L. TECHNOLOGY. 527 



and then separates them sharply, so as to break the current 

 instantaneously. It is thought that this system will be found 

 useful not only for piercing fogs at sea, but also for railway 

 signals. 



IIOLMEs's INEXTINGUISHABLE SIGNAL-LAMP. 



An inextinguishable and self-igniting signal-lamp lately in- 

 vented by Holmes has some important peculiarities which 

 render it likely to be of practical application under many cir- 

 cumstances, especially in view of the fact that it is self-ignit- 

 ing, that its flame can neither be extinguished by water nor 

 other means, and that it is incapable of setting fire to objects, 

 while, at the same time, its light is extremely brilliant and of 

 long duration. The new lamp consists of a cylindrical ves- 

 sel of tin with a conical point, and provided below with a 

 tube six inches in length. The vessel is to be filled entirely 

 with fragments of phosphide of calcium, and the tube solder- 

 ed up air-tight, so that the preparation can be kept for many 

 years without change. When the lamp is to be used the tip 

 of the cone is to be cut off, and an opening made at the end 

 of the narrow tube referred to, and the lamp inserted in a 

 wooden float and thrown into the water. The Avater pene- 

 trates through the lower end of the tube and comes into con- 

 tact with the phosphide of calcium, and is decomposed, with 

 the formation of a phosphureted hydrogen gas, which is de- 

 veloped in great quantity, and which, escaping through the 

 open tube of the cone, becomes ignited and burns in contact 

 with the atmospheric air. 



The phosphide of calcium can be prepared by heating pieces 

 of chalk with amorphous phosphorus in a crucible to a white 

 heat. At this temperature the chalk takes up the vaporized 

 phosphorus, and combines with it to form the phosphide of 

 calcium. 



Another method of preparing this substance consists in 

 heating small fragments of freshly-burned lime to a white 

 heat in a Hessian crucible, and throwing upon it, from time 

 to time, small dry pieces of phosphorus, covering up the cru- 

 cible tightly immediately after each introduction of the phos- 

 phorus. The lime is changed into the " liver of phosphorus" 

 (a mixture of phosphide of calcium and phosphate of lime), 

 while a considerable quantity of phosphorus vapor is burned. 

 The resultant substance is dark brown or almost black. 





