RUPERT'S DROPS. 167 



These drops are also called, on the continent, Larmes Batavi. 

 ques, or Hatavian Tears. 



All glass, not regularly annealed, or, in other words, cooled 

 suddenly instead of progressively, has a tendency towards the same 

 frangibility. Thus, in common window glass, if it be properly 

 annealed, the diamond cuts it with moderate ease, making an uni- 

 form smooth furrow, at first dark, but gradually opening, and 

 appearing like a bright silver thread : but when the glass is badly 

 annealed, the diamond works with much more difficulty, the cut 

 opens very slowly, and often flies into a different direction, or the 

 glass entirely breaks. 



There is another equally curious glass toy, formed upon the 

 same principle, and evincing the same ellect, called the Bologna 

 phial. This is simply a phial, of any shape whatever, made of any 

 kind of glass, but much thicker at the bottom than at top, and 

 cooled immediately, without annealing. These -being pretty stout, 

 from their thickness will bear a smart blow from a wooden mallet, 

 or any blunt instrument, or the concussion of a leaden bullet drop, 

 ped from a considerable height, without injury : but if any sharp 

 body, howevi r small, such as a large grain of sand, or which is still 

 better, the shiver of a gun. flint, be dropped in from only a few inches 

 height, the bottom cracks all around, just above the thickest part, 

 and drops off. The same effect takes place, if the bottom be slightly 

 scratched with any hard body. When very brittle, if a hard 

 angular substance, as a cut diamond, be dropt in, it will sometimes 

 pass through the bottom, though very thick, with apparently as 

 little resistance as through a spider's web. These glasses, when 

 they have received the first injury, do not always crack immediately, 

 but remain whole, sometimes for a few minutes, sometimes for hours, 

 and then suddenly give way. 



[Pantologia, Aikin'sChem. Diet. 



