134 Domestic Science 



The change of water into steam is attended by an 

 enormous increase of bulk, the steam produced from a 

 given volume of water occupying more than 1600 times 

 the volume of the water from which it was formed. 

 If the water be boiled in a confined space, such as the 

 boiler of a steam-engine, great increase of pressure 

 results as a consequence of the production of steam, 

 and it is this pressure which sets in motion the movable 

 parts of the engine and causes it to perform work. 



That chemical change, when effected by heat, is 

 also capable of doing work may be easily grasped when 

 one considers the result of the explosion of a blasting 

 cartridge, loaded with dynamite and packed tightly 

 into a small hole drilled into the rocks in a quarry, 

 when the burning end of the fuse attached to it trans- 

 mits heat in sufficient quantity to cause the constituents 

 of the dynamite to change into new bodies. Most of 

 these are gases and occupy many thousand times the 

 volume of the original explosive. Their sudden pro- 

 duction, assisted by their very considerable expansion 

 under the influence of the large quantity of heat 

 simultaneously liberated during the chemical change, 

 is enough to split open even the hardest rocks. 



In conclusion, we will emphasise the general in- 

 ference obtainable by consideration of the matters dealt 

 with in this chapter, viz. 



Heat is a form of energy. 



QUESTIONS 



1. A cylindrical leaden clock-weight, 6" long, weighs 12 Ib. 

 When the clock is fully wound up, the bottom of the weight is 8 ft. 

 4 in. from the floor. Express the potential energy of the weight 

 in this position in foot-pounds. 



