The loosening of the tubes likewise acts injuriously upon the plates, which the pressure causes to bend outwardly. The result is that the tubes may become completely detached. Sulphurous fuel corrodes the extremities of the tubes near the fire-box and also notably attacks the hind extremities, in the interior, against the tube-plate. It likewise renders brittle those tubes whose metal is bad, so that they split either of themselves or at the least effort made to tighten them up in the tube-plate. In tubes made of poor metal these brittle places are not only found near the plates, but also in other parts. The tubes likewise have to undergo too lively a combustion when the boilers are driven. Leakages from the tubes often proceed from the fact that an expansion of the boiler lengthwise is prevented, or from a cooling of the tubes by a current of air which passes, without becoming heated, through a badly covered grate. Leakages may also occur if a boiler that has just been emptied is filled too soon. It will be seen that the causes of the deterioration of tubes are numerous; and the repairs that they give rise to in railway shops are therefore very important, and are generally known as a whole. Yet they differ in some points of detail according to the shop in which they are made, so that it may not be without utility to pass them in review, in order to compare the results of the practice of several persons pursuing the same object. The author of this article has had, during a long experience, occasion to make such comparisons: several of the methods that he describes were derived by him in shops that he directed, and have been applied upon a large scale; and numerous visits to other shops have permitted him to see different processes and to judge of results. The different repairs to be made in boiler tubes may be classified as follows: 1. Repairs to leaky tubes. 2. Removal of worn-out tubes. 3. Repair of tubes in service, and putting them in place again. 1. REPAIR OF LEAKY TUBES. Leakages at the point of insertion of the tubes are still generally and exclusively repaired by means of roller apparatus for opening the tubes, and with which an endeavor is made to tighten the latter in the hole in the tube-plate. The cones which were formerly employed injured the ends of the tubes by splitting them; if the workman was not very skillful, the holes in the plate became oval; and fractures likewise quite often occurred between the holes in the plate itself. The best apparatus to open the tubes are those in which the wedge that separates the rollers is actuated by a screw; those in which the wedge is driven in by a hammer are scarcely better than the old cones.