and replace them with improved modern incandescent burners on the Welsbach principle. Finally, he says that he will be pleased to make all of these improvements for the sum of $21.50.

You now wonder if it will pay to go to this expense. Just do a little figuring. A Welsbach incandescent gas lamp, consuming 3 cubic feet of gas per hour, gives from 50 to 60 candlepower of light. Let us be modest and call it 50 candlepower which is 10 candlepower lower than the manufacturer's

gone. Now, suppose you take an economical streak and consult an intelligent plumber, the object being to ascertain how your gas bills can be reduced to a minimum without decreasing the brilliancy of the illumination. Like a doctor, the plumber tries to get you to explain the "symptoms of the case," and you, like his other customers, persist in talking so ridiculously that he decides to go up and see for himself. The first thing he does is to get the facts from your wife. Then he reads the pressure at one of the burners with the glass U tube shown in Fig. 3. This tube is filled with water up to the zero mark, and of course the water stands at the same level in the two legs of the tube; but, when the gas key is opened, the pressure of the gas immediately forces the water down in the column a and consequently up in the column b until it reaches a mark, say, midway between 2 and 3 on the scale. This indicates a pressure of 2.5 inches, which is very modest indeed, the average pressure being in the neighborhood of 3 inches.

Now he asks you to light the ten gas jets. They are lighted in the usual manner, and he sees the waste at a glance. Every jet is turned on full force and they all blaze like (a), Fig. 1. That settles it. He goes back to the shop and writes out a report, in which

FIG. 4.

claim. These ten Welsbach lamps, in use for 3 hours each night for a month, would consume 3X3 X 10 X 30 = 2,700 cubic feet of gas-which, at $2 per thousand feet, will cost you $5.40 for the month. Place this amount against your old bill of $15.23, and you will find that you have saved almost $10.00. But this is not the only gain; you get about 3 times as much light as you had before.

In case some reader is not acquainted with the construction of the incandescent gas lamp of the Welsbach type, let us refer to Fig. 4, which shows such a lamp, complete, with the gas burning, and to Fig. 5, which is a section through the same lamp. burner is of the ordinary Bunsen type. The

The

gas enters at a and the air at i. The mixture burns on top of a wire-gauze cover b, producing great heat but practically no light. This heat is transformed into light by a hollow tubular network, or mantle c, which is suspended over and around the burner by a wire support d. This mantle is composed of threads of an incombustible material, which becomes brilliantly incandescent when highly heated. It is made by saturating a delicately woven cotton fabric with a dense solution of earthy oxides, which is baked on the network. When the mantle is about to be used, its temperature is raised high enough to destroy the cotton fibers, leaving the coating of oxide standing as a network of fragile crust. This fragile nature of the mantles is at present the only drawback to the general use of incandescent gas lamps.

Now we will try to show how a consumer can read his own meter. Fig. 2 shows a meter dial of the ordinary type. When the pointers all point to the zero mark on their respective dials, the meter is said to be at zero. If the meter is at zero, and a certain amount of gas is allowed to pass through it, the number of cubic feet of gas passing through the meter will be indicated on the

dials. If the meter is not at zero, however, the number of cubic feet of gas which has actually passed through during the time specified is equal to the difference between the number indicated upon the dials, before the gas was allowed to pass through the meter, and that indicated when the gas has flowed through. The top dial is marked Two Feet, which means when two cubic feet

of gas have passed through the meter, the pointer of this dial will have made one revolution. When 1,000 cubic feet of gas have passed through the meter, the pointer of the dial to the right, which is marked 1 Thousand, will have made one complete revolution, and the pointer of the 10 Thousand dial will have moved from 0 to 1. the right has made

HOME STUDY.

When the pointer to another revolution, the pointer of the middle dial will have moved from 1 to 2, which means that two complete revolutions of the pointer to the right have been made. When the middle pointer has made one complete revolution, the pointer to the left will have moved from 0 to 1 on the 100 Thousand dial, which means that of 100,000, or 10,000 cubic feet, have passed through the meter.

To read a meter dial of this description, first write down from each dial the figure which the pointer has just passed, then annex two ciphers to the right; the number so obtained will be the amount of gas in cubic feet which the meter has measured.

Thus, the pointers on the dial in Fig. 2 indicate that 41,800 cubic feet of gas have passed through the meter. When the pointer to the left has made one complete revolution, the process of indication is repeated. The pointers all move from the smaller to the larger figures, just like the hands of a clock.

Now that you can read your own meter, just watch the gas company closely, and discover that the officials are honest and your bills accurate. Then withdraw your doubts and feel at rest.

E

VERY form of matter possesses certain properties which are peculiar to and characteristic of all matter of the same kind. Such properties are of two classes, namely, physical and chemical.

