organic substances develop when treated with an alkali. These calculi often contain a quantity of urate of soda.

4. PHOSPHATE OF LIME CALCULI.

Alone on charcoal they blacken, emit the odor of burning organic matter, and finally burn white. They do not fuse. Their behavior resembles in general that of phosphate of lime.

They are proved not to consist of silica, by swelling up with soda and not fusing to a glass, as well as by giving a regulus of phosphide of iron, when dissolved in boracic acid and fused with iron.

5. AMMONIACAL PHOSPHATE OF MAGNESIA CALCULI.

Heated alone on platinum foil they smell strongly of salts of ammonia, blacken, intumesce, and if the heat be increased, burn. greyish-white. They fuse readily to an enamel-like bead of the same color.

They give a transparent glass with borax and microcosmic salt, which, with a large quantity of the assay, becomes opaline on cooling.

With soda they fuse to a white, swollen slag, which becomes infusible on the addition of more of the flux.

With boracic acid and iron they give readily a regulus of phosphide of iron.

With nitrate of cobalt they give a dark red glass.

6. CALCULI COMPOSED OF THE PHOSPHATES OF LIME AND
MAGNESIA. Calculi fusibiles.

These are recognized by the slight ammoniacal odor they emit, arising principally from the destruction of organic matter in the calculus. They fuse far more readily than any others to an enamel-white bead, which does not become red with the oxide of cobalt, but brownish-black.

7. CALCULI COMPOSED OF OXALATE OF LIME.

Calculi moriformes.

Alone they smell of urine when first heated. The more strongly crystalline varieties become duller and lighter colored. After being slightly heated, the residuum effervesces with a few drops of nitric acid, and after being strongly heated on charcoal caustic lime remains; this has an alkaline reaction on reddened litmus paper, and generally crumbles to powder when moistened. This is not the case, however, if the calculus contains at the same time phosphate of lime.

8. CALCULI CONTAINING SILICA.

They leave after ignition a greyish, infusible, and sometimes slaggy ash, which, when mixed with soda, slowly dissolves to a more or less transparent glass.

9. CYSTIC OXIDE CALCULI.

These behave, before the Blowpipe, very much like calculi composed of uric acid; they do not fuse, but take fire readily, and burn with a bluish-green flame, emitting a strongly acid smell of a peculiar character, somewhat resembling that of hydrocyanic acid. They leave an ash which is not alkaline, and which fuses in a strong heat to a greyish-white mass.

They are distinguished from uric acid calculi by the smell which they emit when burning, and by not giving a red color with nitric acid.