But whether this congelation be simply made by cold, or also by co-operation of any nitrous coagulum, or spirit of Salt the principle of concretion; whereby we observe that ice may be made with Salt and Snow by the fire side; as is also observable from Ice made by Saltpetre and water, duly mixed and strongly agitated at any time of the year, were a very considerable enquiry. For thereby we might clear the generation of Snow, Hail, and hoary Frosts, the piercing qualities of some winds, the coldness of Caverns, and some Cells. We might more sensibly conceive how Salt-petre fixeth the flying spirits of Minerals in Chymical Preparations, and how by this congealing quality it becomes an useful medicine in Fevers. Again, The difference of their concretion is collectible from their dissolution; which being many ways performable in Ice, is few ways effected in Crystal. Now the causes of liquation are contrary to those of concretion; and as the Atoms and indivisible parcels are united, so are they in an opposite way disjoyned. That which is concreted by exsiccation or expression of humidity, will be resolved by humectation, as Earth, Dirt, and Clay; that which is coagulated by a fiery siccity, will suffer colliquation from an aqueous humidity, as Salt and Sugar, which are easily dissoluble in water, but not without difficulty in oyl, and well rectified spirits of Wine. That which is concreted by cold, will dissolve by a moist heat, if it consist of watery parts, as Gums, Arabick, Tragacanth, Ammoniac and others; in an airy heat or oyl, as all resinous bodies, Turpentine, Pitch, and Frankincense; in both, as gummy resinous bodies, Mastick, Camphire and Storax; in neither, as neutrals and bodies anomalous hereto, as Bdellium, Myrrhe, and others. Some by a violent dry heat, as Metals; which although corrodible by waters, yet will they not suffer a liquation from the powerfullest heat, communicable unto that element. Some will dissolve by this heat although their ingredients be earthy, as Glass, whose materials are fine Sand, and the ashes of Chali or Fearn; [SN: _The original ingredients of Glass._] and so will Salt run with fire, although it be concreted by heat. And this way may be effected a liquation in Crystal, but not without some difficulty; that is, calcination or reducing it by Art into a subtle powder; by which way and a vitreous commixture, Glasses are sometime made hereof, and it becomes the chiefest ground for artificial and factitious gemms. But the same way of solution is common also unto many Stones; and not onely Beryls and Cornelians, but Flints and Pebbles, are subject unto fusion, and will run like Glass in fire.