Physical properties are such properties of matter as may be manifest without change in the identity of the molecule. The physical properties of any form of matter may be recognized without changing it into something else. For example, we easily recognize in alcohol certain characteristic properties. It is a liquid, is transparent, has a certain specific gravity, and a peculiar taste and smell, etc. These various properties may be recognized simply by examining the alcohol as alcohol, and without in any way changing its identity.

Chemical properties are those which are not manifest without change in the identity of the molecule. The chemical properties of matter cannot be ascertained by any means that will leave it the same as it was before. Alcohol possesses the property of combustion; it can be readily burned. But this property cannot possibly be recognized by examination, however carefully the examination is made. That it possesses this property can be ascertained only by burning it. But it will then be alcohol no longer; it will have been changed into heat and gas. The alcohol had possessed this property ever since it became alcohol, but it could not manifest it without ceasing to exist as alcohol, that is, without changing the identity of its molecule.

Each chemical element which enters into the composition of a substance may be common to various substances, but the proportion in which the elements are combined is characteristic of each particular substance. Hence, chemical properties are characteristic properties. In what follows, however, the chemical properties of matter will not be further noticed, but attention will be directed chiefly to its physical properties

It may be well, now, to notice that, in addition to its characteristic properties, matter possesses certain physical properties that are common to all matter. Such properties

are called universal, or general, properties. The most prominent universal properties of matter are extension, impenetrability, weight, inertia, porosity, compressibility, expansibility, elasticity, divisibility, mobility, and indestructibility. Only a few of these properties will here be specially noticed.

Extension is that property of matter which enables and requires it to occupy space. It relates to the size and form of a body, and comprehends the three dimensions of length, breadth, and thickness. It is an inherent and essential property that is common to every possible form of matter. It is involved in the very definition of matter, namely, anything that occupies space. No one can conceive of a body that does not occupy space, or take up room. Hence, it must have size -must have length, breadth, and thickness. Consequently, it must also have form, or shape.

Impenetrability is that property of matter which prevents a body from occupying, at the same time, the space occupied by another body. Two bodies cannot occupy exactly the same space at the same time. This is a direct result of the property of extension. A body occupies and requires space; it cannot exist without occupying space; and the same space, when thus occupied, cannot be occupied by another body. Examples illustrating this property are very common. you fill a glass with water, you cannot put more water, or anything else, into it without forcing the water to run out over the edge of the glass.

If

Weight is the term commonly applied to the measure of the effect of gravitation. All bodies of matter possess weight, although we do not readily recognize this property in bodies whose weight is less than that of the medium surrounding them, as, for instance, the weight of a gas that is lighter than the earth's atmosphere. As commonly used, however, the term weight generally refers to bodies upon the earth's surface, and its meaning in this connection is sufficiently understood and does not require explanation here.

Inertia is that property of matter which

renders it incapable of changing its condition of rest or motion. We are prone to get the impression that all bodies tend to a state of rest, because most bodies with which we are familiar come to that state upon the earth's surface. But material bodies have no inherent tendency toward a state of rest any more than toward a state of motion. Matter is entirely incapable of changing its condition, whether of rest or of motion. When in motion, its tendency is to always continue to move in the same direction and at the same rate of motion, and it would always so continue if it were not opposed by some external force. Examples of the effect of inertia are to be found on every hand. A ball cannot throw itself; it requires the application of an external force to put it in motion. And, when put in motion by being thrown, it cannot stop itself, but would continue on in the same direction and at the same speed, were it not for the resistance of the air and the effect of gravity.

Elasticity is that property of matter which gives to all bodies the tendency to recover their original form and size when these have been changed by any external force. All material bodies possess this property, although some substances possess it only to a slight degree. Every known substance, when subjected to external pressure, will be reduced in size, because every known substance is, to some extent, compressible. If the pressure does not exceed certain limits, every known substance will, upon the removal of the pressure, recover its original size. Fluids are not elastic with reference to form, but are perfectly elastic with reference to size, without regard to the amount of pressure. Solids are elastic with reference to both form and size, within certain limits. If the pressure or force applied upon a solid body exceeds certain limits, varying with the substance, the body will not recover its original form and size, but will undergo permanent deformation.

Indestructibility is that property of matter which renders it incapable of being destroyed. We cannot by any possible means destroy matter. Science teaches us that the universe contains today, not only exactly the same amount of matter, but even the same quantity of each element, that it has contained ever since time began. Forms of matter have undergone changes that were great indeed, but not one particle, not even one elementary atom, has been either gained or lost. Water from the ocean is evaporated into the air by heat, and

is carried by the winds out over the land, where, becoming condensed, it falls as rain upon the earth, and, finding its way to a watercourse, is again carried away to the ocean. But not one iota is destroyed-not even so much as the millionth part of the finest particle of mist. The sprout from the acorn, gathering sustenance from the ground and atmosphere, becomes a great tree; it is, perhaps, cut down and burned as wood, or it may stand until blown over by the wind and then lie upon the ground until it rots. In either case, its elements return partly to the ground and partly to the atmosphere, whence they came. But not one atom is lost or destroyed.

