The St. Johns herald., 1894-11-08
CLASS WORKING.
Ehe Delicate Process Is Attended with
 Much Uncertainty,

Ehe Deuc8te Process Is AcCenOeQ W1Ic
 Mnch Uncertainty.
 A writer in the Optician states that glass is a substance which, as the glass blower says, has will of its own. It is very often difficult to tell how par ticular piece is going to act under cer- tain conditions, even after having tested other pieces of the same ''batch." When subjected to the heat one end of a tube will sometimes respond diff ferently from the other end. This is in a measure due to unequal chilling, occasioned possibly by sudden draught of air while it is in process of manufacture No piece of glass is absolutely reliable. Its working is, therefore, at certain stages, moc,c un- certain, and one person may have en- tiTely different experiences from another. It is chameleonlike, and every process succeeds better with those who seem to have knaclz which is generally obtained by long practice.
 The cutting of glass heads the list of the uncertain processes, for it has no definite cleavage, and its separation is modified by the surrounding tempera- ture. The simplest separation is on fiat glass in straight line. Here all that is necessary is a deep and regular firm and speedy bend away from the main piece, a.nd the parts crack along the desired line. These glazier's dia- moRds may be purchased and general ly prove satisfactory, but it is more economical to purchase from some dia- mond cutter a small splinter, and in- sert this into a piece of brass rod hay ing small hole drilled into enc end. The splinter should now be cemented filed a little upon the side nearest the ruler, to obtain, after trial, the best cutting angle for the diamond. Another instrument for cutting glass less cx- penSive than the diamond is the glass blowers knife, which is piece of thin steel tempered glass hard by heating it cherry red and then plunging it into ice-cold water or mercury. The edge should be sharpened by rubbing it upon an old, rough emery grindstone until fine saw-like notches appear. It is then ready for use and should, if much used, be sharpened repeatedly.
 To cut tubes, carefully scratch at right angles to the axis deep notch, either with the diamond, triangular file or a glass blowers knife. Heat piece of glass rod until small globule appears on the end and press this upon the scratch. The glass will thus be heat o1 oI ,4.41 , xl-. an unequal expansion takes place, the scratch giving direction to the line of fracture, and the tube cracks evenly if its thickness is uniform. In the case of variable thickness uneven edges re- suit, and these must be filed down to avoid sharp, cutting splinters. Many recipes and directions have been given for cutting bottles. Wetting an asbes- tos string with turpentine and setting it on fire produces considerable heat in the glass immediately underneath it. By quickly removing the string and plunging the bottle into cool water the unequal strain takes place and the parts separate. It is this locating of the heat that causes the glass to crack as we wish it. The easiest method, if the means be at hand, is to employ a platinum wire, which should be heated white hot by the passage of heavy electric current. By wrapping the wire round heavy bottle or jar and allowing the current to pass for ten or fifteen seconds the stoutest walled yes sel may be easily separated if touched on the heated line with cloth dipped. in water.