1      Last week, we visited a large factory where they make window glass.
  Special rollers took hold of the sheet at either side and carried it upwards.  
  Here some men lowered a metal frame into the liquid.  
  They then fed the mixture into a big hot oven.  
  Our guide told us that at this stage it was necessary for the glass to cool slowly as this would make it very strong.  
  At a height of 30 feet, the sheet of the glass became cool and another machine cut it into big pieces which workmen stored away together.  
  Then they added some broken glass to the mixture as this helps it to melt.  
  We first saw workmen mixing sands and other materials together in the right amounts.  
  At the far end of the oven, a stream of liquid glass came out.  
  As the frame came up, it pulled away a hot sheet of glass.  
  11    Finally the glass was ready for use.