These two illustrations will serve to indicate, to some extent, the continued round of transforming change that is undergone by the material bodies composing the universe, without the slightest gain or loss. Matter is indestructible.

The characteristic physical properties of matter are numerous and of great variety. Each characteristic property is generally common to many different forms of matter, as a property, but, in the different forms of matter, varies greatly in degree, depending largely upon the intensity of molecular attraction, or cohesion and adhesion, inherent in each form. Among the most important characteristic properties of matter are hardness, tenacity, ductility, malleability, toughness, and brittleness.

Hardness is that property of matter tending to resist any attempt to force a passage between its particles. The hardness of a substance is measured, in a general way, by the degree of difficulty with which it may be scratched or indented by another substance. Hardness is a variety or special aspect of the molecular attraction, or cohesive force, which holds the particles composing any body in position and prevents disintegration. With reference to hardness, no fixed law can be stated. Certain substances possess the property to a high degree, while others do not. Some substances, also, which do not themselves possess the property to a very high degree, produce a great degree of hardness in certain other substances, when combined with them. Carbon is not itself a very hard substance, but a small percentage of it, properly combined with iron, produces exceedingly hard steel. Fluids do not possess the property of hardness.

Tenacity is that property of matter by virtue of which a force tending to tear its particles asunder is, by some bodies, resisted.

The strength of any material is due, principally, to its tenacity. That tenacity is also a particular aspect of cohesion will be at once recognized. The tenacity of any substance can be measured by ascertaining the greatest weight that can be hung from, and sustained by, a piece shaped in the form of a rod or wire, the area of whose cross-section is known. As the resistance will be uniform over the cross-section, if the amount of weight sustained is divided by the area of the cross-section, the quotient will be the tenacity of the substance per unit of crosssection. Hence, it is evident that, for any given material, the tenacity is directly proportional to the area of the cross-section. This is a well known and important law of tenacity. Four rods, each 1 inch square, will carry four times the load that can be carried by one of the rods. A bar of the same material, having a sectional area of 4 square inches, will carry as much as the four bars, or four times as much as one of the bars having 1 square inch of cross-section. In this country, the square inch is generally taken as the unit of sectional area for measuring tenacity.

Ductility is that property of matter by virtue of which some bodies are capable of being drawn out into wires or threads. Some substances are very ductile. Platinum wire has been drawn out to a diameter of only sob of an inch. Glass, at a red heat, is exceedingly ductile. Most of the ordinary metals possess the property of ductility to a considerable extent.

Malleability is that property which renders some forms of matter capable of being beaten or rolled into thin sheets. Some of the common metals possess this property to a remarkable degree. Lead is very malleable, and can be rolled into very thin sheets. Steel has been rolled into sheets as thin as ordinary paper. Gold, which is the most malleable of all metals, has been beaten so thin as to require 282,000 sheets to give a thickness of 1 inch.

Toughness is that property of matter which enables it to undergo a limited amount of bending, twisting, and similar rough usage, without material injury. It is, however, probable that all substances are to some

extent injured by even the smallest amount of bending or twisting, but the injury to some substances from a limited distortion is so slight as to be imperceptible. Toughness may be said to embrace, to some extent, the properties of ductility and malleability.

Brittleness is that property of matter which renders some bodies susceptible of being easily broken or fractured by a blow. A peculiar and important condition characteristic of this property is that certain substances, on being broken, always exhibit the same form of fracture. This fact is of great value in enabling geologists to recognize the composition of rocks. Most ordinary rocks are brittle and can be readily broken by a forcible blow.

Brittleness must not be considered as the opposite of hardness, or due to lack of either hardness, tenacity, or elasticity, for a substance may possess all three properties to a high degree and still be very brittle. Steel is much harder and more tenacious than copper; yet, at the same time, it is much more brittle. Glass is almost perfectly elastic, but also very brittle; the same may be said of some qualities of steel. Brittleness is more nearly the opposite of ductility, malleability, and toughness, especially of the last. A substance that possesses to a high degree the properties of ductility, malleability, and toughness cannot be very brittle. Indeed, in the physical tests of metals, the measure of ductility and the bending test for toughness are both accepted as indicating freedom from brittleness.

The above characteristic properties of matter are those of the most importance, as indicating the adaptability and value of any substance for any particular purpose. For the different members of important structures, and for all purposes where strength is required, a high degree of tenacity is essential, and a considerable degree of toughness is very desirable. For a cutting tool, hardness is the most essential property. For the manufacture of wire, ductility is the property desired; while, for many ornamental purposes, toughness and malleability are the important properties. The desired physical properties of any material are determined by the use to which it is to be put.