Ships and Shipping. 165 



Then 4x2x2 = 16 cubic feet each. 

 9 cases. 



144 

 •025 



720 

 288 



{2to tons) 3*6oo = 3 tons 12 cwt. 



In order to arrive at dead weight tonnage, it is neces- 

 sary that the density or specific gravity of the body or 

 goods should be known. 



Specific gravity or weight, is the term used to denote 

 the weight of bodies compared with similar bulks of pure 

 water; the standard found as the unit of gravity is rain 

 water, and is written water I'ooo. A cubic foot of pure 

 water at 60° F. weighs 1,000 ozs. Avoirdupois. Thus 

 the difference between the weight of water and an equal 

 bulk of any other substance is found. For example :— 

 Water ...I'ooo'i an equal bulk of marble is 2*7 times 

 Marble ...2*716/ as heavy as water. 

 Water ...i"ooo 1 an equal bulk of cork is less than one- 

 Cork ... '240/ fourth the gravity of water. 

 Water ...I'ooo 1 an equal bulk of cast iron is 7*2 times 

 Cast Iron 7*207 / as heavy as water. 



Thus, if by mensuration we obtain the capacity of any 

 substance in some determined part, the weight of which 

 has been ascertained by experiment, we have then simply 

 to multiply the measurement by the gravity in order to 

 arrive at its weight ; in other words, by known specific 

 gravities of goods the weight of these goods may be cal- 

 culated from culjical measurements. 



