12 GLASS-CUTTING. PASTILLE. 



ginal globe asunder, and each separate portion forms an 

 independent sphere. 



It is very desirable to perform this and other similar experiments 

 in glass vessels with flat sides, because objects appear distorted if 

 seen through the sides of glass vessels which are curved : they 

 would only present a correct appearance by looking at them from 

 above. Such vessels with flat rectangular sides are rather ex- 

 pensive, but may be procured by removing the neck from the 

 square bottles in which foreign liqueurs are sometimes imported. 

 A piece of ignited charcoal, or of pastille, held in contact with 

 glass immediately in front of a crack, will serve to extend it in any 

 desired direction, so as to cut off a neck or rim, etc. A useful 

 pastille may be made in the following manner: 25 CC alcohol, or 

 about 20 grammes (see article 7), are poured over 4 grammes 

 gum benzoin, and an equal weight of solid storax, in a small glass, 

 and allowed to stand for a day, during which it is repeatedly 

 shaken. A solution is also made of 20 grammes gum arabic and 

 8 grammes gum tragacanth in 120 CC water (120 grammes). This 

 is boiled in a small tin pot, with continual stirring and occasional 

 addition of water to replace that which has boiled away, until the 

 whole is dissolved. Both solutions, with any sediment, are then 

 transferred to a mortar and well rubbed together with about 70 

 or 80 grammes powdered wood charcoal, until the mass is suffi- 

 ciently thick to be rolled on a board into quill-shaped sticks, from 

 10 to 15 cm long, and from 6 to 8 mm in thickness, which are ex- 

 posed for a day or two to the air to dry. Such a stick, when 

 lighted in the flame of a candle, may be kept alight by gently 

 blowing on it occasionally. It mast be kept in close contact with 

 the glass but without pressure, and from time to time turned so as 

 to prevent it from burning on one side only. The first crack at 

 the edge of a piece of glass, or at the neck of a bottle, is obtained 

 by making a scratch in the glass with a triangular file, and heating 

 it with charcoal or pastille until a crack is formed. This requires 

 sometimes strong blowing and some patience, but is safer than 

 heating the glass and bringinga drop of water upon the heated place, 

 which often produces several irregular cracks. It will be well to 

 practise the operation first on a piece of common glass before 

 undertaking it with the vessel intended for the apparatus. The 

 pastille is best extinguished by pushing the lighted end 3 or 4 cm 

 deep into dry sand, or into the end of a glass tube large enough to 

 admit it easily, it will then be ready for use, and easily lighted 

 when again required. The sharp edges along the crack should 

 be rounded off upon a common grindstone which is turned slowly. 





