Cast-iron drains are now very often used in place of earthenware pipes, and there is a great deal to be said in their favour, especially since the invention of several processes whereby the interior is prevented from rusting and scaling. Pipes of this material are useful underground in rows of houses, and wherever straight lines of delivery are obtainable, and compared with drain pipes of earthenware, with their necessary surrounding of concrete, they would prove not more expensive. Unfortunately, however, this system cannot always be adopted, unless the house has been planned with a view to this method of drainage; and in most houses it will be observed that the pipes would have to run in front of fireplaces and across doorways if above ground. When iron piping is used, great care should be taken with the jointing, to see that it is properly packed, and with material calculated to last as long as the pipe itself. Iron pipes with merely leaded joints are subject to galvanic action, whereby the iron, sooner or later, thins out by corrosion, the iron perishing by “abnormal local oxidation,” as has been very forcibly stated by B. H. Thwaite. When iron is contiguous with lead, a galvanic action is set up, and, the latter being electro-negative to the iron, the iron suffers. There ought, therefore, always to be an assistant packing in the pipe, and the majority of engineers make use of this. Eassie advises in addition, a luting of Portland cement with the other materials, which may include a previous stuffing of fibrous packing material together with the old-fashioned iron filings and acids. Given the best kind of drain to lay down, there is still the question as to where to lay it, and here lamentable errors are frequently made. The chief fault perpetrated in this particular is the laying of drains inside a house, when they might just as easily have been laid outside. When a drain is laid down, care is exercised to get the pipes as much as possible in straight lines; and at each departure from a straight line a manhole is formed, enabling any one to inspect the drain at any time, by lifting the manhole cover. If a lighted candle is placed at the bottom of the drain in the manholes, the freedom of the drain from obstructions can be ascertained by looking from manhole to manhole. These inspection chambers should be placed at every departure from a straight line, and where several drains junction together; thus each drain delivery is open to sight, and rods can easily be introduced up the drain pipe should any obstruction occur. These inspection chambers are always best protected by an iron manhole cover, fitting down perfectly into their iron frames, which are sunk into the stone floor.