and their Chemical Examination. 447 



is discriminated chiefly by forming a yello'w compound with ni- 

 tric acid, instead of a pink one as in the case of Uthic acid. 

 That called the fusible calculus is a compound of the ammo- 

 niaco-magnesian phosphate, and of the phosphate of lime cal- 

 culus ; and is characterized by its easy fusibility, as its name 

 imports. 



A fine tile, or in lieu of it the bottom of a china saucer or 

 plate of glass, will suffice ; a feather and glass rod ; a spirit 

 lamp, and platinum spoon, with a glass mortar and pestle, form 

 the aggregate of the simple apparatus required : a blow-pipe 

 will be seldom needed. 



Pure caustic potassa in concentrated solution, and sulphuric, 

 nitric, muriatic and acetic acids, constitute the amount of the 

 re-agents. 



In external and physical characters, 1. The lithic acid cal- 

 culi are yellowish or reddish yellow, and especially on being 

 wetted ; 2. The oxalate of lime (or mulberry) calculus is gray, 

 sometimes deep brown, in undulated layers ; 3. The siliceous 

 calculus (which is at any rate rare) wears the same aspect as 

 that of the oxalate of hme; or it may be less coloured; 4. The 

 ammoniaco-magnesian phosphate (or triple) calculus is white, 

 crystalline and semi-transparent; 5. The phosphate of lime cal- 

 culus is white, opake, and non-crystalline ; 6. Dr. Prout has 

 described the lithate of ammonia calculus as being of an ash 

 gray. 



A fi-agment of the calculus to be examined is next reduced 

 to fine powder, and a portion of this powder exposed in a pla- 

 tinum spoon to the heat afforded by the spirit lamp. If it 

 blackens and burns away, leaving no residuum, I conclude it to 

 be wholly compounded of lithic acid, or lithate of ammonia. 

 A further portion of the comminuted powder is then mixed 

 with concentrated solution of caustic potassa; and if visible va- 

 pours are developed, on the approach of a feather dipt in mu- 

 riatic acid, it may be concluded that it is composed of lithate of 

 ammonia. 



It^ instead of the previous indication, it loses a})parently no- 

 thing by calculation, and after being thus intensely ignited 

 does not vitrity, I conclude it to be, either the oxalate of lime 

 calculus, or that of the phos})liate of lime. If it is vitrified at 

 a red heat, then it may be inferred to be the triple calculus ; and 

 if it fuses, the fusible one. In order to distinguish whether it 

 be the nuilberry calculus (oxalate of lime), or that of the phos- 

 phate of lime, bring a drop <jf acetic acid in contact after calci- 

 nation, when cold : if it eflervesces, it is the oxalate of lime cal- 

 culus. It may, hov.'ever, still be so, and not ellervescc: a lit- 

 tle of the powder .sliuuld therefore, after calcination, be tlirowii 



into 



