PHARAOH'S SERPENTS. 315 



designated by the pompous title of Pharaotis serpents. For making these, 

 some sulpho-cyanide of potassium is poured into a solution of nitrate acid or* 

 mercury, which forms a precipitate of sulpho-cyanide of mercury. This is a 

 white, combustible powder, which after passing through a filter, should be 

 transformed into a stiff pulp by means of water containing a solution of gum. 

 The pulp is afterwards mixed with a small quantity of nitrate of potash, 

 and fashioned into cones or cylinders of about an inch and a quarter in 

 length, which should be thoroughly dried. The egg thus obtained can be 

 hatched by the simple application of a lighted match, and gives rise to the 

 phenomenon. The sulpho-cyanide slowly expands, the cylinder increases in 

 length, and changes to a yellowish substance, which dilates and extends to a 

 length of twenty or five-and-twenty inches. It has the appearance of a 



Fig. 303. Iodide of cyanogen. 



genuine serpent, which has just started into existence, and stretches out its 

 tortuous coils, endeavouring to escape from its narrow prison (fig. 304). 

 The residue is composed partly of cyanide of mercury and of para-cyanogen; 

 it constitutes a very poisonous substance, which should be immediately 

 thrown away or burned. It can be easily powdered into dust in the fingers.. 

 During the decomposition of the sulpho-cyanide of mercury, quantities of 

 sulphurous acid are thrown off, and it is to be regretted that Pharaoh's 

 serpent should herald his appearance by such a disagreeable, suffocating 

 odour. 



After these few preliminary experiments, we will endeavour to show 

 the interest afforded by the study of chemistry in relation to the commonest 

 substances of every-day life. We will first consider the nature of a few 

 pinches of salt. We know that kitchen salt, or sea salt, is white or greyish, 

 according to its degree of purity ; that it has a peculiar flavour, is soluble 



