=152. Special Bookcases.=--In Section 146 a form of special wall-case is described which is suitable for storing folio and quarto volumes. In very large libraries it may be necessary to provide additional storage space for bound files of newspapers, extra large folios and prints. Files of newspapers can be stored in a special form of double rack, as illustrated in Fig. 36. As small libraries will bind only the files of local papers, the provision by them of shelves for this purpose need not be a very serious matter. =153.= Large folio volumes are best kept flat on sliding trays or shelves. When they are kept upright they are very apt to suffer through the heavy leaves sagging and dragging at the binding. Valuable folios should always be kept in flat positions. A suitable method of storage is to provide a large double-sided case, with a sloping top, which can be used for consulting the books. The shelves should be arranged to slide out and in on runners, and each shelf may have a brass handle on its fore-edge to enable it to be easily pulled out. The dimensions of such a case will depend upon the number of folios to be stored and their size, but the following illustration (Fig. 37) will be found suitable for all ordinary purposes. [Illustration: FIG. 36.--Rack for Bound Newspapers (Section 152).] This case will store about 150 to 200 folio volumes, according to their thickness, which is ample space for all ordinary municipal public libraries. The shelves of this case should be covered on their upper surfaces with leather or thick cloth. A similar style of rack can be used for storing large collections of prints, the only difference being that the prints would be kept in special boxes as described in Section 307, which would take the place of volumes. =154.= In calculating the number of volumes which can be shelved in a given space, the following general rules will be found fairly accurate:-- Nine lending library books will occupy one foot run of space. Eight reference library books will occupy one foot run of space. Allowance must be made, in calculating from plans, for the space occupied by uprights, etc., and care must be taken to reckon dwarf bookcases only according to their capacity. If nine inches are allowed as the average height of books, which will give eight shelves to a tier seven feet six inches high, excluding cornices, plinth or thickness of shelves, then a single-sided case of the dimensions shown in Section 146 will store 216 volumes in a lending library and about 192 in a reference library. A double-sided case will hold 432 and 384 volumes respectively. [Illustration: FIG. 37.--Section and Elevation of Case for Large Folio Books (Section 153).]