270 EARTHS. 



Pure baryta is useful to the chemist as a test, particularly for the 

 discovery of carbonic acid, either free or combined. Its muriate is 

 used by physicians in scrofula, &ic. The sulphate is the most abund- 

 ant form, and it is convertible into every other, by certain processes 

 which will be mentioned in their proper place. 



3. POLARITY Electro-positive ; it resorts to the negative pole in 

 the galvanic circuit. 



4. COMBINING WEIGHT, 70. This is the number of Dr. Thom- 

 son. Berzelius states it at 50.66, but the former number is gene- 

 rally adopted. 



SEC. III. STRONTIA. 



1. NAME. From the lead mine of Strontian, in Argyleshire in 

 Scotland, whence the minerals containing it were first brought. 



2. DISCOVERY. By Dr. Thomas Hope,* then and still, professor 

 of chemistry in the Univ. Edin. Anno. 1791. 



3. PREPARATION. The same as that of baryta. f 



4. PROPERTIES. 



(a.) The result of the igneous decomposition of the nitrate is a 

 grayish porous substance ; sp. gr. approaching that of baryta. 



(b.) With water, slacks violently, like baryta and lime, and the 

 theory is the same ; the powder of the dry substance irritates the 

 nostrils and lungs. 



(c.) After slacking, no more water being used than is necessary, 

 the earth remains in the form of white powder ; it is then a hydrate 

 consisting of strontia, one proportion, 52, and one of water 9=61. 

 The hydrate fuses readily at ignition, but is not decomposed by the 

 strongest heat of a wind furnace. 



(d.) More water being added, it dissolves in about 40 parts ; if 

 the water be boiling hot, it dissolves in 20 parts of that fluid, and crys- 

 tals are formed on cooling, having the form of thin quadrangular 

 plates, sometimes square, oftener parallelograms, not over J of an 

 inch in diameter.J 



(e.) After being heated, the dry earth remaining, is about 32 per 

 cent. ; the crystals contain 1 proportion of earth, 52, and 12 of wa- 

 ter, 108=160. 



(/.) At 60, soluble in 51 J parts of water ; boiling water takes up 

 half its weight. 



* Dr. Crawford observed a difference between the muriate of strontia and that of 

 baryta, in 1790. Klaproth confirmed the views of Dr. Hope. 



t Vide Edin. Trans. IV, 44. 



t In both cases, the decomposition of the sulphate is the cheapest process ; see the 

 articles sulphate of baryta and sulphate of strontia. The carbonate is managed 

 with the greatest ease. 



