The distillate passes into a row of condensers, to each of which is attached a receptacle or receiver. It is needless to state that the condensing capacity should be in excess of theoretical requirements. The fractions are of varying strengths and quality; that portion, with a density less than 14 deg. Tw. (19.4 deg. B.), is returned to the treated-lyes tank. The other portion of the distillate is concentrated by means of a dry steam coil in a suitable vessel under a 28 inch vacuum. When sufficiently concentrated the glycerine may be decolorised, if necessary, by treating with 1 per cent. animal charcoal and passing through a filter press, from which it issues as "dynamite glycerine". The residue in the still, consisting of 50-60 per cent. glycerine and varying proportions of various sodium salts--_e.g._ acetate, chloride, sulphate, and combinations with non-volatile organic acids--is generally boiled with water and treated with acid. The tar, which is separated, floats on the surface as the liquor is cooling, and may be removed by ladles, or the whole mixed with waste charcoal, and filtered. The filtrate is then evaporated, when the volatile organic acids are driven off; the concentrated liquor is finally mixed with crude glycerine which is ready for distillation, or it may be distilled separately. _Distilled Glycerine._--This class of commercial glycerine, although of limited use in various other branches of industry, finds its chief outlet in the manufacture of explosives. Specifications are usually given in contracts drawn up between buyers and sellers, to which the product must conform. The chief stipulation for dynamite glycerine is its behaviour in the nitration test. When glycerine is gradually added to a cold mixture of strong nitric and sulphuric acids, it is converted into nitro-glycerine, which separates as an oily layer on the surface of the acid. The more definite and rapid the separation, the more suitable is the glycerine for dynamite-making. Dynamite glycerine should be free from arsenic, lime, chlorides, and fatty acids, the inorganic matter should not amount to more than 0.1 per cent., and a portion diluted and treated with nitrate of silver solution should give no turbidity or discoloration in ten minutes. The specific gravity should be 1.262 at 15 deg. C. (59 deg. F.) and the colour somewhat yellow. _Chemically pure glycerine_ or double distilled glycerine is produced by redistilling "once distilled" glycerine. Every care is taken to avoid all fractions which do not withstand the nitrate of silver test. The distillation is very carefully performed under strict supervision.