This is made by rubbing together three parts by weight of mercury, and five of prepared chalk, till the metal is extinguished. The mercury is not so thoroughly divided in this preparation as in the blue pill; and, therefore, though the proportion of the metal is much greater, its effects on the system are even milder; as, according to the observations of Mialhe, the conversion into a soluble form in the stomach and bowels takes place more slowly, the less finely the mercury is comminuted.

Mercury with chalk is a grayish powder, which effervesces with an acid, and loses the metal by evaporation with heat, the chalk remaining. Globules of mercury can generally be seen in it with the aid of a magnifying glass.

This is the mildest of the mercurials, and is often preferred in infantile cases on this account, as well as for the antacid properties of the accompanying chalk. But, though somewhat milder than the blue pill, it is less certain. it is more frequently used as an alterative, in infantile disorders of the alimentary canal, with light or clay-coloured stools, indicating defective action of the liver, than for its sialagogue operation. it is sometimes, however, employed in the syphilis of infants.

The dose for adults, in reference to its effects on the system, would be from five to thirty grains, for children two or three grains; but, when intended merely as an alterative in infantile diarrhoea, it may be given in the dose of a grain, every two or three hours through the day. it should be given in powder; as, in the form of pill, the contraction of the material on drying is apt to cause globules of the metal to form.

The Dublin College formerly directed a similar preparation, made with magnesia instead of chalk, and denominated Hydrargyrum cum Magnesia, or Mercury with Magnesia. it had similar properties with the preceding, and might be preferably used should a laxative effect be desired.