Page:Experimental researches in chemistry and.djvu/168

1825.] out through the fluid; and afterwards, on cooling the vessel, the liquid descends into it. A small spirit-lamp flame being now applied at the upper part of the long neck, softens the glass, which is then to be drawn out to a fine point and sealed. In this state the substance may be preserved clean and pure for any length of time.

If a small portion be required for an experiment, the extreme point of the neck is to be opened by pinching it off the tube is then to be inclined until the quantity required has entered the neck, where, by capillary attraction, it will form a small column, and the tube being warmed by the hand, the atmosphere within it will expand and expel the portion of fluid on to the place required. A very little practice will enable the experimenter to judge of the quantity he is forcing out, and in this way he may take a portion not larger than the 1-20th of a common drop, or he may take the whole contents of the tube. When the quantity required has been taken out, the tube is to be placed in an upright position, and the flame of a lamp or candle, or even a piece of paper, closes the aperture in a moment and as perfectly as before.

I have found these tubes very serviceable when working with substances either very small in quantity or obtained with great difficulty, in consequence of the entire prevention of waste resulting from their use. They are easily labeled by scratching the name of the substance with a diamond on them, and may conveniently be retained by putting several of them together into a tumbler, or other glass of that kind.

Composition of Crystals of Sulphate of Soda.

is known that when a hot strong solution of sulphate of soda is put into a vessel and closed up, it may be reduced to common temperatures without crystallizing, although, if the vessel be opened, abundance of crystals will immediately form. It has also frequently been observed, that in some circumstances crystals would form in the solution during cooling, even though the vessel had not been opened or agitated. These crystals, when observed in the solution, are very transparent and of a large size; they are quadrangular prisms, with dihedral summits.