the time nor the wit to become a sound scholar nor a profound mathematician. But he may, if he understand his privilege aright, linger for a while in the groves of 'practically useless' knowledge. He may learn what literature meant in an age when it was concerned only with the essentials of simplicity; he may read the lessons of history when history was still separate from political intrigue. And though he forgets his Greek grammar, though in middle life he can not construe a page of Virgil, yet he carries away from this irrational interlude a vague impression of beauty which no other course of education will ever give him." Even for the schoolmen "a vague impression of beauty," whatever that may mean, seems rather unpractical as an educational _ultima Thule_. =The Purple of Cassius.=--There are few substances in the field of inorganic chemistry on which so much speculation and actual work has been expended as the so-called purple of Cassius. A recent article by Mr. C. L. Reese, in the Chemical News, contains some interesting information regarding this curious compound. Up to the present time there have, it seems, been two views held as to its chemical nature--one that it is a mixture of stannic acid and metallic gold; the other, that of Berzelius, that it is substantially a chemical compound of purple gold oxide with the oxides of tin possibly mixed with an excess of stannic acid. It has seemed very likely that the substance is a chemical compound of acid character, and that the solubility in ammonia is due to the formation of a salt, but it has been found that by oxidation of stannous chloride and by allowing very dilute solutions of stannic chloride to stand, the "hydrogel" of stannic acid separated out, which, on the addition of a few drops of ammonia, liquefied and so became soluble in water, just as the purple of Cassius does. There can therefore be no salt formation here. Some comparatively recent work by Richard Zsigmondy, however, seems to have finally cleared up the chemical nature of this curious substance. Its formation is explained by assuming that when stannous chloride is added to a sufficiently dilute solution of gold chloride the latter is immediately reduced to metallic gold while stannic chloride is formed. Generally after a few seconds the liquid becomes red, but the purple is not precipitated for several days, unless it is heated. The gold is not precipitated as a black powder because the stannic chloride formed is immediately hydrolized into hydrochloric acid and the hydrate of stannic acid. The latter prevents the aggregation of the gold particles, and the stannic acid remains in solution as a colloid, which on standing gradually changes under the influence of the dilute hydrochloric acid to an insoluble form, the "hydrogel" of stannic acid. By heating, this change takes place immediately. The properties of the purple of Cassius depend on the properties and character of the