The colour of natural cement is ______

Which of the following is not a solid lubricant?

We can obtain lake asphalt from lakes at _____

In the wet process in the manufacturing of portland cement, argillaceous material is thoroughly mixed with water in ____…

During the setting action of the cement, tricalcium aluminate is formed within ____ after adding water to the cement.

Plaster of Paris is ______

Tensile strength of leather belts should be about ___

Which of the following is not a natural abrasive?