272 EARTHS. 



heat, even that of a lamp, gives up its excess of oxygen, and becomes 

 protoxide. It acts like the nitrates upon burning coals, causing in- 

 creased combustion. When it is moist, it gradually loses the oxygen, 

 and rapidly in hot water. It appears to contain just twice as much 

 oxygen as the protoxide or strontia. 



4. COMBINING WEIGHT. This is estimated at 44. 



5. POLARITY. Electro-positive; resorts to the negative pole of 

 the galvanic battery. 



6. USES, &tc. Strontia has the same uses in chemistry as baryta. 

 It is a test for carbonic and sulphuric acids ; as a natural production, 

 it is more rare, especially its carbonate ; its sulphate is found abund- 

 antly in Put-in-Bay, Lake Erie ; at Detroit, Mackinaw, Lockport, &c. 



The salts of strontia are not poisonous ; the pure earth is acrimoni- 

 ous like the other alkaline bodies. 



The natural and artificial compounds of baryta, are heavier than 

 those of strontia, and there are various points of difference found in 

 their combinations. The nitrate of strontia is used to give a blood 

 red color to artificial fire works.* 



SEC. IV. MAGNESIA. 



1. DISCOVERY. In the beginning of the eighteenth century, ex- 

 posed for sale as a panacea at Rome, by a canon, who called it pow- 

 der of Count Palma ; but Dr. Black, in 1755, was the first person 

 who distinguished it clearly from other substances. 



2. PREPARATION. 



(a.) In the arts. From the muriate and sulphate of magnesia, 

 found in sea and saline water ; they are decomposed by alkalies, or 

 usually by their carbonates ; magnesia may be extracted by acids from 

 magnesian stones, and the salts thus obtained can be decomposed as 

 above. 



(&.) In Chemistry. Ignite the common carbonate of the shops, 

 or dissolve the sulphate and decompose it by any alkali or alkaline 

 carbonate, wash thoroughly, and ignite the precipitate. 



3. PROPERTIES. 



(a.) In light spongy masses, or in a friable powder, which forms 

 with water a paste destitute of cohesion ; the carbonate is commonly 

 seen in cubical cakes. 



(b.) Sp.gr. 2.3; still the cakes float awhile on water, till they 

 are filled by absorption. 



(c.) Taste insipid, or slightly earthy ; lime mixed with it some- 

 times communicates to it a slight degree of acrimony. 



(d.) Mild, harmless, and without corrosive action on the living or 

 dead animal organs. 



* Ure, 2d Ed. 743. 



