BY CLEAVAGE, ETC. 37 
sulphuric acid, a flash of light, accompanied by a 
shg¢ht 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- 
eerous 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. 
