Hermetic Sealing. We cannot better explain this process than by showing how finely-divided lead may be got into a glass tube closed at both ends. This seems no easy matter at first glance, but it becomes easy, just as all other things come easy, when we know the way. We will suppose our readers universally to be well aware that the apple got into the dumpling when the crust was soft dough; which fact being known, they may easily comprehend how lead or anything else may be got into a crust of glass, provided only the glass can be reduced to a state of doughy consistence - a condition most easily effected by means of heat. To proceed, then, with our experiment. Procure some goulard-extract, and throw into it some tartaric acid. dissolved in water, until nothing more falls down, or, to use a chemical term, until all is precipitated. That which falls is tartrate of lead. Collect it on a filter of blotting-paper, and set it in a warm place to dry.
Whilst it is drying, proceed as follows: Procure a piece of English flint glass tube (which is the sort that most readily melts), somewhat of this diameter and thickness. A thicker piece, or a tube of larger bore, a beginner in chemistry could not manage to work. Let the piece be about eight inches long. Next light the spirit-lamp, having trimmed the -wick in such a manner as to yield a good flame. Hold the tube in the flame and near its point, somewhat about three inches from one end of the tube. Whilst the tube is thus exposed to the heat, never allow it to rest for an instant, but keep revolving it, pulling at the same time. Very soon the tube will assume this appearance, which, when observed, the two pieces of the tube, 1 and 2 respectively, being twisted in reverse directions, and a final pull being given, No. 2 will separate like this - That is to say, closed at one end, open at the other. Allow it to cool. When cold, put in the tartrate of lead (provided it be quite dry). and when in, carefully draw out the tube like this - that is to say, permitting a very fine tube at the point (a). Next apply the spirit lamp flame to the tartrate as long as any smoke escapes, by which means the tartrate of lead is what chemists term decomposed, every portion of it except lead and charcoal resulting from the operation being evolved in the gaseous form. When this point is arrived at (known by the cessation of smoke), remelt the fine tube at (a) and separate the two pieces of tube with a twist. The lead in a very fine state of subdivision, and intimately mixed with charcoal, will be now what is called hermetically sealed into the glass tube, and may be caused to inflame at pleasure by breaking off one end of the closed tube, and shaking it into the air.