Little Johnny was approached by the lifeguard at the public swimming pool.
"You're not allowed to pee in the pool," said the lifeguard. "I'm going to report you."
"But everyone pees in the pool," insisted Little Johnny.
"That may be," said the lifeguard, "but not from the diving board!"
Portland cementIn 1824, in Yorkshire, England, Joseph Aspdin, a stone mason, patented Portland cement, made by burning finely pulverized lime and clay at high temperatures in kilns (UK patent No. 5022). Thus Aspdin had made a manufactured counterpart to natural or Roman cement - a crude formulation of lime and volcanic ash used as early as 27 BC. Aspdin produced a hydraulic cement that would harden with the addition of water. He named his invention "Portland cement" not only to distinguish it from Roman cement, but also as a marketing tool: concrete made from his new cement resembled a highly prized building stone quarried on the Isle of Portland off the British coast. Like flour in a fruit cake, cement glues aggregate (sand or gravel) together to make a "rock" (concrete). |
