Referring to the qualities that I have previously cited as being required in a high explosive for military purposes, it is sooner or later found that nearly all the novelties proposed lack some of the essentials and soon disappear from the advertising world only to be succeeded by others.  The most common defect is lack of keeping qualities.  They will either absorb moisture or will evaporate; or further chemical action will go on among the constituents, making them dangerously sensitive or completely inert, or they will separate mechanically according to their specific gravities.

For further clearness on the subject of the shell charges which have so far been discussed, the following table is added of weight and sizes of shells for United States naval guns, with their bursting charges of powder: 

6-inch com. cast steel shell 31/2 to 4 cal. long, wt. 100 lb., charge 6  lb.
8  "       "          "         "          "        250     "      141/2 lb.
10  "       "          "         "          "        500     "      27   "
12  "       "          "         "          "        850     "      45   "

Armor-piercing forged steel shell.

6-inch, 3 calibers long, weight 100 lb, charge 11/2 lb.
8  "         "          "       250    "       3   "
10  "         "          "       500    "       51/2  "
12  "         "          "       850    "      11   "

The chief efficiency of small quantities of high explosives having reduced itself to the case of armor-piercing projectiles, it next became evident that there was an entirely new field for high explosives into which powder had entered but little, and this was the introduction of huge torpedo shells, which did nor rely for their efficiency upon the dispersion of the pieces of the shell, but upon the devastating force of the bursting charge itself upon everything within the radius of its explosive effect.  It is in this field that we may look for the most remarkable results, and it is here that the absolute power of the explosive thrown is of the utmost importance, provided that it can be safely used.  Attention was at once turned in Europe to the manufacture of large projectiles with great capacity for bursting charges, and it has resulted in the production of a class of shells 41/2 to 6 calibers long, with walls only 0.4 of an inch thick.  (If they are made thinner, they will swell and jam in the gun when fired.)

These shells are used in long guns up to 6 and 81/2 inches caliber, and in mortars up to 11.2 inches.  They are made from disks of steel, 3 to 4 feet in diameter and 1 inch thick, and are forced into shape by hydraulic presses.  The base is usually screwed in, but some of the German shell are made in two halves which screw together.  The Italians were the first in this new field of investigation, but the Germans soon followed, and after trying various materials were at length reasonably successful with gun-cotton soaked in paraffin.  Their 8.4 inch mortar shells of 5 calibers contain 42 pounds; those of 6 calibers contain 57 pounds; and the 11.2 inch mortar shells of 5 calibers contain 110 pounds.