I asked how, and when, all the crystals and precious stones and salts in the world could ever have been in a fluid state.
“One thing at a time,” said my uncle: “that question would lead us quite away from ice. I was going to tell you, that water, in the same manner as salt or metals, when it ceases to be fluid, which happens at the temperature of 32° of Fahrenheit’s thermometer, assumes a constant regular form. Now, Bertha,” he said, “examine this lump of ice, which was in the broken glass, both with and without your magnifying glass—and tell me how it appears.”
I told him, that to my naked eye it seemed as if there were lines crossing and recrossing one another in an uneven manner; but that, with the glass, it appeared like a collection of little spears with pointed ends, laid very closely together and mostly darting from the places where the ice had touched either the bulb or the side of the glass vessel.
“Yes,” said my uncle, “that is what I wished you to observe;—when ice begins to form on the surface of water, several of those spear-shaped spicula shoot from the edge of whatever contains the water, or from any solid body which happens to be in the water,—a bit of wood or even a straw.”
I interrupted my uncle to beg he would explain the word spicula—I know he is never displeased at being interrupted by a question of that sort.
He told me that spiculum is a Latin word, and means a dart or an arrow, or sometimes the sting of a bee,—spicula is the plural, and is commonly used in English to express any small pointed bodies.
“To return to the ice,” said he: “that first set of spicula serve as bases for a new set, and these again for others; each single spiculum diverges or spreads from its own base at an angle of nearly 60°, and therefore they all cross each other in an infinite variety of directions, and this process continues till one even sheet of ice is formed.” I asked my uncle, if the reason why the ice occupies more space than the water was, that those spicula or crystals, from their shape, and from shooting in various directions, cannot lie so closely together as the minute particles of water.—
“Yes,” said he, “you are perfectly right—a proof of this is, that it requires great power to compress water in the smallest degree; while the hardest ice, if pounded, may be easily forced into a smaller space.”
We all again examined the formation of the ice in the broken glasses, and I saw the pretty little spicula quite distinctly—we then went to breakfast, leaving the bulbs to thaw quietly in their cold bath.
11th.—After the hyacinth roots were thawed yesterday, they were placed in a warm room; and we had a great deal of conversation about the different effects of heat and cold, according to the different bodies that are exposed to them. I learned that extreme heat is necessary to liquefy steel, platina, or porcelain; some metals require far less, and Mrs. P. says she once bought in a toy shop, some spoons made of bismuth, tin and lead, which melted in a cup of hot tea. The warmth of the skin is sufficient to thaw frozen water. On the other hand, the degree of cold requisite to render mercury solid is very great, while that which forms ice is moderate.