82 SCIENTIFIC RECREATIONS. 



as a given weight of water will weigh as much when converted into ice or 

 developed into steam.' The half ounce of water will weigh half an ounce as 

 ice or as steam, but the volume or bulk will vary greatly, as will be understood 

 when we state that one cubic inch of water will produce 1,700 cubic inches 

 of steam, and i^ T cubic inch of ice ; but at the same time each will yield,, 

 when decomposed, just the same amount of oxygen and hydrogen. 



Let us now consider the Effects of Heat upon Water. We have all seen 

 the vapour that hangs above a locomotive engine. We call it " steam." It 

 is not pure steam, for steam is really invisible. The visible vapour is steam 

 on its way to become water again. On a very hot dry day we cannot 

 distinguish the vapour at all. 



The first effect of heat upon water is to expand it ; and as the heat 

 is applied we know that the water continues to expand and bubble up ; and' 

 at last, when the temperature is as high as 2 1 2, we say water " boils " 

 that is, at that heat it begins to pass away in vapour, and you will find 

 that the temperature of the steam is the same as the boiling water. While 

 undergoing this transformation, the water increases in volume to 1,700 times 

 its original bulk, although it will weigh the same as the water. So steam 

 has 1,700 less specific gravity than water. 



It is perhaps scarcely necessary to remind our readers that water, when 

 heated, assumes tremendous force. Air likewise expands with great violence, 

 and the vessels containing either steam or air frequently burst, with destruc- 

 tive effects. Solid bodies also expand when heated, and the most useful and 

 accurate observations have been made, so that the temperatures at which solid 

 bodies expand are now exactly known. Air also expands by heat. 



While speaking of Expansion by Heat, we may remark that a rapid 

 movement is imparted to the air by Heat. In any ordinary room the air 

 below is cool, while if we mount a ladder to hang up a picture, for instance,, 

 we shall find the air quite hot near the ceiling. This is quite in keeping 

 with the effects of heat upon water. The hot particles rise to the top in a 

 vessel, and thus a motion is conveyed to the water. So in our rooms. The 

 heated air rushes up the chimney and causes a draught, and this produces 

 motion, as we have seen by fig. 39, in which the cardboard spiral was set in 

 motion by heated air. A balloon will ascend, because it is filled with heated 

 air or gas ; and we all have seen the paper balloons which will ascend if a 

 sponge containing spirit of wine be set on fire underneath them. 



Winds are also only currents of air produced by unequal temperature 

 in different places. The heated air ascends, and the colder fluid rushes in 

 sometimes with great velocity to fill the space. " Land " and " sea " breezes 

 are constant ; the cool air blows in from the sea during the day, and as the 

 land cools more rapidly at night, the breeze passes out again. When we 

 touch upon Meteorology ', we will have more to say respecting Air Currents and 

 the various Atmospheric Phenomena. 



We know that water can be made to boil by heat, but it is not perhaps 

 generally known that it will apparently boil by cold, and the experiment may 



