176 SCIENCE OF COMMON THINGS. 



Temperature of scalding water. General effects of heat. 



1155 At what temperature do metals burn when handled f 



Metals cannot be handled when raised to a tempe- 

 ratnre of more than one hundred and twenty degrees. 



1156 At what temperature does water scald 7 



At one hundred and fifty degrees. 



1157 To what extent can the human system sustain the influence of 

 heated air f 



Workmen enter ovens, in the manufacture of moulds 

 of plaster of Paris, in which the thermometer stands 

 100 above the temperature of boiling water, and sustain 

 no injury. 



If the person so entering a heated oven should hold next to his skin a 

 piece of metal, the latter would absorb heat with sufficient rapidity to 

 burn the surface with which it was in contact. 



1158 Why is there so great a difference between the burning tempera- 

 ture of 'metals and air f 



The metals absorb heat quickly, and part with it 

 freely ; the air absorbs heat very slowly, and does not 

 readily part with it. 



1159 What class of bodies allow heat to pass freely through them,? 



Transparent bodies of little density, as the air, the 

 various gases, etc., etc. 



CHAPTEE VII. 



EFFECT OF HEAT. 

 116 O What effect has heat upon substances generally f 



It expands them, or enlarges their dimensions. 



1161 Are the dimensions of every kind of matter regulated by heatf 



They are; its increase, with few exceptions, separates 

 the particles of bodies to a greater distance from each 

 other, producing expansion, so that the same quantity 



