Calcareous Genus. 39 



taking up the calcareous Earth, and the vola- 

 tile alkali uniting to the tungften acid; at 

 laft the tungften acid is precipitated from the 

 volatile alkali in the form of a white powder, 

 by faturating the alkali with any other acid. 

 This powder is foluble in 20 times its weight 

 of boiling water, and then reddens litmus, 

 has an acid tafte, and with lime water pro- 

 duces a regenerated tungften ; its fpecific 

 gravity is about 3,600. 



SPECIES V. 



Mild Calcareous Earth mixed 'with a notable 

 Proportion of Magnefia* 



I. VARIETY. 



Compound Spar. 



This ftone is defcribed by Mr. Woulfe. 

 Phil. Tranf. 1779* p. 29. It is there faid to 

 be either white and femitranfparent, or of a 

 pearl colour, or reddifh, or of different {hades 

 of brown or yellow, of a peculiar glofs or 

 brightnefs, like gold, brafs, or copper ; and 

 to confift of flat, folid, and rhomboidal 

 chryftals, and harder than calcareous fpars, 

 Jt effervefces with acids. 



One hundred parts of it contain 60 of mild 

 calcareous Earth, 35 of mild muriatic, and 



D 4 5 



