GENERAL PROPERTIES OF METALS. 53 



Cyanogen and Hydrogen. — Hydrocyanic acid^ Cyanhydric acid, 

 Prussic acid, Cyll. Prepared in the anhydrous form, by passing 

 sulphuretted hydrogen over fragments of bicyanide of mercury, con- 

 tained in a horizontal glass tube, and receiving the product in a 

 vessel surrounded with a freezing mixture. Gentle heat is applied 

 to the tube, and the cyanogen reacting with the sulphuretted hydro- 

 gen, produces hydrocyanic acid and the sulphuret of mercury. 



Prop. — A thin, colourless liquid, exceedingly volatile ; sp. gr. 

 •7058 ; boils at 79° and freezes at 0° ; has a powerful characteristic 

 odour of peach blossoms or oil of bitter almonds ; has a very feeble 

 acid reaction ; unites with water and alcohol in all proportions. In 

 its anhydrous state it is one of the must poisonous sulDstances known. 

 The best antidotes are chlorine and ammonia. It is very liable to 

 decomposition, especially if exposed to the light. 



The solution of hydrocyanic acid is best prepared by the action 

 of dilute sulphuric acid on the ferrocyanide of potassium. 



Hydrocyanic acid is an organic product, being frequently met 

 with in the vegetable kingdom. It is believed, however, not to pre- 

 exist in vegetables, but to be due to the mutual reaction of two or- 

 ganic principles, named aniygdaline and emulsine, or synaptase^ 

 with water. 



CHAPTER II. 



METALS. 



GENERAL PROPERTIES. 



They are all conductors of heat and electricity ; they are positive 

 electrics ; they are opaque ; possess generally a well-marked lustre, 

 termed metallic; are generally good reflectors of light. The num- 

 ber generally admitted by chemists is forty-two. They vary greatly 

 in specific gravity, — between potassium, which is lighter than water, 

 and platinum which is twenty-one times as heavy. 



Properties which are peculiar to certain metals. — Malleability, 

 ductility, tenacity, the iveldirig process, hardness, and the crystal- 

 line structure. 



All are solid at common temperatures, except mercury. Their 

 fusing point varies very much — ranging between mercury, which is 

 — 39°, and platinum, which is infusible at the heat of a smith's forge. 



Metals often unite together to form alloys. When mercury unites 

 with another metal, the compound is named an amalgam. Ex- 

 amples of alloys : brass, from copper and zinc ; bronze, from copper 

 and tin ; hdl-metal, from copper and tin ; type-metal, from antimony 



5* 



