the tubes made of copper in all bodies in which it is employed. Iron must, in fact, be carefully avoided in every part of apparatus which comes in contact with extract-liquor or its vapour. Besides the Yaryan, there are several other evaporators in which the spray principle is more or less completely employed. The simplest of these consists in substituting for the heating coil of an ordinary vacuum-pan a copper steam-box traversed by vertical tubes open at both top and bottom. This is immersed in the liquid to be evaporated, which enters at the bottom of the tubes and is sprayed out at the top. Paul Neubäcker, of Danzig, constructs a pan on this principle with a very ingenious arrangement for the destruction of foam, which seems worth attention. [Illustration: FIG. 84.--Section of Yaryan Evaporator.] It is unfortunately impossible to carry the evaporation of extracts much further than sp. g. 1·2 with spray apparatus, as thicker liquors are apt to clog the tubes, which are then difficult to clean, so that even liquid extracts are usually finished in vacuum-pans of the ordinary type, which may also be arranged in multiple effect. In the case of a solid extract, the evaporation must be carried on until it is as thick as can be run from the apparatus. To do this satisfactorily, stirrers must be provided to keep the extract in motion so long as it is in the pan. The thick, hot, liquid extract is then run into boxes lined with paper, or other suitable material, where it is allowed to cool and to solidify. The pan for the final evaporation of solid extracts should be planned so as to allow of easy cleaning and ready access to its interior, so that if accidentally the evaporation is carried so far that the liquid will not run out, the clearing of the pan may be a comparatively easy matter. It is also important that the extract-exit should be of large size. Probably a broad and somewhat shallow pan, heated merely by a steam jacket, and fitted with rotating stirrers, is the most suitable.