A great deal has been said about the cement proper to use for uniting the parts of the aquarium. Some authors tell us that any cement containing either lime or lead will be sure to injure the fish; but this must evidently depend very much upon the condition in which these materials are present in the cement.

White lead and ordinary building lime would probably be bad; but we have had tanks cemented with mixtures containing litharge, and also others containing good hydraulic cement, and after long exposure to pure water and to water containing carbonic acid, neither the lead nor the lime seemed to be dissolved to an extent that could be detected by the most delicate chemical tests, and neither did the plants or animals seem to suffer from any injurious effects. We therefore feel satisfied that the cements described in the article Cements in the former part of this work will fulfill every requirement.