Asphalt, also known as "Silajatu" literally means stone and lac. The term is applied to certain bituminous substances said to exude from rocks during the hot weather. It is said to be produced in the Vindhya and other mountains where iron abounds. It is a dark sticky unctuous substance resembling bdellium in appearance. It has a bitter taste and a strong smell resembling stale cow"s urine. Over platinum foil it burns with a little inflammable smoke and leaves a large quantity of ashes consisting chiefly of lime, magnesia, silica and iron in a mixed state of proto and peroxide.

Processing of Asphalt
Asphalt or Silajatu is prepared for medicinal use by being washed with cold water and then rubbed into an emulsion with its bulk of hot water or milk in an iron pot. This emulsion is exposed to the sun, when a black cream like substance collects on its surface; and this is removed. The process is continued as long as any cream rises. If the mixture becomes too thick, hot water is added from time to time as required, but too much water should not be added at once, for then the cream will not rise to the surface. The silajatu thus collected is dried in the sun and preserved for use. The dregs at the bottom are thrown away. The extract of silajatu thus obtained is purified by being soaked in a decoction of the following plants, namely, Shorea robusta (sala), Buchanania latifolia (piala), Terminalia tomentosa (asana) and Acacia catecliu (khadira).

Benefits of Asphalt
Silajatu is regarded as a powerful alterative tonic and is considered especially useful in urinary diseases, diabetes, gravel, anaemia, consumption, cough and skin diseases.

Dose of Asphalt in Medicine
The extract of Asphalt is given in doses of 6 to 12 grains. In strangury or painful micturition it is given with honey or with the decoction of Tribulus terrestris (gokshura). In urinary complaints it is given in combination with preparations of lead or tin. As an alterative tonic, it is used in combination with iron, as in the following called Yogaraja.

Yogaraja: Take asphalt, prepared iron, iron pyrites and silver, each 5 parts, of the three myrobalans, ginger, black pepper and long pepper, plumbago root and baberang seeds, each 1 part, sugar 8 parts. Powder, mix and make into a confection with honey. Dose should be about half a tola. This medicine is considered a valuable alterative tonic, and is used in anaemia, jaundice, consumption, chronic fever, skin diseases, urinary diseases, piles, etc.