Commercial glycerin is mostly obtained from the "spent lyes" of the soap-maker.
In the van Ruymbeke process the spent lyes are allowed to settle, and then treated with "persulphate of iron," the exact composition of which is a trade secret, but it is possibly a mixture of ferric and ferrous sulphates.
Potash lyes also may be bought direct, but in some cases they are sharpened or causticized by the soap-boiler himself from the carbonate.
Soft Soap. - Soft soaps are made with potash lyes, although in practice a small quantity of soda is also used to give the soap some consistence.
Distillation in a vacuum is practised in two forms: - if the pump draws off steam as well as air it is termed a "wet" air-pump; if it only draws off air, it is a "dry" air-pump. In the glycerin industry the lyes obtained by saponifying the fats are first evaporated with "wet vacuum" and finally distilled with closed and live steam and a "dry vacuum."
The manufacture of alcohol from the sulphite lyes of the wood-pulp industry was contemplated, but carbide, although produced in increasing quantities, was not considered as a possible raw material owing to its greater importance as a source of the fertilizer cyanamide.
In Sweden, where wood pulp is made in enormous quantities, the manufacture of alcohol from the waste sulphite lyes is carried on, and it was estimated that in 1920 the probable capacity was in the neighbourhood of 8,000,000 gal.; the actual production, however, amounted to about 2,750,000 gal.
He is now very well, and though I fear he is under some small degree of melancholy, yet I think there is no reason to suspect it bath at all touched his understanding, and I hope never will; and so I am sure all ought to wish, that love learning or the honour of our nation, which it is a sign how much it is looked after, when such a person as Mr Newton lyes so neglected by those in power."
Norway also produces sulphite lyes and alcohol from them on a smaller scale.