It is the same as that used in constructing the tanks of the Zoological Gardens, London. One part, by measure, say a gill of litharge; 1 gill of plaster of Paris; l gill of dry, white sand; 1/3 of a gill of finely powdered resin. Sift, and keep corked tight until required lot use, when it is to be made into a putty by mixing in boiled oil (linseed) with a little patent drier added. Never use it after it has Men mixed (that is, with the oil) over fifteen hours. This cement can be used for marine as well as fresh-water aquaria, as it resists the action of salt water. The tank can be used immediately, but it is best to give it three or four hours to dry.