98 MODERN FRUIT MARKETING 



of the different materials, water under normal conditions 

 has been given the value of one. Taking then, water as 

 a standard, the other materials in their relative insulat- 

 ing power would be as follows : 



Water 1. 



Sand 1.01 



Brick 2. 



Cement 2.25 



Stone 2.95 



Iron 80. 



Copper 455. 



Furs 0.13 



Wood 0.14 to 0.24 



Wool 0.06 



Building paper 0.05 



Dead air space 0.03 



It will be noted from these figures that dead air or 

 confined air is the best practical insulator against heat 

 or cold. The best known insulator is a vacuum. The 

 principle of the common thermos bottle is simply the 

 insulating from outside temperature by the use of an 

 almost perfect vacuum. Also, the principles of the com- 

 mon fireless cooker is a perfect insulation to keep the 

 heat confined to the inside of the cooker. Wood is the 

 most common of all insulating materials, and perhaps 

 building paper, sheet cork, and sawdust in the order 

 named are of the next in importance. As a rule, the 

 harder mineral substances are poorer insulators than the 

 vegetable substances, and so stone, brick or cement where 

 used, have to be associated with some of the better insu- 

 lating materials. 



Method of Insulation. For the most part the outside 

 of cold storage houses is built of either concrete or brick. 

 These are of sufficient strength to support the weight 



