SCIENCE OF COMMON THINGS. 157 



Steam is invisible. Liquids become no hotter after boiling. 



Steam is really invisible / and the half inch (between 

 the spout and the " stream of mist") is the real steam, 

 before it has been condensed by air. 



1O15 Why is not all the steam invisible as well as that half inch ? 



Because the invisible particles are condensed ly the 

 cold air, and, rolling one into another, look like a thick 

 mist. 



1O1B What becomes of the steam, for it soon vanisJies f 



After it has been condensed into mist, it is dissolved 

 by the air, and dispersed abroad as invisible vapor. 



lOlT* And what becomes of the invisible vapor f 



Being lighter than air, it ascends to the upper regions 

 of the atmosphere, where (being again condensed) it con- 

 tributes to form clouds. 



1O1S Why do sugar, salt, &c., retard the progress of boiling f 



Because they increase the density of water ; and 

 whatever increases the density of a fluid retards its 

 boiling. 



1O19 Why can liquids impart no additional heat after they boil f 



Because all additional heat is spent in making steam. 

 Hence w r ater will not boil a vessel of water immersed in 

 it, because it cannot impart to it 212 of heat; but 

 "brine w T ill, because it can impart more than 212 of heat 

 before it is itself converted into steam. 



Ether . . boils at 100 degrees 

 Alcohol . . " 173| " 

 Water . . . l( 212 " 

 Water, with one- fifth salt, 

 boils at. . . 219 " 



Syrup . . boils at 221 degrees. 

 Oil of turpentine 314 " 

 Sulphuric acid 472 " 

 Linseed oil " 640 " 

 Mercury . . " 656 " 



Any liquid which boils at a lower degree, can be made to boil if im- 

 mersed in a liquid which boils at a higher degree. Thus a cup of ether 

 can be made to boil in a vessel of water ; a cup of water, in a vessel of 

 brine or syrup ; but a cup of water will not boil if immersed in ether, nor 

 a cup of syrup in water. 



1OJ3O Is the boiling point of the same liquid always constant ? 



Yes, under the same conditions / but it is liable to be 

 affected by various circumstances. 



1OS1 What cause has a powerful influence in regulating the boiling 

 point of liquids f 



The pressure of the atmosphere : if the pressure be 



