CALORIFIC POWER OF FUELS. 



fitting in an opening of the removable conical cover E. This 

 is prepared (Fig. 2 1) in advance, and is covered with a layer 

 of gum lac applied in a strong alcoholic solution. When the 

 first coat is dry, a second one is put on and 

 dried in a stove. Berthelot says that the 

 combination of these two coatings, one elas- 

 tic and soft, the other hard and brittle, 

 resists very well the enormous pressure on 

 the cone. This cone, lightly greased, is put 

 into the conical opening in the bomb cover, 

 and screwed up tight by means of a nut. It 

 is well to protect the base of the cone by a 

 film of mica. 



An electric current passed through E 

 (Fig. 21) reddens the spiral of very thin 

 iron wire f placed between the platinum 

 wires and one of the supports 55 of the cap- 

 sule cc containing the substance m. This iron wire soon 

 burns and kindles the combustible. 



Fig. 22 gives a general and complete internal view. 

 The iron spiral is formed of an iron wire -^ millimetre 

 (0.004 inch) thick, rolled up on a spindle. The wire may be 

 weighed, or by using the same length of wire always have the 

 same weight. 



The spiral is attached on one side to the cone, and on the 

 other side by means of a platinum wire to the platinum sup- 

 porting the fuel, taking care that the iron has no straight por- 

 tions. The support of the capsule or platinum-foil is then 

 fixed in the cover, by aid o the screw, arranging it so that 

 the spiral is directly over the combustible used. The cover 

 is put on, turning it gently to make the contact more perfect. 

 The nut is tightened and the wire carefully screwed up, 

 always using wooden tongs to prevent injuring the bomb. 



The form of the bomb is such as permits filling the calo- 

 rimeter with the smallest possible quantity of water a neces- 



