39 ° 
Dr. Wollaston's Analysis of 
Fusible Calculus. 
My next subject of inquiry has been a species of calculus, 
that was first ascertained to differ from that of Scheele by 
Mr. Tennant; who found that when urged by the heat of a 
blow-pipe, instead of being nearly consumed, it left a large 
proportion fused into an opaque white glass, which he conjec- 
tured to be phosphorated lime united with other phosphoric 
salts of the urine, but never attempted a more minute analysis. 
Stones of this kind are always whiter than those described 
by Scheele, and some specimens are perfectly white. The 
greater part of them have an appearance of sparkling crystals; 
which are most discernible where two crusts of a laminated 
stone have been separated from each other. 
I lately had an opportunity of procuring these crystals alone, 
voided in the form of a white sand, and thence of determining 
the nature of the compound stone, in which these are cemented 
by other ingredients. 
The crystals consist of phosphoric acid, magnesia, and vo- 
latile alkali : the stone contains also phosphorated lime, and ge- 
nerally some lithic acid. 
The form of the crystals is a short trilateral prism, having 
one angle a right angle, and the other two equal, terminated 
by a pyramid of three or six 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 phosporated quicksilver is obtained, 
