STATE HORTICULTURAL SOCIETY. 177 



If we desire the compound steam possessed also of this mecha- 

 nical property — motion or power — we cause it to be made within 

 the confines of a steam boiler, and even here should the quantity 

 of heat employed in a given time be too small, the compound does 

 not advance beyond the condition of warm or hot water. On 

 the other hand, should the heat be of sufficient intensity and ap- 

 plied rapidly enough, the resulting compound is steam possessed 

 of mechanical energy known and denominated as a pressure of a 

 certain number of pounds to the square inch, and therefore 

 capable, mechanically, of developing an equivalent of motion or 

 power. 



In this form it is extremely infractions and unstable, and if at 

 once liberated from the confines of the boiler, it immediately ex- 

 pands to the full volume, developing all the motion and power 

 due to the pressure, and then as quickly resolves to its normal 

 components — heat and water ; and the heat is disseminated 

 through the surrounding atmosphere, while the water falls to the 

 earth. Or, on the other hand, if a body or an element low in 

 the scale of temperature be placed in contact with the boiler, the 

 steam immediately releases all the heat it contains above 212°, 

 the pressure within the boiler is as instantaneously removed, a 

 vacuum produced, and the boiler collapsed from without by the 

 pressure of the surroundiag atmosphere. 



Again, should the pressure of steam within the boiler be greater 

 than the boiler can withstand, the latter breaks and opens and 

 the steam escapes into the open air. 



It is not necessary to enter upon the details of an instance in 

 which this powerful and fitful compound of chemical and me- 

 chanical energy as daily generated in our steam boilers through- 

 out the land finds escape from its confines and spreads havoc and 

 ruin in every direction. The concentrated heat is instantly ex- 

 pended in converting the atoms of water each into 1,700 volumes 

 of steam, and for a moment of time space is unsufficient to accom- 

 modate the immense increase in volume. 



The phenomena of combined force or power and chemical change 

 as witnessed daily in the use of steam, is, however, but the coun- 

 terpart of that seen in the action of water under the influence of 

 frigorific or freezing mixtures. In steam the atoms of water are 

 disseminated through a large space, while in the latter they are 

 locked up in the smallest space possible. 



Subjected to the action of a mixture of snow or ice and com- 

 mon salt in the proportion twelve to one the temperature of 

 23 



