Having thus pinched and tied the case, so as not to give way, put it into the mould without its foot, and, with a small mallet, drive the former hard on the end piece, which will force the neck close and smooth. When this is done, cut the case to its proper length, allowing, from the neck to the edge of the mouth, half a diameter, which is equal to the height of the nipple. Then take out the former, and drive the case over the piercer with the long rammer, and the vent will be of a proper size. Wheel cases are sometimes driven on a nipple, with a point to close the neck, and make the vent of the size required; which, in most cases, is generally 1/4th of their interior diameter. As it is very often difficult, when the cases are rolled, to draw the roller out, a hole must be made in its handle, and a pin, as a purchase, put in. The machine for pinching cases consists of a treadle, which, when pressed hard with the foot, will act upon a cord, and draw it tight. The cord runs over a small pulley, and is fixed to an upright piece. It is wound once round the case, between the former and end piece; and when the cord is drawn, the case is brought together. Cases are commonly rolled wet for wheels and fixed pieces; and when they are required to contain a great length of charge, the method of making these cases is thus: The paper must be cut as usual, except the last, which ought not to have a slope. Having it ready, paste each sheet on one side, and then fold down the first sheet as before directed; but be careful that the paste does not touch the upper side of the fold. If the roller be wetted, it will tear the paper in drawing it out. In pasting the last sheet, observe not to wet the last turn or two in that part where it is to be pinched; for if that part be damp, the pinching cord will stick to it, and tear the paper. Therefore, in choaking those cases, roll a bit of dry paper once round the case, before the pinching cord is used. This paper is to be taken off after the operation. The rolling board, and all other methods, according to the former directions for the rolling and pinching of cases, must be used for these, as well as other cases. See _Encyclopedia Britannica_, vol. xv, p. 692. Morel, in a practical work, (_Traité Practique des Feux d'Artifice_) speaking of rocket cases, observes, that the rule is, to give to their thickness, half the interior diameter, or half the diameter of the roller. If the roller, for instance, were half an inch, the case should be 1/4th of an inch in thickness. A rocket is divided into three equal parts; two for the interior diameter, and one for the thickness of the case.