“Yes, I have no doubt that he has pulverized them as well as it can be done in a mortar. But it is not possible to make them as fine in that way as they do in the powder-mills. Then, to mix them properly, they ought to be wet and ground together a long time. We can’t stop to do that.
“And now, first,” he continued, “I want you all to observe how these various materials will burn by themselves, and then see how differently they will burn together.”
Mr. Holiday then took up a coal of fire, and put it upon the shovel; and he asked Jonas to hold it for him in the fireplace, under the throat of the chimney, so that the smoke and fumes might not come out into the room. He then took from the cup which had the sulphur in it, a little of the sulphur upon the point of his knife, and laid it down gently upon the coal of fire. It burned with a very small and faint blue flame. It burned very slowly, and the flame continued for some time; but the flame was not much bigger than the sulphur itself which caused it.
He then tried the same experiment with the saltpetre. The effect was very different, though in this case there was scarcely any flame. It made a little faint flash, accompanied with a slight crackling sound. Then he tried the charcoal, but it did not appear to burn at all. It lay in a little black heap upon the burning coal, just as Mr. Holiday put it on. After a time, however, it began to grow red upon the under side, and finally became red throughout; and then it could hardly be distinguished in appearance from the coal which it was lying upon.
“So you see,” said Mr. Holiday, “that these three ingredients are not very combustible by themselves; at least, they burn very quietly, and with very little flame. Now, we will mix them together. We want a tea-spoon Dorothy.”
“And the mortar. I can mix them better in the mortar.”
So Dorothy brought the mortar, too. Mr. Holiday measured out six tea-spoonfuls of saltpetre from the cup which contained that ingredient, and put it into the mortar.
“There must be about six times as much saltpetre as sulphur and charcoal,” said he. “That is not exact, but it will be near enough, I presume. Now, I will put in one tea-spoonful of sulphur and one of charcoal. I suppose, however, I ought to go by the weight, and not by bulk.”
“What do you mean by that, sir?” said James.