.BF CLEAVAGE, ETC. 37 



sulphuric acid, a flash, of light, accompanied by a 

 slight explosion, is immediately remarked. If 

 small pieces of cork happen to fall upon melted 

 chlorate of potash, so frequently used to obtain 

 oxygen gas, a flash of light appears ; the gas is 

 at first rapidly evolved from the retort, but in 

 an instant an absorption takes place, the water 

 is sucked up into it, and the apparatus broken. 

 When chloride of amide (formerly called chloride 

 of nitrogen) explodes, much light is evolved : the 

 preparation and explosion of this substance are 

 exceedingly dangerous. Potassium takes fire upon 

 water, and burns with a purple flame ; I have also 

 seen sodium shoot out flashes of yellow light in 

 the same circumstances. Nitric acid decomposes 

 oil of turpentine, producing a great flame. When 

 great quantities of lime are slacked in a dark 

 place, not only heat but light is emitted, as was 

 formerly observed by Pelletier.* Also, in a dan- 

 gerous experiment made by myself, when sodium 



* There are substances called Kacodyles, (one of which is 

 formed when acetate of potash and arsenious acid are distilled 

 together,) which take fire spontaneously when they come in con- 

 tact with atmospheric air : they are liquid, and possess a nauseous 

 odour. Homberg's pyrophorus, which takes fire in the air, is an 

 example of intense chemical action with production of heat and 

 light. It is prepared by calcining alum with organic matters and 

 cooling the mixture slowly. It must not be mistaken for Hom- 

 berg's phosphorus, which is melted chloride of calcium, and 

 which, as we have seen, becomes luminous when submitted to 

 rapid friction, or when struck with a hard body. 



