| Caliber for bombs. | Length of the fuse. | Weight of the charge. | |||
| Bombs of | 4 in. diam. | 1¼ | inches. | 2 oz. | cannon powder. |
| ---- | 6 do. — | 1⅔ | do. | 5 oz. | do. —— do. |
| ---- | 9 do. — | 2 | do. | 6 oz. | do. —— do. |
| ---- | 12 do. — | 2 | do. | 9 oz. | do. —— do. |
Having made some remarks respecting bombs, we will now offer a few observations concerning mortars; and although we have, on a former occasion, mentioned something respecting them, yet we deem a few remarks on this head not improper at this time.
Mortars, from five to six inches bore, are usually made of pasteboard and canvass. The canvass is first soaked in a gelato-amylaceous paste, or paste composed of half glue and half flour; and, when put on, is covered with sheets of pasteboard, which are glued or pasted. For various kinds of paste, see [Pasteboard.]
When the case, or mortar is to be formed, cylinders of wood as formers are employed. They are of different diameters, according to the size of the mortars, that are to be made. For four-inch mortars, inch formers; for six-inch, one and a half inch formers, &c. After they are rolled and pasted on the former, they are dried on it. As to their strength, this depends on the thickness of the case. A mortar of four inches in interior diameter, ought to be six inches in exterior diameter, and those of six in interior, should be nine, exterior. The cases being formed, we next have turned as many cylinders of walnut, as cases or pots. These cylinders are short. In each is formed a conical chamber, in the shape of the letter V, which is afterwards lined with tin or brass, to prevent the action of the powder. They are then glued and put into the end of each pot, about the length of an inch, and further secured by nails.
The chamber is designed to receive the powder, and its conical form enables it to act with all its force immediately on the bomb. A flat bottom would not have this advantage, as the powder in that case would have more room, and consequently its force be divided. They are sometimes, however, made flat.
The charge for these mortars, as a general rule, is 1/30th part of the weight of the bomb.
When mortars are to be larger than the sizes we have mentioned, it is necessary to have them of metal, and for this purpose copper is generally employed. Its thickness should be one-fourth of an inch, for a nine-inch mortar; and half an inch, for twelve-inch mortars. A cone of copper is to be made in the same way as above mentioned. This is secured, and made solid by means of lead.
In experiments and exhibitions, the powder, we may observe, must be of the same strength.
We find then, that mortars, for the discharge of bombs, or balloons, are differently made from those which are used for throwing iron-shells. In fire-works, the design of mortars is to project the balloon in a vertical direction, which, being furnished with a fuse as in ordinary shells, receives the fire from the gun-powder; and at a given time, according to the length of the fuse, the fire is communicated to the balloon, which bursts and scatters its contents in the atmosphere. The furniture for balloons being various, and in a larger quantity than could be contained in the heads of rockets, (except the Congreve,) the appearance is more grand and impressive. It is obvious, that, when they burst, fire is communicated to the whole at the same time; and the quantity of powder is usually sufficient, not only to burst the shell, but also to throw the contents to some distance. The height, to which balloons ascend, depends, of course, on the quantity of gunpowder put in the mortar. The quantity is generally regulated.