By the return of the governors boat I have taken the liberty of sending six barrels of the waterproof cement, the materials of which, were first discovered by my father on the James, and York rivers. Previous to its use, the cement should be made moist throughout, with clean water, in which state it must remain two or three days, to give time for the lime to slack perfectly: then it must be worked like common brick morter, taking care to temper it, until it becomes tough and plastic; when it may be used on bricks which have been made wet; for it will not adhere to dry bricks. I recommend to you to have the bricks of the cistern taken up for a foot below the surface of the earth and laid with the cement, and plaistered inside and out. After the cement is put on the bricks, it should be kept from the sun for several days, until it becomes hard; when the water may be let in.

I take the liberty to enclose two notes written by my father to Majr Gibbon on the subject of cements, for Mr Coffee to see. the specimens refered to are given to the boatman who promises to deliver them.

If it will not trespass too much on you, I shall be highly gratified by an expression of your opinion of the subject, after you have seen the substances which are intended as a substitute for Puzzolona, and which by the chimical analysis of Dr Cullen are nearly the same. In addition to the specimens sent by the boatman;1 the governor2 took up a piece of the shale as it was taken from the bank, and a piece of the same which has been burnt.

The cement in the casks is composed of a basaltic rock found near this place, and lime made of the fossil stone. This substance has succeeded in all our experiments; but my father thinks it inferior to the burnt shale.