Dynamite is combined with twenty-five per cent. of inert matter as an absorbent; for this large proportion of unexploding substance, Nobel sought an active substitute. This, he thought, might be a substance which would dissolve in nitro-glycerine so as to form a homogenous paste. Now for a sagacious experiment with a liquid brought to his hand by accident. Whilst experimenting in search of such a material, he one day cut his finger and sent out for some collodion to form an artificial skin to protect the wound; having used a few drops for that purpose, it occurred to him to pour the remainder into some nitro-glycerine, and he thus discovered blasting glycerine, which he patented in December, 1875. Collodion is made by dissolving a gun-cotton in a volatile solvent, a mixture of ether and alcohol, and Nobel suggested that the viscous substance thus obtained should be mixed with the nitro-glycerine so as to form a jelly. On further experiment the jelly was dispensed with, and blasting gelatine was made, as it is now, by warming the nitro-glycerine, and adding about eight per cent. of a gun-cotton which was found to be soluble in nitro-glycerine. The new explosive, half as strong again as dynamite, was too violent to be applicable to any but the hardest rock. Nobel, however, discovered how to moderate its action, and gelatine dynamite and gelignite were manufactured by the addition of saltpetre and wood-meal to a blasting gelatine of less consistency than that employed without such admixture. Blasting gelatine was used in large quantities in the piercing of the St. Gothard tunnel, where the rock was so hard that no satisfactory work could be done without it. Since then the use of the gelatine explosives has increased more and more, and in some countries they have entirely superseded dynamite. Nobel Invents Smokeless Powder.