" Acting on carborundum
with chlorine--also, you remember, a product of electrical
dissolution--the chlorine displaces the carbon, forming silicon
tetra-chloride (SiCl_{4}), a colorless liquid resembling chloroform.
When this comes in contact with moist air it gives off thick, white
fumes, for water decomposes it, giving a white powder (silicon
hydroxide) and hydrochloric acid. If ammonia is present the acid will
unite with it, giving further white fumes of the salt, ammonium
chloride. So a mixture of two parts of silicon chloride with one part of
dry ammonia was used in the war to produce smoke-screens for the
concealment of the movements of troops, batteries and vessels or put in
shells so the outlook could see where they burst and so get the range.
Titanium tetra-chloride, a similar substance, proved 50 per cent. better
than silicon, but phosphorus--which also we get from the electric
furnace--was the most effective mistifier of all.
Before the introduction of the artificial abrasives fine grinding was
mostly done by emery, which is an impure form of aluminum oxide found in
nature.
Pages:
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379