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Now, if a class is reciting a lesson dismissed from a first-class newsin Physiology on respiration and paper, and he would deserve it. the pupils are thinking of a page The buoyancy of air can be nicely in the book rather than of them- shown by the bubble with some selves, it may bring the subject simple contrivance to generate hyhome and add much interest if two drogen with which good balloons scholars be called before the class, are filled. one—the largest boy-to take a Prepare apparatus as in Fig. I, deep breath and blow all he can a stout bottle. a cork through into the bubble while the other which passes a short piece of glass with ruler measures its diameter. tubing, a rubber tube one foot Then the volume of this sphere is long, and a pipe. Now pour water calculated on the board by those into the bottle to a depth of about who know some mensuration and two inches, and add some scraps of the "vital capacity, 230 cubic zinc, old sheet zinc will do or, if inches” as stated in the book will zinc cannot be procured, carpet begin to mean something.

tacks or small nails will do. Now While our fleet was lying before pour upon these sulphuric acid Santiago it was not certainly about one-twelfth as much as there known for a long time whether or is water. Gas will be given off not Cervera was in the harbor nor which will now blow the bubble. how much of his fleet was there. At first hold the mouth of the pipe

down until the bubble is the size of a hen's egg, then suddenly invert it and allow to blow until it shows signs of breaking away, when a quick motion to one side will liberate the bubble which ascends to the ceiling. The pipe can again be dipped into the soap solution and the operation continued at pleasure. This gas is hydrogen for Zn+H2SO, =ZnSO4 +2H It is used in balloons because it is the lightest gas and the

balloon rises for the same reason So Americans raised balloons from that a cork will rise to the surface their ships to get a view of the har- of water. Air is 144 times as heavy bor. A reporter for one of our pa- as hydrogen, while oxygen is 16 pers described these as filled with times as heavy as hydrogen, hence oxygen. Such a reporter would be if a bubble is blown with oxygen it


will rapidly fall to the floor. It is O=H20, and if the room had been heavier than air and sinks for the filled with hydrogen and the bubble same reason that a stone will sink filled with oxygen exactly the in water. This same apparatus same phenomena would have been may be used to generate (CO2) observed, except that the bubble carbon dioxide, the only difference would descend instead of ascend. being that marble must be substi- Blow a small bubble with air from tuted for zinc. CaCO3+H2SO4= the lungs, then connect the pipe CaSO4+H20+CO,, hence the with the hydrogen generator and gas is CO, and a bubble blown swell the bubble to about three with this will sink very rapidly to times that size. Release the bubble the floor, and if allowed to fall upon and light it, when a loud report will a candle flame it will extinguish it, be heard because of the sudden while an oxygen bubble falling up- union of the oxygen and hydrogen on the flame will cause it to burn which were intimately mixed. brilliantly. This will illustrate the This fact has suggested a way of difference between these two gases producing rain in dry seasons. It in an important particular.

was noticed, during the civil war If, while the hydrogen bubble, that almost invariably after a batabove described, is ascending a tle in which there was heavy canlighted match be plunged into it nonading there would be a heavy there will be a sudden, though shower of rain, so that there quiet, flash of light and all will dis- seemed to be some connection beappear. This nicely illustrates the tween these powder explosions and union of the hydrogen in the bub- the condensation of the water ble and the oxygen in the air. vapor in the air; so it seemed reaThis subject of combustion is sonable that if huge balloons filled poorly understood even by some with one part oxygen and two parts educated people. They say, for

They say, for hydrogen be allowed to ascend and example, that wood and coal will have attached to them a time fuse burn as though any one thing could to cause the union of these great be a combustible. Combustion is volumes of gas, there would be always a chemical union of at least such agitation of air in this region two elements. We forget the at- that condensation and precipitation mosphere of diluted oxygen in would follow. After all methods which we are constantly bathed. have been tried, however, the rainNow,that burning hydrogen bubble, makers do not yet enjoy the full raised to the proper temperature confidence of the public. by the lighted match, simply united The soap bubble is spherical bewith the oxygen of the air and wa- cause the film is stretched, or unter was the product; thus, 2H+ der tension. This can be easily

