Fernan Gomez followed in 1469, and opened trade with the Gold Coast; and in 1484 Diogo Cao discovered the mouth of the Congo.
Thus if we wish to ascertain the thermal effect of the action Mg+CaO =MgO+Ca, we may write, knowing the heats of formation of CaO and Mg0 to be 131000 and 146000 respectively, 0-131000 = 0-146000+x x =15000 cal.
The following is an analysis of a specimen of English pressed glass; S102, 70.68%; Na 2 0, 18.38%; CaO, 5.45%; BaO, 4.17%; Al 2 0 3, 0.33%; and Fe203, o.
It combines directly with most elements, including nitrogen; this can be taken advantage of in forming almost a perfect vacuum, the oxygen combining to form the oxide, CaO, and the nitrogen to form the nitride, Ca 3 N 2.
The element is not found in the free state in nature, nor to any large extent in combination, occurring chiefly as chrome-ironstone, Cr 2 O 3 FeO, and occasionally being found as crocoisite, PbCrO 4, chrome-ochre, Cr 2 0 3, and chromegarnet, CaO Cr 2 O 3.3SiO 2, while it is also the cause of the colour in serpentine, chrome-mica and the emerald.
