264 EARTHS. 



directed through the flame of an alcohol lamp, for the purpose of 

 producing a signal light, which can be seen at a great distance. 



5. POLARITY. It is attracted to the negative pole in the galvanic 

 circuit, and is therefore electro-positive. 



6. Combining weight, 28, as will be seen more particularly under 

 calcium, the basis of lime. 



7. PHARMACEUTICAL PREPARATION. This is the same that has 

 been already described in giving the process for quick lime. 



CALCIUM. 



1. DISCOVERY. In 1808, in Sweden, by Prof. Berzelius and 

 Dr. Pontin ; afterwards obtained by Sir H. Davy in England. The- 

 nard attributes the first observation to Dr. Seebeck. 



2. PROCESS. 



(a.) A cup or capsule, made of moistened lime, or sulphate of 

 lime, containing a globule of mercury, is placed on a metallic dish; 

 the negative wire of the galvanic battery of 100 pairs, in good action, 

 is made to touch the mercury, and the positive wire is brought in 

 contact with the under side of the metallic support. An amalgam of 

 mercury and calcium is formed, but the process must be continued 

 a good while in order to obtain any manageable quantity ; in a small 

 (green*) glass retort, or tube closed at one end, this amalgam is dis- 

 tilled, with naptha, which rises first, then the mercury, and the cal- 

 cium remains in an atmosphere of vapor of naptha, for which nitro- 

 gen may be substituted. 



(b.) When potassium, in vapor, was passed through quick lime 

 heated to whiteness, the potassium acquired oxygen, and became 

 potash, and a dark gray substance, with metallic lustre, was found 

 imbedded in the potash, and it was evidently calcium, more or less 

 perfectly reduced, because it effervesced violently in water, and 

 formed a solution of lime. 



3. PEROXIDE. This is formed when oxygen gas is passed over 

 lime ignited in a tube ; the exact proportions are not known, but it is 

 supposed to contain twice as much oxygen as the protoxide. 



In the moist way, the oxygenized water of Thenard forms the same 

 peroxide. 



4. PROPERTIES. Little known. 



(a.) Color, white, like that of silver, and with the same lustre ; 

 sinks in water. 



(b.) Ignited in a tube in which the distillation of the amalgam was 

 going on, it took fire when the tube broke, and burnt with an intense 



* Because white glass contains oxide of lead, whose oxygen would change the 

 calcium to the state of oxide, or lime. 



