Note 3 bis — Chapter XVII · BORON, ALUMINIUM, AND THE ANALOGOUS METALS OF THE THIRD GROUP

P. Chigeffsky showed in 1884 (at Geneva) that in the evaporation of saline solutions many salts are carried off by the vapour—for instance, if a solution of potash containing about 17–20 grams of K2CO3 per litre be boiled, about 5 milligrams of salt are carried off for every litre of water evaporated. With Li2CO3 the amount of salt carried over is infinitesimal, and with Na2CO3 it is half that given by K2CO3. The volatilisation of B2O3 under these circumstances is incomparably greater—for instance, when a solution containing 14 grams of B2O3 per litre is boiled, every litre of water evaporated carries over about 350 milligrams of B2O3. When Chigeffsky passed steam through a tube containing B2O3 at 400°, it carried over so much of this substance that the flame of a Bunsen's burner into which the steam was led gave a distinct green coloration; but when, instead of steam, air was passed through the tube there was no coloration whatever. By placing a tube with a cold surface in steam containing B2O3, Chigeffsky obtained a crystalline deposit of the hydrate B(OH)3 on the surface of the tube. Besides this, he found that the amount of B2O3 carried over by steam increases with the temperature, and that crystals of B(OH)3 placed in an atmosphere of steam (although perfectly still) volatilise, which shows that this is not a matter of mechanical transfer, but is based on the capacity of B2O3 and B(OH)3 to pass into a state of vapour in an atmosphere of steam.