32 PdiL(;ri~d Cbrrc.~l)o~dcnce.

ACID PROOF CEMENT, l'Ailade[phia, 3larch 22d, 1869.

Mr. Editor :--Thinking that the following suggestion may be of use to, or improved upon by some of the readers of the JournaZ of the Franlclin Institute, I oflbr it with these ideas for what it may be worth. It frequently happens that the chemist requires some means for protecting cork from the destructive action of vapors such as arise from boiling nitric acid. I think that the plan here mentioned, may possibly meet this requirement. Finding it necessary to con- nect a glass tube with a wide-mouthed flask, and in so doing to use a cork which was exposed to the action of the fumes from boiling nitric acid for several hours, I found the best preservative to con- sist of a coating of silicate of soda and powdered glass. The cork having been bored to suit the size of the tube, was soaked for two or three hours in a solution of silicate of soda, consisting of one part of commercial concentrated solution, to three parts of water. The tube was next inserted, and when dry, the cork was covered with a paste made by mixing the condensed solution of the silicate with powdered glass in such proportion as to form a mass of about the same consistence as that of putty. This is spread on the under surface, and then washed with a solution of chloride of calcium. It soon hardens, so I think it advisable to make the connection with the flask whilst the paste is in a plastic state, and to allow it to be- come solid before applying heat to the vessel containing the acid.

Corks protected in this manner, were but slightly acted upon, though remaining over the boiling nitric acid more than four hours~ and over hot acid for ten. In some instances, when not entirely covered, the vapor softened the cork beneath the silicate to the depth of about a quarter of an inch, but the cement proved suffi- ciently strong to form a compact diaphragm, enabling the tube to be removed from the flask without danger of the fluid contained being contaminated. I would suggest also the application of this cement as a luting for chemical apparatus for general use, as I find that it remains unaffected even when immersed in strong nitric, sul- phur, or muriatic acids. The immersion in these liquids was made whilst the plaster was still soft, with the only perceptible effect of hardening the same immediately. Yours, &e.,

]~OB'T. F. FAIRTIqOI~NE.