FLUIDITY. 3i) 



appears to be attained in the long absence of the sun during a 

 polar winter, as Captain Parry found the thermometer to fall as 

 low as 55 at Melville Island, and Ross more lately observed 

 a temperature so low as 60. 



FLUIDITY AS AN EFFECT OF HEAT. 



We have already adverted to one of the general effects of 

 heat upon bodies, namely, its power of causing them to expand 

 which demanded our earliest attention, as it involves the princi- 

 ple of the thermometer. But heat, besides effecting changes in 

 the bulk, is capable of effecting changes in the state of bodies. 

 Matter is presented to us in three very dissimilar states or 

 forms, namely, in the solid, liquid, and gaseous forms. It is 

 believed that no body is restricted to any one of these forms, 

 but that the state of bodies depends entirely upon the tempe- 

 rature in which they are placed. In the lowest temperatures, 

 they are all solid, in higher temperatures they are converted 

 into liquids, and in the highest of ah 1 they become elastic gases. 

 The particular temperatures at which bodies undergo these 

 changes are exceedingly various, but they are always constant 

 for the same body. The first effect then of heat on the state of 

 bodies is the conversion of solids into liquids ; or heat is the 

 cause of fluidity. 



Some substances, in liquefying, pass through an intermediate 

 condition, in which it is difficult to say whether they are liquids 

 or solids. Thus tallow, wax, and several other bodies, pass 

 through every possible degree of softness before they attain 

 complete fluidity. Such bodies, however, are in general mix- 

 tures of two or more substances, which crystallize imperfectly. 

 But ice, and the great majority of bodies, pass immediately from 

 the solid into the liquid state. The temperatures at which 

 bodies undergo this change are exceedingly various: 

 Lead melts at 612 Olive oil melts at :W 



Bismuth 476 Ice 32 



Tin 442 Milk 30 



Sulphur 232 Wines 20 



Wax 142 Oil of turpentine 14 



Spermaceti 112 Mercury 39 



Phosphorus 108 Liquid ammonia 46 



Tallow 92 Ether 46 



Oil of Anise 50 



