1\Q PHILOSOPHICAL TRANSACTIONS. [ANNO 17Q7. 



nesia, and volatile alkali : the stone contains also phosphorated lime, and generally 

 some lithie acid. The form of the crystals is a short trilateral prism, having one 

 angle a right angle, and the other 1 equal, terminated by a pyramid of 3 or 6 

 sides. 



(6) By heat the volatile alkali may be driven off from the crystals, and they are 

 rendered opaque, or may be partially fused. The phosphorated magnesia may then 

 be dissolved in nitrous acid ; and by addition of quicksilver dissolved in the same 

 acid, a precipitate of phosphorated quicksilver is obtained, from which the quick- 

 silver may be expelled by heat, and the acid procured separate. By addition of 

 vitriolic acid to the remaining solution, Epsom salt is formed, and may be crystal- 

 lized, after the requisite evaporation of the nitrous acid, and separation of any re- 

 dundant quicksilver. — (7) These crystals require a very large quantity of water for 

 their solution, but are readily soluble in most if not all acids ; viz. vitriolic, nitrous, 

 marine, phosphoric, saccharine, and acetous ; and when precipitated from them re- 

 assume the crystalline form. — (8) From the solution in marine acid, sal ammoniac 

 may be obtained by sublimation. 



(9) Though the analysis is satisfactory, the synthetic proof is, if possible, still 

 more so. After dissolving magnesia in phosphoric acid, the addition of volatile 

 alkali immediately forms the crystalline precipitate, having the same figure and 

 properties as the original crystals. — (10) If volatile alkali be cautiously mixed with 

 recent urine, the same compound will be formed ; the first appearance that takes 

 place when a sufficient quantity of alkali has been gradually added, is a precipitate 

 of these triple crystals. These constitute the greater part of the fusible stone ; so 

 that a previous acquaintance with their properties is necessary, in order to compre- 

 hend justly the nature of the compound stone in which they are contained. The 

 most direct analysis of the compound stone is effected by the successive action of 

 distilled vinegar, marine acid, and caustic vegetable alkali. 



(11) Distilled vinegar acts but slowly on the calculus when entire; but when 

 powdered, it immediately dissolves the triple crystals, which may be again precipi- 

 tated from it as crystals by volatile alkali ; and if the solution has not been aided 

 by heat, scarcely any of the phosphorated lime will be found blended with them. 

 In one trial the triple crystals exceeded T %- of the quantity employed ; but it seemed 

 unnecessary to determine the exact proportion which they bear to the other ingre- 

 dients in any one instance, as that proportion must vary in different specimens of 

 such an assemblage of substances not chemically combined. Marine acid, poured 

 on the remainder, dissolves the phosphorated lime, leaving a very small residuum. 

 This is soluble in caustic vegetable alkali entirely, and has every other property of 

 mere lithie acid. The presence of volatile alkali in the compound stone may be 

 shown in various ways. 



(12) In the distillation of this stone, there arises, first volatile alkali in great 

 abundance, a little fetid oil, and lithie acid. There remains a large proportion 

 charred. Water poured on the remaining coal dissolves an extremely small quantity 



