1825.] Composition of Crystals of Sulphate of Soda. 153 



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 atmo- 

 sphere 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 l-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 scratch- 

 ing the name of the substance with a diamond on them, and 

 may conveniently be retained by putting several of them toge- 

 ther into a tumbler, or other glass of that kind. 



Composition of Crystals of Sulphate of Soda*. 

 IT 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. 



* Quarterly Journal of Science, xix. 153. 