shown by blowing a bubble five or on a basin of water and instantly it six inches in diameter and then re- will spread over the whole surface. move the pipe from the mouth, Now, the surface of water acts very when the bubble will rapidly con- much as if a thin elastic membrane tract driving all the air it contains were tightly stretched over the waout through the pipe stem. As ter and fastened all around to the compared with other shapes a sides of the basin and so when the sphere has the least surface for the oil broke this, it dragged the oil same volume of substances, and so, out with it in all directions. as the film is trying to make its The old experiment of floating a area as small as possible it puts its needle on water is a clear demoncontents in the form of a sphere. stration of this strong surface tenThis is well shown in falling drops sion or water-skin. of rain, which are round because In the soap solution it is the of the surface tension of water, and surface tension which keeps the when this surface tension bears a film stretched on both sides from certain ratio to the mass of water point to point of its support. This within, one drop will rebound on can be nicely shown by preparing striking another and it cannot be a wire as shown in Fig. 2 and tyeasily broken up. So that, under ordinary conditions, we are neither deluged by great masses of water coming down from the clouds altogether, nor does the rain fall as fine mist. Even the shot-maker takes advantage of this principle. If his melted lead be separated into small globules, they will be spherical while freely falling and if they fall far enough will harden before they strike the water at the bottom.

The surface tension of water is much greater than that of the soap solution, but the soap solution has another property called surface viscosity by virtue of which it can be enormously stretched as in ing to one side a loop of thread. blowing a large bubble. Water has By dipping this into a saucer full this property only in a slight de- of the soap solution it will be easy gree.

to bring away a thin film in which Let a drop of petroleum fall up- the thread will hang as shown in


the figure, but if the part of the film When we speak of the film as bewithin the loop be now pricked ing only a molecule in thickness with a pencil point and broken the we are speaking of exceedingly

small quantities, but the physicist and chemist knows something about molecules and atoms as certainly as the mechanic knows about masses.

Ordinary gold leaf is about 1-300000 of an inch in thickness but may be thinned out to 1-4000000 of an inch and is still more than a molecule thick. Leslie tells us of a single grain of musk which was known to perfume a large room for a space of twenty years. The number of molecules in this grain of musk must have been exceedingly numerous that the air, fre

quently changed, could be by it, thread will immediately be pulled filled with odor sufficient to affect out in all directions forming a circle the olfactory nerves. as illustrated in Fig. 3.

The most striking exhibit of the film is seen in Fig. 4. Dip a tumbler into the solution and, taking away a film, place the tumbler as in the figure. Place the eye so as to

Fig. 4 receive the rays of light reflected from the film and soon will appear a beautiful display of colored bands which no drawing can accurately represent. These colors are caused by the interference of light waves bv which some of the components of white light are destroyed while others come on to the eye. Knowing the length of the waves of light it is possible to calculate the thickness of the film and hence to ap- The number of waves in red light proach the size of the molecule. is 395 X 1012 in one second and for

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violet 760 X 1012, and as light travels only 185,000 miles in one second, each wave is very short and when white light falls upon the film a part is reflected directly toward the eye, while another part passes through and is reflected from the posterior side of the film, so that whenever the film is of such a thickness that the wave which passes twice through lags one-half a wave length behind that reflected from the front those waves will be destroyed, and we receive no longer the sensation of white light but only that of the other components which have not been destroyed. These bright bands of light appear first at the top where the film is thinnest and gradually spread over all; but in a short time new bands will cease to appear at the top, a light uniform tint will take their place, soon to be succeeded by a gray tint, when the film always breaks. This gray tint indicates a degree of tenuity where the film is one molecule in thickness and to stretch it any further would be to convert the liquid into a

gas. There is evidence that the film in the region of the gray was about 1-500000000 of an inch thick,which, from other evidence, is about the thickness of a molecule.

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Take A B equal to the greater number, and A E equal to the less; E B will then be equal to 53. Complete the square A B C D, and take B M equal to E B. Then draw E N parallel to B C, and RM parallel to A B.

The square R Q N D is the square of the smaller number; and the two equal rectangles, Q MCN and AE Q R, together with the square EBM Q, is the difference between the squares of greater and smaller numbers.

The area of the square E B M Q=53'=2809. Then 107592809 =7950, the area of the two equal


By Ed. M. Mills. The following problems will not be found too difficult for very ordinary eighth grade pupils, and they will serve herewith to illustrate the

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