The Power That Preserves | My Web Site Page 290 Chapter 03 Page 05

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~Hot air~ is the oxidising agent in roasting operations. The sulphur and arsenic of such minerals as mispickel and pyrites are oxidised by the hot air and pass off as sulphur dioxide and "white arsenic." The metals generally remain in the form of oxide, mixed with more or less sulphate and arsenate. The residue may remain as a powdery substance (a calx), in which case the process of roasting is termed calcination; or it may be a pasty mass or liquid. In the calcination of somewhat fusible minerals, the roasting should be done at a low temperature to avoid clotting; arsenic and sulphur being with difficulty burnt off from the clotted mineral. A low temperature, however, favours the formation of sulphates; and these (if not removed) would reappear in a subsequent reduction as sulphides. These sulphates may be decomposed by a higher temperature towards the end of the operation; their removal is rendered more certain by rubbing up the calx with some culm and re-roasting, or by strongly heating the calx after the addition of solid ammonic carbonate. In roasting operations, as large a surface of the substance as possible should be exposed to the air. If done in a crucible, the crucible should be of the Cornish type, short and open, not long and narrow. For calcinations, _roasting dishes_ are useful: these are broad and shallow, not unlike saucers, but unglazed. In those cases in which the products of the roasting are liquid at the temperature used, a _scorifier_ (fig. 38) is suitable if it is desired to keep the liquid; but if the liquid is best drained off as quickly as it is formed, a _cupel_ (fig. 5) should be used.

These territorial assumptions on the part of Massachusetts much increased the king's hostility. This probably would not have proved fatal had it not been re-enforced by the determination of the merchants and manufacturers of the mother-country to crush what they feared was becoming a rival power beyond seas. They insisted upon full enforcement of the Navigation Laws, which made America's foreign trade in a cruel degree subservient to English interest. So incorrigible was the colony, it was found that this end could be compassed only by the abrogation of the charter, so that English law might become immediately valid in Massachusetts, colonial laws to the contrary notwithstanding. Accordingly, in 1684, the charter was vacated and the colonists ceased to be free, their old government with its popular representation giving way to an arbitrary commission.

I dare say you notice that all the birds in this picture have long beaks. We may be sure from this that they live in places and seek for their food in ways in which long beaks are just what they want. The fact is they are all marsh birds, and the soil of marshes being wet and soft, and full of worms, these long beaks enable them to probe it, and so get at the worms. I think the beaks of birds afford a striking example of how good God is in adapting creatures to the mode of life He has appointed for them. The eagles and hawks, you know, are provided with strong, short bills to enable them to seize and tear flesh. Those of canaries and all the finches are just the very instruments to crack seeds with. Parrots, with their tremendous weapons, can crush the hardest nuts of the tropic forest. The crossbill is fitted with a wonderful tool for tearing fir-cones to pieces. Robins and the other warblers have soft bills, which are all they want for eating insects and grubs.

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