TRENDS
Synthetic soils show promise for commercial hydroponics in the very near future.
The change over from loam to peat and the introduction of plastic granules to alter the physical characteristics of peat suggest that the methods are nom feasible (hTew Sci., M a y 21, 1970, p 381). For instance, the development of a 700 per cent synthetzc soil medium to grow tomatoes may be possible. Tomatoes can be rooted in the porous, rigid, heat-resistant medium through which a nutrient supply lzne and an electronic heating coil run. Excess nutrient solution would drain into a channel alongside, to be replenished and recycled. A t the end of the season the shoots would be cut off, and the heating elements turned up high enough to sterilize the medium and oxidize the roots to caibon dioxide. Replanting could start 24 hours later. The economics of such a system would depend on the insulation propertips of the medium. The most promising medium to date has been polyurethane foam granulps. The study of fast reactions by techniques developed for use with lasers is possible
in processes in the picosecond range. These improvements depended on the introduction of the laser into photochemistry. Of the various types, solid-state lasers have so f a r found the most extensive use in t h i s j e l d . I n this technique, a light pulse is required to excite enough of the species to alter the transmittance of the monitoring light beam by a measurable amount. T h e solid-state laser, when operated as described by L. Patterson and G. Porter (Chem. Brit. Vol. 6, N o . 6, June 1970,pp 246-2501, produces stimulated radiation of irregular intensity over a period that may extend to hundreds of microseconds; howpver, it does not provide the time resolution desired. Rut, by applying a Q-switching technique to the laser, it is possible to produce a highly reproduciblejash of a f e w nanoseconds, which has enough energy to meet the excitation requirements of the method. The result is a giant pulse of several joules that may be conjned to under 20 nanoseconds duration. Preparation of ultrafine powders and large sized powders with unusual surface
structures is now possible. A n account is given by B. Waldie, Department of Chemical Engineering, Heriot- W a t t University, Edinburgh, Scotland (Trans. Inst. Chem. Eng., Vol. 48, 1970, pp T90-T94) of current research into the preparation of powders in high-temperature plasmas, and a completed study of electrically conducting suspensions f or M.H.D. energy conversion is reviewed. There are indications that some of the feed particles by-pass the plasma hot-zone, thus reducing the proportion of feed converted to ultrajne particles. Estimates of the energy costs for producing ultrajne silica in a plasma suggest that the plasma process is worth considering, but furthur exjerimental work is needed on several aspects of theprocess. Balsa i s used in a nuclear bubble chamber as an insulation medium to prevent heat transfer. The balsa is used to solve a heat-transfer problem: thermally insulating a saturated liquid hydrogen that is at a higher temperature above a piston (36-in. diameter stainless steel) than a supercooled liquid hydrogen is below a piston (Prod. Eng., Val. 14, hro. 74, July 6, 7970,p 58). An advantage of this material is that with a reduction in temperature its thermal conductivity decreases as a straight-line function. I n addition, the mechanical properties of balsa improve substantially at cryogenic temperatures. I t has a high Lompressive and horizontal shear strength, and it can take up to 100yooverload in shock or impact loads for short durations, in addition to being very light in weight. 2
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
